Organic carbon and nitrogen composition in the sediment of the Kara Sea, Arctic Ocean during the Last Glacial Maximum to Holocene times

Abstract

A sharp decrease in C-org/N-tot ratios and apparently heavier stable isotope ratios of C-org and N-tot (delta C-13(org) and delta N-15(tot)) after deglaciation were observed in sediment cores St-25 and St-34 collected from the Saint Anna Trough in the Kara Sea, exhibiting a change of sediment origin from terrestrial to marine during the LGM and Holocene times. Organic nitrogen (N-org) contributed about 40% to total nitrogen (N-tot) during the Holocene, but the Norg fraction was hardly observed in the lower LGM sediments ( below 120 cm depth in St-25 and beneath 170 cm in St-34). This may be due to a permanent cover of sea ice in the area during the LGM. In addition, the delta C-13 values for OClabile and OCresi were remarkably different between LGM and Holocene sediment. The unexpected lighter delta C-13 values for OCresi for the LGM period might be due to methanotrophic bacteria in the sediment of Kara Sea.