Resolving Heterogeneity in CO₂ Uptake Potential in the Greenland Coastal Ocean

The oceans play a pivotal role in mitigating climate change by sequestering approximately 25% of annually emitted carbon dioxide (CO₂). High-latitude oceans, especially the Arctic continental shelves, emerge as crucial CO₂ sinks due to their cold, low saline, and highly productive ecosystems. However, these heterogeneous regions remain inadequately understood, hindering accurate assessments of their carbon dynamics. This study investigates variation in pCO₂ levels during peak ice sheet melt, in the Greenland coastal ocean and estimates rates of air-sea exchange across 6° of latitude. The East and West coast of Greenland displayed distinct regions with unique controlling factors. Though, both coasts represent CO₂ sinks in summer. Geographical variation in pCO₂ and air-sea exchange was linked intricately to freshwater export from the Greenland ice sheet and levels of primary production in these ecosystems. Air-sea exchange of CO₂ ranged from 0.23 to -64 mmol m^-2 day^-1. However, we found that flux estimation faces substantial uncertainties (up to 672%) due to wind product averaging and gas exchange formula selection. Upscaling only heightens this uncertainty leading to wide ranging estimates of Greenland coastal CO₂ uptake between -16 and -26 Tg C year^-1 (This study, Dai et al., 2022, https://doi.org/10.1146/annurev-earth-032320-090746; Laruelle et al., 2014, https://doi.org/10.1002/2014gb004832). Obtaining a reliable assessment of air-sea CO₂ exchange necessitates data collection across seasons, and, even more so, refinement of the gas transfer velocity estimations in the Arctic coastal zone.