Marks, Steffen (2021) Die Rolle des submarine Grundwassereintrags für die Verteilung von Methan (CH4) und Lachgas (N2O) in der Beltsee. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 51 pp.

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Abstract

Besides carbon dioxide (CO2) methane (CH4) and nitrous oxide (N2O) are the most climate relevant trace gases in the atmosphere. Even though the major part of their emissions comes from anthropogenic sources, the oceans still play an important role in the dynamics of climate gas production, consumption, uptake and release. The Belt Sea is part of the coastal regions, which make a great contribution to the marine emissions. Submarine Groundwaters discharges have frequently been detected in the study area. This study investigates the relation between submarine groundwater discharge and the distribution of the trace gases in the water column on the basis of samples, which have been taken in the Kiel Bay in October 2019 and August 2020. The samples from 2019 showed relatively low variations in the concentrations of CH4 and N2O between the surface waters and the deep waters. The CH4 concentrations ranged between 6 nmol L-1 and 46 nmol L-1. The surface waters showed a distinct supersaturation of CH4 with respect to atmospheric equilibrium of 191 % - 509 %. The concentrations of N2O were between 9 nmol L-1 and 13 nmol L-1. The surface waters showed saturations with N2O of 92 % to 104 %. The samples of 2020 had greater variations in the concentrations of the surface waters and the deep waters. The CH4 concentrations ranged between 7 nmol L-1 and 445 nmol L-1 and between 3 nmol L-1 and 14 nmol L-1 for nitrous oxide, respectively. This led to saturations of the surface waters of 263 % to 1838 % for CH4 and 111 % to 120 % for N2O. Investigations of groundwater tracers like 222Rn and several isotopes of Ra yielded no distinct information about submarine groundwater discharges for 2019 nor for 2020. However, the elevated CH4 concentrations and the low concentrations of N2O from August 2020 could be associated with already known spots of submarine groundwater discharge (also known as “pockmarks”) in the area of the Eckernförde Bay.

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