Effects Of Sea Ice And Ice Shelf On The Ocean Processes In Prydz Bay, Antarctica

? The Prydz Bay is the focus region of Chinese Antarctic research, where sea ice has obviously seasonal variation and the largest ice shelf in the eastern Antarctica, Amery Ice Shelf (AIS), locates. The processes of sea ice and ice shelf have crucial impacts on water mass and circulation in the Prydz Bay. The specific study of the Prydz Bay can not only benefit us to understand further the processes and interaction of sea ice, ice shelf and ocean, but also help us to solve the focus question of whether the Antarctic Bottom Water could form locally in the Prydz Bay.Firstly, the high-resolution sea ice concentration data from 2003 to 2008 download from the National Snow and Ice Data Center (NSIDC) were used to reveal the variation of sea ice in the Prydz Bay, and the reason of the sea ice variation was analyzed combining with oceanographic dynamics. The study indicated that the freezing and thawing stages went through 7 months and 5 months respectively, and the months with largest sea ice thawing rate were October and November, mainly due to the decrease of sea ice concentration, while the months with largest freezing rate were April and June, mainly due to the northward expending of ice edge. In the melting period, sea ice had the bidirectional melting feature for the existence of Cape Darnley polynyas, Prydz Bay polynyas and Barrier Bay polynyas in the coast of the Prydz Bay, i.e., sea ice melted from north to south in abyssal ocean, and from south to north in the coast region of Prydz Bay. Near the mouth of Prydz Bay, there were persistent ice tongues at Fram Bank and Four Ladies Bank, and the low sea ice concentration region between them was corresponding to the path of warm water intruding to the Prydz Bay. The Antarctic Circumpolar Current turned north when flowing through the middle of the Kerguelen Plateau, and induced sea ice edge more north (~57°S) in winter time than other region in the same longitude. The divergent surface circulation and warm upwelling in the Antarctic Divergence could restrict sea ice freezing and congregating resulting in low sea ice concentration region.Secondly, CTD data in front of AIS from CHINARE in 2003, 2005, 2006, 2008, and 2009, as well as sea ice concentration and NCEP shortwave radiation data were used to analyze the features of summer surface water in Prydz Bay, and to calculate heat content increase of surface water in front of the AIS and the total shortwave radiation flux into the ocean. Then heat content and shortwave radiation was contrasted to reveal the effect of sea ice on surface water. The study indicated that there were surface water with high-temperature and low-salinity and shelf water with low-temperature and high-salinity in the ocean at front of AIS in summer. The temperature and salinity character of surface water varied greatly, and did not have obvious core, while those of shelf water were relatively stable, and the salinity was higher in the west than that in the east. The minimum of salinity is located on the surface, but the maximum of temperature is usually located in the sub-surface. The temperature of surface water in austral summer has obvious inter-annual variation. Surface water appeared high-temperature characteristics obviously different from that of shelf water in 2003, 2005, 2006 and 2009, but the difference is not obvious in 2001, ???2002 and 2008, especially in the west section in front of AIS. The spatial distribution of temperature and salinity, as well as the thickness of surface water, had obviously inter-annual variations. The maximum flux of short-wave radiation did not appear in the basin in the low latitude, but appeared in the Cape Darnley polynyas and Mackenzie polynyas in the west, Prydz Bay polynyas and Barrier Bay polynyas in the east of the Prydz Bay, corresponding to the sea ice distribution. The warm water formed in the sensible-heat polynyas of Prydz Bay and Barrier Bay in the sea ice melting process can reach east of AIS from eastern Prydz bay following the cyclonic circulation, and make the surface water of east stations in front of AIS has high heat content. Ice production and brine rejection in latent-heat polynyas of Mackenzie Bay decrease temperature and increase salinity of the ocean below it, so the surface water in west of AIS has low heat content. At the same time, the Mackenzie Bay polynyas can absorb more short wave radiation flux in the west of AIS than that in the east, so short-wave radiation flux and heat content of surface water in east and west of AIS front section presented an inverse distribution pattern. Therefore, the distribution of sea ice had an important impact on surface water features, while the impact is not local and direct but is the outcome of circulation and polynyas processes. The thermodynamic and dynamic factors should be considered together in analysis.At last, The CTD data in front of AIS, and the meridional sections data in 2003 from CHINARE, as well as the current data in 2001 and 2003 from Australian and in 2009 from CHINARE were used to study the spatial distribution of Ice Shelf Water (ISW). The horizontal and vertical movements of ISW were discussed, and the flux of ?ISW and fresh water were calculated, in order to analyze the effects of ice shelf on ocean processes. The results indicated that the relatively cold and fresh ISW existed in front of the AIS, within the depth range of 100?600 m under the seasonal thermocline, as several discrete water blocks with cold cores. ISW had obvious temporal and spatial variations and the spatial distribution pattern changed largely after 2005. Most of ISW concentrated in west of 73°E during years from 2001 to 2003 and 2006, but it was widespread to east of ice shelf front section in 2005 and 2008. In all observing years, a small amount of cold ISW always occurred at west end of the AIS front section, where the coldest ISW in the whole section also existed in the years 2001, 2003 and 2006. Considering general circulation pattern under the AIS, i.e. water diving under ice shelf at the east and leaving from it at the west, the ISW flowing out from west end of the AIS front might have experienced the longest cooling period under ice shelf, so it would have the lowest temperature. Implied by the analysis of data in meridian sections in the Prydz Bay in 2003, ISW in the west could spread north to the continental break along east flank of the Fram Bank near 70.5°E, mixing with the upwelling Circumpolar Deep Water (CDW), and possibly contribute to the formation of AABW. The ISW appears wandering character in front of AIS. Only when the observing stations are located south to the ISW edge, the ISW can be observed. So the ISW appears several discrete water blocks with cold cores. West of the AIS front is the outflow region of ISW. The upwelling due to outward transport of sea ice and surface water in Mackenzie Bay polynyas could help ISW to rise and transport north in the west of Prydz Bay after ISW flew out from the cavity under ice shelf base. Affected by current, the north extent of ISW also had inter-annual variation. The ISW flux along front of AIS is 1.4±0.6 Sv, which is comparable with that (1.6±0.5 Sv) at the northern end of the Filchner Depression in Weddell Sea.