Multidecadal warming of subsurface temperature in the Indian sector of the Southern Ocean

Long-term variations of subsurface layer temperature were examined for 32 years (1966-1998) of continuous observations in the Indian sector of the Southern Ocean. The data analyzed consist of observations from Japanese Antarctic Research Expeditions and also from other countries. Significant warming trends of about 0.004degreesC x yr(-1) were observed at all depths from 200 to 900 m to the north of the southern Antarctic Circumpolar Current (ACC) front [Orsi et al., 1995]. The rates of warming increase with increasing depth from 0.003degreesC x yr(-1) at 200 m to 0.012degreesC x yr(-1) (statistically significant) at 900 m in the region close to the front. These warming trends were also found after applying a technique to correct for differences in the data sampling locations. The warming tendency in the frontal region is consistent with the assumption of a southward shift of the front and may have a relationship with the observed retreat of sea ice edge.