Methane pathways within sea ice and seawater in the Arctic Ocean: an observational study
This PhD thesis highlights the role of the cycles of sea ice formation and melt on the methane (CH4) pathways in the Arctic Ocean, considering the release of dissolved CH4 into the ocean as an alternative pathway to the ice-air CH4 flux. In this dissertation, CH4 concentration and its stable carbon...
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| Other Authors: | , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Universität Bremen
2021
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| Subjects: | |
| Online Access: | https://media.suub.uni-bremen.de/handle/elib/5657 https://doi.org/10.26092/elib/1357 https://nbn-resolving.org/urn:nbn:de:gbv:46-elib56575 |
| Summary: | This PhD thesis highlights the role of the cycles of sea ice formation and melt on the methane (CH4) pathways in the Arctic Ocean, considering the release of dissolved CH4 into the ocean as an alternative pathway to the ice-air CH4 flux. In this dissertation, CH4 concentration and its stable carbon isotopic signature (13C-CH4) were combined with oceanographic data, and the stable oxygen isotopic signature of seawater (18O-H2O) as a water mass tracer to follow the pathways of CH4. The CH4 pathways were traced within sea ice and at the sea ice-seawater interface in the Arctic Ocean and on an Arctic shelf region, to infer its potential sources and main sinks at the sea ice-ocean-atmosphere interface. Methane is a potent greenhouse gas contributing to global warming. Because of a phenomenon called Arctic amplification (warming is twice as large in the Arctic than in the global mean), the most notable changes due to global warming are currently happening in the Arctic. Arctic amplification of global warming is causing a rapid decrease in summer sea ice extent in the Arctic Ocean. Thin and more fragile first-year ice (FYI), which is more susceptible to oceanic and atmospheric forcing, is replacing complex structured and thick multi-year ice. Sea ice contributes to control the gas exchange between the ocean and the atmosphere. Hence, changes in the ice regime are likely to influence the CH4 pathways in the Arctic Ocean. In Publication I, we analyzed the CH4 concentration and the 13C-CH4 in both sea ice and seawater. The expedition PS106.1 took place on a drifting ice floe north of Svalbard during late spring 2017. We report on different storage durations of CH4 within FYI and ridged/rafted ice and supersaturation (CH4 excess) in surface waters. We found that the ice types and/or structures influence the fate of CH4. During the early melt season, when basal melting starts and the ice still holds impermeable ice layers at its surface, CH4 released from sea ice into the seawater is the predominant pathway. The excess ... |
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