Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability

Matthis Auger (1) , Rosemary Morrow (2) , Élodie Kestenare (2) , Jean-Baptiste Sallée (1) , Rebecca Cowley (3)

1 PROTEO - Processus et interactions de fine échelle océanique
2 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
3 CSIRO-MAR - CSIRO Marine and Atmospheric Research

Despite playing a major role in global ocean heat storage, the Southern Ocean remains the most sparsely measured region of the global ocean. Here, a unique 25-year temperature time-series of the upper 800 m, repeated several times a year across the Southern Ocean, allows us to document the long-term change within water-masses and how it compares to the interannual variability. Three regions stand out as having strong trends that dominate over interannual variability: warming of the subantarctic waters (0.29 ± 0.09 °C per decade); cooling of the near-surface subpolar waters (−0.07 ± 0.04 °C per decade); and warming of the subsurface subpolar deep waters (0.04 ± 0.01 °C per decade). Although this subsurface warming of subpolar deep waters is small, it is the most robust long-term trend of our section, being in a region with weak interannual variability. This robust warming is associated with a large shoaling of the maximum temperature core in the subpolar deep water (39 ± 09 m per decade), which has been significantly underestimated by a factor of 3 to 10 in past studies. We find temperature changes of comparable magnitude to those reported in Amundsen–Bellingshausen Seas, which calls for a reconsideration of current ocean changes with important consequences for our understanding of future Antarctic ice-sheet mass loss.

Domaines: Géophysique [physics.geo-ph]

Matthis Auger, Rosemary Morrow, Élodie Kestenare, Jean-Baptiste Sallée, Rebecca Cowley. Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability. Nature Communications, 2021, 12, pp.514. ⟨10.1038/s41467-020-20781-1⟩. ⟨hal-03127689⟩