Organic Proxy Disturbance in the Dead Sea Basin at the Beginning of the Holocene

Abstract:

Paleoenvironmental reconstruction is among the main targets of the International Continental Drilling Program (ICDP)-sponsored Dead Sea Deep Drilling Project (DSDDP). Around 450 meters of core were retrieved and currently several multi-disciplinary studies are being performed in this almost continuous sedimentary record. Careful attention has been directed to understanding the microbial communities living in the hypersaline sediment and the potential impact they might have on biogeochemical cycles both in the lake and in the Dead Sea precursors. Studies have highlighted the potential for microbial activity in the lake, in spite of its hypersalinity, and the putative influence of microbial communities on the geochemical record, especially with respect to reconstruction of the carbon and sulfur cycles. More recently, geomicrobiological and geochemical studies with samples obtained during the DSDDP have revealed the potential for methane production (methanogenesis) in the subsurface; this can greatly impact the carbon isotope record in the subsurface and could skew any paleoenvironmental interpretation. By combining carbon, sulfur and oxygen isotopes from the interstitial pore water and the surrounding sediment, including a lithological facies study and biomarker analysis, we highlight that the period following massive gypsum precipitation in the Dead Sea, at the onset of the Holocene, has been subject to major changes. At this time, variations in the level of the lake, accompanied by water mixing, have supposedly initiated intense microbial activity in the paleo-water column and probably within the sediment after its burial, as indicated by specific authigenic Fe-S mineralizations. Sulfur isotope evidence from the pore fluids suggests that these Fe-S precipitations may be microbial in nature. While no DNA could be extracted from this interval to allow a microbial diversity study, the retrieval, among others, of non-isoprenoid macrocyclic glycerol diethers potentially calls for the presence and influence of extremophiles involved in sulfur cycling. Current work will help unravel the extent of the biological impact on proxies that could be used for paleoclimatic studies. Additionally, this work highlights the importance of routinely implementing geobiological studies within the ICDP framework.