Extreme CO2 Release and Its Mechanism in the Subarctic North Pacific During the Winters of 1999–2001

In this study, the air-sea carbon dioxide flux (FCO₂) in the subarctic North Pacific is investigated using three data products from 1985 to 2016. Extreme CO₂ release occurred during the winters of 1999–2001 with an average FCO₂ anomaly of 1.09 mol C m⁻² y⁻¹ across the three data products, which is remarkably higher than that in other years (−0.11 mol C m⁻² y⁻¹). Empirical analysis reveals that this event is primarily driven by increased carbon dioxide partial pressure (ΔpCO₂), whose contribution to the event is greater than the wind speed at 10 m, followed by sea surface temperature (SST) and salinity impacts. Specifically, the intensification of pCO_2sea (which contributes 58% of the FCO₂ anomaly) is induced by the upwelling of dissolved inorganic carbon (DIC) due to the increase in Ekman pumping caused by the positive anomaly of wind stress curl associated with the Victoria mode of the SST. Moreover, the weakening of pCO_2atm is induced by the negative anomaly of sea level pressure (contributing 9% to the FCO₂ anomaly), which is also related to the mode and the reduction in the mole fraction of CO₂ (contributing 11% to the FCO₂ anomaly), which is related to fossil fuel emissions. Ultimately, the sea surface pCO₂ is significantly oversaturated relative to the atmosphere, triggering extreme CO₂ release in the subarctic North Pacific. This study enhances our understanding of the natural variability of carbon fluxes in the North Pacific.