Quaternary Siliceous Microfossils of the Equatorial Atlantic and Their Role for Paleoceanographic Reconstructions

Abstract

The paper presents the quantitative and taxonomic analysis of siliceous microfossils (diatoms and radiolarians) of the ANS-33047 deepsea core (08°16,380′ N, 31°42,870′ W, 4027 mbsl, 5,16 mbsf), from the southern part of the Cape Verde Basin in the eastern equatorial Atlantic. We recognized two groups of radiolarians representing typical tropical-equatorial and temperate North Atlantic microfauna. The assemblage of fossil diatoms includes tropical-equatorial species, as well as freshwater diatoms which indicate the aeolian transfer of particulate matter from Africa. Sporadic distribution of diatoms and radiolarians indicates pulsatile character of silica accumulation in the equatorial zone during the Quaternary, i.e. intermittent periods with relatively intense and definitely weak silica accumulation. Both diatoms and radiolarians were dominant silica producers during the short intervals of marine isotope stages (MIS) 13-8. Their higher concentrations at ca. 513, 430, 300, and 250 ka probably reflect the penetration of highly productive waters of the Equatorial Divergence into the study area. Low numbers of diatoms coupled with the radiolarian abundance during some intervals of MIS 7-1 are probably the evidence of less productive conditions in the surface water layer and the alternating influence of deep-water paleo-upwellings, primarily on the subsurface. The peak of the freshwater diatoms at ca. 464 ka (MIS 12) indicates the possible intensification of deflation processes and the Tropical Easterly Jet transporting aeolian dust f rom African arid areas to the Atlantic Ocean.