Acoustic survey of sea floor features in Asköfjärden

University essay from Stockholms universitet/Institutionen för geologiska vetenskaper

Abstract: Marine geological surveys in Asköfjärden in the southern Stockholm Archipelago hasrevealed step like features in the sediments on the Baltic sea floor. The aim of this project is toanalyse the steps and possible formation processes from the survey data. The data used aretaken from the acoustic instruments multibeam echosunder and Chirp sonar sediment profiler.The multibeam reveal the seafloor topography and can detect water column features. TheChirp sonar produce sub-bottom profiles showing the sediments down to some tens of metersunderneath the sea floor. The multibeam data show multiple crescent shaped steps as well aselliptically shaped “pockmarks”. Water column data show what could be interpreted as seepsfrom the sea floor under these features. The sub bottom profile show deformation and fluidsignatures under the steps. Gas signatures and what could be other fluids are present. Theinterpretation concludes that the formation could be from either gas or groundwater seeps. Nodefinitive conclusions can be made from the data available for the present study, andapetrophysical or geochemical study of the study area cold provide further understanding ofthe formation of the steps.

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