Julian P. Sachs et al., Nature Geoscience, June 2009: Southward movement of the Pacific intertropical convergence zone AD 1400–1850

Nature Geoscience, 2 (2009) 519-525, published online 28 June 2009; doi:10.1038/ngeo554

Southward movement of the Pacific intertropical convergence zone AD 1400–1850

Julian P. Sachs^1,*, Dirk Sachse^1,4, Rienk H. Smittenberg^1,4, Zhaohui Zhang^1,4, David S. Battisti² and Stjepko Golubic³

Abstract

Tropical rainfall patterns control the subsistence lifestyle of more than one billion people. Seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone, which is characterized by deep convection causing heavy rainfall near 10^° N in boreal summer and 3^° N in boreal winter. Dynamic controls on the position of the intertropical convergence zone are debated, but palaeoclimatic evidence from continental Asia, Africa and the Americas suggests that it has shifted substantially during the past millennium, reaching its southernmost position some time during the Little Ice Age (AD 1400–1850). However, without records from the meteorological core of the intertropical convergence zone in the Pacific Ocean, quantitative constraints on its position are lacking. Here we report microbiological, molecular and hydrogen isotopic evidence from lake sediments in the Northern Line Islands, Galápagos and Palau indicating that the Pacific intertropical convergence zone was south of its modern position for most of the past millennium, by as much as 500 km during the Little Ice Age. A colder Northern Hemisphere at that time, possibly resulting from lower solar irradiance, may have driven the intertropical convergence zone south. We conclude that small changes in Earth's radiation budget may profoundly affect tropical rainfall.

1. School of Oceanography, University of Washington, Seattle, WA 98195, USA
2. Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
3. Biological Science Center, Boston University, Boston, MA 02215, USA
4. Present addresses: DFG-Leibniz Center for Surface Process and Climate Studies, Institut für Geowissenschaften, Universität Potsdam, 14476 Potsdam, Germany (D.S.); Geological Institute, ETH Zürich, 8092 Zürich, Switzerland (R.H.S.); Department of Earth Sciences, Nanjing University, Nanjing, 210093, China (Z.Z.)

*Correspondence, e-mail: jsachs@u.washington.edu

Link to abstract: http://www.nature.com/ngeo/journal/v2/n7/abs/ngeo554.html