The diagram shows the principle of a hydrothermal vent. Magmatic processes provide the driving mechanism for hydrothermal circulation through oceanic rocks. Seawater with a starting temperature of around 2°C seeps through the lavas above a magmachamber and are heated to around 400°C. The hot water dissolves minerals in from the surrounding rocks. We now have what is called a hydrothermal fluid. When the hydrothermal fluids exit the chimney and mix with the cold seawater sulfide and sulfate precipitates. Most hydrothermal vents are found at an average depth of about 2,100 meters in areas of seafloor spreading along the Mid-Ocean Ridge System. The vents are formed in fields hundreds of meters wide.
A team of scientists have now pinpointed six spots on the remote Pacific Antarctic Ridge, where they think vents are likely to be found. The sites are described in a paper published in the journal Geophysical Research Letters.
When a seafloor vent erupts, it releases gases rich in rare helium-3, an isotope found in the magma bubbling below the vent. The team analysed the distribution of helium isotopes along an oceanic transect at 67°S to identify previously unobserved hydrothermal activity in the Pacific sector of the Southern Ocean. Combining the geochemical information provided by the helium isotope anomaly with independent hydrographic information from the Southern Ocean, they traced the source of the hydrothermal input to the Pacific Antarctic Ridge south of 55°S, one of the major global mid-ocean ridge systems, which has until now been a ‘blank spot’ on the global map of hydrothermal venting. Apart from volcanic activity spreading mid ocean ridges are also characterised by earthquakes and can be traced by their seismic foot prints across the oceans like in the image from USGS here below.
The Pacific Antarctic Ridge is the spreading ridge dividing the Antarctic Plate from the Pacific Plate. The sites identified by the team cover about 540 km of ridge line, or about 7 % of the total 7000 km long ridge. This chain of volcanic mountains lies about 5 km below the ocean surface, and its km high peaks are cut by steep canyons and fracture zones created as the sea floor spreads apart. It is a cold and lonely stretch of ocean, far from land or commercial shipping lanes.
Winckler et al.
Mantle helium reveals Southern Ocean hydrothermal venting
Geophysical Research Letters, 2010; 37 (5): L05601