NOAA/WDS Paleoclimatology - Kennedy and Brassell 1992 Alkenones, Santa Barbara Basin

Organic molecules preserved in sediments, especially long-chain alkenones, can preserve and record evidence of past climate variations. A dependence of alkenone distributions on temperature has been recognized in cultures of the unicellular coccolithophorid alga Emiliania huxleyi, which survives in sediments and water-column participates. Through this dependence, stratigraphic profiles of the degree of alkenone unsaturation (expressed as Uk37, values) have been shown in several oceanic settings to reflect long-term changes in sea surface temperatures associated with glacial–interglacial cycles. Here we show that annual variations in alkenone unsaturation in laminated sediments from the Santa Barbara basin, off the shore of California, reveal increases in water temperatures which can be linked directly to the observed sequence of El Niño events in the twentieth century. The range and variations in water temperatures, calculated from Uk37 values (12.8–15.2 °C) using the relationship established from culture experiments, broadly correspond to the annually averaged temperatures (11.3–15.2 °C) measured intermittently by the CalCOFI programme at 20 m depth between 1953 and 1984. These results show that, in favourable settings, alkenone unsaturation profiles can provide an annually resolved record of oceanic temperaturechanges, and may constitute a valuable tool for describing and evaluating the history of global climate variability and change.