CORE-TOP CALIBRATION OF THE ALKENONE INDEX VS SEA-SURFACE TEMPERATUREIN THE INDIAN-OCEAN

The alkenone index (U-37(K')) has been calibrated against sea surface temperature (SST) using a suite of 54 surface sediments from the India n Ocean (20 degrees N to 45 degrees S), spanning temperatures between 6 and 29 degrees C (0.2 < U-37(K') < 1.0). A computerized oceanographi c atlas has been used to calculate modern SST for the coring sites. We have constructed two sets of U-37(K')-SST calibrations for various wa ter depths between 10 and 50 m. The first set is based on the comparis on of U-37(K') with annual mean temperatures for all cores. In the sec ond set, we assume that U-37(K') values in surface sediments are linke d to seasonal productivity patterns, and U-37(K') is compared with mea n temperatures at limes of yearly production maximum. In both calibrat ions, the U-37(K') values are strongly correlated with SST, with a bes t fit obtained using temperatures from 10 m and seasonal productivity patterns. The regression line is similar to that found with laboratory cultures of E. huxleyi, and with other calibrations based on recent s ediments from other oceans. Above 24 degrees C the slope of our U-37(K ')-SST relationship is smaller (approximately 0.020 U-37(K') unit degr ees C-1) than the general slope (approximately 0.033). (C) 1997 Elsevi er Science Ltd.