Three ship-based observational campaigns were conducted to survey sea ice and snow in Prydz Bay and the surrounding waters （64.40＆#176;S-69.40＆#176;S, 76.11＆#176;E-81.29＆#176;E） from 28 November 2012 to 3 February 2013. In this paper, we present the sea ice extent and its variation, and the ice and snow thickness distributions and their variations with time in the observed zone. In the pack ice zone, the southern edge of the pack ice changed little, whereas the northern edge retreated signiifcantly during the two earlier observation periods. Compared with the pack ice, the fast ice exhibited a signiifcantly slower variation in extent with its northernmost edge retreating southwards by 6.7 km at a rate of 0.37 km？d-1. Generally, ice showed an increment in thickness with increasing latitude from the end of November to the middle of December. Ice and snow thickness followed an approximate normal distribution during the two earlier observations （79.7＆#177;28.9 cm, 79.1＆#177;19.1 cm for ice thickness, and 11.6＆#177;6.1 cm, 9.6＆#177;3.4 cm for snow thickness, respectively）, and the distribution tended to be more concentrated in mid-December than in late November. The expected value of ice thickness decreased by 0.6 cm, whereas that of snow thickness decreased by 2 cm from 28 November to 18 December 2012. Ice thickness distribution showed no obvious regularity between 31 January and 3 February, 2013.
The thermodynamic properties of snow cover on sea ice play a key role in the ice-ocean-atmosphere system and have been a focus of recent scientiifc research. In this study, we investigated the thermodynamic properties of snow cover on sea ice in the Nella Fjord, Prydz Bay, East Antarctica （69＆#176;20′S, 76＆#176;07′E）, near the Chinese Antarctic Zhongshan Station. Our observations were carried out during the 29th Chinese National Antarctic Research Expedition. We found that the vertical temperature proifle of snow cover changed considerably in response to changes in air temperature and solar radiation during the summer. Associated with the changes in the temperature proifle were lfuctuations in the temperature gradient within the upper 10 cm of the snow cover. Results of previous research have shown that the thermal conductivity of snow is strongly correlated with snow density. To calculate the thermal conductivity in this study, we measured densities in three snow pits. The calculated thermal conductivity ranged from 0.258-0.569 W？m-1？K-1. We present these datasets to show how involved parameters changed, and to contribute to a better understanding of melting processes in the snow cover on sea ice.
Historical surface drifter observations collected from the Southern Ocean are used to study the near-surface structure, variability, and energy characteristics of the Antarctic Circumpolar Current （ACC）. A strong, nearly zonal ACC combined with complex fronts dominates the circulation system in the Southern Ocean. Standard variance ellipses indicate that both the Agulhas Return Current and the East Australian Warm Current are stable supplements of the near-surface ACC, and that the anticyclonic gyre formed by the Brazil warm current and the Malvinas cold current is stable throughout the year. During austral winter, the current velocity increases because of the enhanced westerly wind. Aroused by the meridional motion of the ACC, the meridional velocity shows greater instability characteristics than the zonal velocity does over the core current. Additionally, the ACC exhibits an eastward declining trend in the core current velocity from southern Africa. The characteristics of the ACC are also argued from the perspective of energy. The energy distribution suggests that the mean kinetic energy （MKE）, eddy kinetic energy （EKE）, and are strong over the core currents of the ACC. However, in contrast, EKE/MKE suggests there is much less （more） eddy dissipation in regions with strong （weak） energy distribution. Both meridional and zonal energy variations are studied to illustrate additional details of the ACC energy characteristics. Generally, all the energy forms except EKE/MKE present west-east reducing trends, which coincide with the velocity statistics. Eddy dissipation has a much greater effect on MKE in the northern part of the Southern Ocean.
