Incorporating those variables, however, was not enough.
The GEOS-Chem model, which is backed by rigorous environmental observations and more than a decade of scientific review, quantifies the complex nuances of the ocean-ice-atmosphere environment. It takes into account, for example, ocean mixing at various depths, the chemistry of mercury in the ocean and the atmosphere, and the mechanisms of atmospheric deposition and re-emission.
When the Harvard team adapted it for their Arctic mercury simulations, the only adjustment that could explain the spike in summertime concentrations was the incorporation of a large source to the Arctic Ocean from circumpolar rivers. This source had not been recognized previously.
As it turns out, approximately twice as much mercury in the Arctic Ocean originates from the rivers as from the atmosphere.
"At this point we can only speculate as to how the mercury enters the river systems, but it appears that climate change may play a large role," says Jacob. "As global temperatures rise, we begin to see areas of permafrost thawing and releasing mercury that was locked in the soil; we also see the hydrological cycle changing, increasing the amount of runoff from precipitation that enters the rivers."
"Another contributing factor," he adds, "could be runoff from gold, silver, and mercury mines in Siberia, which may be polluting the water nearby. We know next to nothing about these pollution sources."
As the contaminated river water flows into the Arctic Ocean, Jacob says, the surface layer of the ocean becomes supersaturated, leading to what scientists call an "evasion" of mercury from the ocean into
|Contact: Caroline Perry|