Bastian, Daniel (2021) Distribution and pathways of dissolved methane (CH4) in the water column of the East Greenland shelf. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 89 pp.

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Abstract

Methane (CH4) is the second most relevant greenhouse gas on Earth. Polar and subpolar regions are highly sensitive to climate change and the increasing melting rates of seasonal and (multi-) annual ice are projected to have severe impacts on their marine ecosystems. However, the knowledge about the distribution and pathways of dissolved CH4 and how it is affected by melting in these regions is sparse - or particularly for the East Greenland shelf (EGS), non-existent. To shed light on the CH4 cycling on the EGS, extensive sampling was conducted throughout the area during the melting season in July 2019 onboard the research vessel MARIA S. MERIAN during the cruise MSM85. Enhanced CH4 saturations (max.: 173 %) were observed in surface waters in connection with meltwater. This resulted in pronounced gradients between the near-shore area and the open ocean. Meltwater associated with amplified CH4 was characterized by low oxygen uptake, aerated conditions, low Chl-α and N-limitation which reflect the post-bloom phase of water masses influenced by seasonal ice coverage. The surface layer was near equilibrium with the atmosphere for the entire shelf with respect to dissolved CH4 and the overall mean sea-air CH4 flux of the EGS was -0.11 ±1.5 μmol/m² s (range: -3.8 – 3.12 μmol/m² s). Therefore, at the time of sampling, the EGS acted neither as a significant sink nor source for atmospheric CH4, in contrast to most of the global coastal regions where CH4 is supersaturated with respect to atmospheric equilibrium. Enhanced CH4 concentrations at depth were mainly found on the shelf (max.: 66.85 nmol/kg) in association with Arctic-derived water of the East Greenland Current (EGC). Open ocean stations were largely undersaturated for CH4 while coastal locations were near equilibrium or supersaturated, suggesting that the projected rising melting rates could potentially turn the site into a source for atmospheric CH4.

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