Seasonal Variability of the Subtropical Front in the Tasman Sea Inferred Using Remotely Sensed Sea Surface Temperature and Salinity Data

The Subtropical Front (STF) defines the northern boundary of the Southern Ocean, forming a surface water mass boundary where cool, fresh Subantarctic Water converges and mixes with warmer, saline Subtropical Water. Both the meridional position and oceanography of the STF can have a substantial influence on atmospheric circulation, marine ecosystem functioning and regional climate. Yet, in contrast to other Southern Ocean fronts, the mechanisms that control the position of the STF remain poorly understood, largely owing to a scarcity of repeat observations. Here, we will provide new insights into the seasonal variability of the STF in the Tasman Sea, by synthesizing information derived from remotely sensed sea surface temperature (SST) and sea surface salinity (SSS) products. Combining this information enables us to develop a statistical view of the annual and seasonal mean STF position for this region, which is not possible from the sparse historical hydrographic survey data. We will present evidence that any seasonal migration of the STF in the Tasman Sea is small (< 1° latitude), consistent with previous observations from the South Atlantic and southeast Indian Ocean. This limited seasonal variability is contrary to previous inferences that the STF undergoes a large (5-7° latitude) seasonal migration throughout the Southern Hemisphere. We also suggest, based on comparisons between the seasonal migration of the STF and the southern hemisphere subtropical high-pressure belt, that the role played by atmospheric forcing in determining the position of the STF is much less obvious than has previously been assumed, at least on seasonal time scales. These results underscore a need to revisit traditional views of the mechanisms that control the position of the STF, and highlights the utility of remotely sensed SSS measurements for studying the variability of large-scale oceanic fronts.