Annual Mixed Layer Carbon Budget For The West Antarctic Peninsula Continental Shelf: Insights From Year-Round Mooring Measurements

For the first time the annual carbon budget on the West Antarctic Peninsula shelf was studied with continuously measured CO2 system parameters (pH and pCO(2)) from a subsurface mooring. The temporal evolution of the mixed layer dissolved inorganic carbon (DIC) is investigated via a mass balance. The annual mixed layer DIC inventory change was 1.1 +/- 0.4 mol m(-2) yr(-1), which was mainly regulated by biological drawdown (-2.8 +/- 2.4 mol m(-2) yr(-1)), diapycnal eddy diffusion (2.6 +/- 1.3 mol m(-2) yr(-1)), entrainment/detrainment (0.9 +/- 0.4 mol m(-2) yr(-1)), and air-water gas exchange (0.4 +/- 2.1 mol m(-2) yr(-1)). Significant carbon drawdown was observed in the spring and summer, which was replenished by the physical processes mentioned above. These observations suggest this area is an annual atmosphere CO2 sink with a mixed layer net community production of 2.8 +/- 2.4 mol m(-2) yr(-1). These results highlight the significant seasonality in the DIC mass balance and the necessity of year-round continuous observations for robust assessments of biogeochemical cycling in this region.Plain Language Summary With continuously measured CO2 system parameters (pH and pCO(2)) from submerged sensors on an oceanographic mooring, for the first time we captured the seasonal and annual changes of surface dissolved inorganic carbon (DIC) on the West Antarctic Peninsula shelf. The annual DIC inventory change was mainly controlled by biological consumption of DIC (e.g., DIC consumption from photosynthesis). Physical processes like diffusion, upwelling/downwelling, and airwater CO2 exchange also played important roles. Significant biological consumption of DIC was observed in the spring and summer, which was replenished by the physical processes mentioned above. These observations suggest that over a complete seasonal cycle, this area absorbs CO2 from the atmosphere and produces significant amount of organic carbon through photosynthesis. These results highlight the significant seasonal variations in the DIC mass balance and the necessity of year-round continuous observations for robust assessments of biogeochemical cycling in this region.