Temperature and Salinity Effects on Alkenone Ratios Measured in Surface Sediments from the Indian Ocean

Author： Sonzogni C. Bard E. Rostek F. Dollfus D. Rosell-Mele A. Eglinton G.

ISSN： 0033-5894

Source： Quaternary Research, Vol.47, Iss.3, 1997-05, pp. : 344-355

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20#°N-45#°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index ( U 37 K' ) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. The U 37 K' versus SST relationship for Indian Ocean sediments ( U 37 K' = 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops gives U 37 K' = 0.031 T + 0.084 ( R = 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24#° and 29#°C, however, the slope seems to decrease to about 0.02 U 37 K' unit/#°C. For Indian Ocean core tops, the ratios of total C 37 alkenones/total C 38 alkenones and the slope of the U 37 K' -SST relationship are similar to those previously observed for cultures of Emiliania huxleyi but different from those previously published for Gephyrocapsa oceanica. Either E. huxleyi is a major producer of alkenones in the Indian Ocean or strains of G. oceanica living in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C 37 alkenones to total C 38 alkenones lack clear geographic pattern in the Indian Ocean.