PALEOSALINITY, PALEONUTRIENTS, AND PROVENANCE: INTERPRETING ARCHAEAL BIOMARKERS FROM THE WATER COLUMN AND SEDIMENTS

We present an ecologically based biomarker method to estimate past salinity changes in marine to hypersaline paleoenvironments. In modern settings, the relative ratio of acyclic diether and tetraether lipids (Archaeol and Caldarchaeol Ecometric; ACE = 100 * A/A+C) synthesized by Archaea correlates with salinity over the range of 30-250 psu. We evaluated the utility and preservation of the ACE-salinity relationship in sedimentary organic matter using samples from two sequences deposited during the time just prior to the Messinian Salinity Crisis. Archaeal lipids and ACE in particular have potential to characterize salinity variations within dessication and refilling of basins in climatically sensitive seas (e.g. Dead Sea, Permian Delaware Basin). This novel approach to salinity reconstruction offers the important advantages of preservation under conditions where isotopic proxies are absent or altered and sensitivity over a salinity range that complements mineralogical assemblage data, while also giving new ecological information about ancient microbial communities. In the fresh-to-normal marine range, archaeal lipids track other environmental properties which generally occlude the influence of salinity in archaeal biomarkers from these settings. Detailed examination of ether lipids within the fresh and marine waters from diverse aquatic and oceanographic provinces revealed pronounced patterns in lipid distribution. We related these patterns to environmental and ecological factors using multivariate statistical tools and propose a relationship between the biological provenance and these robust distribution patterns. Collectively, this work shows that analysis of archaeal lipids promises novel and important insights to past ocean biogeochemistry.