A late spring surge in the open water of the Antarctic sea ice pack

Mean annual cycles of open water area within the Antarctic sea ice pack are presented for 1978-87 and 1987-97, compiled using mean daily data. A minim um of the open water area occurs in mid February, followed by a steady incr ease until a plateau is established in October, before a sudden surge in ea rly November to a peak of 4.5 x 10(6) km(2). As this Antarctic Open water S urge (AOS) occurs on timescales of around one month, its temporal structure only becomes truly clear when using daily means. The AOS is shown to be th e result of the relative timings of the sea ice area and extent annual cycl es. It is suggested these reflect the late spring crossing of the Antarctic circumpolar trough over the sea ice edge, thus shifting the dominant winds (Ekman forcing) from westerly (northerly) to easterly (southerly).