The discovery of Lake Hephaestus, the youngest athalassohaline deep-sea formation on Earth

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).

Microbiome and ecology of a hot spring-microbialite system on the Trans-Himalayan Plateau

“…In addition, the system has lower, but significant, concentrations of sulfite, sulfide and lithium. Borates, sodium, bicarbonate, thiosulfate, sulfate, sulfite, and sulfide are kosmotropic 11 , and it is possible that their cumulative kosmotropic activity enables colonization of high-temperature sites by the mesophilic taxa, a phenomenon which parallels the way in which kosmotropes facilitate colonization of chaotropic environments 5,7,10,19 . We believe that the kosmotropic ions within the Shivlinga's system might also enhance biotic activity of the thermotolerant microbes present.…”

Prokaryotic and viral community of the sulfate‐rich crust from Peñahueca ephemeral lake, an astrobiology analogue

“…Strains of this genus have been isolated from salt lakes (Hua et al, 2008, Jeon et al, 2008Daas et al, 2017), saline soils (Yang et al, 2011;Lee et al, 2015), and deep-sea hypersaline anoxic sediments (DHALs) of the Mediterranean Sea (Sass et al, 2008). DHALs also harbour a high concentration of magnesium and sulfate and are considered to be one of the most extreme hypersaline systems in the planet (La Cono et al, 2011, 2019Yakimov et al, 2013). Other Firmicutes have been found in several hypersaline environments accounting for different percentages of the bacterial 16S rRNA sequences: e.g.…”

Deep Hypersaline Anoxic Basins as Untapped Reservoir of Polyextremophilic Prokaryotes of Biotechnological Interest

“…DHABs were discovered at the end of the last century on the seafloor in different deep-sea areas (at depths ranging from 630 m to 3580 m) around the globe (Figure 1), including the Mediterranean Sea [10,11], the Red Sea [12][13][14] and the Gulf of Mexico [15]. Intriguingly, the discovery of new DHABs is still ongoing, such as with the recent discovery of the new Thetis, Kyros, and Haephestus basins in the Mediterranean Sea [16][17][18]. To date, with the recent finding of these new DHABs, 35 basins have been discovered around the world.…”

“…Chemical and physical characteristics are specific to each DHAB and greatly vary depending on how the brine was formed along with the geographic localization ( Table 1). The majority of the DHABs are thalassohaline (most of the dissolved ions are represented by those composing the overlaying seawater), whereas the Discovery, Kryos, and Hephaestus basins are athalassohaline and are characterized by high Mg 2+ concentrations likely deriving from the dissolution of magnesium chloride salts (i.e., bischofite [18]) Overall, DHABs can be subdivided into four different systems: the seawater-brine interface, brines, the brine-sediment interface, and the sediments underlying the brines. Each of these features is characterized by specific conditions such as the steep halocline at the water-brine interface or the Discovery Overall, DHABs can be subdivided into four different systems: the seawater-brine interface, brines, the brine-sediment interface, and the sediments underlying the brines.…”

“…The high density of the brine prevents their mixing with the overlying oxygenated seawater, thus making the DHABs completely anoxic [16]. Their different hydrochemistry and physical separation for thousands of years has made these systems greatly interesting for scientists due to their potential similarity with extraterrestrial environments [18,34,37]. Despite their extreme conditions, many studies have provided evidence of a highly active prokaryotic community and of the presence of living metazoans, greatly extending our knowledge regarding the limits of organisms' adaptions to life [20,27,[38][39][40][41][42][43][44][45][46][47][48].…”