Over geological times, the evolution of carbon isotope compositions of carbonates (δ13Ccarb) in sedimentary record highlights many positive isotopic excursions (CIEs), reflecting significant perturbations of the carbon cycle in Earth surface environments. Although generally interpreted as a consequence of an increase of organic carbon burial in sediments, the lack of high organic carbon content, as well as the strong spatial and temporal variability, observed in many sedimentary successions recording CIEs challenge this postulate. Among other alternative hypothesis involving regional or local control, the potential influence of methanogenesis, i.e. the biological process of anaerobic organic matter degradation producing methane (CH4), has been raised; its ability to generate similar isotopic signatures has been demonstrated in modern analogue. Although the processes behind CIEs are questioned, providing more information about methanogenesis impact is challenging based on traditional isotopic tool like δ13Ccarb, as its isotopic effect on is similar to that of organic carbon burial increase. Recently, stable isotope compositions of metals used as enzymatic cofactors of CH4-related processes were investigated to explore their potential as biomarkers of methanogenesis. During the last decade, significant advances have been made on using Ni isotopes as tracers of methanogenesis but important challenges remain to better constrains both their potential and limit. In order to improve our understanding of CH4 cycle and its impact on Earth’s surface environments through geological times, we will investigate further the potential of Ni isotopes and its potential couplings with traditional stable isotope in various modern settings and past environments to enhance our ability to track and discriminate the influence of CH4-related processes through Earth’s history.

Wave-modulated Arctic Air-sea eXchanges and Turbulence (WAAXT) is a project designed to improve our understanding of ocean boundary layer processes in a changing Arctic Ocean. Sea ice extent in the Arctic Ocean has been decreasing since the beginning of the satellite era, meaning that open-water, as opposed to under-ice, oceanographic processes are becoming increasingly important for Arctic dynamics. One of the most fundamental differences between the open and ice-covered oceans is the presence of surface waves. Surface waves and wave-driven processes drastically alter air-sea fluxes, upper-ocean turbulence, and the dominant dynamical balance in the upper ocean. WAAXT will be based on a series of field experiments to study the small-scale processes associated with this emerging wave climate, with a particular focus on near-surface turbulence. Three major effects of wave processes will be targeted: 1) Modification and suppression of ice formation by wave motions and the associated elevated near-surface turbulence. 2) Physical breakup of sea ice by wave motions, and the associated contributions to the modification of air-sea fluxes, upper-ocean structure, and melt rates. 3) Interactions between wave-driven turbulence, especially breaking and Langmuir circulations, with the unique salinity-based stratification in the Arctic basin. A key aspect of these processes is their horizontal variability, which will be captured using a multi-platform approach. Experimental work will begin in a natural laboratory in the Saint Lawrence Estuary and move to the Arctic as scientific and technical capacity is developed. The long-term goal for WAAXT is to produce the data and parameterizations needed to understand climate-scale feedbacks associated with the emerging wave climate in the Arctic basin.

The United Nations has expressed concern over the potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in the next century, which could cause climate and weather alterations that lead to various socio-economic stresses, especially in agriculture, fisheries, infrastructure maintenance and social migration. The value of information associated with a continuous observational record of the AMOC system, which enables confident prediction of future trend, has been estimated to be tens of billions of euros. While instrumental observations of the AMOC system are only available for the last decades, we must rely on proxy indicators in natural archives to capture the long-term trend of ocean circulation throughout the Industrial Age, and further back in time when there were little anthropogenic carbon emissions. Such a long-term record is particularly important for the subpolar North Atlantic: a region of deep convection that maintains the AMOC, susceptible to freshening as a result of increasing Arctic ice melt. This project aims to develop the first comprehensive, long-term record of subpolar North Atlantic circulation through cross-disciplinary, cross-border collaboration between the French Institute for Ocean Science (host), University of Iceland (secondment), and Copenhagen University. The proposed study will compile new proxy analyses with the expanding coverage of instrumental observations to provide a confident reconstruction of the region’s hydrography and dynamics over the past two millennia. Ultimately, the project findings will be effectively delivered to the decision makers, the young generation and the general public through participation in policy works at JPI Oceans (placement), university teaching and outreach activities. The multimodal delivery of project findings aims to raise awareness of the severity of a long-term AMOC decline and to facilitate cooperation for timely mitigation of potential socio-economic consequences.