Biogeochemical processes at the Krasniy Yar seepage area (Lake Baikal) and a comparison with oceanic seeps

Abstract

The expulsion of sedimentary, methane-rich fluids to bottom waters is a widespread process in Lake Baikal (eastern Siberia), resulting in deep water cold seep systems comparable in size and frequency to those of oceanic, high-productivity continental margins. Little is known, however, about how biogeochemical processes in Baikal cold seeps compare with those of oceanic cold seeps. In this paper, we present new pore water chemistry data from the Krasniy Yar seepage area located on the slope near the Selenga river delta. We compare biogeochemical processes deduced from these pore water chemical profiles with processes prevalent at oceanic cold seeps of highly productive continental margins. This comparison allows to draw the following conclusions: (1) in sediments not affected by seepage the fresh water mass of Lake Baikal results in a very low relative importance of the nitrogenous and sulfidic geochemical zones compared to the ocean; (2) diagenetic processes involving silicate minerals are, however, similar in Lake Baikal and the ocean; (3) fluid advection rates in cold seep sediments are similar in Lake Baikal and ocean systems but (4) the deep methane flux of Baikal seeps is mitigated by reaction with O2, and possibly Mn(IV) and Fe(III) oxides, whereas in oceanic sediments the main methane-consuming process is the anaerobic oxidation of methane with sulfate. Lake Baikal cold seep sediments are therefore nearly devoid of authigenic carbonate minerals and have a reduced capacity to decrease the deep methane flux.