Upwelling and productivity changes inferred from a temperature record in the central equatorial Pacific

Abstract

A SERIES of C_37–39 alkenones synthesized by prymnesiophyte algae is commonly preserved in marine sediments, and can be used for estimating past sea surface temperatures (SSTs)^1,2. Here we present an alkenone analysis of sediments taken from the central equatorial Pacific Ocean (core W8402A-14GC; 0° 57′N, 138° 57′W) which shows that SST varied slightly (<2°C) but coherently with Milankovitch insolation cycles over the past 250 kyr. The in-phase response of the SST to the precessional component of insolation indicates that this part of the SST time series may be driven by changes in local trade-wind strength, and the longer 100-kyr eccentricity component indicates a response to basin-wide South Pacific winds. Using a simple heat-balance model, we use our palaeotemperature record to constrain the upwelling rates that have occurred in the past. Similar SST records from the eastern Pacific could constrain the horizontal advection component of the SST record and allow for better estimates of upwelling. Upwelling and palaeoproductivity then could be compared to determine whether changes in equatorial nutrient levels actually cause equivalent changes in productivity.