Cold seeps explained

DR ASHLEY ROWDEN
Cold seeps are areas of the seafloor where hydrocarbon-rich fluids seep out onto the seabed. The fluids are predominantly made up of methane but also hydrogen sulphide, and in some instances, the reaction between those chemicals and bacteria can lead to the formation of hard substrates, calcium carbonates, which can form isolated rocks or reefs.

They can be found for instance along continental margins where seafloor sediments can come together, and one set of sediments can start to bury the others, and in those convergent places, the methane can get squeezed by the pressure up towards the surface of the seabed, sometimes tracking along fissures which have been caused by tectonic activity

Around New Zealand, the main location for seeps that we know of is along the Hikurangi Margin, so that’s an area of the slope that extends roughly from the East Cape down to the eastern entrance to the Cook Strait, and the seeps, where they occur along that margin, generally are found between 600 metres and 1000 metres of depth.

At the seeps, which is rich in methane and hydrogen sulphide, there can exist bacteria, and these bacteria can process the methane or the hydrogen sulphide. They metabolise it. They use it to produce sugars for their own energy. They’re a special type of bacteria, and they’re known as chemosynthetic bacteria. So they’re deriving their energy from a chemical process, so that’s different from the process, for instance, where you derive energy from the Sun, which is photosynthesis. And these bacteria then form the basis of a development of a chemosynthetic community, so that’s other organisms which are associated with the presence of this bacteria and rely either directly on this bacteria or indirectly on the bacteria.

Acknowledgements:
Dr Jens Greinert, Royal Netherlands Institute for Sea Research
National Institute of Water and Atmospheric Research (NIWA)