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

MARIA EMILIA BRAVO; FEDERICO D. ESTEBAN; CESAR ARTUNDUAGA; FERMIN I. PALMA; SEBASTIAN PRINCIPI; LISA ANN LEVIN; JUAN PABLO ORMAZABAL; JOSE ISOLA; ALEJANDRO TASSONE

Atenas

Conferencia; Regional Conference on Geomorphology; 2019

International Association of Geomorphologists

Methane gas seeps are widely distributed, however, only a small fraction of the seeps from the seabed have been discovered as indicated by the fact that new fndings are reported every year. Gas seep studies in the deep sea of Argentina are scarce, and do not characterize geological and biological features. This work is part of a multidisciplinary study intended to establish the trophic contribution of methane seepages in the Malvinas Basin. To that end, we analyzed a superfcial and sub-superfcial analysis of 2D multi-channel seismic data provided by the Argentine Secretary of Energy and selected an area characterized by chimneys and pockmarks to target in an exhaustive survey onboard the Austral oceanographic vessel. This survey was carried out using multibeam (EM122) and single beam echo sounders (EK80) to obtain detailed bathymetric data, as well as a sub-bottom profler to obtain ultra-high resolution seismic data from the shallow sediment column. The results identifed a pockmark-like feld. From these, a pockmark with active gas seepage (evidenced by gas plumes in the water column) was selected for seafloor sampling. This pockmark has an elliptical shape and is located at 450 m water depth. Its diameter is 400 m and its depth varies between 2 and 6 m with a slope of 3º. Acoustic turbidity in contact with the surface of the seabed of the pockmark indicates that the seeping gas is mainly methane. This gas would come from a deep source, since it was observed associated with a chimney having an enhanced reflector in the multi-channel 2D records. These results allow, with a high margin of certainity, the sampling of the benthic communities associated with gas seepage.