With the CACOON project, we aim to quantify the effect of changing freshwater export and terrestrial permafrost thaw on the type and fate of river-borne organic matter (OM) delivered to Arctic coastal waters, and resultant changes on ecosystem functioning in the coastal Arctic Ocean. The CACOON ice expedition was the first step to set the observational basis for the projects combined observational, experimental and modelling approach. With the gained sample material, we will conduct laboratory experiments to parameterise the susceptibility of terrigenous carbon to abiotic and biotic transformation and losses, and then use the results from these to deliver a marine ecosystem model capable of representing the major biogeochemical cycles of carbon, nutrients and OM cycling in these regions. We will apply this model to assess how future changes to freshwater runoff and terrigenous carbon fluxes alter the biogeochemical structure and function of shelf ecosystems. Our aims for the project are the following: • generate novel seasonally-explicit datasets of OM source and transformation across the Lena River nearshore environments • identify and parameterise key abiotic and biotic processes affecting terrestrial organic matter fluxes from land-to-ocean • deliver projections of how future changes to freshwater runoff and terrestrial organic matter fluxes will alter the biogeochemical structure and function of shelf ecosystems.