Winter to summer evolution of <i>p</i>CO<sub>2</sub> in surface water and air–sea CO<sub>2</sub> flux in the seasonal ice zone of the Southern Ocean

Abstract

Abstract. Partial pressure of CO2 (pCO2) in surface water and vertical profiles of the aqueous carbonate system were measured during austral summer in the Indian sector of the Southern Ocean (64–67° S, 32–58° E) in January~2006 to understand the CO2 dynamics of seawater in the seasonal ice zone. Surface-water pCO2 ranged from 275 to 400 μatm, and longitudinal variations reflected the dominant influence of water temperature and dilution by sea-ice meltwater between 32° and 40° E and biological productivity between 40° and 58° E. Using carbonate system data from the temperature minimum layer, we examined the winter-to-summer evolution of surface-water pCO2 and the factors affecting it. Our results indicate that pCO2 increased by as much as 32 μatm, resulting mainly from the increase in water temperature. In synchrony with changes in sea ice concentration and surface-water pCO2, air–sea CO2 flux with considering the exchange of CO2 between sea ice and atmosphere, changed from −1.1 to +0.9 mmol C m−2 day−1 between winter and summer. These results suggest that for the atmosphere, the seasonal ice zone acts as a CO2 sink in winter and a CO2 source in summer immediately after ice melt. Subsequent biological productivity likely decreases surface-water pCO2 and air–sea CO2 flux becomes negative, such that in summer the study area is a CO2 sink with respect to the atmosphere.

Carbon cycling dynamics in the seasonal sea-ice zone of East Antarctica

“…Those waters that were dominated by surface warming, resulting in decreased gas solubility, are associated with the relatively warmer waters of the Weddell Gyre in the northwest sector of the study area (Figures h and i), which agrees with the findings of Nomura et al . [] who found a similar temperature control on surface f CO 2 values in this region. The variability driven by photosynthesis occurs over the shelf and slope with a second region observed offshore, north of the SACCF.…”

Variability in sea ice carbonate chemistry: a case study comparing the importance of ikaite precipitation, bottom-ice algae, and currents across an invisible polynya

“…Gas exchange between the sea ice and the overlying atmosphere can also play a role in sea ice carbonate chemistry, at least in the upper layers of the ice. During ice formation, some brine is rejected upwards, allowing CO 2 to off-gas to the atmosphere (Geilfus et al, 2013;Nomura et al, 2014). In the frazil crystal structures of surface ice, the high brine fraction creates high enough permeability (relative to layers immediately below it) for this outgassing to occur over a layer several centimetres thick (Moreau et al, 2015).…”