http://hdl.handle.net/2122/144 Search the Channel search http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/3751 Title: Historical behaviour of Dome C and Talos Dome (East Antarctica) as investigated by snow accumulation and ice velocity measurements <br/> <br/>Authors: Urbini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Frezzotti, M.; enea casaccia; Gandolfi, S.; università di bologna; Vincent, C.; LGGE Grenoble; Scarchilli, C.; enea casaccia; Vittuari, V.; università di bologna; Fily, M.; LGGE Grenoble <br/> <br/>Abstract: Ice divide–dome behaviour is used for ice sheet mass balance studies and interpretation of ice core records. In order to characterize the historical behaviour (last 400 yr) of Dome C and Talos Dome (East Antarctica), ice velocities have been measured since 1996 using a GPS system, and the palaeo-spatial variability of snow accumulation has been surveyed using snow radar and firn cores. The snow accumulation distribution of both domes indicates distributions of accumulation that are non-symmetrical in relation to dome morphology. Changes in spatial distributions have been observed over the last few centuries, with a decrease in snow accumulation gradient along the wind direction at Talos Dome and a counter-clockwise rotation of accumulation distribution in the northern part of Dome C. Observations at Dome C reveal a significant increase in accumulation since the 1950s, which could correlate to altered snow accumulation patterns due to changes in snowfall trajectory. Snow accumulation mechanisms are different at the two domes: a wind-driven snow accumulation process operates at Talos Dome, whereas snowfall trajectory direction is the main factor at Dome C. Repeated GPS measurements made at Talos Dome have highlighted changes in ice velocity, with a deceleration in the NE portion, acceleration in the SW portion and migration of dome summit, which are apparently correlated with changes in accumulation distribution. The observed behaviour in accumulation and velocity indicates that even the most remote areas of East Antarctica have changed from a decadal to secular scale. http://hdl.handle.net/2122/3573 Title: On the shape of reflecting surfaces investigated by a 60 MHz radar <br/> <br/>Authors: Bianchi, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sciacca, U.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tabacco, I. E.; Universita` di Milano — Sezione Geofisica, Milan, Italy; Zirizzotti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia <br/> <br/>Abstract: Radio echo sounding (RES) systems for ice thickness measurements are practically the only suitable equipment for large-scale radar flight surveys in polar regions. The length of the radio wave carrier does not allow the employment of sophisticated antennas, so folded dipoles are used, arranged beneath the wings. As a consequence, the transmitted radio wave beam illuminates a relatively large area, making the power of the echo signal related in a significant way to the shape of the reflecting surfaces. An electromagnetic analysis shows that the amplitude variations detected by the system, under certain conditions, are mainly due to focusing or defocusing effects determined by the shape of the reflectors. http://hdl.handle.net/2122/3453 Title: Modelling approach to the assessment of biogenic fluxes at a selected Ross Sea site, Antarctica <br/> <br/>Authors: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Coluccelli, A.; UNIVPM, Italy; Ravaioli, M.; CNR-ISMAR; Giglio, F.; CNR-ISMAR; Langone, L.; CNR-ISMAR; Azzaro, M.; CNR-IAMC; Azzaro, F.; CNR-IAMC; La Ferla, R.; CNR-IAMC; Cozzi, S.; CNR-ISMAR; Catalano, G.; CNR-ISMAR <br/> <br/>Abstract: Abstract Several biogeochemical data have been collected in the last 10 years of Italian activity in Antarctica (ABIOCLEAR, ROSSMIZE, BIOSESO-I/II). A comprehensive 1-D biogeochemical model was implemented as a tool to link observations with processes and to investigate the mechanisms that regulate the flux of biogenic material through the water column. The model is ideally located at station B (175^{o}E - 74^{o}S) and was set up to reproduce the seasonal cycle of phytoplankton and organic matter fluxes as forced by the dominant water column physics over the period 1990-2001. Austral spring-summer bloom conditions are assessed by comparing simulated nutrient drawdown, primary production rates, bacterial respiration and biomass with the available observations. The simulated biogenic fluxes of carbon, nitrogen and silica have been compared with the fluxes derived from sediment traps data. The model reproduces quite well the magnitude of the biogenic fluxes, expecially those observed in the bottom sediment trap, but the peaks are delayed in time. Sensitivity experiments have shown that the characterization of detritus, the choice of the sinking velocity and the degradation rates are crucial for the timing and magnitude of the vertical fluxes. An increase of velocity leads to a shift towards observation but also to an overestimation of the deposition flux which can be counteracted by higher bacterial remineralization rates. Model results suggest that observed fluxes could be explained by the size-distribution and quality of the locally-produced biogenic material. It is hypothesized that the bottom sediment trap collects material originated from rapid sinking of particles and also from previous years production periods, likely modulated by advective and aggregation mechanisms which are still not resolved by the model. http://hdl.handle.net/2122/3435 Title: Development of a numerical model of sea ice for biogeochemical studies. Part 1: Sea-ice thermodynamics <br/> <br/>Authors: Tedesco, L.; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Haapala, J.; Finnish Institute of Marine Research, Helsinki, Finland; Stipa, T.; Finnish Institute of Marine Research, Helsinki, Finland <br/> <br/>Abstract: A fully prognostic 1-D thermodynamic model, functional for studies of sea-ice biogeochemistry is developed to better understand the physical processes and the interactions between the environment and the sea-ice ecosystem. The physical model is capable of simulating seasonal changes of snow and ice thickness. Particular attention is paid to reproduce the snow-ice and the superimposed ice formation which play important roles in the dynamics of sea ice algae. The assessment of the model capabilities is done in 1979--1993 at four different stations in the Baltic Sea. A sensitivity analysis stresses the importance of adequate surface forcing functions to properly simulate the onset of sea ice. Our results show that thickness of the ice layers and timing of the melting are in good agreement with the observed data and confirm that one of the key variables in modelling sea-ice thermodynamics is the snow layer and its metamorphism.