Arctic biota contain higher mercury levels than elsewhere. The Arctic Ocean is key to understand the drivers because bioaccumulating methylmercury is formed from inorganic mercury within the ocean. Based on the recent Arctic Monitoring and Assessment Programme and new observations, we revise the mercury and methylmercury budget in the Arctic Ocean. We find that the revised Arctic Ocean mercury budget (~1,870 Mg) is lower than previous estimates (2,847–7,920 Mg) and implies higher sensitivity to changes in climate and emissions. Particulate mercury settling (122 ± 55 Mg/y) from surface waters to the shelf sediments is the largest mercury removal mechanism in the ocean. The revised Arctic Ocean Hg mass balance suggests that mercury burial in shelf sediments (42 ± 31 Mg/y) is underestimated by up to 52.2 ± 43.5 Mg/y. The Arctic Ocean methylmercury budget presents with 523 Mg about 28% of the total mercury budget. The residence time against losses of methylmercury longer (25 y) compared to total mercury (9 y), and 16.5 Mg/y are exported to the Atlantic Ocean. The revised budgets highlight the sensitivity of the Arctic Ocean to external mercury inputs and we expect persisting high methylmercury levels in the future.

Authors: Lars-Eric Heimbürger-Boavida, Stephen G. Kohler, Hélène Angot, Murat V. Ardelan, Johannes Bieser, Andrea G. Bravo, Warren RL Cairns, John Chételat, Jesper H. Christensen, Ashu Dastoor, Maria G. Digernes, Thomas A. Douglas, Aurélie Dufour, Sofi Jonsson, MarKn Jiskra, Gretchen Lescord, Robert P. Mason, Michelle Nerentorp Mastromonaco, David S. McLagan, Kuria Ndungu, Daniel Obrist, Peter M. Outridge, Mariia V. Petrova, Kyra A. St. Pierre, Andrei Ryjkov, Nicolas Sanchez, Amina T. Schartup, Anica Simić, Anne L. Soerensen, Kenjiro Toyota, Oleg Travnikov, Liisa Ukonmaanaho, Feiyue Wang, Simon J. Wilson, ChrisKan Zdanowicz