Effects of ice melting on Cu, Cd and Pb profiles in Ross Sea waters (Antarctica)

In the framework of the Italian Research Programme in Antarctica, evolution of dissolved and particulate Cu, Cd and Pb profiles in the coastal waters of Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was studied during the Austral Summer 1997/98. In order to relate the distributions of trace meta ls with the physical and biological processes, a series of temperature and salinity measures were made, and water samples were collected to determine nutrients and chlorophyll. Samples of pack ice and marine microlayer (50-15 0 mum) were also collected and analysed. Concerning the surface layer, it was found that metal concentrations are ma inly affected by the dynamic of the pack ice melting and phytoplankton acti vity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melt or removed. Direct release of particulate C u from ice was clearly shown by surface maxima and by the high concentratio ns of suspended particulate matter and particulate metals found in the ice core section interfaced with the seawater. Differently, the high amount of Cd in the particulate included in the pack ice seems not to affect the conc entration in surface particulate; on the contrary, the corresponding increa se of dissolved Cd indicates that it is released in dissolved form when the pack ice melts. Surface distribution is further complicated by the effect of phytoplankton activity, which removes Cu and Cd from water, incorporatin g them into organic particulate. Finally, in absence of pack ice, there is evidence of inputs of Ph and Cu due to atmospheric dust brought into the co lumn water through marine microlayer. In intermediate and deep waters, the vertical distribution of Pb and Cd was characterised by substantially constant profiles, while Cu shown, during t he end of the summer and in absence of a well-defined water column stratifi cation, a "scavenging-type" distribution which overlaps its "nutrient-type" behaviour.