Variability in chemical properties and in ventilation of the Ross Sea (Antarctica) waters and links to climate change.

The Ross Sea (Antarctica) plays a significant role in the Southern Ocean carbon cycle by functioning as a major regional oceanic CO2 sink and in the regional cycling of other essential bio elements, such as nitrogen, phosphorus and iron. Sea ice dynamics control the surface waters (AASW) physical and chemical features and influence phytoplankton composition which has been shown to affect the relative concentrations of dissolved inorganic carbon and bioelements. Climate change feedbacks (AASW warming , reduction in sea ice extent and convective mixing) could decrease the supply of iron to surface waters during the growing season, although these impacts might be balanced out by increased inputs of iron- rich glacial and sea ice melt water (Smith et al., 2012). Substantial shifts in the chemistry of the oceans driven by anthropogenic CO2 have occurred in recent times causing the phenomenon known as Ocean Acidification (OA), which is measurable by a decrease in pH and a shift in the carbonate equilibria. The Ross Sea is vulnerable to OA due to its relatively low total alkalinity (AT) and because of increased CO2 solubility in cold water (McNeil et al., 2010). The Ross Sea contributes to the larger global ocean’s overturning circulation, through the formation of dense High Salinity Shelf Water (HSSW) and the flow of Antarctic Bottom Water (AABW) off the shelf with profound effects on the heat budget of the Earth and impacts the regional and global climate. AABW plays a significant role in the cooling and in the ventilation of the deep layers north of the western Ross Sea as it contains high oxygen concentration, consistent with the deepening of the surface water involved in the HSSW formation and in the export of inorganic carbon, particularly in the capture of the anthropogenic CO2. Dropping formation rates, which lead to a reduced ventilation of Antarctic deep and bottom water masses, could have far reaching consequence like a declining uptake of CO2 by the oceans, which would certainly amplify an ongoing global warming. The chemical properties in the Ross Sea shelf area have been extensively studied by Italian Antarctic Research Program (PNRA) CLIMA, T-Rex and RoME Projects between 1998 and 2016, which has lead to an improvement in our understanding of their variability to ongoing climate perturbations. The most relevant findings will be presented in this communication.