Shedding light on Arctic Mercury

Arctic biota contain higher mercury levels than elsewhere. The Arctic Ocean is key to understand the drivers because bioaccumulating neurotoxin methylmercury is formed from inorganic mercury within the ocean itself. Based on the recent Arctic Monitoring and Assessment Programme ( and new observations, the mercury budget in the Arctic Ocean was revised (Dastoor et al, 2022). The revised Arctic Ocean mercury budget (~1,870 Mg) is lower than previous estimates (2,847–7,920 tons) and this implies a higher sensitivity to climate change and anthropogenic emissions. Particulate mercury settling (122 ± 55 tons per year) from surface waters to the shelf sediments is the largest mercury removal mechanism in the Arctic Ocean. The revised Arctic Ocean mass balance suggests that mercury burial in shelf sediments (42 ± 31 tons per year) may be underestimated by over 100% (52.2 ± 43.5 tons per year).

New research is now shining a light on mercury cycling on the Arctic shelf. On Arctic oceanographic cruises  in August and December 2019, PhD candidate Stephen G Kohler and coworkers collected seawater samples for mercury, lead and manganese measurements. In the illuminated Arctic summer, surface seawater has elevated concentrations of mercury. As the seasons change and the Arctic descends into its long, dark winter, little is known about mercury and its behavior during the polar night. In a new publication, Kohler et al. (2022, see reference below) find that mercury concentrations on an Arctic Ocean shelf sea decrease about 33% from summer to winter. They propose an additional transport mechanism where manganese released from the shelf actively scavenges mercury from the water column. Methylmercury concentrations did not change with seasons. The persistent methylmercury concentrations are likely driven by a lower affinity for particles and the presence of gaseous species. The results update the current understanding of Arctic mercury cycling and require budgets and models to be reevaluated with a seasonal aspect. The residence time of methylmercury is longer (25 years) compared to inorganic mercury (3 years), and high methylmercury levels can be expected in the future.

Figure: Total mercury concentrations mesured in summer (top panel) and winter (bottom panel). Stephen G. Kohler and his colleagues find that mercury concentrations on an Arctic Ocean shelf sea decrease about 33% from summer to winter.


A Dastoor, H Angot, J Bieser, J Christensen, T Douglas, LE Heimbürger-Boavida, M Jiskra, R Mason, D McLagan, D Obrist, P Outridge, M Petrova, A Ryjkov, K St. Pierre, A Schartup, A Soerensen, O Travnikov, K Toyota, S Wilson, C Zdanowicz. Arctic mercury cycling. Nature Reviews Earth & Environment 3 : 270-286, (2022). 2022-03-22. –

SG Kohler, LE Heimbürger-Boavida, MV Petrova, MG Digernes, N Sanchez, A Dufour, A Simic, K Ndungu, MV Ardelan. Arctic Ocean’s wintertime mercury concentrations limited by seasonal loss on the shelf. Nature Geoscience (2022). 2022-07-18. Access the paper:

Latest highlights

Science Highlights

Radium and barium tracers as bridges between GEOSECS and GEOTRACES programmes!

van Beek and his colleagues released radium-226 and barium data collected in the North Pacific in 2002.


Science Highlights

High resolution of dissolved and particulate barium distributions in the Atlantic and Pacific Ocean reveal the importance of the margin sources on the oceanic Ba budget

Rahman and co-workers performed intensive samplings and analyses of barium along the GEOTRACES GA03 and GP16 transects.


Science Highlights

Insight on the aluminium cycling during the inter-monsoon period in the Arabian Sea and Equatorial Indian Ocean

Full vertical water column profiles were established by Singh and Singh along the GI05 transect in the Indian Ocean during the fall inter-monsoon period in 2015.


Science Highlights

The most important thorium-234 disequilibrium compilation you ever saw

Elena Ceballos-Romero and her colleagues propose a comprehensive global oceanic compilation of Thorium-234 measurements.