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

• Main Authors: Turney, Christian, Fogwill, Christopher, Palmer, Jonathan G, van Sebille, Erik, Thomas, Zoë, McGlone, Matt S, Richardson, Sarah, Wilmshurst, J M, Fenwick, Pavla, Zunz, Violette, Rainsley, Eleanor
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Research Online 2017
• Subjects: Medicine and Health Sciences; Social and Behavioral Sciences; Antarctic; Austral; Pacific; Southern Ocean; Antarc*; Ice Sheet
• Online Access: https://ro.uow.edu.au/smhpapers/4563; https://ro.uow.edu.au/cgi/viewcontent.cgi?article=5587&context=smhpapers

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.