Eolian-transported freshwater diatoms and phytoliths across the equatorialAtlantic record: Temporal changes in Saharan dust transport patterns

The deposition of freshwater diatoms (FD) and phytotliths (P) was determine d from sediment traps for a wide region (20 degrees N-7 degrees S) in the t ropical and equatorial Atlantic, along a N-S transect in the eastern equato rial Atlantic around 10 degrees W and in the western equatorial Atlantic ar ound 25 degrees W. These siliceous organisms are derived from the Sahara an d Sahel regions of Africa, and eolian transport with direct settling over t he open ocean is assumed to be the transport agent. Depositional rates of F D and P revealed strong coupling with seasonal changes in Saharan dust tran sport that are associated with seasonal precipitation patterns, major wind systems, and the geographical extension of the dust plume across the Atlant ic. Mean daily fluxes were highest south of Cape Verde (FD = 9 x 10(4) valv es m(-2) d(-1); P = 2 x 10(4) bodies m(-2) d(-1)), moderately high off Cape Blanc and in the Guinea Basin north of the equator (of the order of 3 x 10 (4) valves m(-2) d(-1) for FD, and 0.7 x 10(4) bodies m(-2) d(-1) for P), a nd consistently low south of the equator and in the western equatorial Atla ntic. In traps north of the equator, seasonal changes were marked. Aulacose ira granulata and A. islandica were the most abundant FU in the traps, rega rdless of trap location and season. However, the number of FD species was h igher in the Cape Blanc and Cape Verde areas. The morphological diversity ( shape and size) of the P assemblage decreased with increasing distance from the African continent. Patterns of FD and P accumulation rates in surface sediments coincided with those in the traps. Robust freshwater diatom and p hytolith records associated with seasonal eolian transport from Saharan and Sahelian regions into the Atlantic furnish clues that can help in our pres ent understanding of the processes linking transport between land, atmosphe re, and ocean.