Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction

• Published in: Climate of the Past
• Main Authors: Turney, Chris S. M., Fogwill, Christopher J., Palmer, Jonathan G., van Sebille, Erik, Thomas, Zoë, McGlone, Matt, Richardson, Sarah, Wilmshurst, Janet M., Fenwick, Pavla, Zunz, Violette, Goosse, Hugues, Wilson, Kerry-Jayne, Carter, Lionel, Lipson, Mathew, Jones, Richard T., Harsch, Melanie, Clark, Graeme, Marzinelli, Ezequiel, Rogers, Tracey, Rainsley, Eleanor, Ciasto, Laura, Waterman, Stephanie, Thomas, Elizabeth R., Visbeck, Martin
• Other Authors: UCL - SST/ELI/ELIC - Earth & Climate
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2017
• Subjects: CISM:CECI; Antarc*; Antarctic; Ice Sheet; Southern Ocean
• Online Access: http://hdl.handle.net/2078.1/183726; https://doi.org/10.5194/cp-13-231-2017

Occupying about 14 % of the world’s surface, the Southern Ocean plays a fundamental role in ocean and atmosphere circulation, carbon cycling and Antarctic ice-sheet dynamics. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine–atmosphere–ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54◦ S). Our annually resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the 1940s, a phenomenon predating the observational record. Climate reanalysis and modelling show a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer. Our results suggest that modern observed high interannual variability was established across the mid-twentieth century, and that the influence of contemporary equatorial Pacific temperatures may now be a permanent feature across the mid- to high latitudes.