a, Representative profiles of total dissolved Hg from the North Atlantic near Bermuda (triangles), from the South Atlantic (diamonds) and the northeast Pacific Ocean (circles; the station labelled ‘SAFe’). b, Global vertical distribution of Premin as interpolated from WOCE data (http://www.ewoce.org). Transect (black lines) is shown to the right. Figure generated using Ocean Data View (http://odv.awi.de/). AIW, Atlantic Intermediate water; NADW, North Atlantic Deep Water; AABW, Antarctic Bottom Water; PDW, Pacific Deep Water. Graphic: Lamborg, 2014

By Anne Casselman
6 August 2014

(Nature) – Mercury levels in the upper ocean have tripled since the beginning of the Industrial Revolution, and human activities are to blame, researchers report today in Nature.

Although several computer models have estimated the amount of marine mercury, the new analysis provides the first global measurements. It fills in a critical piece of the global environmental picture, tracking not just the amount of mercury in the world's oceans, but where it came from and at what depths it is found.

“Nobody's attempted to do a more comprehensive overview of all the oceans and get an estimate of total mercury in the surface and some deeper waters before,” says David Streets, an energy and environment policy scientist at Argonne National Laboratory in Lemont, Illinois, who was not involved in the study.

Researchers collected thousands of water samples during eight research cruises to the North and South Atlantic and Pacific oceans between 2006 and 2011. To determine how mercury levels had changed over time, they compared samples of seawater from depths down to 5 kilometres with water closer to the surface, which had been more recently exposed to mercury pollution from land and air.

Their analysis reveals that human activities — mostly the burning of fossil fuels, but also mining — had boosted the mercury levels in the upper 100 metres of the ocean by a factor of 3.4 since the beginning of the Industrial Revolution. The total amount of anthropogenic mercury in the world's seas now stands at 290 million moles, with the highest levels in the Arctic and North Atlantic oceans.

“They were really able to look back in time with their study,” says Noelle Eckley Selin, an atmospheric chemist at the Massachusetts Institute of Technology in Cambridge, who was not involved in the study. [more]

Humans have tripled mercury levels in upper ocean

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