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    Interannual variability of polynya extent in the Antarctic Ocean

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    M. Naganobu and K. Segawa (Japan)
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    There are two general kinds of polynya (an ice-free area within sea ice borders), coastal polynya and open ocean polynya, in the Southern Ocean. Polynya accelerates oceanic and atmospheric processes by exposing the surface of ocean to the atmosphere. Additionally, we think that the coastal polynyas influence biological activity in the winter and spring season. However, there are no minute reports on the place, time and shape of the coastal polynyas. Accordingly, we pursued the transition of the coastal polynyas using satellite image data of sea ice concentrations by the NSIDC (National Snow and Ice Data Center, USA).
    Time series of polynyas extent per a day were calculated from 1978 to 1998 and converted into the yearly mean. The time series of the yearly mean in the whole Antarctic Ocean are trending upper after the latter half of the 1980s. The time series around the Antarctic Peninsula are trending like a pulse wave. In the whole Antarctic Ocean, peak years of polynyas extent are in the 1981/82 (from July 1981 to June 1982), 1991/92 and 1995/96. In the Antarctic Peninsula area, peak years are in 1980/81, 1987/88 and 1992/93.