Deltaic Lake Sediments as Recorders of Past Carbon Export from Arctic River Drainage Basins
Arctic Research Initiative
2008 Funded Project
Northern watersheds store vast amounts of organic carbon (OC) for millennia, much of which is held within permafrost soils. However, increasing temperatures in the Arctic appear to be destabilizing these soils, potentially leading to abrupt carbon release from this major reservoir. A significant fraction of OC mobilized from permafrost may enter arctic rivers, resulting in increased fluxes to the Arctic Ocean, with implications for the global carbon cycle, as well as for Arctic ecosystems. In order to assess whether the flux and composition of fluvial OC is changing as a result of warming, we need to establish a historical context for river hydrology and carbon export from Arctic rivers. Lakes developed in Arctic river deltas receive fluvial sediment and particulate OC (POC) from flooding during the spring freshet, and the underlying sediments hold promise as excellent archives of past drainage basin dynamics. Preliminary sedimentological and stratigraphic analysis of a core collected from the Mackenzie Delta in April 2007 indicate that deltaic lake sediments contain exquisite, annually resolved records of past changes in fluvial supply. We propose to undertake new fieldwork and laboratory measurements through the Arctic Research Initiative in order to: (i) build a more complete picture of the deltaic sedimentation in the Mackenzie system to provide a better understanding of its hydrological history; (ii) perform detailed down-core geochemical analyses to assess whether the flux and age of POC discharged by Arctic rivers has increased from the pre-industrial era to the present day, and whether any variations over the past few decades exceed natural variability observed during intervals predating anthropogenic perturbation (e.g., the Medieval Warm Period and the Little Ice Age). The results stemming from this project will serve as a benchmark for assessing potential future changes in OC export as a consequence of accelerated warming of the Arctic.