Elucidating the influence of freshwater and sympagic inputs on biogeochemical cycling in the Canadian Arctic Archipelago

Sammendrag

The Canadian Arctic Archipelago (CAA) receives significant freshwater inputs from rivers, sea ice, and glacial melt that influence ocean processes and biogeochemical cycles. This study presents a baseline dataset of hydrography and isotopic composition of seawater and suspended particulate organic matter from summer 2019, providing a framework to evaluate long-term biogeochemical changes due to Arctic shifts. Using salinity-δ18O relationships, temperature, Chl-a fluorescence, and macronutrients, interactions between ocean, cryosphere, and terrestrial inputs were characterized. δ18O indicated glacial and sea ice melt contributions associated with salinity-influenced stratification and depleted surface nutrients. Notably, surface nitrate + nitrite in the freshest waters (0.06–1.2 μM at S = 25–29) showed no enrichment compared to saline waters (S > 30), with no correlation between nutrients and salinity. Depleted δ15NPON (particulate organic nitrogen) and δ13CPOC (particulate organic carbon) were observed across the region. Low temperatures, pCO2, and sea ice likely contributed to low δ13CPOC, although overlapping drivers of PON and POC isotopic signatures remain unclear. δ13CPOC values became enriched with increasing POC concentration (r2 = 0.45 surface, r2 = 0.61 at Chl-a maximum), with the most depleted values (−34 ‰) at the lowest POC. Enriched δ13CPOC and δ15NPON correlated with elevated carbon (C) biomass in channels with sea ice, possibly linked to sympagic algal inputs. Nitrogen limitation occurred across transects, with N:P (NO3:PO4) ratios consistently below Redfield (16:1), unalleviated by freshwater inputs. These observations serve as a reference for future studies on freshwater impacts on Arctic productivity, with July–August sampling reflecting post-bloom conditions where freshwater primarily acts as a barrier to mixing, not a nutrient source.