Hydroacoustic and geochemical traces of marine gas seepage in the North Sea

This PhD thesis consists of a general introduction Chapter I, followed by three stand-alone Chapters II-IV, a general conclusion Chapter V, and supplemental content in the Appendix. Chapter II is the reprint of a published paper that outlines the feasibility of ship-born gas bubble detection with conventional multibeam mapping sonar and its advantages compared to single beam sounders. Chapter III consists of a submitted manuscript describing the use of a prototype in situ multibeam bubble monitoring system (GasQuant) and illustrates the device’s potential to resolve tempo-spatial variation of gas seepage. Due to technical difficulties, the aspired calibration of GasQuant failed and a quantitative analysis of the echo signals could not be accomplished. Even though, gas bubble acoustic inversion theory and principle limitations are discussed in Appendix B. Furthermore we attach a registered patented generic algorithm in Appendix A to e.g. automatically detect rising gas bubbles in sonar data. Chapter IV covers the seepage at a specific seep site in the North Sea combining acoustic and geochemical methods. Thus, the source strength of the respective seep field could be determined and the further fate of methane seepage in the North Sea is discussed. This Chapter is again in the form of a manuscript for a peer reviewed journal and will be submitted shortly. Two peer-reviewed Co-authorship publications abstracts related to this work can additionally be found in the Appendix C and Appendix D.

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