Combined Effect of Anthropogenic and "Natural" Carbon on Acidification of the Subsurface Ocean Water at the Tip of the Antarctic Peninsula

Dissolved inorganic carbon, total alkalinity, and dissolved N2O samples of upper 500 m were collected at the tip of the Antarctic Peninsula during the 32nd Chinese Antarctic National Research Expedition. The pH and anthropogenic carbon were calculated and the results show that the patterns of anthropogenic carbon uptake and acidification progresses are different in two adjacent regions of this study area. In the region of Weddell-Scotia confluence, hydrographic processes such as convection prompt the transport of anthropogenic carbon into the subsurface layer, whereas in the region east of Powell Basin, where stratification existed, the downward transport of anthropogenic carbon to this depth is inhibited. However, the pH values indicate that the acidification status of the subsurface waters that are influenced by the above two hydrographic features are similar or even identical at a certain depth range. The progress of ocean acidification in the well-ventilated region are dominated by anthropogenic carbon uptake, while in the adjacent well-stratified region, anthropogenic carbon uptake and in situ remineralization of organic matter or horizontal advection of carbon rich water masses or both. In the later region, anthropogenic carbon uptake and in situ remineralization (or horizontal advection) contribute 40% and 60% to pH decline, respectively, suggesting that pH value in water mass of this region may significantly influenced by natural processes.