NSFGEO-NERC: WOOD-BASED CARBON DISCHARGE TO THE ARCTIC OCEAN

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Erosion processes mobilize and deliver organic carbon (OC) from soils and plants and can supply it to rivers. The resultant discharge of carbon by rivers to the world's oceans is globally significant, with current estimates of 160 Mega tonnes of carbon per year in particulate OC (POC, larger than 0.2 microns) and 200 Mega tonnes of carbon per year in dissolved OC (DOC, smaller than 0.2 microns). These estimates, however, do not account for material larger than about half a centimeter, including pieces of large wood. Few studies have investigated the large-scale patterns of wood delivery, decay, and transport in rivers, and so we have limited knowledge of how large wood influences OC discharge to the ocean. This knowledge gap leads to our primary research goals, which are to (i) quantify annual carbon discharge in the form of large wood versus other sources of DOC and POC from the Mackenzie River drainage of Canada to the Arctic Ocean and (ii) estimate storage volume, residence time, and decay rates of large wood in the drainage basin. Our focus on the Mackenzie River is based on the fact it is the largest source of river sediment and POC to the Arctic Ocean, and anecdotally has large volumes of wood moving through its delta to the ocean, but these fluxes have not been measured.The transformative aspects of the proposed research are: (1) quantification of proportions of OC exported as wood versus finer material from a large river, providing insight into the relative importance of different sources of OC under modern day conditions, and (2) the first assessment of the relative ages of material across the full range of particulate sizes carried by a large river from < 500 microns to large wood, providing a clearer basis for predicting how changes in the fate of coarser OC and large wood may impact the carbon cycle under a warming climate. This project will also substantially advance understanding of wood dynamics in large river basins under a warming climate that will alter wood recruitment, transport, and deposition processes, altering timing, volume, and placement of wood exports to the Mackenzie Delta and the Arctic.