~ ESL. This is to certify that the thesis entitled DISTRIBUTION AND PROVENANCE OF PALYNOMORPHS IN NORTHEAST ATLANTIC AEROSOLS AND BOTTOM SEDIMENTS presented by Michael Brendan Melia has been accepted towards fulfillment of the requirements for Ph D degree in .QEQngL. Major professor Date February 14, 1980 0-7 639 OVERDUE FINES: 25¢ per day per item RETURNIM; LIBRARY MATERIALS: Place in book neturn to remove charge from circulation records . 11/ “a. “2;- PM W ./ DISTRIBUTION AND PROVENANCE OF PALYNOMORPHS IN NORTHEAST ATLANTIC AEROSOLS AND BOTTOM SEDIMENTS By Michael Brendan Melia A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Geology 1980 ABSTRACT DISTRIBUTION AND PROVENANCE OF PALYNOMORPHS IN NORTHEAST ATLANTIC AEROSOLS AND BOTTOM SEDIMENTS By Michael Brendan Melia Eolian dust and bottom sediment samples from the Northeastern Atlantic, off the coast of Northwest Africa were studied palynologically. Standard chemical and phys- ical laboratory techniques were used to isolate the paly- nomorphs. Samples were examined primarily for their terrestrial plant detritus (pollen, spores, opal phytoliths and freshwater diatoms) but observations about marine entities were also made. The spatial distributions of various palynomorphs were mapped and this facilitated detection of three distinct geographic palynofloras. A northern palynoflora consisted of pollen derived primarily from the Mediterranean basin, a central or Saharan palynoflora was characterized by pollen derived from desert plants (especially grasses) and a southern Tropical-Equatorial palynoflora was not only composed of pollen derived from tropical plants but also included up to 50% allochthonous pollen from the drier interior of West Africa. Palynomorph distributions are related closely to both source vegetation and to atmospheric and oceanic transport Michael Brendan Melia mechanisms. The quantity of pollen and spores per gram of bottom sediment ranges from greater than 2000 off the Saharan coast in Mauritania to less than 50 in deep ocean basins. Pollen and spores in Mediterranean aerosols may exceed #0 per cubic meter of air during the summer and range between 4 to 6 for tropical aerosols during the winter. TrOpical aerosols and bottom sediments contained the greatest abundance of fungal spores. The abundance of dinoflagellates and microforaminifera in bottom sediments is directly related to the area of upwelling off the West African coast. The distribution of opal phytoliths and freshwater diatoms in both aerosols and bottom sediments indicates that dust storms are the major transporting agents for these entities from the interior of West Africa to the Gulf of Guinea. These storms are also an important agent for the transport of pollen to the trOpical atmosphere. Distances of transport for Mediterranean pollen may exceed 5000 km and distances on the order of 6000-7000 km are indicated for freshwater diatoms in eolian dust over the Atlantic Ocean, having originated in Chad or Niger. ACKNOWLEDGEMENTS The author wishes to acknowledge the assistance and encouragement given throughout this study by Dr. Aureal T. Cross of the Department of Geology and the Department of Botany and Plant Pathology, Michigan State University, and who served as chairman of the doctoral guidance committee and thesis advisor. Appreciation is also extended to Dr. G. J. Larson and Dr. C. E. Prouty of the Department of Geology and Dr. R. E. Taggart of the Department of Botany and Plant Pathology who also served on the guidance committee. Dr. Fred K. Lepple of the Naval Research Laboratory, Washington, D. C. generously supplied most of the eolian dust and African soil samples for the study. Bottom sediment samples were supplied by the Lamont-Doherty Geological Observatory under Office of Naval Research ONR contract NOOOth-75-C-0210 and NSF contract NSF-OCE76 180h9. In addition, air filter samples from the "Atlantis II"-20 cruise were supplied by Dr. Victor E. Noshkin of Woods Hole Oceanographic Institution. Financial assistance for the study was in part provided by a grant obtained from the Department of Geology, Michigan State University and underwritten by Chevron Oil Co., and ii by a Grant-in-Aid of Research from Sigma Xi, The Scientific Research Society of North America. Finally, due thanks must be extended to my wife, Dorcas, for typing the manuscript and to both my wife and daughters, Tabatha and Susan, for providing much spiritual support during the preparation and completion of this dissertation. iii TABLE OF CONTENTS LIST OF TABLES .0...IO...O..0...OOOOOOOOOOOOOOOOOOOOC LIST OF FIGURES .0...OOOOOOOOOOOOIOCOOOOOC.0.....0... INTRODUCTION 00.0.0.0...OOOOOOOOOOOOOIOOOOO0.0.0.0... Materials and Methods 0....00.000000000000000... ObJeCtiveS Of the Study OOOOOOOOOOOOOOOOOOOOOOCO Background to the Nature of the Problem ........ PREVIOUS WORK 0.0...OOOOOOOOOOOOOOOOCOOOOOO0.0.0.0... Palyn01ogy ..................................... Ocean Bottom Sediments oooooocooocooooocooo Organic Matter in Eolian Dust ............. weSt Africa ooooocooooocooooooooooooooooooo Aer05018 and DUSt Storms ooooocccooocoocoocooooo THE WEST AFRICAN CONTINENT I...OOOOOOOOOOOOOOOOOOO... Geography oooooooooooococooooc00.000000000000000 G601ogy ooocoococo-cocoooooooooooooooooooooooooo Climate ooooooooooccocoonooooooooocoooooooocoooo vegetation ococcoco...ccoococoon-00000000000000. BaCkground 0.0.0.0....OOOOOOOOOOOCOOOOOOOCC Detail OOOOCOOOOOOOOOOOOOOOOOOOOOOOOOOOCOOO THE NORTHEAST ATLANTIC OCEAN OOOOOOOOOOOOOOOOOOOOOOOO oceanography ooooocoooocoococoocoooooocooooocooo Bathymetry cococooooooooocooooooooooocooooo ocean currents ooooooo0.0000000000000000... upwelling 0.00....0.0.0.0....OOOOOOOOOOOCOO sediments O...O...0.0000000000000000000000C DATA COLLECTION 00.0.0000...0.00000000000000000000000 Types Of samples OOO...O...OOOOOOOOOOOOOOOOOOOOO MethOds Of COlleCtion .0...OOOOOOOOOOOOOOOCOCOOC Sample Treatment oooooooocococoooooooccooooooooo IntrOduCtion .‘CCCC....C................... iv Page vii viii u-ul BOttom sedj-ments .0.00000000000000000000000 Air Filter samples coco-000.000.000.000...- West African Land-based Samples and Wind- erOdj-ble SOils 0.0.0.0....OOOOOOOOOOOOOOC Microscopy OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Quantitative Examination .................. Qualitative Examination OOOOOOOOOOOOOOOOOOO PhOtography cocoo-000000.00...coco-0000000000000 African Reference Samples ...................... African Palynological Literature ............... Literature on Specific Vegetation Arrays in Northwestern Africa Used in the Study ........ PRESENTATION OF DATA C...OOOOOOOOOOOOOOOOOO0.00.00... IntrOduCtion 0.0.0.000...OOOOOOOOOOOOOOOOOOOOOOC ANA-IJYSIS OF DATA 0.0.0.0....OOOOOOOOOOOOO0.0.0.000... Introduction oooooooooooooooooooooocoocoo-coo... Palynomorph Distributions 00000000000000.0000... Terrestrially Derived Entities ............ POllen and Spores .................... Fungal Spores ........................ Opal Phyt01iths oooooooooooooooooooooo Freshwater Diatoms ................... Marine Entities ........C...‘.............. Dj-nOflagellates ...................... MiCrOfOraminifera oooooooooooooooooooo Palynofloral Zonation 000000000000oooooooooooooo Mediterranean Palynoflora ................. Saharan Palynoflora ....................... Tropical-Equatorial PalynOflora 0.0.0.0000. Freshwater Diatom Flora 0.0000000000000000. DISCUSSIOIJ O'COOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Palynomorph Provenance ooooooooooo000.000.00.000 Seasonal Provenance and Transport .............. Temporal Considerations in Aerosol Sampling .... Distance of Transport with Relation to Size of Pal-ynomorph 0.00.00.00.00.0.000000000000000... Relationship of Palynomorph Distribution Patterns to Transport Mechanisms ............. Surface Ocean Currents .................... Deep Ocean Currents ....................... muVial Transport 0.0.0.0....OOOOIOOOOOOOOO Eolian Transport and Storms ............... Mechanisms for Incorporation of Palynomorphs into the Atmosphere and Subsequent Transport . The Use of Deep-Sea Palynology for Determining Terrestrial Vegetation Zones in the Geologic Record 0......O....0...OOOOOOOOOOOOOOOOOCOCCCC CONCLUSIONS .0...OOOOOOOIOCOOOOOOOOCOOOOOOOOOOOCOOOCC BIBLIOGRAPHY .00...0.00IOOOOOOOOOO0.000000000000000CC APPENDIX C...000......0..0..O...OOOOOOOOOOOOOCOOOOOOO EXPLANATION OF PLATES PLATES vi Page 138 140 162 171 172 LIST OF TABLES Table 1 Surface Location of Core Samples in Atlantic ocean .00...OOOOOOOOOOOOOOOOOOOOO00.00000... 2 Collection Data for Land-based Aerosols ...... 3 Collection Data for "Atlantis II"-1973 AerOSOJ-S O...OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 4 Collection Data for "Atlantis II"-1966 Aer0801s .OOOOOOOOOOOOOOOOOO000.000.0000.... 5 Numbers of Major Types of Palynomorphs Per Cubic Meter of Air Sampled During "Atlantis II"-1966 Cruise .................. vii Page #6 47 #8 109 Figure 10 11 12 13 14 LIST OF FIGURES Location of "Atlantis II"-1973 and West African Aerosol Samples and West African 3011 samples .OOOOOOOOIOOOOIOOOOOO00.00.... Location of "Atlantis II"-1966 Aerosol Sample TranSGCts .COOOCOOCOCOCOCCCCOOOCCOOCOOC.... Location of Core Top Samples Used in the Study .COOOOOOOOOOOOO0.0.0.0....0.0.0.0.... Geologic Sketch Map of Northwest Africa ..... General Climatic Zonation of Northwest Africa .COOOOCOCOOOOOOOOOOOOOOOOOOOOOOOCOOO Simplified Physiography of the Northwest African Continent and Direction of Major Surface Winds During Various Seasons ...... Major Vegetation Zones of Northwest Africa .. Simplified Bathymetry of the Northeast Atlantic ocean .0.0....OOOOOOOOOOOOOOOOO... Simplified Ocean Currents for the Northeast Atlantic Ocean ............................ Distribution of Pollen and Spores in Northeast Atlantic Aerosols (1973) ........ Distribution of Pollen and Spores in Northeast Atlantic Bottom Sediments ....... Distribution of Fungal Spores in Northeast Atlantic AerOSOlS (1973) 0.0000000000000000 Distribution of Fungal Spores in Northeast Atlantic Bottom Sediments ................. Distribution of Opal Phytoliths in Northeast Atlantic Aerosols (winter 1973) ........... viii Page :- 22 21+ 27 38 no 62 63 64 65 66 Figure 15 16 17 18 19 20 21 22 23 21+ 25 26 27 28 29 30 31 Distribution of Opal Phytoliths in Northeast Atlantic BOttom Sediments gggoggoggooooooo. Distribution of Freshwater Diatoms in Northeast Atlantic Aerosols (winter 1973) . Distribution of Freshwater Diatom Fragments in Northeast Atlantic Aerosols (winter 1973) OCCOOCOOOCOOOOOOOOOCOOOOOOOOOOOOOOOOO Distribution of Freshwater Diatoms in Northeast Atlantic Bottom Sediments ....... Major Distribution Areas for Freshwater Diatoms in Bottom Sediments ............... Distribution of Dinoflagellates in Northeast Atlantic Bottom Sediments ................. Dinoflagellate to Pollen and Spore Ratio in Northeast Atlantic Bottom Sediments ....... Distribution of Microforams in Northeast Atlantic Bottom Sediments ................. Distribution of Bisaccate Pollen in Northeast Atlantic Aerosols (1973) .................. Distribution of Bisaccate Pollen in Northeast Atlantic Bottom Sediments ................. Distribution of uercus Pollen in Northeast Atlantic Aerosols (1973) .................. Distribution of "Quercus" Pollen in Northeast Atlantic Bottom Sediments ................. Distribution of Betula Pollen in Northeast Atlantic Aerosols (1973) .................. Distribution of Betula Pollen in Northeast Atlantic Bottom Sediments ................. Distribution of Olea Pollen in Northeast Atlantic Aerosols (1973) .................. Distribution of Umbelliferae Pollen in Northeast Atlantic Aerosols (1973) ........ Distribution of Cupressaceae Pollen in Northeast Atlantic Aerosols (1973) ........ ix Page 67 68 69 7O 71 72 75 711 75 76 77 78 79 8O 81 82 83 Figure Page 32 Distribution of Alnus Pollen in Northeast Atlantic Aerosols (1973) .................. 8A 33 Distribution of Gramineae Pollen in Northeast Atlantic Aerosols (1973) .................. 85 34 Distribution of Ulmus Pollen in Northeast Atlantic AerOSOiS {1973) OOOOOOOOOOOOOOOOOO 86 35 Southern Limits for Ulmus and Car a Pollen in Northeast Atlantic Bottom Segiments .... 87 36 Distribution of Cheno-Am Pollen in Northeast Atlantic Aerosols (1973) .................. 88 37 Distribution of Cheno-Am Pollen in Northeast Atlantic Bottom Sediments ................. 89 38 Distribution of Gramineae and Cyperaceae Pollen in Northeast Atlantic Bottom SGdimentS cocoa-00.0000000000000000000.0000 90 39 Distribution of Compositae Pollen in Northeast Atlantic Aerosols (1973) ........ 91 #0 Distribution of Compositae Pollen in Northeast Atlantic Bottom Sediments ....... 92 #1 Distribution of Palmae Pollen in Northeast Atlantic Aerosols (winter 1973) ........... 93 42 Distribution of Palmae Pollen in Northeast Atlantic Bottom Sediments ................. 94 43 Distribution of Mangrove Pollen in Northeast Atlantic Bottom Sediments ................. 95 44 Distribution of Melosira ranulata in Northeast Atlantic Aerosols (winter 1973) . 96 #5 Distribution of Melosira granulata in Northeast Atlantic Bottom Sediments ....... 97 46 Distribution of C clotella sp. in Northeast Atlantic Aerosols (winter 1973) ........... 98 47 Distribution of Cxclotella sp. in Northeast Atlantic Bottom Sediments ................. 99 48 Distributional Decrease in Size of Melosira sp. Seaward from the West African Coast (winter1973) .00...OOOOOOOOOOOOOOOOOOCCOOO 100 X INTRODUCTION Materials and Methods Northwest African aerosols collected above the eastern Atlantic Ocean were examined for presence of pollen, spores and other palynomorphs in conjunction with similar studies of ocean bottom sediments and West African surface samples. Forty dust samples collected on filters by high volume (hi-vol) air samplers aboard R/V "Atlantis II" (Woods Hole Oceanographic Institution) during the period January 25-October 13, 1973, along a series of transects off the coast of Northwest Africa (Figure 1), were made available for study by Dr. Fred K. Lepple. Dr. Lepple also supplied an additional forty aerosol and soil samples from land- based stations on the continent of West Africa (see Figure 1 for locations and eXplanations of samples). In addition to the above dust samples, thirteen additional filter samples from the "Atlantis II" cruise (February to May 1966) had been obtained from Dr. Noshkin at WOOdS Hole prior to the study. These were also collected above the Atlantic Ocean (see Figure 2). A total of seventy-one bottom sediment samples (core tops) were selected and made available from Lamont-Doherty Geological Observatory (see Figure 3 and Table 1 for 1 no ans—om Haom 50E: emu; Ea magma H82: :32: smog can $91.5 3232.. so 8333 .. spawns P2 .o 3.2 .o_n .on .o. .3. a _ _ _ _ _ =Il= :0. to .01 IO :11: .20.: 3.23.... o a .330 :5: 2:23.. .20.: 1.21 .106— “ lullal % \ .21.. gm .001 J8 1. _ _ ‘0‘ 000 mpoomnmha manamm Howonm¢ mmmpleH mfipqmapd: no soapmooq .N on:Mfim 3.2 .3 3.2 _ .0 F b p _ .b 0' 0v 0 000 .0. a...) -.(U bel q a u... t .2 :33 .o0 n in a . _ _ q #2” 2%. .B. 32A hvzpw on» ma vow: woamswm mos onoo mo soapmooa .m muswfim pg: .0 2r . o .rn _ w r ._N .Wn ”n. as .m-s~> n O . 1 o .c. -> ca-cn>o coll . a¢~-o_>.. oo~-a_>c Blue Q mn~a~N>c m¢~1o—>O ~a~10~>c m2 u->c snug; o 373, c 5&5; o as . >.. can-o_> -_-~m>. nm~-a~> c .o_- ~ao o C Ncm-a_>.. .o. - om~-o~,o am a_>c mon-o_,.. m~-s_>o co_-- co_-ama an~-c~>o NO: n, O. o QCM1o—>O . ON.) .0 no. . 2..., undo @MNION) O . ,I O ‘ mm NM 1 QO—IMN>O «I 3: 5.3-8,. Sta, 0 .. 8:: 5-2,. as, o 1.2 nm-. so os_-~_>o o.~-o~>o m-->. as- ~>o an-~m» - .m-c_>o c~_-a~>o is ~n>o ao_-a~>o o oem-a~> Q 0 hw1~m> o sm~u->o 02.1 s .o. 53.3 3723 .a-c_a. .o-n~>.. o 8.2., o 1. n 0. C..8(‘ NUNONN? so.-. >.. ..u am_-->.~s_--,c ~a-cn>. mo-~n .0.-a~>. ,oes-~n>o ,o ~s_-->c b M 0 w . K1?) 0 CV 3 P Q nutONC . A — _ _ _ low c. o o . . . . _ .2 .2 .9 .3 5 Table 1. Surface Location of Core Samples in Atlantic Ocean Maceration Core Latitude Longitude Depth Numbers Name (m) M51958, 2058 V17-157 9‘21'N 18‘38'W 4082 M51959, 2059 V17-158 12’ 23'N 18' 551111 l1358 M51960, 2060 V19-287 1' 26'N 2’ 401111 5110 M51961, 2061 V19-295 2' 37'N 6' 71111 4605 M51962, 2062 V19-296 1' 25'N 9’ 5111 5017 M51963, 2063 V19-297 2' 37'N 12" 01w 4122 M51964, 2064 V19-298 3' 39'N 15' 31W £1792 M51965, 2065 1119-300 6' 53'N 19’ 2811-1 4263 M51966, 2066 V19-3o2 10' 15'N 25' 221111 5583 M51967, 2067 1119-303 12' 471111 27‘ 471w 5426 M51968, 2068 V19-304 15 32'N 30' 21w 5398 M51969, 2069 V20-235 8' 28'N 30‘ 8111 5242 M51970, 2070 1120-236 11' 59'N 32' 361111 5916 M51971, 2071 1120-237 14' 12'N 34" 271w 5978 M51972, 2072 1120-238 16' 28'N 36' 191111 5233 M51973, 2073 V20-240 21‘ 4'N 39’ 5111.11 5446 M51974, 2074 1122-181 2‘ 2115 16' 541111 4012-4438 M51975, 2075 V22-185 2’ 34'N 19141111 4587 M51976, 2076 1122-198 14’ 35'N 17' 39. v51w 1082 M51977, 2077 V22-209 19’1.5'N 29' 9"” £1735 M51978, 2078 1122-211 20’ 42'N 31 271111 4402 M51979, 2079 V26-44 18'50.3'N 24'28.5'W 3966 M51980, 2080 v27-141 35‘ 28.7'N 24' 56.4' 111 4506 M51981, 2081 1127-142 36’ 59.9'N 22' 54.11111 4726 M51982, 2082 v27-159 33‘ 58.9'N 13° 19.61111 4444 M51983, 2083 v27-167 25‘ 56.2'N 26' 35.11111 5099 M51984, 2084 V27-177 5‘ 52.3'N 28° 39.8'w 4109 M51985, 2085 V30-37 1' 52'N 26' 45111 3828 M51986, 2086 V30-38 1' 4515 25‘ 39111 5138 M81987, 2087 V30-48 17‘ 7.3'N 1919.9'W 3351 M51988, 2088 V3o-49 18' 26.21 21' 4.61111 3093 M51989, 2089 V32-04 34' 39.081 32' 50.86111 3596 M81990, 2090 V32-05 34’ 09.59' 29' 39.04' W 3376 M51991 , 2091 1132-29 28’ 25.381 19‘ 22.13111 4371 M81992, 2092 V32-30 23’ 46.2' 20' 115.63' W 4675 M51993. 2093 V32-31 27‘ 39.94' 22’ 14.28”? l1893 M81994. 2094 V32-37 25‘ 27.93' 19' 13.8“” 3406 M52131 , 2179 V4-7 38' 30'N 42' 501111 4965 M52132 V9-29 3‘ 47.5'N 311' 37' W 4675 M52133, 2180 V10-81 29' 58111 12' 55.5111 536 M52134, 2181 V10-84 24° 23.5'N 24‘ 03.51111 5255 M52135, 2182 V12-5 21’ 12111 45‘ 211111 3003 M52136, 2183 V16-23 13‘15'N 40' 40111 4886 M52137, 2184 1117-160 21' 22'N 24' 021111 4861 M52138, 2185 1117-166 34‘ 56'N 45‘ 211111 4210 M52139. 2186 1123-88 31‘ 06.51111 21’ 57.51111 5031 M52140, 2187 V23-91 29° 35'N 28' 341111 2758 M52141 , 2188 V23-97 24' O7'N 17' 261111 1928 Table 1 (cont'd.) Maceration Numbers M52142, M52143, M52144, M52145, M52146, M82147, M52148, M52149, M52150, M52151, M52152, M52153, M32154: M52155, M52156, M52157 M52158, M82159 M52160, M52161, M52162 M52163, M52164, 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 Core Name V23-108 V26-34 v26-54 v27-162 V27-17O v27-235 V27-253 V27-257 v27-26o v27-262 V29-148 V29-159 V29-164 v29-166 V3O-53 v30-62 V30-72 V30-73 V30-93 Latitude 17’24'N 19’51.2'N 5’28.2's 34:11.9'N 24' 25.8'N 227.4'N 8’08.7'N 27'46.1'N 25'55.8'N 31'44'N 4'15'N 6°16. 4'N 8: O9'N 14: 58. 5'N 22: O2'N 25: 49. 5'N 34: O8'N 32: 43'N 35: 40. 5'N 32: 38'N 20' 7.27'N 17: 58. 34'N 16 O6. 29'N Longitude 43'14'W 36'54.5'W 11'55.9'W 16‘51.51w 34‘ 02.2'w 0'14.9'w 17‘ 34.4' W 36'43.9'W 31'06.21w 36' 08111 2'40'E 12:36. 4'W . 14:19'W $56. 9'W 18: O4'W 16: 55'w 22:19'W 24:13'W , 38: 37.2'w 10:11.8'1‘1 20: 20. 52'W 17: 46. 191w 18' 09.12'w Depth (m) 4367 5601 2906 4281 6224 4854 4726 5136 5590 4061 3892 3768 582 4159 2160 942 5321 5225 4080 2996 3834 2780 2965 7 geographic locations and depths of sampling). M0st samples were studied both qualitatively and quantitatively where possible, each being examined for its terrestrial plant detritus i.e., pollen, spores (including fungal spores), opal phytoliths and freshwater diatoms. The African soil and land-based aerosols, however, were not studied quantitatively since their prime use was for the determination of the provenance of various palynomorphs in the marine aerosols and bottom sediments. Nevertheless, relative percentages of major taxa were determined from the continent-based samples. Comparison was made between bottom sediment palynofloras and airborne palynofloras. Objectives of the Study The objectives of the study included the following: 1) the identification of palynomorphs to lowest taxonomic rank feasible; 2) the determination of their spatial distribution in the atmosphere and bottom sediments; 3) the determination of their relationship to African and Mediterranean vegetation zones (hence determination of provenance); 4) the identification of relationship of palynological distribution to tropospheric and oceanic circulation and hence to the importance of eolian (dust storm), fluvial or oceanic transport mechanisms; and S) determination of the significance of numbers of pollen, spores, freshwater diatoms and opal phytoliths 8 per gram of surface sediment or gram of eolian dust, as an indication of the distance from shoreline, proximity to deltas or stream mouths and distance down-wind from their respective source areas. Background to the Nature of the Problem Northwest Africa is one of the world's major sources of eolian dust. Sediment from this region can be trans- ported in dust storms as far as the mid-Atlantic and has been known to produce haze as far away as the Caribbean (Prospero and Carlson, 1970). Evidence that this eolian dust is incorporated into nearshore sediments is present in the area of upwelling along the northwest coast of Africa and its presence in some deep-sea sediments is also evident. The organic fraction of this terrestrially derived detritus contains various palynomorphs including pollen, spores, bacteria, fungi, opal phytoliths, fresh water diatoms and other plant material (Delany,,g§,§;., 1967; Felger,,gt‘§l., 1967; Folger, 1970; and Parkin, g£,§;., 1972). Periodic dust storms and haze banks extend off the coast of Northwest Africa with a dust pulse frequency of 3 to 4 days (Lepple, 1975). Although dust storm frequency varies during the year, storms are more common in the winter months (January and February) and less frequent in November (Lepple, 1975). Delany gt,gl., (1967) state that in summer, dust most probably originates in M0rocco but as winter progresses, material from south of Dakar, Senegal, 9 may be included in the storms. Plant detritus in aerosols should therefore reflect this seasonal variation in provenance. Rapp (1974), illustrates two areas of major dust storm activity off the coast of Northwest Africa. A northern summer dust front extends from the vicinity of Dakar, Senegal, northward to about Cap Rhir in MOrocco and extends westward to approximately 25’W. A larger winter dust front to the south extends from Cap Blane, Mauritania, in the north to as far south as the equator, eastward to the Niger delta and westward over the Atlantic to about 35‘ W. The annual dust flux in the North Atlantic ranges from 25-37 million tons in and around Barbados (Prospero and Carlson, 1972) to nearly half a billion tons near the northwest African coast during periods of drought (Lepple, 1975). During a 6-hour dust storm in March, 1974, Lepple estimated that 400,000 metric tons of dust were transported offshore along 100 km of West African coastline. Analysis of this dust showed an average carbon content of 2.6%, which is equivalent to 10,000 tons of organic carbon or 20,000 tons of actual organic material. The majority of these organics are of botanical origin. Lepple and Brine (1976), examined the chemistry of several north Atlantic dust samples and analyzed some north African wind-erodible surface sediments in an attempt to determine whether the Sahara was the source of the 10 airborne dust. They found a greater organic content in the eolian dusts than in the North African soils which indicated a "more biologically active area than desert regions" for dust provenance. Again, the present study was expected to shed more light on this problem of dust provenance. Maynard (1976) reported that fresh water diatoms and Opal phytoliths in surface bottom sediments from the Atlantic were especially abundant in the vicinity of Northwest Africa. Although Maynard did not study other palynomorphs in the sediments, such a study of these entities is of the utmost importance to determining the ultimate disposition of continentally derived materials such as pollen and spores. Therefore, a study to compare distri- bution patterns of palynomorphs in ocean bottom sediments to similar data obtained from marine aerosols above those bottom sediments was undertaken. Any correspondance between the two sets of data should provide further insight into the determination of the provenance for the eolian fraction in the deep-sea sediments. Since information about wind and ocean currents and submarine geology is fairly well understood for the Atlantic off Northwest Africa, it was considered that deciphering transport mechanisms for terrigenous particu- lates in this area would be possible. Also, a study of this type (i.e., distributional), under known atmospheric and physical oceanic conditions, might serve as a model 11 for understanding similar situations in the geologic past where atmospheric winds and marine conditions, e.g., proximity to shoreline etc., could only be estimated from a study of the distribution patterns of various palynomorphs. Geological studies of this kind would then become more meaningful if they could be related to similar known physical conditions in the present study. PREVIOUS WORK Palynology Ocean Bottom Sediments: The source and distribution of pollen and spores in surface sediments have been studied in relatively small bodies of water such as bays, gulfs, estuaries and lakes but have not been studied extensively in the Open ocean itself. The classic study by Muller (1959), on the distribution of pollen and spores in the recent Orinoco delta and associated shelf sediments more or less paved the way for later studies involving similar problems, although Koreneva (1957), had reported on studies of surface sediments from the Sea of Okhotsk prior to Muller's 1959 report. Another palynological study by Koreneva (1964), involved the examination of both surface sediments and core material over a large area in the southern Pacific Ocean. Cross gt al., (1966) reported on studies of the sediments of the southern part of the Gulf of California; Bronskiy (1975), studied the distribution of pollen and spores in the surface sediments of the Persian Gulf; Rossignol (1961 and 1973), Vronskiy and Panov (1963) and Koreneva (1971), have worked on recent sediments of the Mediterranean. Rossignol (1969), has also studied recent 12 13 palynological sedimentation in the Dead Sea, and the bottom sediments of the Baltic Sea have been palynologically studied by Lubliner-Mianowska (1962). Shelf and nearshore sediments in various locations have been studied by Groot (1971a and 1971b), Groot g§,gl., (1967), Traverse and Ginsburg (1966 and 1967) and Habib ‘gt,§l., (1971). Shelf sediments off southwestern Africa, much closer to the present study area, have been studied by Davey (1970), and Davey and Rogers, (1975) and off western Africa by Koreneva (1975) and Rossignol-Strick and Duzer (1979). Several workers are presently investigating the distribution of terrestrial palynomorphs in surface sedi- ments from the Open ocean, especially the eastern Pacific (Heusser and Florer, 1973, and Heusser and Balsam, 1977) and the western Atlantic (Heusser, 1977). However, none of these studies integrate both palynological data from bottom sediments and that from air samples above those sediments. Overviews on the study of pollen and spores in marine sediments have also been published. For these the reader is referred to the works of Cross gt.§l., (1966), and Heusser (1978), for additional discussion. It should be mentioned however, that the major concern with oceanic palynologists has been restricted to the study of the subsurface, particularly pre-Pleistocene rocks and sediments. The distribution of dinoflagellates in oceans and 14 bottom sediments has been studied more extensively than purely terrestrial entities such as pollen and spores. The literature on this subject, however, will not be reviewed since the major concern here is with purely ter- restrial palynomorphs. Organic Matter in Eolian Dust: The palynologic investigation of the atmosphere over many parts of the globe has been extensively studied for a number of years and it should be sufficient to mention only those works of relevance to the present study. Ehrenberg (1845), presented the first detailed description of freshwater diatoms and opal phytoliths blown out over the Atlantic from Africa. Later studies on airborne, continentally-derived organic debris in the north Atlantic include those of Meier and Lindberg (1935), Erdtman (1938), the study of airborne fungi by Pady and Kapica (1955) and the study of freshwater diatoms by Kolbe (1957). More recent literature on the subject includes Bowden gt,§l., (1971), Folger (1970 and 1974), Folger gt‘gl., (1967), Gregory (1973) and Stix (1975). Probably the only palynological study concerned with dust storm provenance has been that of Horowitz‘gtlgl., (1975), which involved the eastern Mediterranean area. Organic matter in eolian dust has been studied by Crozat,gt,§l., (1973), along the Ivory Coast, and by Lepple (1975), Lepple and Brine (1976), Simoneit (1977), and Simoneit 23,5l., (1977), over the Atlantic Ocean. 15 Ketseridis,gt,gl., (1976) have also discussed the organic constituents of atmospheric particulates and Handa (1977) discussed land sources of organic matter found in the marine environment. However, most of the latter studies cited were concerned primarily with the chemistry of the particulates rather than the palynology. West Africa: Palynological studies made on the West African continent and concerned with the existing vegetation and modern pollen rain include the following: Van Campo (1957, 1958 and 1974). Van Campo and Hallé’(1959a and 1959b), Van Campo 33 al., (1960 and 1965a), Panelatti (1960), Bronckers (1967), Lobreau gt‘a;., (1969), Guers (1970), Guers gt,al., (1971), Maley (1970 and 1972), and Cour g§,§;., (1975). Saharan palynological studies of surficial deposits primarily concerned with Quaternary vegetation and climatic change include the following: Pons and Quézel (1956 and 1957), Quézel and Martinez (1958, 1960 and 1962), Quézel and Pons (1958), Quézel and Thébault (1959), Quékel (1960), Van Campo and Coque (1960), Van Campo gt'gl., (1964a, 1964b, 1965b, 1966 and 1967), Beucher (1963, 1967, 1971 and 1975), Beucher and Conrad (1963), Van Campo (1964a, 1964b, 1967 and 1975), Maley (1973 and 1977) and Cour and Duzer (1976). Aerosols and Dust Storms Much useful information has been obtained from studies concerned with the geochemistry and mineralogy of bottom 16 sediments and the inorganic fraction of eolian dust, especially with that produced in the Sahara and transported out into the Atlantic. Some of the more recent contribu- tions to Atlantic eolian chemistry and mineralogy are the studies of Delany 33 al., (1967), Prospero (1968), Prospero 23 al., (1970), Parkin 22 al., (1970 and 1972), Chester and Johnson (1971a, 1971b and 1971c), Chester 23 al., (1971 and 1972), Carlson and Prospero (1972), Chester (1972), Aston g; 9;” (1973) and Lepple (1975). Biscaye (1965) and Biscaye and Eittreim (1977) have studied bottom sediments in light of the continental contribution of eolian debris and Biscaye gt al., (1974), have made isotopic studies of aerosols for the purpose of using the information to determine continental dust provenance. Information on the eolian sediment budget of the world's oceans has also been extensively reported on by Windom (1969, 1970, 1975 and 1976) and Windom and Chamberlain (1978). Lepple (p. 5-19, 1975), has reviewed the most important contributions to the study of eolian dust and dust storm phenomena on land and above the ocean, and has also reviewed most of the previous work done on eolian transport in the North Atlantic. Prior to Lepple's study the total knowledge about eolian dust over the ocean off the African coast was based on less than 100 air samples, and no near- source sampling had taken place until his study. THE WEST AFRICAN CONTINENT Geography The study area extends from about 10'E to 50'W and from 58 to 40’N (see Figure 1). The continental portion includes everything between the Gulf of Guinea and the Mediterranean and as far east as the eastern border of Algeria in the north and coastal Gabon in the south. Elevations are between 200 and 1000 m with areas of greater relief in the Atlas mountains in the north and the Guinea Highlands and Fouta Djallon to the south (see Figure 6). In the central Sahara elevations exceed 1000 m in the Air and Hoggar Highlands. Off the coast of Spanish Sahara and M0rocco elevations on the volcanic Canary and Madeira Islands also exceed 1000 m. Major rivers are absent north of 16'N and in southern Spanish Sahara coastal sand dunes evidently block some streams from entering the ocean (Summerhayes gt‘gl., 1976). South of 16’N latitude important perennial streams emptying into the Atlantic are the Senegal and the Gambia, both with headwaters in the Fouta Djallon. Southeast of these are less important streams draining the Guinea Highlands with mouths along the Grain Coast in Sierra Leone and Liberia. 17 18 The Sassandra, Bandama and Comoe’ Rivers drain north- south through the Ivory Coast. These, with the major Ghanan stream, the Volta, all empty into the Gulf of Guinea. The Niger River which heads in the Guinea Highlands is the longest and most important perennial stream in West Africa and its delta in coastal Nigeria is one of the most conspicuous features of the Gulf of Guinea. The annual discharge of the Niger into its delta is approximately 200 x 10’ m’ of fresh water and the supply of sediment is about 18 x 10‘ m’ (NEDECO, 1959 and 1961, in Hospers, 1971). Most of the area north of 16’N is characterized by systems of internal drainage, except for short drainageways in Morocco and Northern Algeria which empty into the Atlantic or Mediterranean. Consequently, large areas of the desert are covered by playas, most of which are found north of ZO'N. They are especially numerous in Spanish Sahara and the area bordering that country in Mauritania. The largest (some being greater than 1000 km’ in area) and most important playas both geologically and economically are found in northern Algeria and Tunisia (Lefond, 1969). Chott Djerid however, in Tunisia exceeds 5000 km‘. Many of the smaller ephemeral lakes are coastal lagoons ("aftouts") and extend intermittently along the coast from Mauritania to Morocco but are especially common in Spanish Sahara. These coastal playas may be important sources of sediments derived by deflation. Some of these sediments may contain 19 palynomorphs (especially diatoms) that may be transported out over and into the Atlantic during the summer by the Northeast Trades. Coastal swamps and lagoons extend from the Ivory Coast to Nigeria. From Sierra Leone to Senegal coastal stream valleys are characteristically drowned or ria-like. Geology Northwest Africa is largely composed of Precambrian shield rocks which are structurally aligned more or less northeast-southwest. These rocks cover approximately two-thirds of the area south of 12'N and much of the Sahara is underlain by either Precambrian or lower Paleozoic rocks, especially in southern and western Mauritania. Western Guinea also has extensive areas of lower Paleozoic rocks (see Figure 4). Of importance to the present study are those areas with deposits of Cretaceous, Tertiary and Quaternary rocks through which the Niger River drains in Mali, Niger and Nigeria. Tertiary rocks and sediments, especially in the Niger delta, could also become reworked and be reincorpor- ated into the sediments being deposited on the bottom of the Gulf of Guinea. The Senegal and Gambia Rivers also drain extensive areas of Upper Cretaceous and Tertiary strata in Senegal. Palynomorphs contained within these rocks could potentially be reworked. Cenozoic rocks are at the surface in coastal Spanish Sahara and in western Mauritania, with extensive dune sands Ooavern ary (dunes) Quaternary tertiary tertiary [mid Mecoceic c eIoceouc lower Paleozoic lower Paleozoic 0 and/or Precambrian I—c—I 10°w o 500 Ian Figure 4. Geologic Sketch Map of Northwest Africa (modified from Grove, 1970) 21 of Quaternary age overlying lower Paleozoic strata. Much of the Sahara (eastern Mauritania, Mali and southern Algeria) is covered by Quaternary dunes overlying rocks of varying ages from Precambrian to Tertiary. The Hoggar Highlands and Air on Azbine are mainly Precambrian although Quaternary volcanics are also present. The Atlas mountains are composed of both Mesozoic and Cenozoic rocks (Triassic to Tertiary with Quaternary deposits especially in the playas) but the rocks are increasingly older to the southwest in Morocco where lower Paleozoics are found. The east-west structural fabric of the Atlas Range was produced during the Alpine orogeny in the late Cenozoic, (Trumpy, 1960), although earlier Hercynian deformation is evident. An excellent account on the geology of West Africa, and Africa in general, is given by Furon, (1963). Climate Although there are numerous systems for classifying African climates those of northwest Africa are primarily latitudinal (Figure 5). Following this, most of the area north of 18'N has an arid (Saharan) climate except for the extreme north, i.e., in Morocco, northern Algeria and Coastal Tunisia, where the climate is dry subtropical or Mediterranean. The Atlas Mountains however, exercise orographic control, and therefore altitudinal zonation is present, with montane and sub-alpine climates generally above 2000 m. 22 Medilerranean Arid (Saharan) Sahel and Dry Coastal Ghanan Savanna tropical Highland Equatorial Monsoon Figure 5. General Climatic Zonation of Northwest Africa (modified from Church, 1968; Grove, 1970 and Hance, 1975) 25 Between 18‘N and 8N the climate can be characterized as Tr0pical-Sudanese with the Sahel occupying the area between 14°N and 18' N and the true Savanna climate between 143N’and.8’N, depending somewhat on altitude. Along the southwestern coast however, in Liberia, Sierra Leone and Guinea, the Savanna is replaced by a true coastal Mensoon climate. The area south of 8'N can be considered truly Equatorial, although in the northern part of this zone the climate becomes more seasonal or 'Semi-equatorial' (Church, 1968). An important aspect in the climatology of northwest Africa is the seasonal movement of two air masses. The largest of these masses is the Tr0pical Continental mass (warm and dry) which extends from northern Algeria south to about 5’N of the equator in winter but only as far south as 18'N in the summer. This seasonal alternation is produced by the northward and inland extension of the smaller mass of Equatorial Maritime air (warm and humid) from the south during the summer months (Church, 1968). Associated with the northern dryer air mass are the North- east Trades (see Figure 6) and with the southern air mass are associated the wet south-westerly or westerly winds (Church, 1968). Associated with the Northeast Trades is the especially warm and dry Harmattan (Figure 6) which blows during the dry season (winter) from the south side of the Sahara and into the Gulf of Guinea. Mest plant growth in West Africa 24 oaooeom. 0:35; an an own; one man Pa. .37: ac 33623 on. 333:8 53.":- auo-ficoz 2: so 29. 6824 not: :8 .m 9334 a W77/Wv \ \V/m x ,\ / 3.. z 25 has ceased at this time, and much organic matter is eroded from various surfaces by this wind and is incorporated into the lower troposphere forming a haze with other dust particles. The present study includes the investigation of such a haze off the coast of Ghana in the Gulf of Guinea. In the north an equivalent hot dry easterly wind blows out from the Sahara during the dry months across Spanish Sahara and Morocco and also carries much dust out into the Atlantic. Over most of the northern fringe of Africa cooler northern westerly air masses prevail for most of the winter months and bring rain to the Mediterranean. During summer months, however, drought prevails as the moist westerly masses move northward. During most of the year the coastal Sahara experiences a more moderate climate than the interior region because the cool Canary Current produces lower air temperatures above the ocean. Major wind patterns for the Northwest African continent and adjoining ocean areas are shown in Figure 6. The average annual precipitation in the Saharan climatic zone is less than 250 mm and over much of this area is less than 100 mm. The greatest precipitation occurs in the coastal Monsoon zone where it averages more than 2000 mm. The Equatorial zone receives between 1000 and 1500 mm of rain per annum generally decreasing north- ward from the coast, except for the dry zone around Accra in coastal Ghana where rainfall may be as low as 500 mm. The Savanna zone receives between 500 and 1000 mm of rain 26 per annum and the Sahel usually less than 500 mm but more than 100 mm. However, in the latter zone during the recent Sahelian drought (1968 to 1973) precipitation values were even lower than 100 mm and consequently this greatly accelerated deflation. Vegetation Background: West African vegetation zones are pri- marily determined by the latitudinal relationship or control of precipitation and relative humidity (Church, 1968). Therefore, vegetation zones are more or less parallel to the climatic zones. This latitudinal zonation of vege- tation is generally the rule except in areas with orographic control or anthropogenic interference (see Figure 7, modified from Church (1968), Eyre (1968) and Grove (1970)). Coastal mangrove forest predominates on the Niger delta and along much of the southern coast of West Africa and westward to as far north as the Senegal River except for the drier coastal scrub and grassland section of Ghana and Togo. It is best deve10ped in the south-western monsoonal climatic region. Tr0pical rain forest on the other hand extends northward from the coast of the Gulf of Guinea to about 8'or 10'N in Liberia, Ivory Coast and Nigeria. North of this forest to about 15'N extends the Sudanese vegetation with broad-leaved tree savanna in the southern part of the zone and thorn tree-tall grass vege- tation in the northern part (Eyre, 1968). From Dakar, Senegal, eastward to Lake Chad and north 27 Is‘w ° IOOOIUII 111]]! Coniferous forest a gue I desert elni -desert scrub Desert Thorn tree-tall .rau s vanna Iread - l eaved tree savanna Tropical highland lorest tropical rain forest Mangrove forest Figure 7. Major Vegetation Zones of Northwest Africa (modified from Church, 1968; Eyre, 1968 and Grove, 1970) 28 of 15‘N to appronmately 17.5'N this area is occupied by Sahel vegetation which is characteristically thorn tree- desert grass savanna. This zone also extends north along a thin coastal strip of Senegal and Mauritania to just north of Nouakchott. Desert and semi-desert scrub vegeta- tion extends north of the Sahelian zone to the Atlas M0untains except where orographic rainfall (notably in the Hoggar) is sufficient to produce maquis and garrigue vegetation, i.e., 'Mediterranean' vegetation characterized by evergreen bushes, maquis being denser and taller than garrigue. On the lower elevations of the southern flank of the Atlas Mountains the dominant vegetation is a combination of garrigue and desert grass, with more characteristically Mediterranean maquis on the northern coastal side of the Atlas (Eyre, 1968). On the higher central Atlas, generally above 1000 m, the North African coniferous forests are found and above 2000 m a montane scrub or shrub zone is found, and above 2500 m a sub-alpine zone. The Fouta Djallon is dominated by a plateau type of vegetation (Church, 1968) whereas the vegetation of the Guinea Highlands is more montane in character. However, vegetational characterization or distinction between either of these two areas and their adjacent lowlands is somewhat difficult. Mention should also be made of the vegetational zonation on the Canary Islands. Here the vegetation from 29 sea level to about 500 m is semi-desert scrub becoming more Mediterranean in character up to about 2000 m. Zones are generally wetter on the northern sides of the islands and consequently a wetter Mediterranean type of vegetation is found there. A wet forest zone with broad-leaved Mediterranean types is found up to about 1300 m (depending upon aspect) with a dryer, needle-leaved (pine savanna) forest up to 2000 m (Bramwell and Bramwell, 1974). Above 2000 m, as in the Atlas mountains, the vegetation becomes montane to sub-alpine in character. Detail: The literature on the flora and vegetation of Northwest Africa is very extensive and detailed. However, the present summary should be sufficient to introduce the reader to those plants and vegetational environments of importance to this study. The mangrove forest mainly occurs in the low-lying coastal swamp land associated with muddy rivers, lagoons and deltas (Church, 1968). Its most extensive development is in the Niger delta and consists of the same species of mangroves as are found along the eastern coast of America (Church, 1968). The commonest species is Rhizophora racemosa (red mangrove), with 3. harrisonii and 3. mangle being of lesser importance. Avicennia africana (white mangrove) is also important and can be found as far north as Cape Timiris in Mauritania (de Naurois and Roux, 1965). Other mangroves do occur but tend to reflect local edaphic, moisture or salinity conditions. The seaward margin of 30 the mangrove swamp may have a rather varied flora which includes species in the Amaranthaceae, Malvaceae, Convol- vulaceae and Papilionaceae (Nielsen, 1965). On the Niger delta (north of the mangroves) a fresh- water swamp forest occurs but it may also be found in freshwater streams and lagoons along much of the West African coast. On the outer periphery of this forest is a zone of floating grass dominated by Vossia cuspidata or floating sedge (Cyperus papyrus). Further inland and on dry stream banks, communities of Pandanus candelabrum (Screw Pine), climbing palms (rattans) and Raphia sp. (Palmae) may be found (Church, 1968). Common arboreal vegetation usually fringing the swamps includes members of the following families: Apocynaceae, Annonaceae, Moraceae, Passifloraceae, Rubiaceae, Euphorbiaceae and Myrtaceae (Nielsen, 1965). The tr0pical rain forest although having been reduced to nearly one half of its total original area is still an important zone for timbering. Mahoganies (ghaya sp.) are important in this respect and occur as part of the upper story in the wettest parts of the rain forest. Other upper story species are found in the following families: Rhizophoraceae, Bombacaceae, Meliaceae, Caesalpiniaceae, Ochnaceae, Sapotaceae, Rubiaceae and Sterculiaceae. In the drier areas members of the Bignoniaceae, Bombacaceae, Combretaceae, Euphorbiaceae, Meliaceae, Mimosaceae, Moraceae, Sterculiaceae and Ulmaceae 31 are well represented (Nielsen, 1965). Lower story species of the rain forest include members of the above families as well as members of the Annonaceae, Apocynaceae, Ebena- ceae, Flacourtiaceae, Rutaceae and Sapindaceae. Nielsen (1965) also includes the following families that are found in the shrub layer but generally not in the arboreal strata, i.e., the Compositae, Menispermaceae, Polygalaceae, Solanaceae, Verbenaceae and the Violaceae. The lianes and climbing shrubs are included in a wide number of families most of which have already been mentioned. The tr0pical rain forest is also the zone for widespread cultivation of the oil palm, Elaeis gpineensis, although it is indigenous to the swampy parts of West Africa. In the southern part of the Sudanese zone the broad- leaved tree savanna consists of both deciduous trees and tall grasses. The grasses include Andropogon sp., Imperata sp., Hyparrhenia sp. and Pennisetum sp. The arboreal vegetation is mostly fire-tolerant and has thick corky bark with the following families well represented: Caesalpiniaceae, Euphorbiaceae, Mimosaceae, Ochnaceae, Rubiaceae, Sapotaceae and Verbenaceae. In addition to these families, shrubs are represented by members of the Annonaceae, Celastraceae, Combretaceae and Loganiaceae (Nielsen, 1965). Common herbaceous families excluding grasses and sedges include: Araceae, Compositae, Iridaceae, Liliaceae, Malvaceae, Orchidaceae and Zingiberaceae. The thorn tree-tall grass savanna (northern Sudanese) 32 is dominated by various arboreal species of Acacia (Mimosaceae), several species in the Caesalpiniaceae and species in the Anacardiaceae, Combretaceae, Dipterocar- paceae, Ebenaceae, Euphorbiaceae, Myrtaceae, Sapotaceae, Sterculiaceae and Verbenaceae. The shrub species are similar to those in the broad-leaved tree savanna except that Protea elliottii (Proteaceae) is also found (Nielsen, 1965). The grasses are also similar. The Sahel vegetation zone can best be described as acacia-desert grass savanna. Arboreal vegetation is short (3 to 6 m) and widely spaced. Many species of acacia (both trees and shrubs) predominate as well as other thorny shrubs such as the African myrrh (Commiphora africana), and shrubs in the family Asclepiadaceae are also very well represented. Other shrubs in the following families are present: Papilionaceae, Caesalpiniaceae (especially the genus Cassia), Tiliaceae, Capparidaceae, Euphorbiaceae and Boraginaceae. The most common herbs are members of the Amaranthaceae but short tussock grasses and sedges tend to dominate the surface. The date palm Phoenix dactylifera is commonly planted in this zone too. Most of the plants of significance to the present study in the Saharan zone are those of herbaceous character. The ChenOpodiaceae are especially well represented as are the Compositae, but to a lesser extent; the former are found especially in saline areas (playas). Grasses include Stipa tenacissima, Lygeum sp., Panicum tur idum, Aristida 35 sp. and Eragrostis sp., (Walter, 1973). Shrubs found in wetter habitats include the genera Tamarix, Nitraria and Ziziphus and in the southern Sahara various acacias (and many other shrubs) are encountered, especially towards the Sahelian transition zone. The southern Saharan woody species tend to have tropical affinity whereas the herbs are mainly Mediterranean (Church, 1968). The coastal Sahara of Morocco has succulent members of the Euphorbiaceae especially Euphorbia sp., and most appear as dwarf shrubs (Walter, 1973). In the Hoggar above 1800 m a garrigue vegetation with Mediterranean counterparts is encountered with important species being glgg laperrini (an endemic relic), Myrtus nivellei, Pistacia atlantica and Verbascum dentifolium (Quezel. 1965). On the Mediterranean side of the Atlas Mountains the maquis vegetation is dominated by sclerophyllous shrubs such as ngg europaea (wild olive), Ceratonia siligua (carob), Pistacia lentiscus (lentisk), Quercus coccifera (Kermes oak), Cistus sp. (cistus) and Arbutus sp. (arbutus) (Eyre, 1968). The so called 'High Maquis' may also have 9, ilgg (Holm oak) and.§ippg halepensis (Aleppo pine), both tall trees, as well as some larger shrubs such as Myrtus commumis,,§pigg arborea (tree heather), Phillyrea pggig and Spartium junceum (Polunin and Huxley, 1966) not all of which are sclerophyllous. On the Saharan side of the Atlas the garrigue has 54 typical maquis species but most communities are character- ized by non-sclerophyllous vegetation including members of the Labiatae and Thymus sp. Garrigue occurs extensively on the northern flank of the Atlas also. Above the maquis and garrigue (evergreen forest) a deciduous forest zone may occur but it is more charac- teristically found on the northern shore of the Mediterr- anean and not on the southern Mediterranean or Atlas shore. This deciduous zone is effectively squeezed out here due to its altitudinal limit of 1000 m where, in the Atlas, the lowland evergreen forest only finally relinquishes its dominance to the coniferous forest above. Between 800 m and 1500 m in Algeria and Morocco the coniferous forests of Pippg halepensis and‘gpigg numidica are present and above these extending up to 2000 m are the famous cedar forests of Cedrus atlantica. In the Canary Islands the lower communities of semi- desert scrub are dominated by members of the Compositae and species of Euphorbia and Aeonium (Crassulaceae). Generally between 400 and 600 m, this lower xerophytic zone merges into a forest scrub zone (Mediterranean in character) with Juniperus phoenicea and'Epigg arborea (Bramwell and Bramwell, 1974). This Juniper scrub zone is better develOped on the southern lepes where a rain shadow is produced by the loftly volcanic mountains, especially on Tenerife where El Teide rises to 3707 m. An evergreen forest zone with broad-leaved trees and 55 shrubby heaths occurs above the Juniper scrub (generally on the wetter northern slopes) and is dominated by arboreal laurels including Laurus azorica, Apollonias barbusana, Persea indica and Ocotea foetens, all of which according to Bramwell and Bramwell (1974) are relicts of an extinct Tertiary Mediterranean flora which, from fossil evidence, occupied southern Europe and northern Africa between 15 to 40 million years B. P. Arbutus canariensis, §gli§ canariensis and half a dozen more trees including evergreen oaks are also important in laurel communities (see Bramwell and Bramwell, 1974, for a more complete list of trees, shrubs and herbs). The laurel zone may extend up to 1300 m. The pine forest, with the endemic Pippg canariensis being the predominant species, is generally found above the more characteristically Mediterranean zones at 1200 m and may extend up to 2000 m. It is an open park-like forest except in areas that have been reforested. The vegetation on the highest peaks of the Canaries, generally above 2000 m, consists of open montane scrub dominated by shrubs in the family Leguminosae (Bramwell and Bramwell, 1974). Many rare endemics are found in this zone. Many of the characteristic species found in the Canary Islands are also found on the Madeiras and Azores. The vegetation found on the Cape Verde Islands is also similar to that of the Canaries but tends to be more xerophytic as it is geographically closer to the Saharan climatic zone. 56 THE NORTHEAST ATLANTIC OCEAN Oceanography Bathymetry: The salient bathymetric features for the portion of the Atlantic related to this study consist of various basins and rises, the latter being associated with volcanic islands or the Mid-Atlantic Ridge (see Figure 8). The Mid-Atlantic Ridge extends more or less along the western border of the study area. The major physiographic feature of the Ridge is the Azores Plateau (the surface of which is generally no deeper than 2000 m) located around 30' N latitude and 30' W longitude. The Cape Verde Terrace extends off the coast of Mauritania for some 1000 km and the ocean above it is generally shallower than 4000 m. The 4000 m submarine contour is closer to the continent around the southern and eastern coasts of West Africa and off Ghana is even as close as 120 km offshore. A line of sea mounts extends from the Azores to Gibraltar and forms the Azores-Gibraltar Ridge. The only other major 'high' is the Sierra Leone Rise which lies some 750 to 1000 km from the coasts of Guinea and Sierra Leone. Major basins and abyssal plains (shown in Figure 8) are often deeper than 6000 m. The continental shelf in 57 58 Chm. 323: use so. .No 3on mega .3383 oanuwooo 1383. sec 634.895 580 6.3532 43226: on... no ESE-flan 63:35... .m 9:62 w... n a.“ y w. 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Approximately 1-2 grams of sediment was sampled from the core tops. Haynard (1976), could find no statistically significant differences between data obtained from trigger weight as opposed to piston cores and so no undue apprehension about the comparison of data from these two types of cores was experienced by the present author. Some of the dust samples supplied by Dr. Lepple were collected by foreign contacts and are not well documented as to the method of sampling, length of sampling, etc., and so data gathered from these samples are viewed with some reservation. Lepple (p. 29-36, 1975) has discussed at length his method of sample collection aboard the R/V "Atlantis II" and so only those features of collection pertinent to the present study will be discussed here. Standard National Air Surveillance Network (U.S.EPA) high volume (hi-vol) air samplers were used by Dr. Lepple to collect the samples. These samplers draw air through a 20 x 25 cm filter at the rate of between 1.0 to 1.8 m’/min and according to Pate and Tabor (1962) effectively remove virtually 100% of the particulates O.3 pm or greater in diameter. Most palyno- morphs are therefore effectively removed by using this type of sampler although those above 90 pm may be excluded. Some bisaccate pollen larger than 90 pm and other very large grains might then be excluded by using this sampling method. Dr. Lepple collected the airborne detritus on pre- 50 weighed glass fiber (Gelman GF-A) or cellulose acetate (Whatman ##1) filters. Those air-filter samples studied in the present report were collected with a standard hi-vol (GMWL-ZOOO) sampler. However, some of the other samples supplied by Dr. Lepple had been collected by an Andersen cascade impactor (Mbdel 65—000) which aerodynamically separates airborne particulates into 5 size fractions. For the collection of marine aerosols samplers were located well forward of the ship's stack and approximately 10 m above the sea surface. Dr. Lepple's other hi-vol samplers were located on the coast of Africa in Mauritania, one at Tour Bleu (9 m above sea level and actually 5 m above ground) and another at Nouadhibou Airport (10 m above ground). The airport sampler was oriented north-northeast being that this was the predominant wind direction and the sampler at Tour Bleu was oriented towards north (Lepple, 1975). Samples from R/V "Atlantis II"-1966 cruise were collected on 20 cm diameter Delbag—Microsorban Dry Lager Air Filter Medium 99/97 Microsorban. Sample Treatment Introduction: Owing to the variety of different sample types in the study any uniform treatment between types was precluded. However, all samples of one particular type or series were treated uniformly except where samples had been collected on different filters. Since filters of three different compositions were used in sampling the 51 aerosols three different maceration schedules were necessary. None of the samples in the study were indurated sediments, consequently no preliminary crushing or sizing was necess- ary. Bottom Sediments: Since both acid insoluble plant microfossils (pollen, spores and dinoflagellates) and acid soluble plant microfossils (diatoms and opal phytoliths) were to be studied in this project two separate processes for concentrating these entities were employed. Schedule 1: Concentration of pollen and spores (a) Place about 0.5 to 3 grams of dry sample (weighed to four decimal places on a mettler balance) in a beaker and cover with HCl (10%); wash three times with distilled water after reaction ceases. (All samples disaggregated at this stage). (b) Cover sample with HF (50%) and allow to stand for 48 hours with frequent stirring; wash while heating one to three times with HCl (10%) to remove silicofluorides; wash three times with distilled water. (c) Separate clays from sample with heavy liquid (anlz of specific gravity 1.95). (d) Transfer sample to 15 ml glass centrifuge tube and dehydrate with glacial acetic acid. (e) Acetolize the sample (acetolysis mixture consists of 1 part concentrated H280. (95%), added slowly to 9 parts acetic anhydride) in a fume hood heating to a temperature of 70-80’0. (Maximum time involved-5 minutes) 52 (f) Reduce the specific gravity with glacial acetic acid and wash once with the same; wash three times with distilled water. (g) Transfer to small vial and cover with H.E.C. (Hydroxyethyl Cellulose WP-09, Union Carbide Corp.). (h) Mix residue thoroughly and transfer one drOp to a coverslip (average dr0p equals 1/200th of total mixed residue) using a Pasteur pipette and effecting as even a distribution as possible. Allow residue to dry on the hot plate and then mount on a microscope slide with one to two drops of H.S.R. (Harleco Synthetic Resin). Allow slides to dry and set in an oven at 35’C for 24 hours. Generally 3 slides were mounted for each sample processed. Schedule 2: Concentration of diatoms and opal phytoliths (a) Place about 0.01 to 0.5 grams of dry sample (weighed to four decimal places on a mettler balance) in a glass beaker and cover with HCl (10%); wash three times with distilled water after reaction ceases. (b) Cover sample with concentrated HNO, (70%) and allow to stand for a few hours; wash three times with dis- tilled water. (c) Pass sample through a 15 pm sieve retaining both fractions. Coarse fraction contains mainly marine diatoms and radiolarians. Fine fraction contains most of the freshwater diatoms and Opal phytoliths. (d) Proceed with (g) and (h) in Schedule 1, for both 53 fractions. Mbunt coarse and fine fractions separately. Air Filter Samples: Samples on glass filters were not examined for diatoms or opal phytoliths. Mbst of these filters were exposed west of 30' W or north of 25' N where concentrations of these entities are usually low in comparison to areas east or south of these coordinates. Schedule 5: Glass filters (Gelman GF-A) (a) Saturate % of filter (125 cm’) with distilled water (enough to cover) then cover with concentrated HF (50%). Reaction is instantaneous and the filter is destroyed immediately. Wash three times with distilled water. (b) Proceed with Schedule 1, sections (d) through (h). Schedule 4: Cellulose filters (Whatman ##1) (a) Place % of filter (125 cm’) in a 90 ml glass centrifuge tube and cover with cold concentrated HzSO. for twenty minutes. The filter is destroyed during this time but pollen and spores are not appreciably degraded. (b) Centrifuge for ten minutes at 1200 RPM. Separate sink fraction from float fraction retaining both. Sink fraction contains mineral particles and siliceous micro- fossils, some heavy fungal spores and very little pollen. Float contains pollen and spores and very little siliceous material. (c) To sink fraction proceed with section (f) in Schedule 1. 5h (d) Clear sink fraction of sample with KOH (5%) and wash 5 times with distilled water. (e) Proceed with sections (g) and (h) in Schedule 1. (f) To the float fraction successively reduce its specific gravity with glacial acetic acid and then distilled water. (g) Clear with ROM (5%) and wash with distilled water three times and then continue with sections (g) and (h) of Schedule 1. Mbunt sink and float fractions separately. Schedule 5: Microsorban filters (a) Place a measured section of filter into a 90 ml glass centrifuge tube. Cover filter with carbon tetrap chloride (CC14). Filter dissolves within a few minutes. (b) Reduce specific gravity slightly, with acetone (adding too much acetone causes the filter to reprecipitate) and centrifuge, retaining both sink and float fractions. (c) Continue to reduce specific gravity of both fractions until solutions are effectively 100% acetone and water miscible. (d) Wash three times with distilled water and re- combine both fractions. (e) Proceed with sections (d) through (h) of Schedule West African Land-based Samples and Wind-erodible Soils: The schedule used for those samples not studied for siliceous entities was identical to that used for glass filters (Schedule 3). Samples studied for opal 55 phytoliths and freshwater diatoms were processed only through sections (g) and (h) of Schedule 1. Microsc0py Not all the samples processed were productive in regard to containing large numbers of palynomorphs. However, all the samples were examined since those that proved to be barren were critical to the study in so far as their geographic distributions were concerned. Therefore, no suitable minimum number of palynomorphs to be counted per sample could be determined. Some of the bottom sedi- ment sample preparations when counted (even at only 100x magnification) provided zero palynomorphs per traverse while some of the aerosol preparations (viewed at 500x magnification) contained over 50 palynomorphs per traverse. Qpantitative Examination: Slides studied for pollen, spores and dinoflagellates were counted at 500x magnifi- cation on a Leitz Ortholux microscope (Michigan State University No. CC 2667) in vertical traverses covering the total area of the cover slip. Rather unproductive slides with small numbers of palynomorphs were first scanned at 100x magnification in order to reduce the time involved in viewing nonessential organic and mineral debris. Those samples prepared for the study of fresh- water diatoms and opal phytoliths were in general counted at 1000K or 500x magnification on a Zeiss phase contrast microscope (Michigan State University No. CC 2702) over a number of random vertical traverses until 200 entities had 56 been counted. The number of traverses in most instances did not exceed ten since some contained over 100 palynomorphs each. In the above procedures every effort was made to identify the palynomorphs to generic and specific taxonomic level. When this was not possible they were identified to familial level or placed in some useful morphological group. The only exception to this was in counting marine dinoflagellates which were all considered as a single discrete category. In order to determine the "absolute" number of some particular taxon or group of palynomorphs in one gram of original sample the following equation was employed: the total number of a particular palynomorph on the number of counted slides x the reciprocal of the aliquot used from the vial of residue x the reciprocal of whatever fraction of one gram was used in processing = total number of that particular taxon in one gram. In order to obtain "absolute" numbers from macerated filter samples the area of filter used had to be related to the total volume of air passed through the filter or the total weight in grams of sediment retained on the filter before the above equation could be used. Qpalitative Examination: In general, the only samples studied qualitatively were those collected as wind-erodible soil or as aerosols above the African continent. They were primarily examined to determine the relative percent- 5? ages and geographic occurrence of particular palynomorph taxa in order to determine the possible provenance and relative importance of the same taxa found in bottom sediments or marine aerosols. Relative abundance was determined by counting up to 200 palynomorphs per sample (generally on three slides) under either the total cover slip surface or a number of random vertical traverses. Some of the less productive samples, however, were rather limited as to the type of data they could provide and could only be studied in relation to the presence or absence of certain taxa, this limitation being generally a function of either sample lithology or collection site geography. Phptggraphy The majority of the photomicrographs (Plates 1-22) were taken with a Leitz Orthomat microscope camera mounted on a Leitz Ortholux microscope using Kodak Panatomic-X film. Photographs were printed on medium weight Kodak polycontrast rapid RC paper. African Reference Samples Reference samples of African pollen and spores from thirty-five individual families in the Michigan State University pollen herbarium were studied and photographed as an aid to identifying some of the palynomorphs in the present study. Other herbarium material was also utilized for determining various taxonomic affinities and at least familial rank for some of the unknown palynomorphs in the 58 study. Afr c P 10 cal L'terature Most of the useful palynological reports with refer- ence to the existing tropical and northern African vegetation have been mentioned in the section on previous work (p. 12 this report). However, the major Ethiopian studies of Bonnefille (1969, 1971a and 1971b) were also extensively used, as was that of Sowunmi (1973), for palynomorphs produced by Nigerian woody plants. Literature on Specific Vegetation Arrays in Northwestern Africa Used in the Study A number of papers were consulted during the study for information about specific vegetation associations in North West Africa in order to facilitate the connection of palynological data with possible source vegetation. The following papers were important for determining vege- tation arrays in Senegal (especially in the vicinity of Dakar where some of the samples in the present study were collected): Trochain (1940), Roberty (1952), Adam (1955, 1956, 1957, 1958, 1961a, 1961b, 1962a, 1962b, 1962c, 1962d, 1963, 1964a, 1964b and 1965), and Berhaut (1967). Adam (1966), also studied the vegetation of the Mauritanian aftouts and this type of information on the coastal vegetation of areas where both air and surface samples were collected (in Mauritania and Spanish Sahara) was of the utmost importance to the present study. Other studies obtained for information on vegetation groups in 59 Mauritania include: Naegelé (1958a, 1958b, 1959 and 1960), Monod (1952 and 195A) for the western Saharan section, and Gauthier-Pilters (1975) for the Zemmour area. Major works consulted for information on the vegetation of the Sahara included: Ozenda (1958) and Quézel (1965). Lapie and Maige (1914), was consulted for information on the forest flora of Algeria, Tunisia and Morocco, as were the more up-to-date Quézel and Santa (1962 and 1963) for the Algerian flora, and Nogre (1961 and 1962) for that of western Morocco. Literature pertinent to the montane or altitudinal vegetation communities in Sierra Leone included Cole (1967 and 1968) and Jaeger (1965) and a comparative study on the forests of Sierra Leone and Liberia by Adam (1969). Liberian coastal vegetation has been studied by Adam (1970). Contributions to the study of Guinean vegetation associations and flora include: Devois (1948), Jaeger and Schnell (1958), Adam (1968), and in the Fouta Djallon, Killian (1951). All of these papers were consulted during the study. Various papers on Ivory Coast pteridophytes used during the study include reports by Des Abbayes 23 §;.. (1951 and 1953), Adams (1956), Des Abbayes and Tardieu- Blot (1956) and Hall and Bigger (1974). Adams and Alston (1955) also studied pteridophytes in Ghana. Literature of a more general nature on the West African vegetation consulted during the study includes 60 the following: Schnell (19h5 and 1950), Roberty (1953, 1954a, 1959b, 19540. 195#d and 1955). Nielsen (1965). Church (1968), Eyre (1971), and Hutchinson and Dalziel (1972). PRESENTATION OF DATA Introduction A series of maps was prepared showing the geographic distribution, abundance or relative frequency for particular taxa of palynomorphs in both aerosol and bottom sediment samples (Figures 10 to #8). Certain interesting distri- bution patterns emerged on the maps and will be discussed in due course. In analyzing the aerosol data, temporal considerations necessitated somewhat disjointed contouring, because samples were collected during different seasons. Those samples collected during the winter were mainly from the Gulf of Guinea and so data from here are contoured as a separate geographic entity. The majority of samples north of the Azores were collected during late spring and early summer and so again are treated as a separate contourable entity. Consequently, absolute numbers of palynomorphs in these two main areas bear no relationship to each other. 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V .3. 100 paws on» 809% undamom .mm mnamoawz r . .4 . p Ammmp Aoudfisv pmmoo nwofium< mo mNHm ma omwouomn Hanowpsnfiuumfia .w: ouswfim ,3. b L Q #1 “\W. o .\11//// o . \l\o/oib b! ‘1 0 ago;- o..eo=< .mi ... : .0! .0 £510.53 :53 3.05.; on... o. .75: do. :50. ...-Eu... :2... .o 2.2.. .1. ‘ .. I'd) ut< owmnm>¢ Homo nmpwsnmoum nopmsnmcph downpm :cHHom canamm tommfifiho mmmpl:HH mflnnmflvd: wnfihsn cmamamm aa< mo poem: canso pom msmnoaosmamm no momma Mono: mo muonsaz "m canoe 110 and one billion diatom fragments per gram of dust (Figure 17). Greater concentrations offshore (in Figure 16) may be associated with the greater numbers of smaller diatoms compared to larger individuals (in particular of Melosira granulata) over 500 km from the coast. Fragmentation of these freshwater diatoms is probably mainly the result of impact and abrasion during aerosol residence. However, some may become broken as a result of alternately wetting and drying at the site of growth (Cross, 1979, pers. commun.), or as a result of water transport before becoming incorporated into the aerosol. Bottom sediments contain appreciable numbers of freshwater diatoms in two areas of the Northeast Atlantic (see Figures 18 and 19). These two areas include a northern zone above 25'N and a more important southern zone south of 20'N. The northern zone is the least important and contains generally less than 0.5 million freshwater diatoms per gram of sediment. Parts of the southern zone contain over 10 million freshwater diatoms per gram of bottom sediment especially towards the Niger delta, off the coasts of Sierra Leone and Liberia and on the Cape Verde terrace west of Dakar, Senegal, 500 km offshore. Although stream transport may be responsible for contributing freshwater diatoms to bottom sediments off Liberia and in the Gulf of Guinea these two areas also coincide with major areas of dust storm activity (at least during 1973) and so a major contribution to 111 bottom sediments may indeed be from eolian sources (cf. Figures 17 and 18). The area of the Atlantic with a high abundance of freshwater diatoms in bottom sediments off Senegal seems to be directly of eolian origin since influence from the Senegal River is not considered to be of importance 500 km offshore. However, concentration by ocean current action should be entertained as a mechanism for producing the pattern observed. The westward bulge of diatom isopleths off the coast of Mauritania and the smaller triangular wedge off Spanish Sahara must be directly related to eolian transport. The former due to the proximity of the Sahel and dry lakes in Mauritania and the latter to the many large coastal sebkas in Spanish Sahara and inland dry lakes along the Mauritania-Spanish Sahara border. Since no large streams can possibly discharge fresh- water diatoms into the Atlantic north of 17’N an estimate of both eolian and fluvial input can be made. It seems possible that up to 1 million diatoms/gram of sediment could be directly related to an eolian source (especially when a concentration of this size is found between 30’W and 40' W and north of 10' N) but when abundances exceed 1 million/gram much of the remainder could be of fluvial origin, (possibly up to 9 million/gram). This is probably an over simplified estimate and underestimates the eolian contribution to bottom sediments which the author considers should be more, especially when diatom concentrations in 112 aerosols south of 10'N may be five times as high as those north of that parallel. Marine Entities: DINOFLAGELLATES: The salient feature in Figure 20 is the north-south linear along the western coast of West Africa. This zone of elevated numbers of marine dino- flagellates per gram of bottom sediment coincides directly with the upwelling zone along the same coast. The Cape Verde terrace can also be delineated by high dinoflagellate abundance as can other physiographic features of the Northeastern Atlantic such as the Canary Basin which is characterized by low abundance of dinoflagellates. However, the Azores Plateau shows low values whereas the Cape Verde Basin shows high absolute values, both contrary to expected results. Another anomally is that observed in the extreme northwest of the study area where high numbers of dino- flagellates are found in bottom sediments west of the Mid-Atlantic Ridge. This area is on the edge of the Sargasso Sea (an area of low productivity) where high numbers of organisms would not be expected in bottom sediments. Another area with low annual net production occurs off the coasts of Guinea and Sierra Leone (Steemann- Nielsen and Jensen, 1957), however, bottom sediments in this area do contain low numbers of dinoflagellates as should be expected. The map showing the ratio of dinoflagellates to 113 pollen and spores per gram of sediment (Figure 21) in general simplifies the data on the previous figure (Figure 20). MICROFORAMINIFERA: Chitinous inner membranes from microforams in bottom sediments (Figure 22) are concen- trated along the area of upwelling with a maximum of BOO/gm of dry sediment off the southern coast of Spanish Sahara and a much higher but isolated maximum directly west of Freetown, Sierra Leone. However, this latter maximum is based on a single sample which was collected in shallower water than the other samples on Figure 22. In general, a decrease in numbers of foram linings can be positively correlated with increasing water depth. Palygofloral Zonation Mediterranean Palynoflora: A characteristically northern palynoflora was encountered in both aerosols and bottom sediments north of 25’N. This flora was character- ized by the following taxa: Olga, Quercus, Betula, Alnus, glmug, and Plantago, bisaccates including Pings and Abigg and members of the Myrtaceae, Umbelliferae, Compositae, Chenopodiaceae-Amaranthaceae, Cruciferae, Gramineae, Cyperaceae and Cupressaceae. During summer (June, 1973) a plume of bisaccate (mainly Pings) pollen in aerosols extended with a tri- angular pattern south from the Azores to the Cape Verde Islands (Figure 25). A general north to south decrease in the relative frequency from 5% to less than 2% was 114 observed but 5% of the atmospheric pollen load for ginnn seems to be too low. However, since aerosols were collected after the main period of pine anthesis (April-May, with Pinnn halepensis being March to May) this may account for the seemingly low amounts in the atmosphere. A somewhat different picture is shown in the relative frequencies of bisaccate pollen in the bottom sediments (Figure 24). The greatest frequency is found west of Madeira and the Canary Islands (up to 60%) and the tri- angular distribution pattern opens out to the northwest and southwest. Part of the northwestern abundance of bisaccate pollen north of 30' N and west of AO' W may be due to North American influence whereas it seems clear that the northeast-southwest elongation of the main part of the distribution pattern is produced by pollen having a southern European and North African provenance (western Mediterranean), being predominantly dispersed by the pre- vailing Northeast Trades. The close spacing of isopleths (Figure 24) west of the Canary Islands may indicate that pollen is transferred from the atmosphere to the ocean somewhere in this vicinity since a rapid drOp in frequency is observed and further southwesterly extension of bisaccate frequencies could be accomplished by ocean current transport. The combined effects of the Northeast Trades and Canary surface current can probably outweigh any northeasterly transport of palynomorphs by Canary bottom currents. The distribution pattern for bisaccate pollen in 115 bottom sediments (Figure 2a) can best be explained after recognition that the pattern is based on relative fre- quencies. The greatest frequency (mentioned above) is some 1000 km due west of the North African coast. The reason for this must be in the fact that bisaccate pollen is both aerodynamically and hydrodynamically best suited for optimum transport when compared to non-saccate pollen grains. Since it travels further away from the African coast than other types of pollen its relative numbers must increase at distance also, even though the absolute numbers of bisaccates may be much greater nearer to the African coast. Qnercus pollen in 1975 aerosols (Figure 25) appears to have a southern European provenance since frequencies increase northwards from the Canary Islands to Madeira. However, distribution patterns in bottom sediments (Figure 26) reflect a Moroccan source for Quercus in addition to that of the Mediterranean area in general. The southern limit for Quercus in bottom sediments seems to be at the 10'N parallel and a clear relationship between prevailing southwestern atmosphere and ocean surface current transport is seen. "Quercoid" pollen of unknown affinity found south of 10°N and east of 20' W is somewhat problematical but is nevertheless plotted on Figure 26. Pollen from Betula shows a southern EurOpean or Moroccan provenance in aerosols (Figure 27) and amounts to over 10% of the atmospheric pollen count east of Madeira. 116 The same source area is suggested from the relative frequencies found in bottom sediments (Figure 28) and Betula can be traced as far south as the equator. The major percentages of Betula are found north and east of Madeira but downwind from the Canary Islands percentages do increase locally. The anomalously high percentage of Betula off the coast of Senegal seems inexplicable. It is quite possible that there is another plant with Betula- like pollen which is not being recognized here (Cross, 1979, pers. commun.). No Betula pollen was encountered in sediments near the coast south from Dakar, Senegal, around the whole coast of West Africa and into the Gulf of Guinea. However, there is a significant distribution of Betula further offshore in part of this area (see Figure 28). It is interesting to note that the eastward bulge in the Betula frequency north of the equator and south of 5’N (Figure 28) coincides with the location of the Equatorial Counter Current. A direct relationship between the two is hard to substantiate however, especially since the current is surficial in character. The transport of Betula pollen through the atmosphere for at least 2000 km (to 30'W) from southern Europe (Figure 27) and 1000 km from the nearest island appears to be demonstrated. It is found as far west as AO'W in bottom sediments and as far south as the equator (Figure 28). Two other taxa have MOroccan or Spanish saharan 117 sources, these being‘ann europaea (Oleaceae) and some members of the Umbelliferae (see Figures 29 and 30). glgn appears not to be transported as far as many other paly- nomorphs originating in MOrocco and local sources in the Canary Islands may be responsible for its high incidence in aerosols off Morocco and Spanish Sahara. ‘ngn euronaea is cultivated on the Canaries and during aerosol sampling must have been in flower (flowering months being May-June). Pollen from some Umbelliferae was found in aerosols as far south as the Canaries but was not encountered in any of the bottom sediments. Surprisingly, Qléé pollen was not encountered in any bottom sediments either. Koreneva (1971), however, has encountered.9;nn pollen in western Mediterran- ean bottom sediments. ann europaea has been observed to demonstrate cyclic variation in pollen production (Pinto da Silva, 1960). Evidently odd numbered years have been those of greatest abundance and so it is not surprising that 50% of the pollen in some aerosols collected during early summer 1973 was of this species. Pollen from the Cupressaceae (Figure 31) has a southern European provenance but nlnng (Figure 32) appears to have a more northern European source. Characterization of relative frequencies for these two taxa in bottom sediments could not be attempted because of discontinuous occurrence . Pollen from various grasses was found in north Atlantic 118 aerosols with highest incidence being due north of the Canary Islands (see Figure 33). However, no appreciable amounts of monOporate pollen were found in Northeast Atlantic bottom sediments east of the Azores or north of the Tr0pic of Cancer (Figure 38). Although pollen from the Myrtaceae is found in both Mediterranean and tropical aerosols (in neither of the bottom sediments),that in the Mediterranean is character- istically larger in size. This is because of the presence of pollen from various species of Eucalyptus. Eucalyptus has been planted all over the Mediterranean and its pollen may comprise an appreciable percentage of the pollen rain throughout that area. Horowitz‘nn‘nl., (1975), found as much as 9% in a January, 1968, storm and in May, 1973, 1% of the pollen rain at the eastern end of the Mediterr- anean was Eucalyptus. In Morocco, Panelatti (1960), also found Eucalyptus pollen present in the atmosphere in the Rabat area. A North American provenance is indicated for some palynomorphs by the occurrence 0f.HlEE§ pollen (Figure 34) in increasing percentages towards the west; transport via the westerlies north of 30'N being the probable mechanism of dispersal towards the east. ylnnn does occur in southern Europe but relative frequency patterns appear to oppose such a provenance for its pollen. Distribution limits for Elnnn pollen in bottom sediments (Figure 35) also tends to indicate a North American source area for this 119 palynomorph. Transport of North American palynomorphs some 4000 to 6000 km is possible during major eastward moving dust storms or if vertical circulation elevates palynomorphs to an eastward moving jet stream. Vertical circulation can be associated with pre-frontal turbulence and convec- tion or post-frontal turbulence associated with a rapidly moving cold front (Healey, 1970). Deposition out of the jet stream could then be produced at a tropopause break where vertical circulation is again associated. Healey (1970) offers the jet stream mechanism for dust transport from Australia to New Zealand and Reiter (1963) has reported on the transport of dust from the Sahara to the European Alps via a jet stream mechanism. Saharan Palynoflora: Dominating both aerosols (Figure 36) and bottom sediments (Figure 37) is the pollen of the ChenOpodiaceae-Amaranthaceae. Bottom sediments off Cap Blanc in Mauritania contained Cheno-Am pollen amounting to over half the total pollen and spore count, and aerosols in the same area between middle March to early April, 1974, (Nouadhibou airport) contained an average of over 30% Cheno-Am pollen out of the total count. During the middle of May, 1973, aerosols still contained 15% Cheno-Am pollen 400 km from the coast of Africa. The distribution pattern for the pollen of grasses and sedges in bottom sediments off the West African 120 continent (Figure 38) indicates a close correspondance to the vegetation from which the pollen is derived. The highest frequencies of the above pollen (up to 50%) extend from Dakar, Senegal, in the south to the Tr0pic of Cancer in the north along the coast of Spanish Sahara. This zone extends through the northern savanna vegetation (thorn tree-tall grass), in Senegal, the Sahel along the coast of Mauritania, and the semi-desert scrub in northern Mauritania and Spanish Sahara (see Figure 7). The 10% relative frequency for pollen of the above taxa off the coast of Ghana and Nigeria (Figure 38) could be related to the coastal dry Ghanan vegetation zone as far as a source of the pollen is concerned, being trans- ported in winter dust storms via the Harmattan. Also, some of the pollen from sedges and grasses growing in the Niger delta area could be transported distances of a few hundred kilometers into the Gulf of Guinea. However, a more continental source for this pollen is indicated and will be discussed later. The much larger zone of such pollen southwest of the Azores may be linked to a North American source, but before this idea can be seriously entertained study should be made of aerosols collected over the western Atlantic during a major North American dust storm. The Compositae are second only to the Cheno-Ams as far as abundance and importance are concerned in Saharan and near Saharan aerosols (Figure 39). Along much of the Saharan coast the relative frequency of Compositae pollen 121 is 15%, however, above the ocean south of the Cape Verde Islands the frequency exceeds 40% (middle February to the end of April, 1973). Comparison of bottom sediments in the Cape Verde vicinity produces fair correspondance to aerosol data with a 30%-40% frequency being the average (see Figure 40). Very low percentages of Compositae pollen are encountered off the coast of Dakar, Senegal, yet frequencies start to increase at about 1000 km from the African continent. It may be possible that the Cape Verde Islands are the major source for Compositae pollen found to the southwest of these islands in the bottom sediments. However, a better eXplanation for this increase in Compositae pollen out to sea is the fact that there is relatively little pollen in abyssal sediments to start with and just a few grains of Compositae pollen (ubiquitous as it is) would naturally overshadow the abundance of any other palynomorphs. Van Campo (1975), reports that the ratio of echinulate to fenestrate Compositae decreases to the south in the Sahara. In the present study a similar observation from the Canary Islands to Dakar, Senegal, was realized, however, fenestrate composite pollen was absent from the Gulf of Guinea. Pollen from the Gramineae that represents a northern or Mediterranean flora is evidently ovoid whereas that from the tropics tends to be more spherical (Van Campo, 1975). This was not generally evident in the present study although monoporate pollen from Niger was 122 almost totally spherical. Tropical-Eguatorial Palynoflora: Major components of this flora included pollen of Palmae (especially Elaeis gnineensis), pollen from mangroves (primarily Rhizonhora sp.) and that from the Euphorbiaceae, Combretaceae, Sterculiaceae, Celastraceae, various members of the Leguminosae, Gramineae and Cyperaceae. Although both Cheno-Am and Compositae pollen in combination accounted for up to 20% of the pollen in aerosols, bottom sediments contained less than 5%. This seems to imply that the winter aerosols contained much extra-equatorial material derived from the interior continent during dust storms, although grass and sedge and legume pollen could have had a local source in the dry coastal zone of Ghana. The most abundant pollen grain in Ghanan aerosols was that from Hynenocardia.nnign (Euphorbiaceae) (up to 26%). This arboreal species grows particularly in the southern Guinean or broad-leaved tree savanna zone. During early to middle March, 1973, palm pollen amounted to 10-15% of the count in aerosols in the Gulf of Guinea (Figure 41), although in bottom sediments it amounted to as much as 30% of the count (see Figure 42). Mangrove pollen between 5-1 % of the total in bottom sediments (Figure 43) was not found in the aerosols. No bisaccate pollen was found in Gulf of Guinea aerosols but in bottom sediments west of Ghana up to 30% of the pollen counted was bladdered (see Figure 24). Two possible reasons for 123 finding bisaccates south of 10'N'are: (1) the pollen had been transported by the Southwesterlies from South Africa or (2) it had been transported via the Guinea Current around the coast of Liberia and as far west as Ghana. The second mechanism of transport is probably the most likely even though neither mechanism offers a very satisfactory explanation. The Tropical-Equatorial Palynoflora seems to be quite impoverished as far as diversity is concerned but this is very probably the result of having only a few bottom sediment samples in the Gulf of Guinea and sampling aerosols during the winter. Freshwater Diatom Flora: The most abundant freshwater diatoms encountered in both aerosols and bottom sediments were species of the genera Melosira and Cyclotella. The most abundant diatom altogether was Melosira granulata with three other species Cyclotella ocellata,‘§. stelligera and Stenhanodiscus astraea following in frequency of occurrence. In general M. granulata was observed to increase in frequency offshore in aerosols (Figure 44) and bottom sediments (Figure 45) but a decrease in bottom sediments offshore was noted in the Gulf of Guinea. Coastal Ghana may be an important source for the diatom (fl. granulata since both aerosols and bottom sediments in this vicinity contain the highest frequencies, and the dry coastal Ghanan climate facilitates the erosion of dessicated algal mats on the Coastal and Lagoonal Lowlands 124 (Lower Volta Plain) when the Harmattan prevails. However, a provenance in Niger is indicated as the major source for most freshwater diatoms in aerosols and will be discussed later. Some of the freshwater diatoms that become incorpor- ated into bottom sediments off the Ghanan coast may also have had their origin in the waters of the Volta River. Since the formation of Lake Volta however, the numbers of diatoms transported to the Gulf will probably have been reduced. The high frequency of‘fl. granulata in bottom sediments off the coast of Liberia is again due to dust storm activity. North of 20’N the numbers of freshwater diatoms in bottom sediments decrease but the high frequencies of M. granulata are due to its cosmopolitanism. It is probably the most abundant freshwater diatom in oceanic sediments anywhere in the world. No data were collected for the abundance of freshwater diatoms in aerosols north of 20'N although these entities are to a minor extent present (Stix, 1975). Figures 46 and 47 show the relative frequencies of the freshwater diatom Cyclotella in both aerosols and bottom sediments. This diatom genus is relatively rare off Ghana where‘fl. granulata greatly overshadows it in importance. This is probably because most of the species of Cyclotella become easily fragmented during atmospheric transport. 125 Cyclotella appears to increase in frequency away from the African continent especially in the Gulf of Guinea and this is probably a result of the larger diatoms dropping out of dust storms closer to the coast. A similar situation is illustrated (Figure 48) by the decrease in size of M. granulata seaward from the West African coast. DISCUSSION Palynomorph Provenance Three palynofloras were recognized in the study which represent in gross form the major climatic-vegetational zones of Northwest Africa. The northern Mediterranean palynoflora was the most complete in so far as repre- senting the major families of plants in the Mediterranean and was the most readily recognizable both in aerosols and bottom sediments. Since both air and oceanic transport systems trend northeast to southwest the similar trend in bottom sediment palynomorph distributions proved to be fortunate. Two general source areas for the Mediterranean palynoflora were recognized i.e., (1) Morocco and (2) Southern Europe. Since both of these areas have a similar flora, local meterological conditions probably determined where in the western Mediterranean the pollen in the aerosols originated. The overall picture of source is better provided by bottom sediment distributions al- though both aerosol and bottom sediment distributions for many taxa are complementary. Certain palynomorphs in the Mediterranean palynoflora appeared to have a more northern provenance e.g., Alnng (perhaps northern Europe) whilst others e.g., Olea may 126 127 have had a more restricted origin (possibly the Canary Islands). Furthermore, a North American provenance is not discounted for a variety of palynomorphs including glnng. The Saharan palynoflora could be directly correlated with its source vegetation in Mauritania, Mali, and Senegal since the major components i.e., pollen from the Gramineae, Cyperaceae and Chenopodiaceae-Amaranthaceae, were derived from the grasslands of the savanna and sahel and the desert scrub areas directly east. Pollen from the Leguminosae was sparse to non-existent in both aerosols and bottom sediments west of the savanna vegetation zone, although in the southern part of the palynofloristic zone in the vicinity of Dakar, Senegal, minor amounts were present. In soil samples from Niger however, the Legumin- osae were well represented palynologically. The reason for soil samples containing large amounts of legume pollen when aerosols contain very little is probably a function of the large size of legume pollen. It is therefore transported only short distances through the atmosphere, mostly by insects and thence by gravity to the soil. Pollen in the Caesalpinioideae and Papilionoideae for instance may reach over 70 um (cf. Baikiaea robynsii, 140 Pm) and that in the Mimosoideae over 100 Pm in polyads. Surface pollen spectra from desert areas south of the Tr0pic of Cancer tend to be dominated by pollen of the Gramineae and Cyperaceae (Van Campo, 1975). In this respect Van Campo cites Assemien (1971), as reporting 128 that in the Sebkha de Chinchane in Mauritania (450 km east of Cap Blanc) pollen is exclusively from the Gramineae and Cyperaceae, as it is in the Sebkha of Taoudenni in Mali (1300 km east of the Cape). In the present study then, it is somewhat surprising that aerosols did not contain appreciable quantities of grass and sedge pollen, although bottom sediment samples off the Saharan coast contained up to 50% of the pollen count in the form of Gramineae and Cyperaceae (cf. Figures 33 and 38). The tropical-equatorial palynoflora was low in diver- sity even though pollen from both savanna or sahel and rain forest vegetation was present. Major reasons for this are: (1) that trees of tropical and equatorial regions are predominantly entomophilous and release little pollen into the air (Whitehead, 1969; Proctor and Yeo, 1972; and Van Campo, 1975), (2) aerosols were collected during the winter dormant season in the Gulf of Guinea, and (3) the prevailing winds are from the southwest and blow onshore except when the winter Harmattan is present. Under the influence of the Harmattan appreciable numbers of pollen grains are injected into the atmosphere (in dust storms). It appears that pollen grains of a semi-desert scrub character (mainly grasses) may be derived from the alluvial plain of Bilma in Niger (18’ N, 12' E) and off the southern and western flank of the Tibesti massif in the vicinity of Faya Largeau in Chad (18'N, 19'E) since this is the source area for dust in the Harmattan (Wilson, 1971, and Kalu, 129 1979). Surface sediments studied palynologically from Niger (southwest of Bilma) show a profile dominated by pollen from grasses and sedges (up to 60%) and so the provenance for grass pollen is probably Niger and Chad rather than coastal Ghana as was mentioned in the previous section. Nevertheless, the latter should not be overlooked as a possible source for such pollen. As the Harmattan blows across Nigeria it incorporates pollen from savanna vegetation into its particulate load and this is probably the reason for high frequencies (26%) of the euphorb Hymenocardia.nn;nn in Gulf of Guinea aerosols. Sowunmi (1976), also finds up to 10% of this pollen grain in honey from the southern savanna zone (broad- leaved tree savanna). Most of the pollen in the Gulf of Guinea aerosols derived from rain forest vegetation is primarily that from canopy species such as inn cordifolia (Sterculiaceae) and members of the Combretaceae. Since the Harmattan traverses many of the West African vegetation zones the palynology of dust storms necessarily reflects this, and elements from desert, savanna and tropical floras are therefore present in the tropicaléequatorial palynoflora. Overlap of palynofloral elements is also found in the desert palynoflora. Here some typically Mediterranean or northern forms e.g., Conylus avellana are found. According to Van Campo (1975), desert paly- nology north of the tropics is influenced appreciably by the pollen produced in the Mediterranean basin. 130 The diatom flora in Gulf of Guinea aerosols indicates that its provenance is probably the same as that of the pollen. All the important species of freshwater diatoms in aerosols are found in the Ennedi highlands area of Chad (see CompEre, 1970) on the western flank of the Tibesti and in Lake Chad itself, in the common corner of Chad, Niger, Nigeria and Cameroon. Seasonal Provenance and Transnort Seasonal changes in both dust transport and provenance are evident and have been reported by a number of workers. The winter provenance in the vicinity of Bilma has been previously discussed (p. 128) and the summer source for dust that is transported out into the Atlantic over Mauritania and Morocco is evidently in the Tamanrasset area to the west of the Hoggar Massif in Algeria (Kalu, 1979). Winter aerosols have plant detritus characteristic of a sahelian or savanna vegetation, and are loaded with diatoms and opal phytoliths. A change in dust provenance during summer should not necessarily change the type of palynological material within the dust since source areas have similar vegetation types. However, pollen and spores from the Mediterranean vegetation are a major component of summer aerosols. Smaller concentrations of freshwater diatoms and opal phytoliths are characteristic of summer dust. During winter, dust is transported by the north- 131 easterlies to the Gulf of Guinea north of the Intertropical Discontinuity (ITD). During summer however, the ITD moves north of the Gulf and hence the major dust trajectory also moves north and west across the desert to affect Mauritania, Morocco and Spanish Sahara. Temnoral Considerations in Aerosol Sampling In studying aerosols palynologically it is of the utmost importance to know the time of flowering of angio- sperms near to sampling. Exemplification of this can be seen in the present study with the distribution of pollen in the atmosphere from ann euronaea (Figure 29) and which is not found anywhere in bottom sediments. Due to the cyclic nature of pollen production by the olive, that which was collected during middle to late June of 1973 at the end of the flowering season probably repre- sents an appreciable percentage of the total glgn pollen produced in Morocco or the Canaries every two years. Therefore, one would expect glnn pollen to be found in bottom sediments in this general area even though it is apparently not. One would have expected pollen from Pinnn to have been more abundant in aerosols than was found in the study, except that these samples were collected after the major pine pollen season. Therefore, as far as relative abundance is concerned for a particular taxon, aerosols and bottom sediment distribution patterns may have little correspondance. 132 A particularly good example of the importance of the time of collection in the analysis of data is demonstrated in Table 5, p. 109. Aerosols were collected from early February to early May, 1966, from Woods Hole, U.S.A., to Freetown, Sierra Leone, and back. Samples collected off the east coast of North America and in the Caribbean (AF 37 and 38) in early February contrast with those collected in similar geographic positions (AF 49 and 50) in early May (see Figure 2, p. 3). No pollen and spores were found in early February compared to nearly 6 per cubic meter of air sampled in early May (Table 5), off the North American coast. Similarly, in the Caribbean, 0.3 pollen and spores per cubic meter of air (9-12 February) contrasts sharply with 3.7 grains per cubic meter of air collected between 29 April and 2 May. Seasonal influence is also apparently demonstrated with the doubling in quantity of palynomorphs in the atmosphere, when comparing aerosols AF 39 (12-14 February) and AF 48 (26-29 April). Distance of Transnort with Relation to Size of Palynomorph Opalescent particulates associated with the Harmattan, in general range between 1.3 to 2 pm in size (El-Fandy, 1953). Most of the organic particulates found in Gulf of Guinea aerosols in the present study (characterized as diatom fragments) were also ca. 2 Pm in size. If these particulates have a Bilma provenance then in transport to the Gulf of Guinea a distance of 2500 km is involved. Freshwater diatoms 10 pm in diameter in appreciable 133 quantities (more than 500 per cubic meter of air) from "Atlantis II"-1966 cruise aerosols were found 3000 to 4000 km from the African continent. If their source was the Bilma alluvial plain or Chad then a total distance of transport greater than 6000 km is possible. Tertiary diatomites on the western flank of the Tibesti Massif may also have served as a source for some of these airborne diatoms. In most instances the size of a pollen grain cannot be accurately related to distance of air transport since under one set of meteorological conditions a large grain may be transported further than a small grain under another set of conditions. The problem of aggregation may also limit the distance to which small grains may be dispersed. In the present study aggregation of small grains especially Cheno-Ams in desert aerosols and Artemisia in Mediterran- ean aerosols, was common (see figure 4 in Plate 8). Since most aggregation involved mineral particulates and palynomorphs, this effectively increased the specific gravity of the palynomorph and probably caused premature sedimentation. Lepple (1978, pers. commun.), indicated that the aggregation of organic particulates with more dense inorganic aerosol components might strongly affect fallout patterns at the sea/air as well as the water/ sediment interfaces. Hence in discussing palynomorph transport, the minimum distance of dispersal is probably the most reasonable estimate that one can make. 134 Relationship of Palynomorph Distribution Patterns to Transport Mechanisms Surface Ocean Currents: The salient oceanic trans- porting agent in the study area is the Canary Current. A clear definition of this agent is demonstrated by the northeast-southwest elongation for the distribution of Quercus pollen in bottom sediments (Figure 26). Although the relative frequency of bisaccate pollen in bottom sediments shows a similar distribution (Figure 24) it appears that it is more related to air transport than Quercus since bisaccate pollen shows its greatest frequency over 1000 km west of Morocco whereas Qnercus only 100 km offshore. Deep Ocean Currents: The plume of both pollen and fungal spore concentrations directly west of Gibraltar may reflect the spreading of the dense saline Mediterranean waters out into the Atlantic, especially since these palynomorphs are lower in concentration closer to the Iberian and Moroccan coasts. Fungal spores however can be better related to the abundance of dinoflagellates north of Madeira. The distribution of Qnercus pollen in bottom sediments (Figure 26) may also reflect the spreading of saline Mediterranean waters out into the Atlantic, even though its distribution was discussed above in relation to surface ocean currents. The influence of this Mediterranean water is evidently felt as far south as the equator and as far 135 west as the Azores (Kuenen, 1950). Fluvial Transport: No clear mechanism involving the fluvial transport of palynomorphs can be demonstrated by the present study. However, certain inordinately high concentrations of pollen and spores south of 15'N (see Figure 11) off the coast of Sierra Leone may be related to fluvial transport and very high concentrations of fungal spores in the Bight of Benin off the Nigerian coast (see Figure 13) may reflect proximity to the Niger delta and transport of fungal spores from its vast hinterland out into the Gulf of Guinea. The low abundance of opal phytoliths in the Gulf of Guinea bottom sediments east of 10'W Opposed to highly abundant freshwater diatoms in the same area probably indicates fluvial transport of diatoms associated with the delta swamps and the whole Niger drainage system. Eolian Transport and Storms: The clearest evidence for palynomorph transport by the wind is demonstrated in most of the previous distribution figures concerned with aerosols (cf. Figures 10, 17, 23, 27, 29 and 34). Distri- bution patterns for palynomorphs in aerosols show clearly that north of 15'N summer aerosols are dependent upon the Northeast Trades for mobility and that during the winter, south of 10'N the Harmattan is the predominant transport agent for palynomorphs (mostly freshwater diatoms). The importance of the winter Harmattan system as a transport mechanism for pollen from Niger and Chad has been emphasized 136 previously. That storms are significant in affecting the distri- bution patterns of palynomorphs in both aerosols and bottom sediments seems unquestionable. The distributions of freshwater diatoms and opal phytoliths off the coasts of Ghana and Liberia attest to this significance, especially in the atmospheric samples but also in the bottom sediments. South of 20' N or 25'N distributions of the above entities in bottom sediments can be related to major dust storm activity and to the distribution of haze frequency shown by Folger np,nl., (1967), and Turekian (1968). Mechanisms for Incorporation of Palynomorphs into the Atmosphere and Subsequent Transport Kalu (1979), discusses dust propagation in light of there being three phases to the process; i.e., the instantaneous, the spreading, and the equilibrium phases. In the instantaneous phase dust particles are injected into the atmosphere due to surface wind and vertical turbulence. According to Kalu (1979), in this phase no horizontal motion is involved. After the dust reaches a particular elevation the wind velocity becomes strong enough to transport it horizontally; this is the second phase in the system of dust propagation. The final or equilibrium stage in the prOpagation system is supposedly controlled by the prevailing winds and evidently starts some hundreds of kilometers downwind of the previous stages (Kalu, 1979). The prevailing wind is the most important meteorological 137 factor controlling dust transport (Kalu, 1979) and in this respect the upper winds are those primarily responsible for its transport, with the 900 mb pressure level being on the average the height of maximum dust transport. At this level wind velocities are around 56 km/hr. Since the threshold value for raising dust off the ground is about 22 km/hr (Morales, 1979) once the dust and pollen gets up above the 900 mb zone (often 1 km above the ground) it should then travel without settling for consid- erable distances. The dust evidently travels with an anvil-like leading front above a lower less dusty atmos- phere. One of the most important factors controlling atmos— pheric dust transport and hence deposition is the moisture content of the atmosphere (Kalu, 1979). The particulates act as condensation nuclei and if the dust storm passes through a humid parcel of air, haze or fog may be produced and then precipitation of the particulate load ensues. The importance of grassland fire as a mechanism for introducing palynomorphs into the atmosphere when compared to dust storms is minimal. Charred plant detritus in aerosols west of the Sahel and the Savanna was sparse. Since temperatures during brush fires may reach 560’C at 50 cm above the ground and 375’C at 1.5 m (Pitot and Masson, 1951) it is unlikely that much grass or sedge pollen could survive this type of treatment. Pollen within the top 1 cm of soil however, would not be appre- 138 ciably affected by these temperatures and along with the soil would be subjected to deflation after the fire. Temperatures at ground level during fires rarely exceeds 100’ C to 140’ C although aberrant temperatures of up to 350'C have been recorded by Pitot and Masson (1951). Even though fire may not be the mechanism of injection of pollen and spores into the atmosphere it may prepare the soil surface for deflation and hence injection afterwards. Opal phytoliths should not be appreciably affected by the above temperatures and injection into the atmosphere from plant tissues is probable during major fires. This could not be substantiated however, in the present study. The Use of Deep-Sea Palynology for Determining Terrestrial Vegetation Zones in the Geologic Record Probably the best indication of an arid or desert vegetation type is the association of pollen from the Gramineae, Cyperaceae, Chenopodiaceae-Amaranthaceae and Compositae. A totally herbaceous character could be eXpected up to 1000 km seaward of the desert coast. However, much caution would have to be exercised in the interpretation of such a palynoflora in the geologic record since wind directions and ocean currents may trans— port other types of pollen into the area. In the present study it is fortunate that the Canary Current turns west- ward north of the Cape Verde Islands and transports many northern pollen types away from the desert coast. The characterization of a Mediterranean vegetation 139 type from bottom sediments should be much more difficult in the fossil record, especially since cool-temperate types of palynomorphs may also become incorporated into those sediments along with palynomorphs from the Medi- terranean. In addition, the producing plants may grow in both vegetation zones. A further problem is that palynomorphs characteristic of a Mediterranean vegetation (such as ann) may not be incorporated into the bottom sediments. Pollen from Quercus and Einnn dominating deep-sea sediments as in the present study, indicate a temperate climate and vegetation just as well as a Medi- terranean type of climate and vegetation. A tropical flora can probably not be reliably deter- mined from bottom sediments unless indicator palynomorphs such as the Palmae or possibly mangroves are present. The tropical palynoflora in the present study contains at least 50% sahelien or savanna type palynomorphs and there- fore only 50% can be considered truly trOpical-equatorial in character. The added problem of low pollen production in the tropics makes it necessary to study those palyno- morphs of low frequency in bottom sediments more carefully. In the geologic record a tropical palynoflora might just as easily be considered semi-arid when high percentages of pollen from dry climatic zones are present. CONCLUSIONS 1) Three palynofloras with specific geographic extent off Northwest Africa were detected in both aerosols and bottom sediments of the Atlantic Ocean. These three palynofloras are here identified as the Mediterranean, the Saharan and the Tropical-Equatorial. 2) The Mediterranean palynoflora is the most diverse (in terms of number of taxa present), the Saharan the most discrete (in terms of ease of characterization) and the Tr0pical-Equatorial the most complex (in terms of demon- strating the greatest amount of overlap in provenance). 3) The freshwater diatom flora of the sediment samples and aerosols is characterized by low diversity with three taxa dominating. 4) Vegetation in southern EurOpe and Morocco serves as the source for the Mediterranean palynoflora; desert playas (sebkas) in Mauritania and Mali west of the Hoggar Highlands are probably the sources for palynomorphs in the Saharan palynoflora; and in the Tropical-Equatorial palynoflora pollen and spores are derived from two sources: (i) the grasslands and desert scrub in Niger and Chad (distal source) and (ii) the tropical rain forest (canOpy stratum) and Mangrove swamps along the coast of the Gulf of Guinea 140 141 (proximal source). 5) The distribution of palynomorphs in aerosols demon- strates preferred orientation to the prevailing wind direction. This same orientation is found in bottom sed- iments but becomes even more pronounced where ocean currents and prevailing wind directions are complementary, as with the case of the Northeast Trades and Canary Current. 6) Freshwater diatoms in bottom sediments are distributed in two major geographic zones. These coincide with the northern (summer) dust storm area north of 25'N and a southern (winter) dust storm area south of 20'N. 7) The upwelling zone off the coast of West Africa is well defined in bottom sediments by a pronounced north- south linear of dinoflagellate concentrations. Both fungal spore and microforam abundances in general parallel the dinoflagellate trend. 8) The abundance of pollen and spores in general decreases offshore from the African continent, although an anomalous area in bottom sediments southwest of the Azores suggests a North American influence on palynomorph sedimentation in the deep-sea, at least as far east as the Mid-Atlantic Ridge. Some American palynomorphs such as ylnnn may even be transported as far east as the Moroccan coast by the Westerlies. 9) Normally, tropical aerosols contain few palynomorphs. Therefore, it is apparent that dust storms are the major transporting agents for pollen and spores (as well as 142 freshwater diatoms and Opal phytoliths) from the West African interior to the Gulf of Guinea. 10) The greatest concentrations of pollen and spores in the atmosphere were found to occur in Mediterranean and Moroccan aerosols (collected during the early summer) and in general were an order of magnitude higher than those found in tropical aerosols, although the latter were collected during winter. However, in bottom sediments, those off the Saharan coast contained the greatest concen- tration of these entities. Fungal spores were the most abundant acid insoluble palynomorphs in both tropical aerosols and bottom sediments. 11) Appreciable quantities of pollen may be transported over the Atlantic by the Northeast Trades over 5000 km downwind from its source in the Mediterranean. Even greater distances of transport are attained by freshwater diatoms and Opal phytoliths from interior West Africa (Chad and Niger) when an overland transport Of 2500 km is included in the figure. Some Of these entities are transported a further 3500 km from the coast of West Africa, although the majority are deposited within 500 km from the shore. 12) Taxa Of pollen very abundant in aerosols are often apparently absent from bottom sediments. 13) To continue the study of a palynological problem as large in scope as that at present, it would be necessary to integrate some data from water column samples at various depths in the ocean wherever and whenever possible. 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P., and Chester, RC} (eds.), Academic Press, v. 5, p. 103-136. Windom, H. L. and Chamberlain, C. F., 1978, Dust-Storm Transport of Sediments to the North Atlantic Ocean: J. Sed. Pet., v. 48, no. 2, p. 385-388. APPENDIX APPENDIX Location of Palynomorphs Photographed (Plates 1-22) in Department of Geology Slide Collection, Michigan State University Figure WHD\JOWfl$WNDJd 10 Figure (Dme‘JOWflfiflfith d PLATE 1 M.S.U. Slide N0. MS1983-1 MSZO28-3 M52023-3 MS2028-3 M82101-3 M52166-1 MS2037-1 M52027-1 MS2166-2 M52025-3 MS1979-2 M82027-2 MS2098-2 M51973-3 M52025-3 MS2167-2 MSI974-3 PLATE M.S.U. Slide MS1983-1 MS197S-1 M52167-2 MS2024-2 PLATE M.S.U. Slide M32028-3 M52027-1 M52028-3 M52028-3 M52028-2 M52028-3 MSZ107-1 M82026-2 M52022-3 MSZO18-3 162 NO. No. Coordinates 39.7 x 115.3 41.7 x 112.6 38.0 x 115.4 41.7 x 119.5 36.0 x 121.8 27.8 x 119.1 31.5 x 120.0 33.8 x 120.0 36.4 x 119.3 40.6 x 119.3 34.0 x 121.7 3907 X 11609 38.5 x 111.2 25.8 x 122.0 #005 X 11205 33.7 X 117.5 28.7 x 127.2 Coordinates 29.7 X 113.5 29.1 x 124.3 37.5 x 115.6 32.7 x 114.6 Coordinates 37.6 x 118.8 3300 X 122.7 35.0 x 117.6 43.5 X 111.6 34.1 x 118.1 40.5 x 114.8 30.1 x 127.0 40.6 x 116.1 35.1 X 113.0 38.5 x 118.1 \fi$WflthCD(Mw\JOWfi$WNhJ‘ “dd-dad Figure fiCDfiHD\JOWfi$WNR)d dd Figure -P\Nh)d 163 PLATE 3 M.S.U. Slide No. M32020-1 MS2167-1 M32036-6 M52205-1 PLATE M.S.U. Slide M52026-2 MS2036-5 M52020-2 MS2026-2 MS2026-2 M52024-1 MS1968-1 M82027-1 MS1982-1 MS2100-3 MS2027-2 M32024-3 MS2167-1 MSZO98-2 MS1970-2 PLATE M.S.U. Slide MS2OZO-1 MS2027-2 M82027-3 MSZO28-2 MS1989-2 MS2024-1 M52027-1 MS2028-3 M52027-2 M52024-1 M32025-1 PLATE M.S.U. Slide M52028-3 M52166-1 MS1977-2 M82028-1 No. No. NO. Coordinates 3h00 X 12403 31,8 x 117.3 28.0 X 122.0 29.7 X 119.0 Coordinates 39.5 x 115.9 35.9 x 125.1 37.9 x 125.1 3308 x 118.8 40.3 x 119.1 3105 X 122.8 3808 X 1206# 31.6 x 120.0 36.4 x 115.5 30.7 x 110.8 32.0 x 117.4 37.7 X 119.5 25.0 x 115.0 28.9 x 119.0 Coordinates 37.9 X 12209 33.8 x 115.0 38.7 x 115.0 32.2 x 117.0 38.6 X 118.9 35.3 X 113.8 38.0 X 114.7 40.9 X 113.0 34.3 x 117.4 30.7 x 122.1 3709 X 119.7 Coordinates 42.7 x 115.5 37.0 X 11608 32.8 x 119.6 37.3 X 125.3 \Nhr#CDWHmNJOWfl$WNRJd Figure \OOPQC“fl#WfiDJd 10 164 PLATE MS2ZO7-1 M32167-2 M32020-1 "51975-3 MSZO36-3 MSZOZ8-3 M51975-1 M82028-3 MS1989-1 PLATE MS2018-3 M52026-1 MS2102-2 MS2025-1 MS2101-2 MS2026-2 MS2020-1 MS1977-1 M52028-3 MS2020-2 MS2192-1 MS1966-1 MS2101-2 PLATE M.S.U. Slide MS2036-2 MS2166-1 MS2166-1 M32166-1 MS2025-2 MS2025-1 MS2025-1 MS2166-2 MSZO36-3 MS2184-2 M52037-3 MS2027-1 MS2100-2 M32036-5 MS2166-1 MS2166-2 6 M.S.U. Slide N0. 7 M.S.U. Slide N0. 8 No. Coordinates 37.8 X 11908 34.8 x 119.2 3500 X 121.6 3505 X 121.1 40.1 x 116.2 39.1 x 117.0 27.7 x 120.4 3008 X 113.5 35.3 x 115.7 Coordinates 33.1 X 117.8 34.3 x 123.8 36.1 x 121.0 3508 X 12#.8 32.4 X 12209 ##06 X 121.8 31.5 X 123.5 3003 X 11605 32.2 x 117.1 38.8 x 120.5 37.4 x 117.3 3206 X 120.8 34.0 X 12007 Coordinates 30.8 x 121.6 35.9 x 112.3 34.5 x 121.0 3508 X 11903 31.0 x 120.0 31.6 x 123.1 29.4 X 123.4 3302 X 112.2 40.1 x 116.7 42.2 x 119.2 35.7 x 124.7 3107 X 12206 26.9 x 115.5 3700 X 11706 39.6 x 121.6 3#o§ X 118.2 Figure $WNRJHCDWHmKJOWfl$WNth ddddd Figure Gflfi$WNhJHCD¢HXKJOWD¥WflhJd ddddddd Figure WHWNJOWflfiWNDJd 165 PLATE MS2027-1 MS2036-4 MS2026-1 M82026-1 M52027-3 MS2026-1 MS2026-2 MS2027-1 M52166-1 MS2025-2 MS2026-2 MS2036-5 MS2036-4 MS2028-3 PLATE M.S.U. Slide M52027-2 MS2025-2 M82036-6 M52026-1 M32036-5 MS2037-1 MS2166-1 M82166-2 MSZO28-2 MS2027-2 MS2027-1 MS2036-6 MS2025-2 MS2028-3 M52167-2 MS2028-2 PLATE M0S0U. Slide MS2042-1 M52038-4 MS1968-3 MS2039-1 MS2039-2 MS2039-1 MS2039-1 M52178-1 MS2178-1 9 M.S.U. Slide NO. 10 No. 11 No. Coordinates 38.4 x 112.4 3607 X 11807 39.8 x 112.8 30.6 X 1230# 3500 X 12207 #202 X 12002 44.5 X 124.2 37.0 x 121.1 33.7 x 113.4 38.9 x 115.3 37.5 x 116.6 36.2 x 120.2 3N05 X 1160# 41.3 X 114.3 Coordinates 32.7 x 119.0 35.5 x 119.2 30.7 x 115.8 39.7 x 124.7 40.0 x 119.6 30.9 x 114.0 27.0 x 121.1 37.2 x 115.4 34.3 X 113.0 3305 X 118.0 30.2 x 115.0 37.5 X 114.5 41.6 x 113.6 4302 X 1170# 33.4 x 117.8 Coordinates 34.6 x 118.6 37.4 x 121.0 2707 X 115.6 35.3 X 120.0 37.1 x 121.9 3402 X 12104 3306 X 118.2 30.3 x 117.3 32.5 x 115.4 Figure 10 11 12 13 14 Figure mum-downthni- 1O —Id-&-fidufl-ldwd 166 PLATE MSZ178-1 MSZO40-3 M52207-2 M52208-2 M52208-1 PLATE MS2031-2 MS2178-2 MSZ178-1 MSZ172-2 MSZO98-2 M82174-1 M52207-1 MSZ178-2 MS2174-2 MS2178-2 M52032-4 MS2031-1 MSZ178-2 MSZO39-1 MSZO42-3 M52032-3 M82172-1 PLATE M.S.U. Slide MS2097-1 MS2178-1 M52098-3 MS2032-2 MS2042-3 M52031-3 M52016-1 MS1967-1 M51967-3 MS1988-1 MSI979-2 MSZ177-1 MS2178-2 MS2178-1 MS1988-2 MS2040-2 M82040-1 MSZ100-1 11 M.S.U. Slide N0. 12 M.S.U. Slide NO. 13 No. Coordinates 30.7 x 114.2 32.4 x 117.4 44.8 x 125.0 37.6 x 111.1 Coordinates 29.3 x 117.6 41.7 x 113.0 37.7 x 117.7 40.6 x 120.7 43.9 X 117.4 28.1 x 112.7 3708 X 119.8 3300 X 121.8 28.7 x 115.6 31.4 x 117.6 42.3 x 114.3 36.6 x 120.2 31.2 x 118.2 40.6 x 117.6 37.2 x 116.2 3808 X 11306 3807 X 11007 Coordinates 40.5 x 126.8 37.7 x 123.4 26.3 x 113.0 34.3 x 114.7 35.6 x 114.3 40.4 x 120.4 35.5 x 119.2 39.4 x 119.2 3701 X 11805 40.6 x 110.6 3902 X 116.2 3705 x 123.0 3#0# X 11600 #303 X 11004 27.0 X 1160# 3003 X 118.2 35.5 x 117.3 Figure WHfi\JGWfl¥WNth Figure (b\JGWfi¢WNth Figure .a\3f 214 PLATE 22 Opal Phytoliths (All figures X1000 unless otherwise stated) Figure 1-9 Dumbbell types 10-11 Barrel morphologic types 12-18 Rods of various sizes PLATE 22 .31. ”pt; _ nmn ...mw . z r .3 dflfim 11.}. w 5,5,5... -- ..o . “Incas-o ..vrmmph4fi Ream...” - .Oi‘. . J