ALBERT

Description: Nitrous oxide (N2O) is one of the most important long-lived greenhouse gases (GHG) responsible for the overall warming of the Earth system, and the strongest ozone-depleting compound in the stratosphere. While the ocean is thought to be a net source of N2O to the atmosphere, at regional and basin-scales there is a large range of variability in terms of its mid-depth water production and consumption, as well as a wide range of physical processes which impact the pool of this GHG in surface waters, posing a significant challenge to both observational and model-based estimates of the annual emissions. Furthermore, although environmental changes such as warming, eutrophication and decrease in sea ice coverage are expected to affect the cycling of N2O, the particular direction of the projected trends is highly uncertain, mostly due to the paucity of measurements in strong source regions and areas of difficult access due to their remote location or extreme weather conditions. In this talk I will present an overview of the current state of knowledge with respect to the exchanges of N2O across the sea-air-ice interfaces, and discuss their relevance in the context of ongoing climate change. To this end, I will use examples from ship-based observations in Eastern Boundary Upwelling Systems (EBUS), the subpolar North Atlantic and the Arctic Ocean. By looking at the contrasting features of these ecosystems and how they affect the marine budget of N2O, I aim to highlight the need of new approaches and priority areas for research on GHGs such as N2O.

Description: The Arctic Ocean is particularly sensitive to climate change. Its ecosystem structure and function are prone to be disturbed by fast warming and massive retreat of sea-ice, which in turn, might result in feedbacks on climate. Moreover, such drastic changes are expected to influence the meridional fluxes of heat, freshwater and biogeochemical tracers between subpolar areas and the Arctic. As the third most important greenhouse gas and major ozone-depleting substance in the stratosphere, nitrous oxide (N2O) is a crucial gas to study in order to assess the ocean’s role in the production and exchange of climate-relevant compounds to the atmosphere. Between 2018 and 2019 we conducted ship-based surveys to elucidate the source-sink dynamics of N2O in the subpolar-polar North Atlantic. Based on results from those campaigns, we show the distribution and spatial variability of surface N2O, which ranged from moderate supersaturation (positive sea-air fluxes) in ice-free subpolar areas to unusually strong undersaturation (negative sea-air fluxes) in partially or fully ice-covered areas. We also present a comprehensive overview of the water column distribution of N2O in the region, and by combining this data with hydrographic and chemical (O2 and inorganic nutrients) information, we trace back the origin of the dominant water masses so as to illustrate the connectivity between the Fram Strait and the Nordic Seas off southeast Greenland. This analysis is used to discuss how the meridional water mass exchange in the region influences the balance of local vs. remote N2O production and its spatial variability. Furthermore, we use the results from collocated molecular analyses (functional gene markers) to infer the occurrence and abundances of the main microbial communities responsible for the cycling of N2O. This contribution is relevant for assessments of expected changes in trace gas emissions with further climate-driven changes in the Arctic Ocean.

Description: Given the climatic relevance of marine-derived trace gases, the investigation of their distribution and emissions from key oceanic regions is a crucial need in our efforts to better understand potential responses of the ocean and the overlying atmosphere to environmental changes such as warming and deoxygenation. Low-oxygen waters connected to coastal upwelling systems and the associated oxygen minimum zones(OMZ) are well-recognized strong sources of several trace gases. Our main goal during the M135-M138 cruises was to assess the distribution of different gases which are relevant for the biogeochemical cycling of carbon and nitrogen in the OMZ off Peru, as well as the spatial and temporal variability of their sea-air fluxes.