Antarctic sea ice variability during 1958–1999: A simulation with a global ice‐ocean model

Abstract

A hindcast simulation is carried out with a global ice‐ocean model driven by the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis daily surface air temperatures and winds in order to document the variability of the Antarctic sea ice cover during 1958–1999. The model consists of an ocean general circulation model coupled to a thermodynamic‐dynamic sea ice model with viscous‐plastic rheology. Its horizontal resolution is of 1.5° × 1.5°. Both the mean state and variability of the Antarctic ice pack over the satellite observing period are reasonably well reproduced by the model. In particular, from November 1978 to September 1998, the model produces an overall increasing trend in ice area (defined as the total area of ice‐covered ocean) of 11,400 ± 2300 km2 yr−1, which falls within the range of current uncertainty. The model annual mean, area‐averaged ice thickness displays no significant trend over 1958–1999. In contrast, a retreat of the pack is simulated during the second half of the 1970s and the beginning of the 1980s, leading to a loss of ice cover of roughly 0.5 × 106 km2 between 1958–1976 and 1982–1999. The marked weakening of the Antarctic semiannual oscillation that occurred since the mid‐to‐late 1970s seems to be partially responsible for this behavior. Part of the modeled decline might however be spurious and due to the 1979 change in the observing systems utilized in the NCEP–NCAR reanalysis. The simulation also reveals a pronounced decadal variability (8–10 years) in both ice area and thickness. Locally, the changes in ice thickness can reach 1 m during a particular cycle.