Establishing Constraints on Carbon Dioxide Fluxes and Transport in a Changing Arctic Ocean Climate System

Quantifying Earth's carbon budget remains an imperative task in the carbon cycle science community. Among its challenges, assessing carbon fluxes over the Arctic Ocean remains an arduous task, due to its remoteness and difficulty to observe. While the global oceans take up carbon in the net, the Arctic Ocean has been found to be regionally variable in both flux sign and magnitude. Coupled with a warming climate and declining sea ice, future projections of the Arctic carbon budget are highly uncertain. As the Arctic climate rapidly warms, there is a critical need for understanding its observed changes and variability, but a lack of long-term observations has historically hindered progress. This work analyzes measurements of atmospheric carbon dioxide (CO2) mixing ratios from an 8-year dataset of measurements obtained over Arctic sea ice (the O-Buoy Network; 2009–2016). These observations, along with measurements from coastal observatories, were analyzed and interpreted with an atmospheric chemical transport model. This model reproduced the observed features of the seasonal cycle and shows that terrestrial biosphere fluxes and synoptic transport explain most CO2 variability over the surface of the Arctic Ocean. Interannually, the coastal observations were more comparable in overall CO2 growth than concurrent measurements over sea ice. Evidence indicating the presence of ocean gas exchange in and around sea ice during periods where this growth discrepancy occurs is discussed. In addition, a Lagrangian trajectory model and airmass contact tracers were used to gain insight into upwind source and sink regions of CO2 residuals over Utqiagvik, Alaska, and O-Buoys within the Beaufort Gyre during distinct periods based on the mean seasonal cycle of CO2. It was found that the terrestrial Arctic-boreal zone did not provide the carbon emissions expected for the large CO2 residual events. Finally, the O-Buoy observations are assimilated into an atmospheric inversion, along with additional datasets of satellite and surface observations. The inversions demonstrated the value of incorporating O-Buoy observations, which helped to constrain scaling factors for ocean and land fluxes over the northern high latitudes. Overall, this work highlights the importance of obtaining continuous observations over the Arctic and Arctic Ocean during this era of rapid biogeochemical change.