Release and Remineralization of Ancient Carbon from Svalbard Glaciers

Within the last two decades several studies have focused on the conundrum of the bioavailability of ancient carbon. In high latitudes this is particularly important, as 40 to 50 % of organic matter (OM) in arctic sediments is estimated to be of petrogenic origin. Arctic Amplification will impact these regions severely in the coming decades. Arctic fjords act as hotspots of carbon burial on a global scale, especially for petrogenic carbon, which makes them an ideal location to study climatically induced changes in OM input to sediments and the related biodegradability of ancient petrogenic carbon. To assess these issues, sediment core HH14-897-MF-GC from Hornsund Fjord on Svalbard was analyzed for changes in OM input using biomarker abundances from 1961 to 2014. Further, the incorporation of ancient carbon by sedimentary bacterial communities was investigated using compound specific radiocarbon dating (CSRD) on intact polar lipid (ILP) derived fatty acids (FA), as indicators for viable microbiota in the sediments. Biomarker abundances indicate only minor changes in sedimentary OM, mainly related to tidewater glacier retreat and subsequent changes in the diagenetic setting caused by lower sedimentation rates. Further, petrogenic and marine OM appear to be the two primary OM sources, with predominantly ancient petrogenic material (>90 %) resulting in bulk sediment ages ranging from 17,327 ± 48 years B.P. at the core top to ages consistently over 24,000 years B.P. below 50 cm sediment depth. Using a two-endmember model, radiocarbon signatures of analyzed IPL-FA suggest incorporation of substantial amounts of ancient petrogenic OM into viable sedimentary bacteria, ranging from 4 to 52 %. Increasing sediment depth and time of sedimentary storage seem to have the most impact on ancient carbon utilization, potentially due to priming