Abstract
Hydrated, magnesium-rich minerals and subglacial brines exist on the martian surface, so the habitability of high-Mg2+ environments on Earth has extraterrestrial (as well as terrestrial) implications. Here, we report the discovery of a MgCl2-dominated (4.72 M) brine lake on the floor of the Mediterranean Ridge that underlies a 3500-m water column, and name it Lake Hephaestus. Stable isotope analyses indicated that the Hephaestus brine is derived from interactions between ancient bishofite-enriched evaporites and subsurface fluids. Analyses of sediment pore waters indicated that the Hephaestus depression had contained the MgCl2 brine for a remarkably short period; only 700 years. Lake Hephaestus is, therefore, the youngest among currently known submarine athalassohaline brine lakes on Earth. Due to its biologically hostile properties (low water-activity and extreme chaotropicity), the Hephaestus brine is devoid of life. By contrast, the seawater-Hephaestus brine interface has been shown to act as refuge for extremely halophilic and magnesium-adapted stratified communities of microbes, even at MgCl2 concentrations that approach the water-activity limit for life (0.653).
Highlights
Hydrated, magnesium-rich minerals and subglacial brines exist on the martian surface, so the habitability of high-Mg2+ environments on Earth has extraterrestrial implications
The seawater-Hephaestus brine interface has been shown to act as refuge for extremely halophilic and magnesium-adapted stratified communities of microbes, even at MgCl2 concentrations that approach the water-activity limit for life (0.653)
Experimental and theoretical insights into weathering of martian basalt reveal that martian brines are likely dominated by magnesium and calcium and so qualitatively different from the sodium-dominated waters that are commonplace on Earth[3]
Summary
SBP produced a sharp crisp line over the basin and hinted at the existence of a brine lake, that we named Hephaestus. This was confirmed by direct conductivity-temperature-dissolved oxygen (CTD) profiling, followed by retrieval of samples of the brine. Chemical characterization of Hephaestus brine confirmed that these two lakes constitute separate hydrologic milieu, it shares the athalassohaline character of the Kryos and Discovery brines; it contains MgCl2 close to saturation (4.72 M). Hephaestus is likely to have originated the same way as the Kryos and Discovery brines that formed by dissolution of bischofite containing 8 g kg−1 Br19. Mmol kg−1 Na+ K+ Mg++ Ca++ Cl− SO4− Br− Principal parameters Practical salinity units, PSU δ18O, ‰ δ2H, ‰ pH Density Temperature, °C Water activity, aw Brine, mbsl Maximum depth Surface area, km[2]
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