L'Atalante basin is a hypersaline brine lake at the bottom of the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

about west of the island of

Crete Crete ( ; , Modern Greek, Modern: , Ancient Greek, Ancient: ) is the largest and most populous of the Greek islands, the List of islands by area, 88th largest island in the world and the List of islands in the Mediterranean#By area, fifth la ...

. It is named for the French ''L'Atalante'', one of the

oceanographic Oceanography (), also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology. It is an Earth science, which covers a wide range of top ...

research vessels involved in its discovery in 1993. L'Atalante and its neighbors the Urania and Discovery deep hyper saline anoxic basins (DHABs) are at most 35,000 years old. They were formed by Messinian evaporite salt deposits dissolving out of the

Mediterranean Ridge The Mediterranean Ridge is a wide ridge in the bed of the Mediterranean Sea, running along a rough quarter circle from Calabria, south of Crete, to the southwest corner of Turkey. It is an accretionary wedge caused by the African Plate subduc ...

and collecting in abyssal depressions about deep. L'Atalante is the smallest of the three; its surface begins at about below sea level.

Description and biology

The L'Atalante basin's salinity is near saturation at 365 (about 8 times that of ordinary seawater), which prevents it from mixing with the oxygenated waters above; therefore, it is completely anoxic. The approximately

halocline A halocline (or salinity chemocline), from the Greek words ''hals'' (salt) and ''klinein'' (to slope), refers to a layer within a body of water ( water column) where there is a sharp change in salinity (salt concentration) with depth. Haloclin ...

between the seawater above and

brine Brine (or briny water) is a high-concentration solution of salt (typically sodium chloride or calcium chloride) in water. In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawat ...

below teems with bacterial and

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

l cells: they are

chemoautotroph A chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototroph ...

s, which feed on

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

from the brine but cannot function without some oxygen. Members of archaeal anaerobic methane oxidizers group 1 (ANME-1) and

haloarchaea Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of prokaryotic archaea under the phylum Euryarchaeota, found in water saturated or nearly saturated with salt. 'Halobacteria' are now recognized as archaea r ...

are found only in the halocline zone. No group of organisms manages to prosper in all three zones. In the brine, there are fewer cells;

extremophile An extremophile () is an organism that is able to live (or in some cases thrive) in extreme environments, i.e., environments with conditions approaching or stretching the limits of what known life can adapt to, such as extreme temperature, press ...

s predominate, including members of the deep-sea

hydrothermal vent Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hot ...

euryarchaeota Methanobacteriota is a phylum in the domain Archaea. Taxonomy The phylum ''Methanobacteriota'' was introduced to prokaryotic nomenclature in 2023. It contains following classes: *Archaeoglobi Garrity & Holt (2002) *Halobacteria Grant ''et al ...

(DHVEs), '' Methanohalophilus'' and ''

Pseudomonadota Pseudomonadota (synonym "Proteobacteria") is a major phylum of gram-negative bacteria. Currently, they are considered the predominant phylum within the domain of bacteria. They are naturally found as pathogenic and free-living (non- parasitic) ...

'' (formerly ''Proteobacteria'').

Eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s are also found in l'Atalante, including

ciliates The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...

(45%), dinoflagellates (21%) and choanoflagellates (10%). The dark gray anoxic sediments at the bottom of L'Atalante lake are covered with a loose black layer.

Microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

s found in the sediments are almost all (90%) various species of ''

Bacillus ''Bacillus'', from Latin "bacillus", meaning "little staff, wand", is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum ''Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-sh ...

''. In 2010, three

metazoan Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ho ...

species, all in the

Loricifera Loricifera (from Latin, ''wikt:lorica, lorica'', corselet (armour) + ''ferre'', to bear) is a phylum of very small to microscopic marine cycloneuralian sediment-dwelling animals with 43 described species and approximately 100 more that hav ...

phylum, were discovered living in the sediment, the first multicellular lifeforms known to live entirely without oxygen.

References

External links

* Stephen Ornes
Animals without oxygen, underwater
ScienceNews for Students, 27 Apr 2010 {{portalbar, Oceans Anoxic waters Oceanic basins of the Atlantic Ocean Mediterranean Sea