Impact of Different Types of Meltwater Runoff on Pelagic and Benthic Processes in Young Sound, NE Greenland

Glacial retreat due to climate warming alters the pathway through which meltwater enters Arctic fjords. In the Tyrolerfjord–Young Sound system (NE Greenland), meltwater is delivered by two contrasting rivers: the Tyroler River, which flows directly from the glacier into the fjord, and the Zackenberg River, which passes through a proglacial lake. We investigated the impact of these different glacial sources on the pelagic system and fjord sediment biogeochemistry, with a focus on carbon and iron cycling. We quantified particulate organic carbon and particulate organic nitrogen, as well as δ13C and δ15N of the organic matter in the suspended and sinking fractions in the water column. In sediment, we quantified total organic carbon (TOC) and total nitrogen, δ13C and δ15N of the organic matter, porewater concentrations of Fe, Mn, and different fractions of solid‐phase Fe, O2 microprofiles and sulfate reduction rates. We find that the passage through a proglacial lake decreases the impact of the glacier on the fjord, as the lake acts as a trap for glacial material, decreasing sediment input to the fjord system. In the fjord sediments, a stronger redox‐cycling of iron was found further away from the rivers, which is mainly driven by the higher TOC content. Overall, our data suggest that, with glacial retreat, the impact of glaciers on the marine and the benthic systems in fjords will become weaker, and reduce long‐term carbon sequestration in Arctic fjord sediments.