Insights Into the Influence of the Greenland Ice Sheet on Oceanic Macronutrient Dynamics From Decades of Historical Data

Abstract Increasing freshwater discharge from the cryosphere has the potential to affect mechanisms that regulate the supply of macronutrients to primary producers in the ocean. Although numerous studies have characterized the biogeochemical effects of freshwater discharge from the Greenland Ice Sheet within fjords, it is unclear to what extent these effects propagate offshore and whether or not seasonal macronutrient availability in Greenland's shelf seas has changed since annual freshwater discharge increased in the mid‐1990s. Here, we collate and scrutinize extensive work undertaken over the past century to constrain macronutrient distributions in Greenland's coastal seas. From 1929 to 2022, over 38,000 publicly available measurements of macronutrient concentrations were made on the Greenland shelf, with over 7,000 within inshore waters. Low salinity waters around Greenland are associated with a modest dSi enrichment (23.01 ± 6.16 μM at zero salinity) matching prior estimates from runoff, whereas extrapolated phosphate and nitrate freshwater endmembers are small or negligible. A north‐to‐south dSi enrichment is evident along both east and west coastlines, which, as well‐described in prior oceanographic work, reflects Arctic Ocean outflow. The direct impact of processes related to the Greenland Ice Sheet on macronutrient distributions is largely confined to fjords, although there are a few cases of nutrient anomalies propagating to the shelf associated with large marine‐terminating glaciers in Sermilik Fjord, Disko Bay, and Nioghalvfjerdsbrae (“the 79° North Glacier”). Furthermore, we identified several oceanic areas of the Greenland shelf with elevated (>2 μM) surface nitrate or dSi concentrations in summer, which likely reflect regionally distinct shelf processes.