Life in the deep sea
Life in the deep sea is sustained essentially by the biological production in sun-lit, top 50-100 m water column. Sinking of dead organisms, their faecal pellets, and calcium carbonate shells of various organisms transfer carbon to the deep sea in a process called the ‘biological pump’. Life thrives in the deep sea in spite of the high hydrostatic pressure, low temperature, complete darkness, and total dependence on food from above. Hydrostatic pressure at the average ocean depth of 3700 m equals 370 atmospheres, but deep-sea organisms have evolved mechanisms to cope even with this extreme condition. Hydrothermal vents are a significant exception to the scarce deep-sea life elsewhere. In and around the vents, the high diversity of life and biomass is sustained purely by the bacteria as symbionts within the animals that thrive there. Chemosynthesis, not photosynthesis, is the process that sustains the food web in the hydrothermal vents.