Recent multi-decadal Southern Ocean surface cooling unlikely caused by Southern Annular Mode trends

• Published in: Geophysical Research Letters
• Other Authors: Dong, Yue (author), Polvani, Lorenzo M. (author), Bonan, David B. (author)
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.1029/2023GL106142

Over recent decades, the Southern Ocean (SO) has experienced multi-decadal surface cooling despite global warming. Earlier studies have proposed that recent SO cooling has been caused by the strengthening of surface westerlies associated with a positive trend of the Southern Annular Mode (SAM) forced by ozone depletion. Here we revisit this hypothesis by examining the relationships between the SAM, zonal winds and SO sea-surface temperature (SST). Applying a low-frequency component analysis to observations, we show that while positive SAM anomalies can induce SST cooling as previously found, this seasonal-to-interannual modulation makes only a small contribution to the observed long-term SO cooling. Global climate models well capture the observed interannual SAM-SST relationship, and yet generally fail to simulate the observed multi-decadal SO cooling. The forced SAM trend in recent decades is thus unlikely the main cause of the observed SO cooling, pointing to a limited role of the Antarctic ozone hole.