Illulissat Fjord mouth, West Greenland: pockmark formation in response to Holocene warming

• Main Authors: Schumann, Kai, Völker, David, Weinrebe, Reimer Wilhelm
• Format: Conference Object
• Language: English
• Published: 2010
• Subjects: Greenland; Ilulissat; Kongsberg; Antarc*; Antarctica
• Online Access: https://oceanrep.geomar.de/id/eprint/8905/; https://oceanrep.geomar.de/id/eprint/8905/1/Acoustic_mapping_Schumann_K_et_al.pdf; http://www.ozean-der-zukunft.de/das-netzwerk/symposium/

Ilulissat Icefjord in West-Greenland is the fastest and most productive iceberg calving area outside Antarctica. Changes in climate exert a first-order control on the retreat of the icefront and the calving of icebergs. Glacial and geological processes related to iceberg calving and transport shape the morphology of the seafloor seaward of the ice front characteristically. Revealing the morphology by high-resolution bathymetric mapping helps to understand these processes. Aim of the project “Iceflow Activity” was to map the bathymetry of Ilulissat Icefjord. During the RV Maria S. Merian cruise in summer 2007 a Kongsberg EM120 and a EM1002 multibeam systems were used to map the areas in front of the fjord mouth. Closer to the ice bergs, the portable Seabeam 1180 multibeam system temporarily mounted on the small local vessel Smilla that could navigate through areas inaccessible to large research vessels. Both datasets were compiled and merged to achieve a comprehensive image of the mapped area. Continuous Parasound sediment profiling during the Merian cruise enable investigation of sedimentary structures. Different morphological features such as ridges, shaped like drumlins and valleys that could be connected to channel systems, directing debris flows to a deposition centre characterize the central part of the survey area. Hera, a series of prominent circular depressions of 80m to 150m in diameter and up to 30m deep have been found and are interpreted as pockmarks. Different formation processes for these structures have been discussed. The lack of the youngest sedimentary unit inside of the easternmost pockmarks indicated by Parasound profiles crossing different pockmarks point to active formation processes, while the westernmost pockmark seems to be inactive. The position of the recently active pockmarks and CTD measurements helped to interpret the pockmarks as structures formed by gas hydrates. The WSW – ENE alignment and a possible age decrease from W to E may indicate the migration of the gas hydrate stability ...