Oceanographic Setting Dominates Methane Transport Through the Water Column in the Shallow Area West of Prins Karls Forland, Arctic Ocean

Anna Silyakova1, Pär Jansson1, Pavel Serov1, Carolyn Alice Graves2, Helge Niemann1,3, Friederike Grundger1, Bénédicte Ferre1 and Jurgen Mienert1, (1)University of Tromsø, Centre for Arctic Gas Hydrates, Environment and Climate (CAGE), Tromsø, Norway, (2)University of Southampton, United Kingdom, (3)University of Basel, Department of Environmental Sciences, Basel, Switzerland
Abstract:
The area west of Prins Karls Forland (PKF, West Spitsbergen) in the Arctic Ocean, restricted to 90 m water depth, is known for a large amount of shallow active gas flares. Gas flares are streams of bubbles that contain mostly methane, which is a potent greenhouse gas. The important questions for many areas with discovered gas flares are: Does this gas reach the atmosphere? What controls the vertical and horizontal distribution of dissolved methane away from the source on the seafloor? Is all dissolved methane detected above gas flares released from those flares or does it partially originate from other areas (eg. Storfjorden, or area of deeper flares on the PKF slope)?

The present study is based on two repeated oceanographic surveys conducted in the summers of 2014 and 2015. During the surveys, we sampled 64 CTD stations in a grid above a 30 x 15 km area with active methane flares. Vertical profiles of temperature (T) and salinity (S), as well as TS diagrams indicate very different oceanographic settings during the two surveys. Warm and saline Atlantic waters originating from the West Spitsbergen Current prevailed during the 2014 campaign. In 2015, in contrast, waters were distinctly less saline and cooler. These waters originate from the East-Spitsbergen current that flows northwards over the shelf from the Barents Sea around the southern tip of Spitsbergen. The water mass was furthermore influenced by local sources from the fjords.

In both years, we observed strong vertical gradients in the distribution of dissolved methane in the water column above gas flares, with only 4% methane concentrations at the sea surface when compared to bottom waters. However, the circulation of the dominant water masses mainly controlled the horizontal distribution of methane in the water column in the specific year. We discuss oceanographic processes and mechanisms responsible for methane transport and transformation in the study area.

This study is funded by CAGE (Centre for Arctic Gas Hydrate, Environment and Climate), Norwegian Research Council grant no. 223259.

Back to: Hydrocarbon Seepage as a Conduit Connecting Deep Subsurface Sediments, Shallow Sediments, the Water Column, and Atmosphere I