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

• 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: Sub Physical Oceanography, Marine and Atmospheric Research
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2017
• Subjects: Global and Planetary Change; Stratigraphy; Palaeontology; Antarctic; Austral; Pacific; Southern Ocean; Antarc*; Ice Sheet
• Online Access: https://dspace.library.uu.nl/handle/1874/349355

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.