EQUATORIAL ATLANTIC SEA-SURFACE TEMPERATURE FOR THE LAST 30-KYR - A COMPARISON OF UK'37, DELTA-O-18 AND FORAMINIFERAL ASSEMBLAGE TEMPERATURE ESTIMATES

A recently developed technique for determining past sea surface temper atures (SST), based on an analysis of the unsaturation ratio of long c hain C37 methyl alkenones produced by Prymnesiophyceae phytoplankton ( U37k'), has been applied to an upper Quaternary sediment core from the equatorial Atlantic. U37k' temperature estimates were compared to tho se obtained from deltaO-18 of the planktonic foraminifer Globigerinoid es sacculifer and of planktonic foraminiferal assemblages for the last glacial cycle. The alkenone method showed 1.8-degrees-C cooling at th e last glacial maximum, about 1/2 to 1/3 of the decrease shown by the isotopic method (6.3-degrees-C) and foraminiferal modern analogue tech nique estimates for the warm season (3.8-degrees-C). Warm season foram iniferal assemblage estimates based on transfer functions are out of p hase with the other estimates, showing a 1.4-degrees-C drop at the las t glacial maximum with an additional 0.9-degrees-C drop in the deglaci ation. Increased alkenone abundances, total organic carbon percentage and foraminiferal accumulation rates in the last glaciation indicate a n increase in productivity of as much as 4 times over present day. The se changes are thought to be due to increased upwelling caused by enha nced winds during the glaciation. If U37k' estimates are correct, as m uch as 50-70% (up to 4.5-degrees-C) of estimated deltaO-18 and modern analogue temperature changes in the last glaciation may have been due to changes in thermocline depth, whereas transfer functions seem more strongly influenced by seasonality changes. This indicates these estim ates may be influenced as strongly by other factors as they are by SST , which in the equatorial Atlantic was only reduced slightly in the la st glaciation.