Summer and winter surveys of the Subtropical Front of the southeastern Indian Ocean 1997–1998

The Subtropical Front (STF) in the region south of Australia was surveyed to determine its location, character, and seasonal variation. The survey consisted of two cruises, during summer and winter of 1998, and used a towed CTD system (SeaSoar). Based on observations, the STF does not appear to be continuous between the Indian and Pacific Oceans in the region south of Tasmania during winter; instead, it appears to end at the continental shelf of western Bass Strait near 40°S. During both seasons, the STF is characterized by moderate to strong density compensation with the horizontal density ratio (Rρ=αΔT/βΔS) close to 1 both in and below the mixed layer. This contrasts with observations in other regions where Rρ tends towards 2 below the mixed layer. We observed a high degree of interleaving, submerged eddies and small scale temperature and salinity variability. This is attributed to the interaction of a front that is density compensated with a local wind field that periodically reverses direction.