Recent Multiâ€Decadal Southern Ocean Surface Cooling Unlikely Caused by Southern Annular Mode Trends

• Published in: Geophysical Research Letters
• Main Authors: Dong, Yue, Polvani, Lorenzo M., Bonan, David B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2024
• Subjects: Antarc*; Antarctic; Southern Ocean
• 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. © 2024 The Authors. Earth's Future published by Wiley Periodicals LLC on behalf of American Geophysical Union. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. This is an open access article under the terms of theCreative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. We thank Edward Doddridge and another anonymous reviewer for constructive comments. YD was supported by the NOAA Climate and Global Change Postdoctoral Fellowship Program, administered by UCAR's Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award NA210AR4310383. DBB was supported by the National Science Foundation (NSF) Graduate Research Fellowship Program (NSF Grant DGE-1745301). LMP is grateful to the US NSF for their continued support, under award #1914569. We use SST from the ERSSTv5 data set (Huang etal.,2017a,2017b), and atmospheric reanalysis ...