Concurrent Decadal Trend Transitions of Sea Ice Concentration and Sea Surface pCO2 in the Beaufort Sea

Interannual climate changes and increasing atmospheric CO2 (AtmCO2) have significantly altered sea surface partial pressure of CO2 (pCO2) in the Beaufort Sea (BS). Yet, their decadal variability and underlying mechanisms remain inadequately understood. Using observational data and the Regional Arctic System Model (RASM), a decreasing trend transition of the BS summer surface pCO2 was identified at around 2010–2012. Sensitivity cases reveal that the decadal trend transition in surface pCO2 (early: 4.12 ± 0.80 μatm/yr, p < 0.05 and late: 1.23 ± 2.22 μatm/yr, p > 0.05) is driven by interannual climate changes. While the long-term increase in AtmCO2 does not directly drive surface pCO2 trend transition, it reduces its magnitude. The sensitivity experiment with no interannual AtmCO2 changes from 1990 reveals that the statistically significant contributor of the decadal trend transition in surface pCO2 is the concurrent transition in sea ice concentration (SIC, early: −0.0120 ± 0.0037/yr, p < 0.05 and late: 0.0101 ± 0.0063/yr, p > 0.05). The decadal trend transitions in the subsurface and deep layer pCO2 are negligible compared to that in the sea surface pCO2 due to the insignificant influence of interannual climate changes on subsurface and deep layer pCO2. The surface pCO2 decadal trend transition is significantly correlated with a trend transition of CO2 sink. On seasonal timescales, the effects of SIC on the decadal trend transition of pCO2 occur primarily within the duration of open-water (DOW), and align with the decadal trend transitions in the open-water start day, end day, and DOW. The magnitude of sea surface pCO2 trend transition increases as the magnitude of the DOW trend transition increases.