Investigating the role of the coupling between the ocean, the sea ice and the atmosphere in the biogeochemical cycle of CH4

The contribution of the ocean to the atmospheric methane (CH4) budget is poorly understood. In polar regions, this contribution is further influenced by the sea-ice cover. Sea ice has long been considered as an inert and impermeable barrier, but recent studies have highlighted the existence of gas fluxes at the atmosphere–sea-ice and sea-ice–seawater interfaces. These fluxes are to date poorly characterized and quantified, so that the role of sea ice as a net sink or source of CH4 is still unclear. The PIPERS (Polynyas, Ice Production, and seasonal Evolution in the Ross Sea) expedition on the icebreaker Nathaniel B. Palmer provided a unique opportunity to investigate the complex coupling between the ocean, the sea ice and the atmosphere, at the beginning of winter 2017. As the season was progressing, we could study how sea-ice formation influences the biogeochemical cycle of CH4. We performed continuous measurements of dissolved CH4 in surface waters together with CH4 mixing ratio in the atmosphere. Discrete samples were also collected both to calibrate continuous systems and to carry out subsequent stable isotope analyses. A total of 17 ice cores dedicated to CH4 concentration measurements were drilled in the Ross Sea pack ice and in the vicinity of the Terra Nova Bay polynya. Additional analyses, such as characterization of ice texture and physical properties, were conducted on these cores. This multiparametric dataset will allows us to determine the distribution of CH4 between the ocean, the sea ice and the atmosphere during sea-ice formation and help us to unravel the net role of sea ice in the CH4 budget.