Clim. Past Discuss., 8, 5083-5108, 2012
www.clim-past-discuss.net/8/5083/2012/
doi:10.5194/cpd-8-5083-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene Western United States
M. J. Winnick1, J. M. Welker2, and C. P. Chamberlain1
1Environmental Earth System Science, Stanford University, USA
2Environment and Natural Resources Institute and Department of Biological Sciences, University of Alaska Anchorage, USA

Abstract. Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric pCO2. During the Pliocene the Western United States was wetter than modern, an observation at odds with our current understanding of future warming scenarios, which involve the expansion and poleward migration of the subtropical dry zone. Here we compare Pliocene oxygen isotope profiles of pedogenic carbonates across the Western US to modern isotopic anomalies in precipitation between phases of the El Niño Southern Oscillation (ENSO). We find that when accounting for seasonality of carbonate formation, isotopic changes through the late Pliocene match modern precipitation isotopic anomalies in El Niño years. Furthermore, isotopic shifts through the late Pliocene mirror changes through the early Pleistocene, which likely represents the southward migration of the westerly storm track caused by growth of the Laurentide Ice Sheet. We propose that the westerly storm track migrated northward through the late Pliocene with the development of the modern Cold Tongue in the East Equatorial Pacific, then returned southward with widespread glaciation in the Northern Hemisphere – a scenario supported by terrestrial climate proxies across the US. Together these data support the proposed existence of background El Niño-like conditions in Western North America during the warm Pliocene. If the Earth behaves similarly with future warming, this observation has important implications with regard to the amount and distribution of precipitation in Western North America.

Citation: Winnick, M. J., Welker, J. M., and Chamberlain, C. P.: Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene Western United States, Clim. Past Discuss., 8, 5083-5108, doi:10.5194/cpd-8-5083-2012, 2012.
 
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