Research paperDynamics of sea-ice biogeochemistry in the coastal Antarctica during transition from summer to winter

- Enderby Basin as a weak sink of CO2 during March and February and as strong sink during January.
- Sea-ice plays a dual role towards climate change.
- Shift in biogeochemical factors regulating pCO2 from summer to early winter.

The seasonality of carbon dioxide partial pressure (pCO2), air-sea CO2 fluxes and associated environmental parameters were investigated in the Antarctic coastal waters. The in-situ survey was carried out from the austral summer till the onset of winter (January 2012, February 2010 and March 2009) in the Enderby Basin. Rapid decrease in pCO2 was evident under the sea-ice cover in January, when both water column and sea-ice algal activity resulted in the removal of nutrients and dissolved inorganic carbon (DIC) and increase in pH. The major highlight of this study is the shift in the dominant biogeochemical factors from summer to early winter. Nutrient limitation (low Si/N), sea-ice cover, low photosynthetically active radiation (PAR), deep mixed layer and high upwelling velocity contributed towards higher pCO2 during March (early winter). CO2 fluxes suggest that the Enderby Basin acts as a strong CO2 sink during January (−81 mmol m−2 d−1), however it acts as a weak sink of CO2 with −2.4 and −1.7 mmol m−2 d−1 during February and March, respectively. The present work, concludes that sea ice plays a dual role towards climate change, by decreasing sea surface pCO2 in summer and enhancing in early winter. Our observations emphasize the need to address seasonal sea-ice driven CO2 flux dynamics in assessing Antarctic contributions to the global oceanic CO2 budget.

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