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R/V METEOR cruise M134

Port Stanley (Falklands) - Punta Arenas (Chile)
16.01.2017 to 18.02.2017

Emissions of free gas from cross-shelf troughs of South Georgia: Distribution, quantification, and sources for methane ebullition sites in sub-Antarctic waters
The overarching goal of Meteor cruise M134 is to increase our knowledge of fluid flow and its related processes in general, and specifically in the area around South Georgia, where this phenomenon is newly discovered. During RV Polarstern cruise ANT-29/4 in March/April 2013, emissions of free gas from sediments in glacial troughs into the water column were detected for the first time at the shelf of South Georgia. Preliminary but not systematically conducted surveys for flare mapping have shown that the emissions are exclusively related to the shelf trough systems and probably sourced from the post-glacial sediments by biogenically produced methane. Nevertheless, active plate movements are known in the area around South Georgia, and migration of deeper gas reservoirs through fault systems might be possible. Methane hydrates are proposed to exist in the sediments in water depths deeper ~370 m. In the frame of Meteor cruise M134 we will apply the modern hydroacoustic systems installed on the vessel to map the distribution of the methane emissions in the shelf troughs, but also over the shelf break. Subsequently, we want to precisely sample and quantify them using ROV Squid to unravel their influence on the seafloor, the bio(geo)chemical processes in the sediments and on the water column. The investigation should be focused on three selected trough systems which are characterized by different geotectonic settings, enabling a better understanding of the source, migration and related processes of the fluid system around South Georgia.

Fig.1.(a) Plate tectonic overview with the South Georgia microplate (SG) located at the eastern part of the North Scotia Ridge. SAM: South American Plate, SCO: Scotia Plate, SAN: Sandwich Plate, ANT: Antarctic Plate (modified after Cunningham et al., 1998). (b) Map of the main tectonic structures of the South Georgia crustal block (after MacDonald and Storey, 1987). The shelf morphology is characterized by at least ten cross-shelf troughs sourcing at the fjords of the island (yellow areas). From Römer et al. (2014), EPSL, 403, 166-177.