Annual cycle of carbonate chemistry and decadal change in coastal Prydz Bay, East Antarctica

The annual cycles of dissolved carbon dioxide (CO2) system parameters were determined for a coastal site in East Antarctica using samples collected from May 2010 to February 2011 in Prydz Bay. These observations show the seasonal influence of ice formation and melt, biological production, and air–sea CO2 flux on changes in total dissolved inorganic carbon (DIC), pHsws and the saturation state of aragonite (Ωar). Net community production of 1.8 ± 0.4 mol C m− 2 in the productive summer months (November–February) caused large seasonal decreases in DIC. The decrease in DIC caused a change in surface water partial pressure of CO2 from values over-saturated with respect to the atmosphere in the ice-covered winter period, to undersaturated waters in the summer months. The study site was estimated to be an annual net sink for CO2 of 0.54 ± 0.11 mol C m− 2 year− 1. The calculated pHsws and Ωar values varied seasonally from 7.99 to 8.20 and 1.19 to 1.92, respectively. The observed variability was compared to similar measurements carried out in 1993–95 at the same location. Natural variability in carbon cycle dynamics caused changes in pHsws that were nearly twice as large as those expected from changes estimated due to the uptake of CO2 from the atmosphere over this time, assuming that the surface waters tracked increases in atmospheric CO2. This highlights the difficulties associated with predicting trends in seawater pH and dissolved CO2 system parameters in dynamic, high latitude, coastal locations with sparse temporal and spatial carbon cycle observations.