Multi-proxy approach to unravel methane emission history of an Arctic cold seep

Abstract

Arctic Ocean sediments contain large amounts of methane in the form of free gas and gas hydrate. This highly dynamic methane reservoir is susceptible to be modified by bottom water warming. The warming may lead to gas hydrate destabilization releasing elevated methane fluxes to the seafloor and seawater. Reconstructing past methane dynamics can be achieved by using specific proxies left in the geological record. In this study, we apply a multi-proxy approach for paleo seepage reconstruction from sediment records at gas hydrate mounds (GHMs) in Storfjordrenna (south of the Svalbard archipelago). These shallow water (∼380 m water depth) systems are potentially vulnerable to global warming related temperature changes. ¹⁴C dating of foraminifera shells indicated an onset of deglaciation in the Storfjordrenna region at ∼20 kyr BP and allowed us to establish a stratigraphic context based on sediment Zr/Rb and Fe/Ca ratios. Several major (between 15 and 17 kyr BP) and minor methane venting phases were identified and interpreted to be related to gas hydrate instability triggered by isostatic adjustment right after the onset of the deglaciation. The detection of all major methane releases was only possible by combining data sets of stable carbon isotope compositions of foraminifera, mineralogy and δ¹³C values of authigenic carbonates, and abundance and stable carbon isotope signatures of lipid biomarkers. The most robust single proxy in this study was provided by the δ¹³C values of archaeal biomarkers. In contrast, the sediment Ba/Ti ratios recorded only the major events. Our results highlight the complexity and heterogeneity of methane dynamics in a small area of some hundred meters across.