Temporal variation of the sea surface CO2/carbonate properties in the Arabian Sea

As part of the U.S. JGOFS program in the Arabian Sea we have measured total CO2 (TCO2), and total alkalinity (TA) throughout the water column at selected station locations. In addition we measured the fugacity of CO2 in surface seawater and in the air above seawater along the cruise tracks. Between 10°N and 20°N, these measurements were repeated five times in January, March, July, November, and December 1995, and show different temporal variations of the carbonate properties in surface seawater depending upon the different regional hydrological and biological regimes. In order to estimate the relative importance of each process (physics, biology and thermodynamics) on the temporal carbon cycle in these regions, we use a 1-D process model initialized with the data from January 1995 and forced with climatological fields. The outputs of the model applied at three locations (10°N 65°E; 14.5°N 65°E; and 19°N 65°E) in the Arabian Sea are compared with US-JGOFS observations. The forcing terms and the ‘standardʹ biological parameters reproduce the CO2 cycle at 10°N and 14.5°N. At 19°N, the ‘standardʹ biological activity has to be reduced by a factor two to approach the observed CO2 concentrations. The model outputs predict seasons of minimum and maximum fCO2 in surface seawater at time periods where no data are available in October and May/June, respectively.