ALKENONE MOLECULAR STRATIGRAPHY IN AN OCEANIC ENVIRONMENT AFFECTED BY GLACIAL FRESHWATER EVENTS

The sedimentary record of a ratio (UK37) of long chain (C-37) unsaturated alkenones is a useful indicator of glacial-interglacial climatic change in the Late Quaternary northern Gulf of Mexico where a planktonic foraminiferal delta O-18-CaCO3 record is complicated by meltwater and/or fluvial events (Williams and Kohl, 1986). Application of a laboratory temperature calibration of the UK37 ratio (Prahl and Wakeham, 1987) to a Pigmy Basin hydraulic piston core record (Deep Sea Drilling Project core 619) suggested that the minimum glacial surface mixed layer (SML) temperature was 8 degrees +/- 1 degrees C colder than the Holocene high SML temperature of 25.6 degrees +/- 0.5 degrees C. This predicted glacial-interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal delta O-18 or foraminiferal assemblage temperature methods (0.8 degrees-2.0 degrees C). This large difference may be caused by local Prymnesiophyte assemblage changes in response to climatically induced hydrographic changes. Interglacial periods may be dominated by pelagic Prymnesiophyte assemblages, while glacial periods may be dominated by neritic assemblages. A combined mechanism of both climatically varying Prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods.