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Proc Natl Acad Sci U S A. 2019 Nov 19;116(47):23455-23460. doi: 10.1073/pnas.1905847116. Epub 2019 Nov 4.

Precession modulation of the South Pacific westerly wind belt over the past million years.

Author information

1
Marine Geology Section, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany; Frank.Lamy@awi.de.
2
Department of Geography, University of California, Berkeley, CA 94720-4740.
3
Marine Geology Section, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany.
4
Center for Marine Environmental Sciences, University of Bremen, 28334 Bremen, Germany.
5
Department of Marine Geology, Leibniz Institute for Baltic Sea Research, 18119 Rostock-Warnemünde, Germany.
6
Department of Physical Geography, Utrecht University, 3584 CB, Utrecht, The Netherlands.
7
Department of Physical Geography, Pontifical Catholic University of Chile, 7820436 Santiago, Chile.
8
Royal Netherlands Institute for Sea Research (NIOZ), Ocean Systems (TX), Utrecht University, 1790 AB, Den Burg, Texel, The Netherlands.
9
Faculty of Science, Department of Earth Sciences, Vrije Universiteit Amsterdam, 1081 HV, Amsterdam, The Netherlands.

Abstract

The southern westerly wind belt (SWW) interacts with the Antarctic Circumpolar Current and strongly impacts the Southern Ocean carbon budget, and Antarctic ice-sheet dynamics across glacial-interglacial cycles. We investigated precipitation-driven sediment input changes to the Southeast Pacific off the southern margin of the Atacama Desert over the past one million years, revealing strong precession (19/23-ka) cycles. Our simulations with 2 ocean-atmosphere general circulation models suggest that observed cyclic rainfall changes are linked to meridional shifts in water vapor transport from the tropical Pacific toward the southern Atacama Desert. These changes reflect a precessional modulation of the split in the austral winter South Pacific jet stream. For precession maxima, we infer significantly enhanced rainfall in the southern Atacama Desert due to a stronger South Pacific split jet with enhanced subtropical/subpolar jets, and a weaker midlatitude jet. Conversely, we derive dry conditions in northern Chile related to reduced subtropical/subpolar jets and an enhanced midlatitude jet for precession minima. The presence of precessional cycles in the Pacific SWW, and lack thereof in other basins, indicate that orbital-scale changes of the SWW were not zonally homogeneous across the Southern Hemisphere, in contrast to the hemispherewide shifts of the SWW suggested for glacial terminations. The strengthening of the jet is unique to the South Pacific realm and might have affected winter-controlled changes in the mixed layer depth, the formation of intermediate water, and the buildup of sea-ice around Antarctica, with implications for the global overturning circulation and the oceanic storage of atmospheric CO2.

KEYWORDS:

orbital cycles; paleoclimate; quaternary; southern westerly wind belt

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