Large ancient organic matter contributions to Arctic marine sediments (Svalbard)

Abstract

Soils, fine-grained ice-rafted detritus (IRD), coals, and marine surface sediments in the Arctic realm (Svalbard)were collected in 2007 and 2008 to characterize organic matter (OM) sources in Arctic marine sediments. Bulkgeochemical (C : N ratio and stable carbon isotopic composition) parameters suggest a predominant marinecontribution to sedimentary OM. The branched and isoprenoid tetraether index (a proxy of soil OM input)indicates that soil OM contribution to the marine sediments is minor. However, the presence of retene (used as anindicator for coal-derived OM), the low carbon preference index and the average chain length of n-alkanes, andthe depleted bulk radiocarbon content (D14C value) suggest that ancient OM of both coal-derived and matureIRD-derived OM is being buried in the Kongsfjord–Krossfjord system of Svalbard in the high Arctic. Therelatively low retene concentrations in the marine surface sediments other than those in close vicinity of NyA˚lesund, previously a coal-mining town, indicated that input of IRD-derived OM was predominantly responsiblefor the generally low D14C value. We applied three-end-member models based on D14C and retene and n-alkaneconcentration data to disentangle relative coal-derived, IRD-derived, and marine OM proportions to sedimentaryOM. Sediments were comprised on average 2% 6 4% of coal-derived OM, 37% 6 17% of IRD-derived OM, and61% 6 18% of marine OM with higher IRD-derived OM deposit in the Kongsvegen glacier front. Our resultshighlight the important role of ancient OM on carbon dynamics in Arctic environments, in particular for benthicfood webs.