Methane Sources and Fate in Two Different Arctic Marginal Seas

• Applicants: Professor Dr. Gerhard Bohrmann; Dr. Susan Mau; Dr. Thomas Pape
• Subject Area: Oceanography
• Term: Funded in 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430936359

The sea air flux of methane, a potent greenhouse gas, from the Arctic marginal seas plays a significant climatic, geopolitical, and social role, but remains one of the most debated topics in ocean sciences. A recent assessment of the Arctic region identified thousands of gigatonnes (1 Gt = 1015 g) of stored carbon, locked in permafrost, oil-gas reserves, and likely in gas hydrates. Considering the faster increase of Arctic temperatures compared to the global average these deposits may constitute important greenhouse gas emissions due to the climate change in the next 100 years. However, the rate of the release and the likelihood to add to the atmospheric methane burden remains difficult to predict. Therefore, Dr. Renat Shakirov located at V.I. Il’ichev Pacific Oceanological Institute, Vladivostok and Dr. Susan Mau situated at the Department of Geosciences at the University of Bremen plan a collaborative research effort. We propose to identify and compare methane sources and fate in two different Arctic marginal seas: Baffin Bay and East Siberian Sea. Baffin Bay is a more than thousand meter deep basin located west of the Greenland ice sheet from where glaciers discharge into the sea. In contrast, the East Siberian Sea is a several tens of meter deep broad shelf region situated offshore land that is marked by permafrost and tundra from where rivers carry their load into the sea. Both areas are seasonally ice covered and show similar changes in sea ice cover and surface warming in the last thirty years. We hypothesize that the methane cycle in the shallow marine shelf setting is more susceptible to global climate change than the area near glacier-covered land in the near future. In order to test the hypothesis, we plan two expeditions, one to the Baffin Bay organized by the German partners and one to the East Siberian Sea organized by the Russian colleagues. During both cruises, we intend to 1) investigate light hydrocarbons (C1-C4) and organic matter in the upper meters of the sediment, 2) map bubble emissions, dissolved methane plumes, and trace elements in the water column, 3) measure the methane sea-air flux, and 4) identify microbial methane turnover rates and the microbial community associated with the methane cycle in the sediment and the water column. These data will allow us to identify 1) the predominant source of methane to the two marginal seas (biogenic versus thermogenic, associated with coal or groundwater discharge), 2) how much methane is currently generated in the sediment, and 3) if methane sea-air flux varies due to fluctuating bubble emissions from the seafloor or due to different rates of aerobic microbial methane oxidation in the water column. This quantitative baseline study will add valuable data to overcome the significant uncertainties in the Arctic methane cycle and might indicate what kind of marginal sea might be more affected by global warming at the time of investigation.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Professor Dr. Renat Shakirov, until 3/2022