Methylmercury subsurface maxima explain mercury accumulation in Canadian Arctic marine mammals

Science Highlights

5 November 2018

Mercury (Hg) concentrations in Canadian Arctic marine mammals were monitored during the last four decades and found to be highly elevated, frequently exceeding toxicity thresholds. Mercury concentrations in marine biota are also found to be generally higher in the western part of the Canadian Arctic than in the east. Thanks to the Canadian Arctic GEOTRACES cruise, Wang and co-authors (2018, see reference below) carried out a high-resolution total mercury and methylmercury (MeHg) measurements from the Canada Basin in the west to the Labrador Sea in the east. Total Hg concentrations show a distinctive longitudinal gradient along the transect with concentrations increasing from the Canada Basin eastward through the Canadian Arctic Archipelago to Baffin Bay, which is opposite to the spatial gradient in mammal Hg.

What is remarkable is the distribution patterns of MeHg. The authors found that MeHg concentrations are lowest at the surface, peak in a subsurface layer (~100–300 m), and subsequently decrease towards the bottom. Longitudinally, the subsurface MeHg peak value is highest in the western part of the section and decreases towards the east, eventually reaching its lowest values in the Labrador Sea. Given that it is MeHg that accumulates and biomagnifies in marine biota and that the MeHg subsurface maxima lie within the depths where Arctic marine biota reside, this gradient readily explains the spatial distribution of Hg levels observed in Canadian Arctic mammals.

Elucidating the processes that generate and maintain this subsurface MeHg maximum is the next challenge…

Figure: Mercury (Hg) concentrations in the marine food web and seawater across the Canadian Arctic and Labrador Sea (Wang et al. 2018). Upper panel: Map of Hg (as total Hg or monomethylmercury) concentrations in two zooplankton species, ringed seals and polar bears along the Canadian GEOTRACES transect based on data collected between 1998 and 2012. Lower panel: Methylmercury (MeHg) concentrations in seawater along the same transect as determined during the 2015 Canadian Arctic GEOTRACES.  Click here to view the image larger.

Reference:

Wang, K., Munson, K. M., Beaupré-Laperrière, A., Mucci, A., Macdonald, R. W., & Wang, F. (2018). Subsurface seawater methylmercury maximum explains biotic mercury concentrations in the Canadian Arctic. Scientific Reports, 8(1), 14465. DOI:  http://doi.org/10.1038/s41598-018-32760-0

Latest highlights

Elevated methylmercury level in Arctic rain and aerosol linked to oceanic dimethylmercury emissions

He and colleagues highlight a previously underappreciated pathway of mercury transport, underscoring its significance to human health.

Unveiling the Complexity of Lead Distribution in the Pacific Ocean: Insights from the GEOTRACES GP15 Transect

This recent study by Jiang and colleagues investigate the distribution and sources of lead in the Pacific Ocean.

Organic matter export rates along a North-South Pacific Ocean section: what three estimating methods tell us

Quay and his colleagues present estimates of the organic matter export rate along the GEOTRACES GP15 cruise section.

East-West contrasting fate and anthropogenic inputs for dissolved trace metals in the Subarctic Pacific Ocean

Chan and co-authors report the full-depth distribution of dissolved nickel, copper, zinc, and cadmium in the North Pacific Ocean.

Rechercher

…