Life in Hydrothermal Vents

Heat loving (thermophillic) animals love to live in places where temperature exceeds 80 degree Celsius, such as, hydrothermal vents. Hydrothermal vents arise where cold sea water interacts with freshly formed hot ocean crust along the chains of submarine volcanoes, called mid-ocean ridges. The basic requirements for hydrothermal circulation are a source of heat and a pathway for sea water to circulate within the rock. It represents significant cooling process for the planet. Hydrothermal activity is a part of the way in which the Earth works and is intimately linked to plate tectonics and occurs almost exclusively to ocean ridges. To Earth scientists, it represents a significant cooling process for the planet. For oceanographer’s hydrothermal fluxes of chemicals, notably, iron, manganese, methane, hydrogen and hydrogen sulfide help to buffer the chemical balance of the ocean and atmosphere. The best estimates suggest that the entire volume of ocean is processed through high temperature vents every ten million years and through deep sea hydrothermal plumes every few thousand years. High temperature venting on the sea floor gives rise to flumes which ascend through the oceanic water column entraining sea water until they reach a level of neutral buoyancy some hundreds of meters above the sea bed. Subsequent lateral spreading of these plumes with their associated signatures in temperature, chemical tracers and suspended particulate material provides a means by which new hydrothermal vent sites can be located.

Submarine thermal springs, also called deep sea hydrothermal vents, have been discovered on the Galapagos Rift and on the East Pacific Rise. They are remarkable in two ways. Firstly, their physicochemical conditions are extreme, since the water emerging from the fissures is hot, anoxic, acidic and contains an enormous amount of hydrogen sulfide. This water mixes with normal surrounding oceanic water, which is cold (2 degree Celsius), contains oxygen at a pressure of more than 50 Torr, no hydrogen sulfide and a pH value around 7.5. Consequently, over a short distance, the physicochemical conditions change steeply. Secondly, in these special waters, a dense biomass is supported by the primary production of sulfide oxidizing bacteria. Large pogonophoran tube worms, clams, mussels and brachyuran crabs are found, some species of this group have never been observed elsewhere. Their physiology is beginning to be known. Hydrothermal activity gives rise to characteristic chemical signatures (sulfide and methane gradients), which vent crustaceans may use to locate active hydrothermal fields, as well as thermal gradients (2 degree Celsius to greater than 360 degree Celsius). Light generated at the vents is enough to support vision in an otherwise aphotic world and could serve as a superfluous near field settlement hint if juveniles approaching the vents can detect it. Through hydrological cycle water is circulated through the depth of the Earth. It has long been suspected that surface material can be carried to the Earth’s deep interior by subduction of ocean crust and sediment, as well as, the residue of ocean creation from depths back to the surface.

In the seismic area (85-degree N, 85-degree E), where volcanic activity was observed in 1999, extremely thick plumes were observed up to 1400 meter and were centred more than 1000 meters off the sea floor. Typical maximum rise height for hydrothermal plumes in the Pacific and Atlantic oceans are 200 to 400 meters. The plumes at 85-degree E in their thickness, height of rise and magnitude of signals indicate the most vigorous hydrothermal venting in the area. Sharp plume in both light scattering and temperature at 2009 meter between 8-degree E and 18-degree E, wide spread plume at 3100 to 3200 meters between 21-degree E and 3e1 degree E were identified along 1100 kilometres section of the Gakkel Ridge in the Arctic ocean. While investigating into the ecology of animals living deep water hydrothermal vents, the crab, Xenograpsus testudinatus have been found to live at enormously high densities around the sulfur rich hydrothermal vents in shallow water at depth less than 200 meters off Taiwan, even though this acidic environment (pH 1.75 to 4.60) is low in nutrients. Thousands of Xenograpsus crabs’ swarms out of their crevices at slack water, when currents are weak or absent and feed frantically on the sea floor over an area of few square meters, on the vast quantity of zooplankton, that are killed by the vent’s sulphurous plumes, and rain down like marine “snow”. These opportunistic feeding behaviours explains how the crab are able to survive in the adverse toxic environment of these shallow hydrothermal vents.