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I have attended several talks about mercury (Hg) in the atmosphere, and particularly Hg atmospheric depletion events (MDEs) in the Arctic at previous conferences. From what I understand, as the duration of the day increases during the Arctic spring, the photochemical reactivity of Hg causes most of it to be washed out of the atmosphere and deposited, either onto ice cover or into the ocean. However, as scientifically rewarding as probing these events may be, the point was made today that researchers should be aware that the real danger lurks elsewhere. Indeed, trends of Hg found in the ocean and its biota, i.e. the Hg that enters the food wed, is decoupled from trends in atmospheric Hg. This was, in essence, the take home message of the keynote talk of today’s session on Hg accumulation on aquatic foodwebs. Robbie MacDonald, from Fisheries and Oceans Canada, expressed his concerns that too much effort is being put into studying MDEs, to the detriment of a better understanding of the Hg cycle in the oceans. We all acknowledge that the Arctic is very vulnerable to global Hg emissions and that the transfer of Hg from the physical system to the biological system occurs in the ocean. Yet, very little is known about Hg geochemistry in the oceans; the Artic Ocean being the least studied. MacDonald further stressed that if the Artic permafrost, which stores a large fraction of the organic carbon on earth, is pushed towards a collapse, the recycling of its organic matter and associated Hg may lead to a massive release of Hg to the Arctic environment.

The title of this post is taken from a paper by Robbie Macdonald in Nature (1996)

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