Dynamic modelling of marine gas hydrates north of the South Shetland Islands (Antarctic Peninsula)

Abstract

In the Antarctic Peninsula, a marine gas hydrate system has been identified based on geophysical data (Lodolo et al., 1993; Tinivella et al., 2002). These data suggest gas hydrates average volume concentration of 6.0 ± 1.2% for in the accretionary wedge of the South Shetlands Islands (Tinivella, 2002). Based on legacy seismic profiles (belonging to 17 oceanographic cruises) retrieved from the Antarctic Seismic Data Library System (SDLS), a continuous Bottom Simulating Reflector (BSR) has been mapped in the accretionary wedge, between Elephant and King George islands. This BSR is located at a sub-bottom depth between ca. 250 ms TWTT in the upper slope and ca. 1s TWTT at the base of the accretionary wedge. The theoretical Base of Gas Hydrate Stability Zone (BGHSZ) calculated with a static model (León et al., 2009) for the present oceanographic conditions (pressure/bathymetry, seafloor temperature, geothermal gradient and salinity) is located 100 to 400 m shallower than this BSR level, considering available geothermal data for the area. The BSR-BGHSZ mismatch points that gas hydrates in the area seem to be in a transient state with respect to their theoretical location calculated from both pure methane and thermogenic compositions. Dynamic models developed with TOUGH+HYDRATE in the frame of ICEFLAME project (PID2020-114856RB-I00, Spanish Ministry of Science and Innovation), reveal two possible scenarios for the above mismatch between BSR and BSGHZ: isostatic rebound and/or tectonic uplift.