Climate reconstruction from a methane influenced environment

Sediment cores have been collected from Vestnesa Ridge, western Svalbard margin, from within and outside an active pockmark with methane gas flares. The lithological log, X-ray, magnetic susceptibility and numerous AMS dates were used to constrain the age model and for high-resolution inter-core correlation. Other proxies used in order to reconstruct the dynamics of changes of bottom water properties as well as North Atlantic hydrography were oxygen and carbon isotopes of benthic and planktonic foraminifera and assemblage counts. The main purpose of the study is to resolve the frequency of CH4 emissions from the seafloor through time in relation to past climate change. The magnetic susceptibility record from the pockmark core shows very low and constant values without the pattern typical for the western Svalbard. The seeping of methane clearly destroyed the signal. Benthic foraminifera within several intervals are depleted in δ13C, indicating increased methane flux from the seafloor. Carbon isotope values measured in planktonic foraminifera shells are also extremely low (<-10 ‰), which can be caused by coating of AOM (Anaerobic oxidation of methane)-derived carbonates (authigenic overgrowth). Moreover methane seepage affects the outcomes of AMS dating. Our results suggest that radiocarbon dates measured in bivalve shells are approximately 3000 cal years too old. In a methane influenced environment a multiproxy approach is necessary for more accurate paleoclimate reconstructions.