L'Atalante basin
Encyclopedia
L'Atalante basin is a hypersaline brine lake
at the bottom of the Mediterranean Sea about 192 kilometres (119.3 mi) west of the island of Crete
. It is named for one of the oceanographic research vessels involved in its discovery in 1993. L'Atalante and its neighbors the Urania and Discovery deep hypersaline anoxic basins (DHABs) are at most 35,000 years old, and were formed by Messinian evaporite
salt deposits dissolving out of the Mediterranean Ridge
and collecting in abyssal depressions about 3000 m (9,842.5 ft) deep. L'Atalante is the smallest of the three; its surface begins at about 3500 m (11,482.9 ft) below sea level.
L'Atalante's salinity, near saturation at 365 (about 8 times ordinary seawater), prevents mixing with the oxygenated waters above, so it is completely anoxic. The approximately 1.5 metres (5 ft) halocline
between the seawater above and brine
below teems with bacterial and archaeal cells: they are chemoautotrophs, which feed on ammonia
from the brine but cannot function without some oxygen. Members of archaeal anaerobic methane oxidizers group 1 (ANME-1) and haloarchaea
are found only in the halocline. No groups manage to prosper above, within and below the halocline. In the brine, the abundance of cells is much lower; extremophiles predominate, including members of the deep-sea hydrothermal vent
euryarchaeota
(DHVEs), Methanohalophilus
and Proteobacteria
. Eukaryotes are also found in l'Atalante, including ciliates (45%), dinoflagellates (21%) and choanoflagellates (10%).
The dark grey anoxic sediments at the bottom of L'Atalante lake are covered with a 1 cm (0.393700787401575 in) loose black layer. Microbes found in the sediments are almost all (90%) various species of Bacillus
.
In 2010, three metazoan species, all in the Loricifera
phylum, were discovered living in the sediment, the first multicellular lifeforms known to live entirely without oxygen.
Brine pool
Brine pools are large areas of brine on the ocean basin. These pools are bodies of water that have a salinity three to five times greater than the surrounding ocean. For deep-sea brine pools, the source of the salt is the dissolution of large salt deposits through salt tectonics...
at the bottom of the Mediterranean Sea about 192 kilometres (119.3 mi) west of the island of Crete
Crete
Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...
. It is named for one of the oceanographic research vessels involved in its discovery in 1993. L'Atalante and its neighbors the Urania and Discovery deep hypersaline anoxic basins (DHABs) are at most 35,000 years old, and were formed by Messinian evaporite
Messinian evaporite
The Messinian evaporite deposit is a geological deposit of evaporites which was found on Sicily and named after the city of Messina. It was later found to underlie much of the bed of the Mediterranean. It was formed during the Messinian salinity crisis....
salt deposits dissolving out of the Mediterranean Ridge
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, and from there eastwards south of Turkey, including Cyprus....
and collecting in abyssal depressions about 3000 m (9,842.5 ft) deep. L'Atalante is the smallest of the three; its surface begins at about 3500 m (11,482.9 ft) below sea level.
L'Atalante's salinity, near saturation at 365 (about 8 times ordinary seawater), prevents mixing with the oxygenated waters above, so it is completely anoxic. The approximately 1.5 metres (5 ft) halocline
Halocline
In oceanography, a halocline is a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water. Because salinity affects the density of seawater, it can play a role in its vertical stratification...
between the seawater above and brine
Brine
Brine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...
below teems with bacterial and archaeal cells: they are chemoautotrophs, which feed on ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
from the brine but cannot function without some oxygen. Members of archaeal anaerobic methane oxidizers group 1 (ANME-1) and haloarchaea
Haloarchaea
Haloarchaea are microrganisms and members of the halophile community, in that they require high salt concentrations to grow. They are a distinct evolutionary branch of the Archaea, and are generally considered extremophiles, although not all members of this group can be considered as such.-Living...
are found only in the halocline. No groups manage to prosper above, within and below the halocline. In the brine, the abundance of cells is much lower; extremophiles predominate, including members of the deep-sea hydrothermal vent
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
euryarchaeota
Euryarchaeota
In the taxonomy of microorganisms, the Euryarchaeota are a phylum of the Archaea.The Euryarchaeota include the methanogens, which produce methane and are often found in intestines, the halobacteria, which survive extreme concentrations of salt, and some extremely thermophilic aerobes and anaerobes...
(DHVEs), Methanohalophilus
Methanohalophilus
In taxonomy, Methanohalophilus is a genus of the Methanosarcinaceae.-External links:...
and Proteobacteria
Proteobacteria
The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....
. Eukaryotes are also found in l'Atalante, including ciliates (45%), dinoflagellates (21%) and choanoflagellates (10%).
The dark grey anoxic sediments at the bottom of L'Atalante lake are covered with a 1 cm (0.393700787401575 in) loose black layer. Microbes found in the sediments are almost all (90%) various species of Bacillus
Bacillus
Bacillus is a genus of Gram-positive, rod-shaped bacteria and a member of the division Firmicutes. Bacillus species can be obligate aerobes or facultative anaerobes, and test positive for the enzyme catalase. Ubiquitous in nature, Bacillus includes both free-living and pathogenic species...
.
In 2010, three metazoan species, all in the Loricifera
Loricifera
Loricifera is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca....
phylum, were discovered living in the sediment, the first multicellular lifeforms known to live entirely without oxygen.