Long-chain alkaenone unsaturation index as sea surface temperature proxy in southwest Bay of Bengal

Abstract

As a proxy of the sea surface temperature (SST), C sub(37) long-chain alkenones (LCAs) preserved in sediments of the southwestern Bay of Bengal and dating back to the last glacial period, were identified in SIM GC-EI MS spectra run at m/z 530.55 (dienone: C sbu(37:2) LCA) and 528.52 (trienone: C sub(37:3) LCA). The yields of LCAs (C sub(37:2) + C sub(37:3)) relative to extractable lipid of the sediment are higher in the glacial than the Holocene sediments by a factor of three. The LCA unsaturation index and the SST calculated from calibration equations showed coherence with delta sup(18)O of the planktonic foraminifer, Globigerinoides ruber. It is inferred that with reference to the Holocene, the last glacial surface sea water was approx. 2.75 degrees C cooler from the alkenone data and was approx. 2‰ more saline from a combination of LCA and d18O data.