The Response of the Subtropical Front to Changes in the Southern Hemisphere Westerly Winds—Evidence From Models and Observations

JGR Oceans (2023)

The Subtropical Front (STF) is an important water mass barrier, between warm, salty, and nutrient-depleted Subtropical Waters of the subtropical gyre to its north, and cold, fresh, but nutrient-rich Subantarctic Waters of the Southern Ocean to its south. The position of the STF is thought to be influenced by the westerly winds. In this study we investigate if the STF shifts in relation to changes in these westerly winds. Our model experiments show that over large parts of the Southern Ocean, the changes in the location of the STF follow changes in the westerly winds, except in regions of strong oceanic currents. The observations show that between 2004 and 2019 a small southward trend of the STF has been detected over most parts of the Southern Ocean as a consequence of southward shift of the westerly winds due to positive Southern Annular Mode (SAM). However, the shift in the STF has not been as large as the shift in the winds, as it has been opposed by the strengthening of the westerly winds. The recent southward shift in the STF has led to an increase in plankton growth south of the STF due to increased mixing of the Subtropical and Subantarctic Waters.