Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperature reconstruction
Van Sebille, E
Climate of the Past
European Geosciences Union (EGU)
© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License.
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.
A large thanks to the captain and crew of the MV Akademik Shokalskiy, and Henk Haazen and Kali Kahn on the Tiama for all their help in the field. Thanks also to Lisa Alexander (CCRC) for the analysis of meteorological datasets and to Jean-Baptiste Sallee, who kindly provided the location of the main fronts of the ACC (Fig. 1). This work was supported by the Australasian Antarctic Expedition 2013–2014, the Australian Research Council (FL100100195, FT120100004, DE130101336, and DP130104156), and the University of New South Wales. Research on the New Zealand subantarctic Campbell Island was undertaken under Department of Conservation National Authorization Numbers 37687-FAU and 39761-RES. Kathy Allen and three anonymous reviewers kindly provided valuable and constructive criticism which improved an earlier version of this paper.
This is the final version of the article. Available from European Geosciences Union (EGU) via the DOI in this record.
Vol. 13, pp. 231 - 248