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

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.The authors deeply appreciate the help of J. I. Lee in providing the core magnetic susceptibility values and the sample site map. We are also grateful for the assistance of T. S. Howe and N. Haubenstock of the Alaska Stable Isotope Facility, University of Alaska, Fairbanks. This study was supported by the Korea Polar Research Institute (KOPRI) project (grant PE07���010)