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

• Published in: Climate of the Past
• Main Authors: C. S. M. Turney, C. J. Fogwill, J. G. Palmer, E. van Sebille, Z. Thomas, M. McGlone, S. Richardson, J. M. Wilmshurst, P. Fenwick, V. Zunz, H. Goosse, K.-J. Wilson, L. Carter, M. Lipson, R. T. Jones, M. Harsch, G. Clark, E. Marzinelli, T. Rogers, E. Rainsley, L. Ciasto, S. Waterman, E. R. Thomas, M. Visbeck
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2017
• Subjects: geo; envir; Antarctic; Austral; Pacific; Southern Ocean; Antarc*; Ice Sheet
• Online Access: https://doi.org/10.5194/cp-13-231-2017; http://www.clim-past.net/13/231/2017/cp-13-231-2017.pdf; https://doaj.org/article/f475d8f6464d41c58b8542768b87b2fd

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.