High organic carbon mineralization rates in sediments of the Ryder and Petermann fjords – effects of subglacial meltwater runoff from the northern Greenland icesheet?

Subglacial runoff plays an important role for coastal marine ecosystems and future coastal Arctic ocean nutrient budgets. The Greenland icesheet has lost about 3600 Gigatons since 1990, and up to 40 percent of this mass may have been transported to the north by marine-terminating outlet glaciers such as the Ryder and Petermann fjords in northern Greenland. Subglacial discharge of meltwater into the fjords is an important component of the mass loss. We present data on nutrient concentrations, dissolved inorganic carbon, sediment oxygen uptake, and sediment carbon mineralization rates in the Ryder and Petermann fjord waters and sediments to understand carbon and nutrient cycling in northern Greenland fjord systems. These are the first data on benthic nutrient and oxygen exchange reported for the Ryder fjord and provide important new constraints on the spatial extent of potential future melting-associated fertilization processes on the northern Greenland coast. Sediments inside the silled fjords in perched basins and close to the glacial tongue had oxygen uptake rates that were up to nine times higher when compared to sediments in the adjacent, near-perennially ice-covered Lincoln Sea. These differences are attributed to the combined effects of lesser ice cover in the fjords, higher light availability, and fertilization from glacial runoff.