SEASONAL VARIABILITY OF CARBONATE SYSTEM CHARACTERISTICS IN A CORAL REEF ECOSYSTEM, SOUTHERN TAIWAN

English Abstract:

The objective of this study is to explore the seasonal variability of carbonate system parameters and to identify the factors affecting the pCO₂ in surface water of a coral reef ecosystem. The total alkalinity (TA), pH and calculated partial pressure of CO₂ (pCO₂) were measured in the water column from a total of 17 stations in the Nanwan Bay, southern Taiwan. The results of the study show that spring and winter hydrographical characteristics and vertical mixing of water column was different from the other seasons and therefore contributing to the discrepancy of data collected as correlation of temperature, salinity, carbonate system parameters for summer and autumn. The control factors of the pCO₂ in surface water during seasonal changes lead to the following conclusion. The non-temperature related effect during spring is greater than temperature related effects. The reverse is true for summer while both temperate and non-temperature related effects more or less offset each other in autumn. One point to note, non-temperature related effects are made up of not only the effect of biological but also vertical mixing of water column and the exchange of gases in the Nanwan Bay. According to calculations, the seasonal data of pCO₂ in surface water is namely 393.7, 406.3, 399.2 and 366.9 µatm, respectively. The seasonal sea-air differences in ΔpCO2 were -3.3, 14.3, 7.2 and -29.1 µatm, respectively. These data indicate that the Nanwan coral reef region is the source of CO₂ in the atmosphere during summer and autumn. The calculation an average sea gases flux of CO₂ is -0.98 gCm^-2year^-1 and the annual absorption of gases is -29.3t. In addition to seasonal variability and fluctuations in temperature, the results suggest that vertical mixing of water column, intermittent upwelling of water and the biological effect also account for the changes in the pCO₂ of the water column in this coral reef ecosystem.