Organic Geochemistry

Sources of organic matter in sediments of the Colville River delta, Alaska: A multi-proxy approach

Thawing of permafrost and subsequent release of organic carbon in the warming Arctic has great potential to influence carbon cycling between the land and ocean. Here, we investigated temporal and spatial differences of organic carbon sources in sediments of Colville River delta and the adjacent Simpson Lagoon, Alaska (USA) over the last ∼50 years, using a multi-proxy approach (lignin, fatty acids, sterols, bulk and compound-specific 13C isotopes). Stations closer to the river mouth showed greater inputs of soil and litter-derived terrestrial material based on the terrestrial inputs indicator (Λ8), soil biomarker (3,5-Bd), and degradation index ([Ad/Al]v), as well as stronger and more frequent watershed-flushing events, coupled with Colville River discharge events, than stations in the lagoon. Values of Λ8, 3,5-Bd, and [Ad/Al]v in sediments ranged from 0.75–2.69, 0.02–0.44 mg/100 mg OC, and 0.23–0.85, respectively. The increase of terrestrial inputs in sediments near the delta for the last ∼50 years is most likely due to increase of river discharge under warmer temperatures in recent decades. Coastal erosion and inputs from other river sources (e.g., Kuparuk and Mackenzie Rivers) also contribute to the organic carbon in sediments of the delta. Rudimentary fatty acid indices reflected two distinct groups of bacteria in these sediments. Additionally, the sterol biomarker 24-ethylcholest-5-en-3β-ol is useful to track peat inputs in the Arctic. Click here to view the full publication.