Every cold seep tells a story: the case study of Leirdjupet Fault Complex, SW Barents Sea

Abstract

Cold seep environments are often associated with chemosynthetic communities at the seafloor, reflecting the spatial distribution and magnitude of methane fluxes in the sediment underneath. Quantifying areal fluxes and rates of consumption via anaerobic oxidation of methane (AOM) is extremely important for better understanding the future response of the benthic filter to climate-induced ocean warming. Short-time-scale transient processes such as tides, seasonal bottom water temperature fluctuations are efficiently recorded in unsteady-state pore water profiles. However, to interpret the long-term trends in methane fluxes and controlling factors one needs to integrate this data with sedimentary proxies and conduct paleo-reconstructions. We present a case study from the SW Barents Sea at Leirdjupet Fault Complex, where active methane seepage has been observed in summer 2018 from 295 m to 350 m water depth and is associated with microbial mats and tubeworms. We discuss the modern seepage conditions based on pore water data and habitat maps generated through Object-Based Image Analysis (OBIA) classification, and discuss the history of seepage recorded in sediment cores. A new ROV survey conducted in June 2021 in the same area revealed a very different situation compared to 2018, consistent with the long-term reconstructions since Late Weichselian deglaciation.