Landfast sea ice forms and remains fixed along the coast for most of its life time. In Prydz Bay, landfast ice is seasonal due to melting, mechanical breakage and drift of ice in summer. Its annual cycle of thickness and temperature was examined using a one-dimensional thermodynamic model. Model calibration was made for March 2006 to March 2007 with forcing based on the Chinese National Antarctic Research Expedition data, which consisted of in situ ice and snow observations and meteorological records at the Zhongshan Station. The observed maximum annual ice thickness was 1.74 m. The ice broke and drifted out in summer when its thickness was 0.5–1.0 m. Oceanic heat flux was estimated by tuning the model with observed ice thickness. In the growth season, it decreased from 25 W m-2 to 5 W m-2, and in summer it recovered back to 25 W m-2. Albedo was important in summer; by model tuning the estimated value was 0.6, consistent with the ice surface being bare all summer. Snow cover was thin, having a minor role. The results can be used to further our understanding of the importance of landfast ice in Antarctica for climate research and high-resolution ice–ocean modelling.
ABSTRACT. Rijpfjorden (808 N, 228 E) is a high-Arctic fjord on Nordaustlandet in the Svalbard archipelago. To monitor the thermodynamic change of sea ice in spring, an ice mass-balance buoy (IMB) was deployed for 2.5 months (10 April-26 June 2011), with accompanying in situ measurements, sea-ice sampling on three occasions and ice-core analysis. Uncertainties and sources of error in in situ measurements and IMB data are discussed. The in situ measurements, ice-core analysis and IMB data together depict the development of snow and ice in spring. Snow and ice thickness exhibited large spatial and temporal variability. After relatively stable conditions with only little change in ice thickness and accumulation of snow, a layer of superimposed ice $0.06 m thick formed at the snow-ice interface due to refreezing of snow meltwater in late spring. Ice thickness (except for growth of superimposed ice) did not change significantly based on in situ observations. In contrast, the under-ice sonar data from the IMB show reflections from a layer deeper than the underside of the ice during the melting phase. This can be explained as a reflection of the sonar pulses from an interface between a freshwater layer under the ice and more saline water below, or as a false-bottom formation.
The ice cover on the Qinghai–Tibetan Plateau plays an important role in the environmental and ecological systems. We analyze the in situ measurements of ice growth and examine the thermal diffusivity of thermokarst lake ice in the Beiluhe basin. We evaluate numerically the change of thermal diffusivity of thermokarst lake ice with changing ice temperature using an optimal control model. In a higher ice temperature regime (–3 to 0°C), the thermal diffusivity of thermokarst lake ice decreases exponentially with increasing ice temperature, and approaches the thermal diffusivity value of fresh water near the freezing-point temperature. In a lower ice temperature regime (–15 to –3°C), the thermal diffusivity increases slowly with decreasing ice temperature.
During the 19th Chinese National Antarctic Research Expedition from December 2002 to January 2003, 1085 icebergs were observed along the cruise track within the range 58–68° S in the Southern Ocean using the marine radar on the R/V Xuelong. These icebergs were located mainly in the Ross Sea, Weddell Sea and Prydz Bay with lengths ranging from 68 to 8169 m. Both power-law and Weibull functions are applied to the curve fitting of cumulative probability distribution of iceberg length in each region. The results reveal that the power-law function underestimates the measured data in the middle of the data, but overestimates them for both the smallest and largest iceberg sizes, whereas the Weibull function underestimates the measured data when iceberg length is large enough. To reduce the relative error increasing with iceberg length, the Weibull function is used only in fitting to iceberg lengths less than a threshold value of iceberg size (Lt) and the power-law function is used in fitting to iceberg lengths >Lt. The improved curve fits show a good correlation over the full range of the data. This clearly reveals that an upper limit of iceberg length exists in the good agreement between the Weibull function and the measured data, which is attributed to different thermodynamic effects on calving processes and subsequent modification of large and small icebergs. In addition, iceberg size in Prydz Bay increases and then decreases when approaching the Amery Ice Shelf as a result of bergy bits and growlers calved from large icebergs in front of the ice shelf.
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