Intensified microbial sulfate reduction in the deep Dead Sea during the early Holocene Mediterranean sapropel 1 deposition

Abstract

The hypersaline Dead Sea and its sediments are natural laboratories for studying extremophile microorganism habitat response to environmental change. In modern times, increased freshwater runoff to the lake surface waters resulted in stratification and dilution of the upper water column followed by microbial blooms. However, whether these events facilitated a microbial response in the deep lake and sediments is obscure. Here we investigate archived evidence of microbial processes and changing regional hydroclimate conditions by reconstructing deep Dead Sea chemical compositions from pore fluid major ion concentration and stable S, O, and C isotopes, together with lipid biomarkers preserved in the hypersaline deep Dead Sea ICDP-drilled core sediments dating to the early Holocene (ca. 10,000 years BP). Following a significant negative lake water balance resulting in salt layer deposits at the start of the Holocene, there was a general period of positive net water balance at 9500-8300 years BP.The pore fluid isotopic composition of sulfate exhibit evidence of intensified microbial sulfate reduction, where both δ 34 S and δ 18 O of sulfate show a sharp increase from estimated base values of 15.0‰ and 13.9‰ to 40.2‰ and 20.4‰, respectively, and a δ 34 S vs. δ 18 O slope of 0.26. The presence of the n-C 17 alkane biomarker in the sediments suggests an increase of cyanobacteria or phytoplankton contribution to the bulk organic matter that reached the deepest parts of the Dead Sea. Although hydrologically disconnected, both the Mediterranean Sea and the Dead Sea microbial ecosystems responded to increased freshwater runoff during the early Holocene, with the former depositing the organic-rich sapropel 1 layer due to anoxic water column conditions. In the Dead Sea prolonged positive net water balance facilitated primary production and algal blooms in the upper waters and intensified microbial sulfate reduction in the hypolimnion and/or at the sediment-brine interface.

Combined Genomic and Imaging Techniques Show Intense Arsenic Enrichment Caused by Detoxification in a Microbial Mat of the Dead Sea Shore

“…High metabolic diversity was found in microbial mats near and within underwater freshwater springs (Ionescu et al., 2012), including phototrophic communities (green and purple sulfur bacteria, cyanobacteria) and potential metal reducers (mainly associated with Fe‐cycling). While life in the Dead Sea brines is strongly limited by hypersalinity and high divalent cation concentrations (Oren, 1999, 2010), dilution of the brine by freshwater spring onshore (Adar et al., 2014; Hirshberg & Ben‐Ami, 2019) or offshore (Häusler, Noriega‐Ortega, et al., 2014; Ionescu et al., 2012), or by heavy rainfalls (Levy et al., 2022; Oren, 1993; Oren et al., 1995), allows the diversification of microbial communities and metabolic potential, including the possible use of other metalloids.…”

Combined genomic and imaging techniques show intense arsenic enrichment caused by detoxification in a microbial mat of the Dead Sea shore

“…High metabolic diversity was found in microbial mats near and within underwater freshwater springs (Ionescu et al, 2012), including phototrophic communities (green and purple sulfur bacteria, cyanobacteria) and potential metal reducers (mainly associated with Fe-cycling). While life in the Dead Sea brines is strongly limited by hypersalinity and high divalent cation concentrations (Oren, 1999(Oren, , 2010, dilution of the brine by freshwater springs onshore (Adar et al, 2014;Hirshberg & Ben-Ami, 2019) or offshore Ionescu et al, 2012), or by heavy rainfalls (Levy et al, 2022;Oren, 1993;Oren et al, 1995), allows diversification of microbial communities and metabolic potential, including the possible use of other metalloids.…”