Suppressed pCO2 in the Southern Ocean Due to the Interaction Between Current and Wind. Issue 12 (30th November 2021)

• Record Type: Journal Article
• Authors: Kwak, Kyungmin; Song, Hajoon; Marshall, John; Seo, Hyodae; McGillicuddy, Dennis J.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-30
• Subjects: Southern Ocean -- Current‐Wind interaction -- CO2 flux -- Air‐Sea interaction -- Biogeochemistry -- DIC; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017884
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The Southern Ocean, an important region for the uptake of anthropogenic carbon dioxide (CO2 ), features strong surface currents due to substantial mesoscale meanders and eddies. These features interact with the wind and modify the momentum transfer from the atmosphere to the ocean. Although such interactions are known to reduce momentum transfer, their impact on air‐sea carbon exchange remains unclear. Using a 1/20° physical‐biogeochemical coupled ocean model, we examined the impact of the current‐wind interaction on the surface carbon concentration and the air‐sea carbon exchange in the Southern Ocean. The current‐wind interaction decreased winter partial pressure of CO2 ( p CO2 ) at the ocean surface mainly south of the northern subantarctic front. It also reduced p CO2 in summer, indicating enhanced uptake, but not to the same extent as the winter loss. Consequently, the net outgassing of CO2 was found to be reduced by approximately 17 % when including current‐wind interaction. These changes stem from the combined effect of vertical mixing and Ekman divergence. A budget analysis of dissolved inorganic carbon (DIC) revealed that a weakening of vertical mixing by current‐wind interaction reduces the carbon supply from below, and particularly so in winter. The weaker wind stress additionally lowers the subsurface DIC concentration in summer, which can affect the vertical diffusive flux of carbon in winter. Our study suggests that ignoring current‐wind interactions in the Southern Ocean can overestimate winter CO2 outgassing. Plain Language Summary: The Southern Ocean, subjected to strong winds and exhibiting highly energetic, eddying flows, is a key region for air‐sea exchange of carbon dioxide (CO2 ). Although the impacts on ocean circulation and mesoscale energetics by current‐wind interaction are beginning to be better understood, it remains unclear how the interaction between the wind and ocean eddies modulates the CO2 exchange. Using a 1/20° physical‐biogeochemical coupled ocean model, we analyze changes in air‐sea CO2 flux induced by current‐wind interaction. The interaction reduces CO2 outgassing in winter and slightly increases CO2 uptake in spring, leading to a 17 % reduction in the net CO2 outgassing. The changes are observed mainly to the south of approximately 55°S. Detailed analysis reveals that the suppression of CO2 outgassing by current‐wind coupling is mainly the result of weaker vertical mixing along with reduced upwelling, which decreases the carbon concentration at the surface. Our study suggests that ignoring the current‐wind interaction in the Southern Ocean can significantly overestimate CO2 outgassing. Key Points: Current‐wind interaction reduces CO₂ outgassing by 17% in the Pacific sector of the Southern Ocean Weaker vertical mixing lowers the partial pressure of CO₂ (pCO₂) to the south of the northern subantarctic front The weaker wind stress and Ekman transport also assist in lowering pCO₂