Scientists for the first time have carried out direct measurements of mercury deposition in the most difficult ultraabyssal part of the ocean in terms of accessibility – the ultra-deep sea zone.
The authors examined two deep-sea trenches in different parts of the Pacific Ocean: the first, Kermadec in the east, and the second, Atacama, in the west, off the coast of Chile. During the work, they took samples from the deepest parts of the gutter: it is from 2 to 6 km.
The results showed that the concentration of mercury at this depth was the highest ever recorded in marine sediments. This is even higher than in many industrial pollution areas.
The bad news is that such high levels of mercury could be representative of the overall increase in anthropogenic mercury releases into the ocean. But the good news is that the ocean troughs act as permanent disposal sites. We can expect that the mercury that ends up there will be buried for many millions of years, and plate tectonics will carry it into the Earth’s upper mantle.
Hameda Sanei, Director of the Lithospheric Organic Carbon Laboratory, Faculty of Earth Sciences
Despite the fact that mercury is removed from the biosphere through troughs, the toxic metal does not completely disappear.
The authors believe that the results of their study will help fill a key knowledge gap about the mercury cycle on the Earth’s surface.