The Peculiar Life of Cold Seeps

The geological origins of cold seeps differ from hydrothermal vents. While vents form from volcanic activity at sea-floor spreading regions, cold seeps instead arise at the other end of oceanic plates, where they are subducted at the continental margin. Their formation begins with the burial of organic material under sediments on the sea-floor. These organic compounds degrade over time, producing methane. Over time, geological processes such as the tectonic compression of sediments at subduction zones forces the methane from deep reservoirs up through the overlying sediments. Anaerobic microbes dwelling below the sediment surface oxidise this methane using sulphate, producing hydrogen sulphide and bicarbonate ions as a byproduct. This hydrogen sulphide, along with any residual methane, then serves as a vital energy source for *chemosynthetic* microbes. Thus, it is a consortium of two distinct sets of microbes that makes primary productivity possible at cold seeps and lay the foundations of food webs here. The result is an environment remarkably similar to hydrothermal vents. We have a flux of sulphide and methane at the sea-floor, chemosynthetic microbes using these compounds, and an abundance of life exploiting this primary productivity, fulfilling similar ecological niches and forming biodiversity hotspots in the deep sea

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