Surface and sub-surface features of an active gas seep in Malvinas Basin (SW Atlantic Ocean)

BRAVO M.E.; ORMAZABAL, J.P; PALMA F.I.; ESTEBAN, F.; PRINCIPI S.; ARTUNDUAGA C.; A. TASSONE; LEVIN L. A.

Athenas

Conferencia; Regional Conference on Geomorphology (IAG); 2019

National and Kapodistrian University of Athens,

Methane gas seeps are widelydistributed, however, only a small fraction of the seeps from the seabed havebeen discovered as indicated by the fact that new findings are reported everyyear. Gas seep studies in the deep sea of Argentina are scarce, and do not characterizegeological and biological features. This work is part of a multidisciplinarystudy intended to establish the trophic contribution of methane seepages in theMalvinas Basin. To that end, we analyzed a superficial and sub-superficialanalysis of 2D multi-channel seismic data provided by the Argentine Secretaryof Energy and selected an area characterized by chimneys and pockmarks to targetin an exhaustive survey onboard the Austral oceanographic vessel. This surveywas carried out using multibeam (EM122) and single beam echo sounders (EK80) toobtain detailed bathymetric data, as well as a sub-bottom profiler to obtainultra-high resolution seismic data from the shallow sediment column. Theresults identified a pockmark-like field. From these, a pockmark with activegas seepage (evidenced by gas plumes in the water column) was selected for seafloorsampling. This pockmark has an elliptical shape and is located at 450 m waterdepth. Its diameter is 400 m and its depth varies between 2 and 6 m with aslope of 3º. Acoustic turbidity in contact with the surface of the seabed ofthe pockmark indicates that the seeping gas is mainly methane. This gas wouldcome from a deep source, since it was observed associated with a chimney havingan enhanced reflector in the multi-channel 2D records. These results allow,with a high margin of certainity, the sampling of the benthic communitiesassociated with gas seepage.