A 19-year time series of underway sea surface salinity (SSS) data from the SURVOSTRAL line between Hobart, Australia and Adelie Land, Antarctica has revealed the distinct patterns of seasonal and interannual variability in two key zones of the Southern Ocean: in the Subantarctic Zone and in the Antarctic Zone. Both regions show a weak seasonal freshening of the surface waters over the summer months, with surface waters becoming shallower, warmer and fresher during the summer heating cycle.In the region north of the Subantarctic Front, interannual variations in the summer SSS signature are linked to the latitudinal movements of the Subtropical Front. When this front shifts southward, more high salinity subtropical waters are brought into the domain. Rather than responding to local wind stress forcing, the interannual SSS variability is strongly linked to southward flow from eastern Tasmania (the Tasman outflow), whose decadal variability responds with a 2-3 year delay to remote wind forcing in the South Pacific (Hill et al., 2008). Over this period, variations in the local surface freshwater forcing make a minor contribution to the SURVOSTRAL SSS signature. There appears to be a regime shift in the surface forcing and the SSS response, before and after the large perturbation in 2001-2002. In the Antarctic Zone, the summer SSS signature shows distinct biannual variations that are correlated with upstream sea-ice coverage in the preceding spring. There is no significant correlation between local precipitation changes and the SURVOSTRAL SSS time series. Rather, the integrated effects of upstream sea-ice melt dominate the interannual variations in SSS at the SURVOSTRAL line. Finally, a simple 2D Lagrangian particle analysis shows that in some years the surface waters circulate for a longer time in the northern part of the domain, where their freshwater content may be reduced by mixing with the surrounding waters.