The report presents the first year observation of current, temperature and salinity measurements of a water column near the Ross lce Shelf (RIS) edge during 1995. Many instruments were moored in this site, where previous international studies confirmed the presence of a persistent outflowing coming from the RIS. Two characterstic waters are present in this area: the first one (Modified Circumpolar Deep Water MCDW) is flowing southward being the Modified Circumpolar Deep Water across the continental shelf break flowing into the Ice Shelf Cavity. The second one is a northward outflowing ice Shelf Water (IS[) tongue, coming tram below the Ross Ice Shelf into the Ross Sea. The interactions between these two water masses and the presence of a third one below the Ross Ice Shelf (the High Salinity Shelf Water, HSSW) maintain the flow, acting as the major heat engine of this sector of the southern ocean. The time history data record of physical variables in relation to the termohaline vertical structure along the Ross Ice Shelf (RIS) acquired during X Italian Antarctic Project (PNRA) campaign is analyzed, giving us the opportunity to estimate the ISW flux coming from below the RIS. The annual mean curent is direted northwest, out of the cavity under the RIS with intensity of about 5 cm/s, contributing to export the cold water formed. Instead, the daily mean currents are generally higher with values reaching often 20 cm/s. The seasonal cycle of temperature at 243 m shows values around -1.45 °C until the end of March, when it rapidly decreases to -185 °C with two important episodes on mid April and mid May, during which it increases for about one week respectively to -1.5 °C and -1.65 °C. It slowly starts raising again by the end of November. Energy spectra showed significantly high level growing during the winter period of sea-ice formation when a vertical kinetic turbulent energy is also maximum. Transport estimates indicate that the Pacific Ocean supplies sufficient heat to melt the ice of the base of the RIS. This basal melting rate is subiect to considerable uncertainty, in part due to the recirculation of sensible complete rotation of about 15 days. At 389 m, values lower than -2 °C are reached for short periods in several occasions in correspondence of salinity more than 34.65, that is the evidence of ISW flowing out from below the RIS. Salinity is about 34.46-34.48 for most of the vear, with corresponding temperature ranging from maximum of -1.1 °C in mid April to -1.8 °C during July-August. Episodes lasting from a few days to more than a week with salinity peaks of more than 34.52 and temperature lower than -2.1 °C, typical of the Ice Shelf Waters formed below the RIS, were also shown. U-velocity shows average values decreasing if compared to 244 m point measurements. Temperature registered at 579 m is almost constant in time around -1.75 °C; U-velocity signal is ranging from -25/25 cm/s, with peaks correlated to the other two sampling points. V-velocity trend is also following the others, with amplitude clearly damped.
Project CLIMA-mooring F 1995 data analysis
Bergamasco A;Meloni R;Carniel S;De Biasio F;Arcari G;
1998
Abstract
The report presents the first year observation of current, temperature and salinity measurements of a water column near the Ross lce Shelf (RIS) edge during 1995. Many instruments were moored in this site, where previous international studies confirmed the presence of a persistent outflowing coming from the RIS. Two characterstic waters are present in this area: the first one (Modified Circumpolar Deep Water MCDW) is flowing southward being the Modified Circumpolar Deep Water across the continental shelf break flowing into the Ice Shelf Cavity. The second one is a northward outflowing ice Shelf Water (IS[) tongue, coming tram below the Ross Ice Shelf into the Ross Sea. The interactions between these two water masses and the presence of a third one below the Ross Ice Shelf (the High Salinity Shelf Water, HSSW) maintain the flow, acting as the major heat engine of this sector of the southern ocean. The time history data record of physical variables in relation to the termohaline vertical structure along the Ross Ice Shelf (RIS) acquired during X Italian Antarctic Project (PNRA) campaign is analyzed, giving us the opportunity to estimate the ISW flux coming from below the RIS. The annual mean curent is direted northwest, out of the cavity under the RIS with intensity of about 5 cm/s, contributing to export the cold water formed. Instead, the daily mean currents are generally higher with values reaching often 20 cm/s. The seasonal cycle of temperature at 243 m shows values around -1.45 °C until the end of March, when it rapidly decreases to -185 °C with two important episodes on mid April and mid May, during which it increases for about one week respectively to -1.5 °C and -1.65 °C. It slowly starts raising again by the end of November. Energy spectra showed significantly high level growing during the winter period of sea-ice formation when a vertical kinetic turbulent energy is also maximum. Transport estimates indicate that the Pacific Ocean supplies sufficient heat to melt the ice of the base of the RIS. This basal melting rate is subiect to considerable uncertainty, in part due to the recirculation of sensible complete rotation of about 15 days. At 389 m, values lower than -2 °C are reached for short periods in several occasions in correspondence of salinity more than 34.65, that is the evidence of ISW flowing out from below the RIS. Salinity is about 34.46-34.48 for most of the vear, with corresponding temperature ranging from maximum of -1.1 °C in mid April to -1.8 °C during July-August. Episodes lasting from a few days to more than a week with salinity peaks of more than 34.52 and temperature lower than -2.1 °C, typical of the Ice Shelf Waters formed below the RIS, were also shown. U-velocity shows average values decreasing if compared to 244 m point measurements. Temperature registered at 579 m is almost constant in time around -1.75 °C; U-velocity signal is ranging from -25/25 cm/s, with peaks correlated to the other two sampling points. V-velocity trend is also following the others, with amplitude clearly damped.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
