Estimates of Arctic Ocean carbon uptake from atmospheric inverse analyses for the period 2000-2017

 The Arctic Ocean is responsible for around 5-10% of oceanic CO2 uptake, despite the region only accounting for approximately 4% of the world's oceans (Bates & Mathis, 2009). In this study, we investigate the exchange of CO2 between the atmosphere and the ocean in the Arctic Ocean for the period 2000-2017. Our estimates are obtained using the GEOSChem-LETKF inverse model system (Chen et al. 2021), in combination with data from the NOAA surface CO2 monitoring network (ObsPack, Cooperative Global Atmospheric Data Integration Project, 2018). We evaluate the impact of alternative representations of the prior flux distribution for air-sea CO2 fluxes. These include the following datasets: Landschutzer et al. (2016), Rodenbeck et al. (2014), and Watson et al. (2020). We present estimates of the long-term trend, year-to-year fluctuations, and regional and seasonal variability in air-sea CO2 exchange in the Arctic Ocean, with a focus on the region north of 58˚N. The sea ice extent of the regional seas of the Arctic Ocean has an influence on the magnitude and seasonality of the regional air-sea CO2 flux. We also investigate the potential links between changes in sea-ice extent and changes in air-sea CO2 fluxes.