Sources of terrigenous inputs to surface sediments of the Colville River Delta and Simpson's Lagoon, Beaufort Sea, Alaska

The provenance of sediments and particulate organic carbon (POC) in the Colville River delta and adjacent Simpson's Lagoon, in the Alaskan Beaufort Sea, was investigated using a variety of bulk and molecular techniques, including stable and radiocarbon isotopes, neodymium isotopes, algal pigments, and lignin-phenols. Additionally, stable carbon isotopes and lignin-phenols were analyzed on four different density fractions from sediments. The Colville River, the largest river in North America with a watershed exclusively located in the high-Arctic tundra, was an important source of terrestrial POC to the western edge of the Lagoon, shown by extremely old radiocarbon ages (fraction modern of 0.165 ± 0.001 close to the river mouth up to 0.418 ± 0.002 farther away). Stations without northern protective barrier islands had large amounts of marine POC input, and evidence of benthic microalgae was found in one area of the Lagoon (chlorophyll-a concentration 35.0 μg gOC^-1 in the high-algal biomass area compared to 1 to 7 μg gOC^-1 outside of it). Stations in the middle and eastern end of the Lagoon showed significant sediment input from coastal erosion (input of peat-indicating non-lignin-phenols 0.079 mg (100mgOC)^-1 in the eastern lagoon compared to 0.022 mg (100mgOC)^-1 near the Colville delta), and on the eastern end of the Lagoon there was evidence of input of Mackenzie River POC, shown with neodymium isotopes and also COP. POC inputs derived from rivers, coastal erosion, and marine productivity were quantified using a ternary mixing model and showed that fluvial supply and coastal erosion were the dominant carbon sources to the Lagoon. This constitutes the first study of POC delivery by the Colville River into a nearshore region and illustrates that continued warming of the high Arctic tundra will likely lead to increased riverine POC delivery to this region of the world. Key PointsSimpson's Lagoon receives POC from a variety of inputsA 3-endmember mixing model indicates coastal erosion is importantThis is the first study of POC delivery by a high-Arctic North American river