Sources and sinks of methane in sea ice: Insights from stable isotopes

We report on methane (CH4) stable isotope (d13C and d2 H) measurements from landfast sea ice collected near Barrow (Utqiagvik, Alaska) and Cape Evans (Antarctica) over the winter-to-spring transition. These measurements provide novel insights into pathways of CH4 production and consumption in sea ice. We found substantial differences between the two sites. Sea ice overlying the shallow shelf of Barrow was supersaturated in CH4 with a clear microbial origin, most likely from methanogenesis in the sediments. We estimated that in situ CH4 oxidation consumed a substantial fraction of the CH4 being supplied to the sea ice, partly explaining the large range of isotopic values observed (d13C between –68.5 and –48.5 ‰ and d2 H between –246 and –104 ‰). Sea ice at Cape Evans was also supersaturated in CH4 but with surprisingly high d13C values (between –46.9 and –13.0 ‰), whereas d2 H values (between –313 and –113 ‰) were in the range of those observed at Barrow.These are the first measurements of CH4 isotopic composition in Antarctic sea ice. Our data set suggests a potential combination of a hydrothermal source, in the vicinity of the Mount Erebus, with aerobic CH4 formation in sea ice, although the metabolic pathway for the latter still needs to be elucidated. Our observations show that sea ice needs to be considered as an active biogeochemical interface, contributing to CH4 production and consumption, which disputes the standing paradigm that sea ice is an inert barrier passively accumulating CH4 at the ocean-atmosphere boundary

The future of Arctic sea-ice biogeochemistry and ice-associated ecosystems

The Arctic sea-ice-scape is rapidly transforming. Increasing light penetration will initiate earlier seasonal primary production. This earlier growing season may be accompanied by an increase in ice algae and phytoplankton biomass, augmenting the emission of dimethylsulfide and capture of carbon dioxide. Secondary production may also increase on the shelves, although the loss of sea ice exacerbates the demise of sea-ice fauna, endemic fish and megafauna. Sea-ice loss may also deliver more methane to the atmosphere, but warmer ice may release fewer halogens, resulting in fewer ozone depletion events. The net changes in carbon drawdown are still highly uncertain. Despite large uncertainties in these assessments, we expect disruptive changes that warrant intensified long-term observations and modelling efforts

Understanding the Origin(s) of Methane in Sea Ice Using Stable Isotope Ratios

In 2012, an unexpected CH4 excess has been reported above open leads in the Arctic Ocean showing that sea ice plays a role in the ocean-atmosphere CH4 dynamics. However, the processes involved there have not yet been identified. We performed CH4 stable isotope (d13C and dD) analyses on sea ice samples, as well as geochemical and physical measurements, to determine the possible pathways involved in CH4 production/removal in or under sea ice. We present results from ice cores collected above the shallow shelf of Barrow (Alaska) from January to June 2009 as well as in the landfast ice of McMurdo Sound (Antarctica) from September to November 2012. We found a clear difference in isotopic signature between the two sites. The McMurdo ice was supersaturated in CH4 and showed isotopic signatures surprisingly enriched in heavy isotopes (d13C between -47 and -12 ‰ and dD between -87 and -350‰). No natural pathways have yet been identified with such isotopic signatures, but we suggest that aerobic CH4 formation in or under the ice might be a candidate. In contrast, the CH4 concentrations were much larger in ice overlying the shallow shelf of Barrow and there the origin of CH4 was clearly biogenic (d13C between -48 and -68 ‰ and dD between -180 and -250‰), thus likely originating from the sediment. In the McMurdo ice, the seasonal evolution shows that CH4 was becoming more enriched in heavy isotopes with time, suggesting the occurrence of aerobic oxidation processes in the ice

Sources and sinks of methane in sea ice: Insights from stable isotopes

We report on methane (CH4) stable isotope (d13C and d2H) measurements from landfast sea ice collected near Barrow (Utqiagvik, Alaska) and Cape Evans (Antarctica) over the winter-to-spring transition. These measurements provide novel insights into pathways of CH4 production and consumption in sea ice. We found substantial differences between the two sites. Sea ice overlying the shallow shelf of Barrow was supersaturated in CH4 with a clear microbial origin, most likely from methanogenesis in the sediments. We estimated that in situ CH4 oxidation consumed a substantial fraction of the CH4 being supplied to the sea ice, partly explaining the large range of isotopic values observed (d13C between -68.5 and -48.5 ‰ and d2H between -246 and -104 ‰). Sea ice at Cape Evans was also supersaturated in CH4 but with surprisingly high d13C values (between -46.9 and -13.0 ‰), whereas d2H values (between -313 and -113 ‰) were in the range of those observed at Barrow.These are the first measurements of CH4 isotopic composition in Antarctic sea ice. Our data set suggests a potential combination of a hydrothermal source, in the vicinity of the Mount Erebus, with aerobic CH4 formation in sea ice, although the metabolic pathway for the latter still needs to be elucidated. Our observations show that sea ice needs to be considered as an active biogeochemical interface, contributing to CH4 production and consumption, which disputes the standing paradigm that sea ice is an inert barrier passively accumulating CH4 at the ocean-atmosphere boundary

Perseverative Thinking Questionnaire (PTQ): French Validation of a Transdiagnostic Measure of Repetitive Negative Thinking

International audienc

Biogeochemistry of Coccolithophore Blooms along the Continental Margin of the Northern Bay of Biscay

info:eu-repo/semantics/publishe

Biogeochemical investigations of coccolithophore blooms along the continental margin of the northern Bay of Biscay: highlights of the PEACE project

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PIPERS: Role of Polynyas on the Atmospheric Budget of Methane and Carbon Dioxide

Coastal polynyas are areas of anomalous open water and thin ice in regions that are otherwise covered by sea ice. They frequently occur around the Antarctic continent in response to strong offshore katabatic wind stresses. The loss of heat from the open ocean to the cold atmosphere can enormously enhance rates of ice production. In polynya areas, the coupling between the atmosphere, sea ice and ocean is complex, and the role of ice formation on the budget of the main climate forcing carbon gases remains unknown. During the PIPERS expedition on the N.B. Palmer from April to June 2017, we performed continuous measurements of methane and carbon dioxide concentrations in the atmosphere and in the surface water from New Zealand to the polynyas of the Ross Sea. Discrete sampling was carried out in parallel to calibrate the continuous systems and to later measure the stable isotope ratios of both gases in the water and in the air. The stable isotope data enable unravelling the pathways involved in gas formation and removal. While the concentrations of both gases were relatively low in the surface waters of polynyas, the preliminary atmospheric data show higher methane and carbon dioxide levels in the atmosphere at locations where sea ice formation was most intense. These data together with the isotopic ratios of both gases and with meteorological data will be discussed to better understand the role of sea ice formation on the exchange of climate forcing gases

Biogeochemistry of a late coccolithophorid bloom at the continental margin of the Bay of Biscay

Recent findings have led to growing concern regarding the impact of ocean acidification on marine calcifyers, but little is known about their biogeochemistry in natural (field) conditions (a major but overlooked pre-requisite for realistic modelling of the future evolution of marine C cycling in a high CO2 world). The changes that will undergo these species in the near future and the biological feedback to decreasing oceanic pH are still open to debate. Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the subpolar and temperate zones of the worlds oceans. Within the framework of the Climate and Atmosphere Belgian Federal Science Policy Office programme, the continental margin of the Northern Bay of Biscay (North Atlantic Ocean) was visited in June 2006 during a transdisciplinary investigation of a late-spring bloom dominated by Ehux. Remote sensing images, transmitted onboard on a daily basis, were of valuable significance to pinpoint the coccolithophorid bloom along the margin, and to sample stations with contrasted biogeochemical properties.We determined 14C-based primary production and calcification rates, as well as pelagic respiration rates (O2 incubations). The magnitude of the biological and carbonate carbon fluxes will be synthesized and discussed in the light of biogeochemical parameters, such as Transparent Exopolymer Particles (TEP), chlorophyll-a, particulate carbon concentrations, particle dynamics and particulate organic carbon export (deduced from 234Th fluxes). Additional information on the bloom biogeochemistry will be presented (activity of dissolved esterase enzymes and bacterial community structure) to emphasize the importance of coccolithophorid blooms in the contemporary carbon cycle

Sources and sinks of methane in sea ice: Insights from stable isotopes

We report on methane (CH4) stable isotope (d13C and d2H) measurements from landfast sea ice collected near Barrow (Utqiagvik, Alaska) and Cape Evans (Antarctica) over the winter-to-spring transition. These measurements provide novel insights into pathways of CH4 production and consumption in sea ice. We found substantial differences between the two sites. Sea ice overlying the shallow shelf of Barrow was supersaturated in CH4 with a clear microbial origin, most likely from methanogenesis in the sediments. We estimated that in situ CH4 oxidation consumed a substantial fraction of the CH4 being supplied to the sea ice, partly explaining the large range of isotopic values observed (d13C between -68.5 and -48.5 ‰ and d2H between -246 and -104 ‰). Sea ice at Cape Evans was also supersaturated in CH4 but with surprisingly high d13C values (between -46.9 and -13.0 ‰), whereas d2H values (between -313 and -113 ‰) were in the range of those observed at Barrow.These are the first measurements of CH4 isotopic composition in Antarctic sea ice. Our data set suggests a potential combination of a hydrothermal source, in the vicinity of the Mount Erebus, with aerobic CH4 formation in sea ice, although the metabolic pathway for the latter still needs to be elucidated. Our observations show that sea ice needs to be considered as an active biogeochemical interface, contributing to CH4 production and consumption, which disputes the standing paradigm that sea ice is an inert barrier passively accumulating CH4 at the ocean-atmosphere boundary