Variability of Air-Sea Fluxes of CO2 and N2O in Polar Ocean Regions

In recent decades the polar oceans have experienced changes in surface temperature and regional circulation associated with large-scale patterns of ocean warming. These ocean regions are important contributors to global budgets of greenhouse gases such as carbon-dioxide (CO₂) and nitrous-oxide (N₂O), and the regional environmental changes have significant influences on the magnitude, trends and variability of air-sea fluxes of these gases (Yasunaka et al. 2024; Zhan et al. 2020).

The Arctic Ocean has been a net sink of atmospheric CO₂ in recent decades, but displays significant heterogeneity in carbon uptake among its regional seas, with changing trends due to regional climate change and sea-ice loss.  The  global ocean is a  net source of N₂O to the atmosphere overall; however the distribution of N₂O fluxes from the Arctic remains poorly characterized, and regional observations indicate several regions of N₂O undersaturation in the surface Arctic Ocean (Kitidis et al. 2010; Zhan et al. 2020).  The Southern Ocean is a major sink for atmospheric anthropogenic CO₂ (e.g., ~40% of global uptake according to recent estimates, Dong et al. 2024). Air-sea CO₂ fluxes in the Southern Ocean are strongly influenced by circulation patterns associated with oceanographic fronts, and CO₂ fluxes display significant seasonal and decadal variability. Flux estimates are subject to uncertainty due to the regional environmental variability and to the sparse network of CO₂ measurements available. Estimates of N₂O fluxes from the Southern Ocean are also poorly quantified for similar reasons; i.e., limited measurements and significant spatial and temporal variability.  Recent syntheses have suggested the region could contribute ~30% of global ocean N₂O emissions (Tian et al. 2020), a disproportionately large component in comparison to the areal extent of the Southern Ocean.

In this work we present recent estimates of air-sea fluxes of CO₂ and N₂O from these polar regions derived from (i) atmospheric inverse model analyses (using the GEOSChem-LETKF framework of Chen et al. 2021), and (ii) an ocean biogeochemical model (NEMO-PlankTOM; Buitenhuis et al. 2018). We focus on the period 2000-2018, and present estimates for regional fluxes,  decadal trends and  inter-annual variations. We also compare our results to previous estimates derived from surface ocean pCO₂ and pN₂O data products and ocean biogeochemistry models.