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

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Abstract
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 pCO2sea (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 pCO2atm 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.

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