Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw

Lechleitner, Franziska A., Breitenbach, Sebastian, Rehfeld, Kira, Ridley, Harriet E., Asmerom, Yemane, Prufer, Keith M., Marwan, Norbert, Goswami, Bedartha, Kennett, Douglas J., Aquino, Valorie V., Polyak, Victor, Haug, Gerald H., Eglinton, Timothy I. and Baldini, James U. L. (2017) Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw. Scientific Reports, 7 (1). ISSN 2045-2322

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Abstract

The presence of a low- to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low- to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low- to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics.

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