L'Atalante basin facts for kids
The L'Atalante basin is a super salty 'lake' found deep at the bottom of the Mediterranean Sea. It is located about 190 kilometers (or 120 miles) west of the island of Crete. Even though it's under more than two miles of water, it's called a 'lake' because its extremely high salt content keeps its water almost completely separate from the normal seawater above it. These very salty underwater lakes are often called brine pools. You can find them in many oceans around the world, like one in the Gulf of Mexico.
35°11′N 21°25′E / 35.18°N 21.41°E
How This Salty Lake Formed
L'Atalante is just one of several very salty lakes hidden beneath the Mediterranean Sea. Millions of years ago, about six million years ago, the Strait of Gibraltar (the narrow opening connecting the Mediterranean to the Atlantic Ocean) closed. This caused the Mediterranean Sea to dry up almost completely, leaving behind a huge amount of salt, much like the Dead Sea or the Great Salt Lake today.
Then, about five million years ago, the Strait of Gibraltar opened again. Water from the Atlantic Ocean rushed in, refilling the basin to form the Mediterranean Sea we know now. Even today, the Atlantic Ocean keeps feeding water into the Mediterranean because more water evaporates from the 'Med' than its rivers can replace. Because of the massive salt deposits left behind and the constant evaporation, the Mediterranean Sea is naturally saltier than the Atlantic Ocean.
The L'Atalante lake, along with its neighbors the Urania and Discovery lakes, are about 35,000 years old. They formed when ancient salt deposits dissolved out of the Mediterranean Ridge. This super salty water then collected in deep dips at the very bottom of the sea. L'Atalante is the smallest of these three lakes. Its surface starts at about 3,500 meters (or 11,500 feet) below sea level.
Super Salty Water
The salinity (salt content) of L'Atalante's water is extremely high, almost at the point of saturation. It's about 36.5% salt, which is roughly eight times saltier than regular seawater! This extreme saltiness is why the water in the brine pool cannot mix with the 'normal' seawater above it.
Because there's no mixing, oxygen from the surface can't get into the brine pool. This means the water in the basin is completely anoxic, which means it has absolutely no oxygen.
Between the normal seawater and the super salty brine, there's a thin (about 1.5 meters or 5 feet) boundary zone called a halocline. In this special zone, the salt content quickly goes up, and the oxygen level drops to zero. This halocline is home to many bacteria and archaea cells. These tiny organisms are chemoautotrophs, meaning they create their own food using chemicals like ammonia from the brine. They need a tiny bit of oxygen to survive. You can also find certain types of methane-eating bacteria and salt-loving archaea only in this halocline.
Life Without Oxygen
Deeper down, in the super salty brine itself, the number of living cells is much lower than in the halocline. The most common life forms here are Extremophiles. These are amazing creatures that can live in very harsh conditions, including some types of archaea and bacteria usually found near deep-sea hydrothermal vents. Even some Eukaryotes (organisms with complex cells, like animals and plants) are found in L'Atalante. These are mostly ciliates (45%), dinoflagellates (21%), and choanoflagellates (10%).
The dark grey, oxygen-free sediments at the bottom of L'Atalante lake are covered with a 1 centimeter (about 0.4 inches) loose black layer. Microbes found in these sediments are almost all (90%) different types of Bacillus bacteria. In 2010, something truly amazing was discovered: three tiny animal species, all belonging to the Loricifera phylum, were found living in this sediment. These were the first multicellular life forms ever known to live entirely without oxygen!
See also
In Spanish: Cuenca de L'Atalante para niños
