Abstract
Abstract. 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.
Highlights
Observations during the second half of the twentieth century suggest significant but spatially complex variability in atmospheric and ocean temperature and circulation (Figs. 1 and S1 in the Supplement), as well as ice-sheet dynamics, across the mid- to high latitudes of the Southern Hemisphere (Jones et al, 2016)
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 be a permanent feature across the mid- to high latitudes
Observations during the second half of the twentieth century suggest significant but spatially complex variability in atmospheric and ocean temperature and circulation (Figs. 1 and S1 in the Supplement), as well as ice-sheet dynamics, across the mid- to high latitudes of the Southern Hemisphere (Jones et al, 2016). These factors include an intensification of western boundary currents (Wu et al, 2012), a strengthening and poleward shift in the summer westerly winds associated with a positive trend in the southern annular mode (SAM) (Marshall, 2003; Abram et al, 2014; Thompson et al, 2011), winter–spring warming over West Antarctica (Steig et al, 2009), latitudinal shifts in the subantarctic and polar fronts associated with the Antarctic Circumpolar Current (ACC) (Langlais et al, 2015), spatial and temporal changes in sea ice extent (Turner et al, 2015; Hobbs et al, 2016), and Antarctic ice-sheet mass loss (Pritchard et al, 2012)
Summary
Observations during the second half of the twentieth century suggest significant but spatially complex variability in atmospheric and ocean temperature and circulation (Figs. 1 and S1 in the Supplement), as well as ice-sheet dynamics, across the mid- to high latitudes of the Southern Hemisphere (Jones et al, 2016). 1 and S1 in the Supplement), as well as ice-sheet dynamics, across the mid- to high latitudes of the Southern Hemisphere (Jones et al, 2016) These factors include an intensification of western boundary currents (Wu et al, 2012), a strengthening and poleward shift in the summer westerly winds associated with a positive trend in the southern annular mode (SAM) (Marshall, 2003; Abram et al, 2014; Thompson et al, 2011), winter–spring warming over West Antarctica (Steig et al, 2009), latitudinal shifts in the subantarctic and polar fronts associated with the Antarctic Circumpolar Current (ACC) (Langlais et al, 2015), spatial and temporal changes in sea ice extent (Turner et al, 2015; Hobbs et al, 2016), and Antarctic ice-sheet mass loss (Pritchard et al, 2012). An improved network of quantified climate-sensitive proxy records across the midto high-latitudes is crucial for exploring climate teleconnections through time (Jones et al, 2016; Abram et al, 2014; Turney et al, 2016a, 2015)
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