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 Corg/Ntot ratios and apparently heavier stable isotope ratios of Corg and Ntot (δ 13Corg and δ 15Ntot) 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 (Norg) contributed about 40% to total nitrogen (Ntot) 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 δ 13C values for OClabile and OCresi were remarkably different between LGM and Holocene sediment. The unexpected lighter δ 13C values for OCresi for the LGM period might be due to methanotrophic bacteria in the sediment of Kara Sea.