Mercury is a trace element of natural origin (volcanic eruptions) and anthropogenic (combustion of fossil fuels, mining). Driven by long-range air, ocean and river transport, mercury contamination is a major concern for the Arctic. Indeed, highly toxic, mercury impacts the physiology and reproduction of wildlife in this region. Furthermore, the Arctic is warming up two to three times faster than any other region of the planet, with consequences for snow cover, permafrost and the extent of sea ice. These changes lead to major changes in biogeochemical fluxes, food webs and, by the same token, could potentially modify the bioavailability of mercury. However, the effects of climate change on mercury contamination in wildlife remain poorly understood.
French and Norwegian researchers have published in the review Environmental Science and Technology a long-term study showing how climate change could influence mercury concentrations in seabirds from Spitsbergen (Norwegian Arctic). This monitoring, carried out over 20 years with the support of the Paul Emile Victor Polar Institute (IPEV), shows that blood levels of mercury in kittiwakes initially decreased by 3% per year from 2000 to 2013. But since then, the trend has reversed, and blood mercury levels have increased by 11 % per year since 2014. How can such a phenomenon be explained? Of nine indicators known to influence mercury bioavailability in the ocean, two stand out as reliable predictors of mercury concentrations in seagulls. These two parameters are the chlorophyll concentrations has in surface waters, that reflect primary production in the marine environmentas well as the extent of the pack ice. The study highlights the essential role of primary production, which, associated with other abiotic or non-abiotic factors, will attract different fish communities and affect the contamination of their predators.
In the early 2000s, high mercury concentrations were probably linked to a greater proportion of strictly arctic fish consumed by gulls (eg arctic cod). The gradual addition of less contaminated subarctic fish (eg capelin) in the diet of birds would then have led to a decrease in mercury concentrations until 2013. Then, the arrival of more contaminated fish from the Atlantic (herring, juvenile cod), associated with a remobilization of mercury in the ocean in response to a more pronounced retreat of the pack ice, could explain the recent increase in mercury contamination.
This study therefore suggests that in response to climate change, the retreat of sea ice and higher primary productivity lead tont “Atlantification” of the Arctic Ocean and impacts mercury contamination of seabirds, via changes in prey fish communities. This work highlights the major interest of seabirds as bioindicators for monitoring contaminants. Such long-term monitoring is essential for measuring the effectiveness of pollution regulation measures, and for understanding the complex interactions between climate change and contamination of polar ecosystems.