Methylmercury subsurface maxima explain mercury accumulation in Canadian Arctic marine mammals

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…

 

18 Wang l
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

Science Highlights

Rare Earth Elements and neodymium isotopes as tracers in the Mediterranean Sea

Garcia-Solsona and co-workers analysed 9 seawater stations around the central Mediterranean Sea…

02.07.2020

Science Highlights

A new model simulates the speciation and dispersion of hydrothermal iron

Roshan and collaborators present new observations of dissolved iron and its physical speciation in the South Pacific

10.06.2020

Science Highlights

Mechanisms driving biological CO2 drawdown in the Subarctic Pacific unraveled

Nishioka and co-authors compiled comprehensive data sets of iron and macronutrients covering the whole subarctic Pacific…

04.06.2020

Science Highlights

The biogeochemical ventures of dissolved iron and manganese across the Arctic Ocean

The spatial distributions and biogeochemical cycling of dissolved Fe (dFe) and dissolved manganese (dMn) across the Arctic Ocean were established during summer and fall 2015. The Canadian GEOTRACES transect extended from the Canada Basin (CB) to the Labrador Sea (LS) via the Canadian Arctic Archipelago (CAA). The surface, subsurface and deep water distributions for both […]

15.05.2020

Rechercher