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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-65
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-65
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jun 2019

Research article | 11 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

Svante Björck1,2, Jesper Sjolte1, Karl Ljung1, Florian Adolphi1,3, Roger Flower4, Rienk H. Smittenberg2, Malin E. Kylander2, Thomas F. Stocker3, Sofia Holmgren1, Hui Jiang5, Raimund Muscheler1, Yamoah K. K. Afrifa6, Jayne E. Rattray7, and Nathalie Van der Putten8 Svante Björck et al.
  • 1Department of Geology, Lund University, SE-22362 Lund, Sweden
  • 2Department of Geological Sciences and the Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden
  • 3University of Bern, Physics Institute, Climate and Environmental Physics, Sidlerstrasse 5, CH-3012 Bern, Switzerland
  • 4Department of Geography, University College London, London WC1E 6BT, UK
  • 5Key Laboratory of Geographic Information Science, East China Normal University, 200062 Shanghai, PR China
  • 6School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT, UK
  • 7Department of Biological Sciences, University of Calgary, Calgary, Canada
  • 8Earth and Climate Cluster, Faculty of Science, Vrije Universiteit, Amsterdam, The Netherlands

Abstract. The period 36–18 ka was a dynamic phase of the last glacial, with large climate shifts in both hemispheres. Through the bipolar seesaw, the Antarctic Isotope Maxima and Greenland DO events were part of a global concert of large scale climate changes. The interaction between atmospheric processes and Atlantic meridional overturning circulation (AMOC) is crucial for such shifts, controlling upwelling- and carbon cycle dynamics, and generating climate tipping points. Here we report the first temperature and humidity record for the glacial period from the central South Atlantic (SA). The presented data resolves ambiguities about atmospheric circulation shifts during bipolar climate events recorded in polar ice cores. A unique lake sediment sequence from Nightingale Island at 37° S in the SA, covering 36.4–18.6 ka, exhibits continuous impact of the Southern Hemisphere Westerlies (SHW), recording shifts in their position and strength. The SHW displayed high latitudinal and strength-wise variability 36–31 ka locked to the bipolar seesaw, followed by 4 ka of slightly falling temperatures, decreasing humidity and fairly southern westerlies. After 27.5 ka temperatures decreased 3–4 °C, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly positioned SHW are correlated with periods of increased CO2 outgassing from the ocean. Changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, it shows that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial.

Svante Björck et al.
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Short summary
Southern Hemisphere westerlies play a key role in regulating global climate. A lake sediment record on a mid-South Atlantic island shows changes of the westerlies and hydroclimate 36.4–18.6 ka. Before 31 ka the westerlies shifted in concert with the bipolar seesaw mechanism in a fairly warm climate, followed by southerly westerlies and falling temperatures. After 27.5 ka temperatures dropped 3 °C with drier conditions, and with shifting westerlies possibly triggering the variable LGM CO2 levels.
Southern Hemisphere westerlies play a key role in regulating global climate. A lake sediment...
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