Pockmarks on the South Aquitaine Margin continental slope: The seabed expression of past fluid circulation and former bottom currents

Abstract

Inactive and mostly elongated pockmarks of 100–200m in dimension were recently discovered on the South Aquitaine Margin continental slope. They are distributed at water depths greater than 350m in both interfluve and sediment-wave areas, and are strongly controlled by the sedimentary morphology and architecture. Water column and seafloor backscatter and sub-bottom profiler data do not exhibit present-day or past gas evidence, e.g., massive and continuous gas releases at the seabed and fossil methane-derived authigenic carbonates. It is thus proposed that the pockmarks originated from a shallow source and result from relatively recent and short-duration gas or water expulsion events. Former near-bottom currents may have contributed to the elongation of these WNW–ESE-oriented pockmarks, whereas present-day weaker near-bottom currents may induce upwelling, contributing to the maintenance of the elongated shapes of the pockmarks.