Friday, 13 January 2012

Deepest hydrothermal vent communities yet found discovered in the Caribbean.

Hydrothermal vents occur on the boundaries between plates in the deep sea, as water percolates through super-heated volcanic rocks soaking up minerals, and is released back into the ocean. They are often called 'black-smokers' because of the dark colouration of the mineral-rich water. The water coming from hydrothermal vents often has temperatures of hundreds of degrees centigrade, well above the boiling point of water at the surface, but remains a liquid in the high pressure environment of the deep sea. The water is also often highly acidic, and laden with potentially toxic metal ions. Despite this deep-sea hydrothermal vents have been shown to support whole communities of animals, witch depend not on energy from green, photosynthesizing plants for survival, but rather of bacteria able to generate energy by consuming the toxic chemicals from the hydrothermal vents.

On 10 January 2012 a team lead by Douglas Connelly of The National Oceanography Centre at the University of Southampton and Jonathan Copley of the Department of Ocean and Earth Science, also at the University of Southampton, published a paper on Nature Communications in which they describe the discovery of two systems of hydrothermal vents on the Mid-Cayman Ridge, 4960 m and 2300 m beneath the Caribbean Sea.

The location of the new hydrothermal vent sites. From Connelly et al. (2012).

The Von Damm Vent field is located on the upper slopes of an undersea mountain, Mount Dent, 13 km to the west of the active spreading centre, at a depth of 2300 m. The water at the vent is rich in hydrogen sulphide (H₂S), and while enriched in metals relative to the surrounding water, is metal poor compared to other deep-sea vents; it appears colourless at the vent rather than black.

The Beebe Vent Field is located 4960 m beneath the surface, 20% deeper than any previousy discovered vent. The water issuing from the vent is not as rich in hydrogen sulphide as the water at the Von Damm site, but it is extremely rich in copper and iron. This creates a visible plume of black water that reaches 1100 m above the vents. The Southampton researchers estimate that for the column to remain discrete from the surrounding water for this far the water must be emerging at about 500 °C (they did not have the means to take a direct temperature reading at this depth).

(a & b) A colony of shrimps on a vent at the Von Damm Vent Field; the water issuing from the vent is colourless. (c & d) Sulphide chimneys issuing black 'smoke'; coloured water at the Beebe Vent Field, which gets its colour from dissolved copper and iron ions. From Connelly et al. (2012)

Both sites had thriving biological communities, dominated by dense colonies of shrimps, containing at least two species of shrimp. The Von Damm site also had extensive mussel beds. Fish, snails, sea anemones and squat lobsters were also present at both sites. This is similar to the fauna found on deep-sea vents on the Mid-Atlantic Ridge.

(a) A a dense colony of shrimps at the Beebe Vent Field. (b) Sea anemones and microbial mats at the Beebe Vent Field. (c) Dead mussel shells on Mount Dent. (d) Possible tube-worm casts on Mount Dent.

See also New deep-sea hydrothermal vent ecosystem discovered in the Southern Ocean.

1 comment:

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