Chlorofluorocarbon distribution in the ross sea water masses

Abstract

Chlorofluorocarbon (CFC11, CFC12 and CFC113) data, collected during the 2000–2001 austral summer, within the framework of the activities of the Climatic Long-Term Interactions for the Mass-Balance in Antarctica (CLIMA) Project of the Italian National Program for Antarctic Research (PNRA) in the Ross Sea, are discussed in the context of hydrographic observations. These data provide an overview of CFC distribution in some of the characteristic water masses found in the Ross Sea. The highest values of CFCs are found in the Antarctic Surface Water (AASW), because of the exchange with the atmosphere, while the lowest concentrations and the highest temperatures define the presence of Circumpolar Deep Water (CDW) in the cast of the analyzed samples. High Salinity Shelf Water (HSSW) can be identified by the highest salinity and by the relatively high content of CFCs. Moreover, the CFCs are useful tracers to study the mixing and overflow processes near the shelf break. In particular, chlorofluorocarbons trace the intrusion onto the shelf of Modified Circumpolar Deep Water (MCDW) off Cape Adare. The relative age of this water mass derived from CFCs ratios indicates that ventilation occurred between 1973 and 1979. The thermohaline structures and CFC distribution reveal at the shelf break the presence of HSSW already mixed with MCDW. Consequently, the density value of the bottom layer is not high enough to produce a strong overflow along the shelf break, causing a less intense ventilation of the deep oceans.