Long-chain alkenones and alkyl alkenoates as palaeotemperature indicators: their production, flux and early sedimentary diagenesis in the Eastern North Atlantic

Abstract

The production and fate of long-chain alkenones and alkenoates was examined with regard to their use as palaeotemperature indicators. Alkenoate abundances were higher than previously reported for other regions and more strongly correlated with temperature than was alkenone unsaturation ( U 37 k ), suggesting biogeographical variability in alkenone and alkenoate production in surface waters. We define the AA 36 ratio to parameterize alkenoate abundance and present an empirical temperature calibration derived from our euphotic zone samples for use in the North Atlantic [ T = 17.35 − 25.12 ( U 37 k ) − 26.73 (AA 36 + 93.90 (U 37 k) (AA 36)]. Significant diagenetic losses of alkenones and alkenoates were found within the water column and near surface sediments. In spite of diagenetic losses, the temperature signal recorded by these compounds in the sediments remains largely unaltered, and corresponds to the euphotic zone water temperature during the springtime period of maximum coccolithophorid production and flux rather than the average annual sea surface temperature.