PRYMNESIOPHYCEAE AS PALEOCEANOGRAPHIC TOOLS: AN OPEN-OCEAN ASSESSMENT OF ALKENONE δDEUTERIUM AS A PALEO-SALINITY PROXY

Abstract

Sea surface salinity (SSS) is arguably the least constrained variable of the past ocean, which is unfortunate because it is a fundamental variable controlling the density of seawater - thus large-scale circulation - and is also reflective of the hydrological cycle. The hydrogen isotopic (δDwater) composition of surface seawater is correlated with SSS. Laboratory algae cultures have shown that δDwater is reflected in biomarkers – for instance, alkenones (δDalkenone), where δDalkenone is linearly correlated with δDwater. However, a large-scale field study testing the validity of this proxy is lacking. This study presents the first evaluation of δDwater and coincident δDalkenone of open-ocean surface alkenone samples from both the Atlantic and Pacific Oceans. The data agree remarkably well with regressions for δDalkenone vs. δDwater observed in laboratory cultures. Scatter in the data is discussed vis-à-vis physiological factors observed in culture to affect the fractionation between δDwater and δDalkenone.