Offshore transport of neritic diatoms as indicators of surface current and trade wind strength in the Plio-Pleistocene eastern equatorial Pacific

Abstract

The taphonomy of neritic diatoms entrained into, and transported offshore by, the Peru and South Equatorial currents may represent fluctuations in surface current and southeast trade wind strength in the eastern equatorial Pacific (EEP). This proposition was investigated through the construction of a neritic/pelagic diatom ratio (NPDR) which is compared with other palaeoceanographic proxies analysed through the Olduvai timeslab (ca. 2.0–1.75 Ma) at Ocean Drilling Program sites 677, 847 and 851: a new sea-surface temperature (SST) record for all the sites is derived from a diatom transfer function, and upwelling and bioproductivity records are provided by previously published radiolarian and CaCO 3 data, respectively, for site 677 only. Results indicate a consistent relationship between proxy records, suggesting that the presence of neritic diatoms in pelagic sediments are most likely attributable to surface current and trade wind variability. The NPDR has the potential of becoming an extremely useful micropalaeontological tool in multi-proxy palaeoceanographic studies of coastal upwelling systems. The palaeoceanographic history of the Olduvai timeslab in the EEP, as indicated by previous studies, is supported and enhanced by the NPDR and new SST data reported here. The early and late periods of the Olduvai timeslab are characterised by strong upwelling, low SST, and high bioproductivity, and increased trade wind strengths inferred from the NPDR. The mid-Olduvai (1.80–1.90 Ma) appears to have been a period of weaker upwelling, higher SSTs, lower bioproductivity and decreased trade wind strength as indicated by the NPDR. The NPDR is important as it increases our understanding of the relationship between palaeoceanographic processes and trade wind strength in the region.