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. Bulk geochemical (C : N ratio and stable carbon isotopic composition) parameters suggest a predominant marine contribution 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 an indicator for coal‐derived OM), the low carbon preference index and the average chain length of n‐alkanes, and the depleted bulk radiocarbon content (Δ14C value) suggest that ancient OM of both coal‐derived and mature IRD‐derived OM is being buried in the Kongsfjord–Krossfjord system of Svalbard in the high Arctic. The relatively low retene concentrations in the marine surface sediments other than those in close vicinity of Ny Ålesund, previously a coal‐mining town, indicated that input of IRD‐derived OM was predominantly responsible for the generally low Δ14C value. We applied three‐end‐member models based on Δ14C and retene and n‐alkane concentration data to disentangle relative coal‐derived, IRD‐derived, and marine OM proportions to sedimentary OM. Sediments were comprised on average 2% ± 4% of coal‐derived OM, 37% ± 17% of IRD‐derived OM, and 61% ± 18% of marine OM with higher IRD‐derived OM deposit in the Kongsvegen glacier front. Our results highlight the important role of ancient OM on carbon dynamics in Arctic environments, in particular for benthic food webs.