Western Greenland Ice-Land-Ocean Interactions: Near-Shore DOC 14C Ages and DOM Composition Along Eastern Baffin Bay

Rapid warming and changing precipitation are transforming the Arctic, especially the Greenland Ice Sheet and Baffin Bay, where major shifts in carbon (C) and water cycles have been influencing marine productivity for the past 20 years. Thinning of the Greenland Ice Sheet and large increases in river and subglacial melt discharge are strengthening the biogeochemical linkages between the land-ice system on Greenland and in the adjoining marine ecosystems. One of the key consequences of these freshwater fluxes into fjords and nearshore regions is injections of dissolved organic matter (DOM) that deliver dissolved organic carbon (DOC) and nutrients from multiple possible sources. These include a) modern biota (i.e. root exudates), b) permafrost landscapes under the ice that are being eroded by subglacial rivers, and c) thawing permafrost in the periglacial landscapes.

In this study, we attempt to answer two critical questions: Does seawater along the west coast of Greenland contain ancient DOC from a land-based source? And, how does the age and composition of DOC and DOM vary with depth and latitude, from Nuuk to Disko Bay to the Uummannaq fjord system? To investigate these questions, we participated in the NW Passage-Baffin Bay 2021 mission aboard the US Coast Guard Cutter Healy. We collected discrete samples of DOC for radiocarbon analysis with accelerator mass spectrometry and of DOM for compound specific analysis with ultra-high performance liquid chromatography - high resolution mass spectrometry at key locations along the west coast of Greenland from near the surface (~10 m) and at depth (~50 m).

We find that our DOC samples exhibit increasing age with increasing depth and latitude. Older samples contain more recalcitrant chemical features (such as lignins, unsaturated low- and high- oxygenation), while younger sample have more labile features (lipids, aliphatics). The correlation of these relative abundances with age is consistent with freshwater glacial inputs of older, more recalcitrant DOC. Our findings suggest that the coupling of these interactions is becoming amplified with the thinning and melting of the Greenland Ice Sheet, stimulating the fjord and nearshore food web, which could lead to impacts in the Native communities that rely on fisheries and marine mammals for commercial and subsistence resources.