Mapping Holocene upwelling in the eastern equatorial Pacific using Radiolaria

Abstract

Recently, an assemblage of Radiolaria characteristic of upwelling has been described from the Peru Current, Oman Margin, and Somalian Gyre regions, and subsequently from the eastern tropical Atlantic. An Upwelling Radiolarian Index (URI) has been developed to monitor temporal variations in upwelling systems. In the present study, the URI has been adapted to map spatial variation in the eastern equatorial Pacific upwelling system using Holocene core-top samples. The results indicate a good correlation between the Holocene URI and the present day thermocline depth, confirming that the component species of the URI are indeed characteristic of upwelling. The URI is a potent tool for reconstructing and monitoring upwelling systems in the geological record, either in time-slice studies over wide geographical areas, or in time-series analysis at one or more sites. Its application is limited only by the availability of well-dated cores, and restrictions by the stratigraphical ranges of the URI component species.