| Daily sea ice concentration data from 2008 to 2012 was downloaded from the National Snow and Ice Data Center and University Bremen to study temporal and spatial variations of Prydz Bay polynya in winter. Combined with wind field reanalysis data, the origin and effect factors of polynya were investigated. Hydrographic data collected during the Antarctic winter from March to June, 2011 by the CTD-tags installed on five elephant seals was analyzed to study the upper water structure evolution and the relationship between polynya and sea ice formation. The contents of this paper was mainly focused on were as follow:Firstly, the morphological characteristics and spatial variations of polynya were studied. Results showed that polynya occurred every month in Prydz Bay in winter from 2008 to 2012, which mainly occurred in front of Amery Ice Shelf(Mac Kenzie Bay) and east of Amery Ice Shelf, as well as in the northern part of Cape Darnley. Polynya in front of Amery ice shelf existed in zonal distribution along the leading edge ice. It reached the mainland in the west and extended to the east along the eastern Amery Ice Shelf front. Besides, it reached 68°S in the north and its life time in the western front was longer than that in the eastern front. The eastern part of Amery Ice Shelf polynya was close to continental ice shelf, which covered less than 1°in zonal and longitudinal direction, respectively. The shape of polynya in Cape Darnley is not fixed, which bordered continent in the south and reached 66.5°S in the north, 71.5°E in the east and 68°E in the west.Secondly, the temporal variations and effect factors of winter polynya in Prydz Bay were analyzed. Due to cooling and freezing, sea ice began to generate since every late March from 2008 to 2012 and polynya gradually formed in coastal area. sea ice developed faster from April which caused more and more obvious annual variation. From May to August. The average area of polynya is 13.24×105km2, maximum of which happened in early April. There existed a significant correlation between offshore wind speed and polynya area. When offshore wind increased, the polynya area increased, and vice versa.Thirdly, the evolution of upper water structure in polynya in winter could be divided into three stages. First stage: Temperature shifted from stratification to homogeneity. Subsurface still maintains warm water characteristics. With the cooling from surface and the strengthening of vertical convective mixing, the subsurface warm water gradually disappeared. Second stage: salinity shifted from stratification to homogeneity. In this stage, the upper salinity increased with the freezing of sea water and the strengthening of vertical convection, both of which uniform the salinity from bottom to top. Last stage: sea water kept cooling and freezing and salinity continued to increase.In the fourth part, the winter ocean heat flux and air-sea exchange in polynya were estimated. Using the seal tags observed temperature and salinity data to estimate the heat flux of three stages of upper ocean structure evolution were-90.93 W?m-2,-82.20 W?m-2 and-43.44 W?m-2, respectively in 2011, and-47.4 W?m-2 in third stages 2012. According to the salinity increasing to estimate the sea ice formation rate were 5.4 cm?d-1, 4.9 cm?d-1 and 2.5 cm?d-1, respectively in 2011, and 5.14 cm?d-1 in 2012. Combined with ERA-Interim reanalysis data, including wind speed, 2m-temperature and heat flux, the analytical results showed that the rate of sea ice formation had a positive correlation with offshore wind, sensible heat flux and latent heat flux, negative correlation with 2m-temperature. |
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