Biological and physical controls of pCO2 and air-sea CO2 fluxes in the austral summer of 2015 in Prydz Bay, East Antarctica

Abstract

The Southern Ocean is the most important carbon sink in the world because of its relatively cold seawater temperature and unique overturning circulation which provides a conduit for atmospheric CO2 to enter into the deep ocean. However, it remains less clear how physical-biogeochemical processes control the carbon source/sink status because of the sparse spatiotemporal coverage of observations in the Southern Ocean, particularly in its coastal areas. The sea surface partial pressure of CO2 (pCO2) and related carbonate system parameters were measured in Prydz Bay during the 31st Chinese National Antarctic Research Expedition (CHINARE) cruise in February 2015. Our results showed a contrast spatial pattern of sea surface pCO2 in the southern and northern regions of the Antarctic Slope Front (ASF), corresponding to their different hydrographic settings. The surface waters over the continental shelf south of the shelf break served as a strong CO2 sink (−35.1 ± 32.1 mmol C m−2 d−1) due to the enhanced net primary production when sea-ice was absent. The surface waters north of the shelf break were found to be a moderate CO2 sink (−7.0 ± 5.9 mmol C m−2 d−1) despite the upwelling of CO2-rich subsurface waters. The high wind velocities have contributed to the overall large magnitude of CO2 sink although the average atmospheric pCO2 was only slightly higher than the sea surface pCO2 (~237–380 μatm). Our results also indicated that Prydz Bay has become a stronger sink of atmospheric CO2 in summer of 2015 (average flux of −21.4 ± 27.3 mmol C m−2 d−1) than that observed in summer of 2000 (average flux of −3.23 mmol C m−2 d−1), as well as other reported fluxes in the continental shelf waters around the Antarctic.