Discovery and chemical composition of the eastmost deep-sea anoxic brine pools in the Eastern Mediterranean Sea

Abstract

Deep-sea anoxic brine pools are unique and extreme, yet habitable environments. However, their extent and processes of formation are not fully understood. Using geophysical analysis and seafloor surveying, we discovered the eastmost brine pools known in the ultraoligotrophic Eastern Mediterranean Sea, at the Palmahim Disturbance offshore Israel (~1150 m water depth). These brine pools are located directly above a ~1km wide piece of the Messinian evaporites section, which was up thrusted to ~350 m below the seafloor. We sampled brines and short cores to characterize the chemical composition of several small (up to 5m diameter) anoxic, methanic and warm (21.6°C) brine pools and adjacent seafloor sediments porewater. The maximal salinities measured at the pools and adjacent porewater were 63.9 and 72 PSU, respectively. The brines are characterized by enriched Na and Cl concentrations by a factor of ~1.8 and depleted Mg, SO4, K and Ca contents by factors of circa 6, 3, 2 and ~1.3, respectively, compared to the ambient seawater. Relations of the major element concentrations reveal a mixing curve between seawater and enriched Na/Cl and depleted Mg/Cl, K/Cl and SO4/Cl end-members, and do not coincide with relics of fossil residual evaporated seawater. We propose their composition reflects: 1) dissolution of Messinian halite (NaCl) by seawater, supported by their low Br/Cl ratios; 2) additional small rise in Na/Cl ratios due to the impact of clay mineral dehydration or/and dissolution of trace (~1% of the Na) amounts of detrital trona (Na3H(CO3)2•2H20), coinciding with the enriched alkalinity concentrations; 3) diagenesis processes depleting Mg, K and SO4, mainly by the formation of authigenic K-rich Mg-smectite, clay mineral dehydration, dolomitization/Mg-calcite precipitation and redox processes. The δ18O and δD values of the Palmahim brine may reflect the impact of clay mineral dehydration. Comparison to all other East Mediterranean brine lakes shows that the Palmahim brine pool system represents similar provenance of brines as observed for the Eastern Mediterranean Napoli, Nadir and Tyro lakes, while potentially recording additional processes attributed to its proximity to the coastal area.

Occurrence and Genesis of Cold‐Seep Authigenic Carbonates from the South‐Eastern Mediterranean Sea

“…Fluids with a low-Mg/Ca ratio (<2) are a prerequisite for the precipitation of LMC (Stanley et al, 2002). Possible sources of fluids with low-Mg/Ca ratios are Mg depleted and Ca enriched brine seeps, with such an example recently found in the vicinity of the studied sites (Charlou et al, 2003;Herut et al, 2022;Huguen et al, 2009). The 18 O values of the Palmahim brine pools (+2.0‰ VSMOW ) are slightly enriched compared to ambient sea water (+1.5‰ VSMOW ; Herut et al, 2022).…”

“…They suggest multiple migration pathways of gas to the sea floor, with potential connectivity to the top of the Messinian evaporites unit and possibly also to deeper levels. In addition, recent discovery of combined brine and gas seepage at the northern part of the PD toe was associated by Herut et al (2022) with fluid flow from the Messinian evaporites. Tayber et al (2019) modelled the hydrate stability in the LB and correlated it with the observed seismic reflectivity.…”

Metabolic handoffs between multiple symbionts may benefit the deep-sea bathymodioline mussels

“…We collected one Idas specimen in 2011, from a carbonate sample that was retrieved from the Palmahim pockmark 32°09.6’N and 34°10.0’E at a depth of 1,036 m, using Hercules remotely operated vehicle (ROV), based on the Nautilus E/V. Multiple individuals were collected in 2021 from the edges of a brine pool at the toe of Palamhim disturbance, at 1,150 m water depth (32° 13.4’ N 34° 10.7’ E) [25], using the work-class SAAB Seaeye Leopard ROV, based on R/V Bat Galim ( Supplementary Fig. S1 ).…”

“…We aimed to characterize the metabolism and physiology of the Idas symbionts, using genome-centric metagenomics, metatranscriptomics and metaproteomics. We collected 14 I. modiolaeformis individuals from hydrocarbon seeps and brine pools, off the shore of Israel [25, 26]. We hypothesized that the secondary symbionts may contribute to holobiont fitness by providing important functions, based on metabolic handoffs.…”

Four Zn(ii)-5-(2-carboxy-phenoxy)-1,3-benzenedicarboxylate coordination polymers induced by different N-ligands: synthesis, structure, and fluorescence detection for BPA and IMH

“…Tricyclic antidepressants have a significant impact on aquatic organisms, and the primary components in simulated seawater, K + , Na + , Ca 2+ , Mg 2+ , Cl − , F − , and I − , were used as interference agents. 52 IMH was added to the suspensions, and a blank was prepared without IMH. As shown in Fig.…”