Winnick: Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United States
Fig. 1. Modern El Ni˜no precipitation anomalies, isotope localities, and reconstructed Pliocene conditions. Anomalous annual El Ni˜no precipitation calculated with CMAP precipitation data from 1979– 2008; CMAP precipitation data provided by the NOAA/OAR/ESRL PSD, Boulder, CO, USA, from their Web site at http://www.esrl. noaa.gov/psd/. Purple stars show isotope record localities used in this study. Blue circles represent reconstructions of wetter-thanmodern Pliocene conditions, and red circles represent reconstructions of drier-than-modern Pliocene conditions.
Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United States
Abstract. Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO 2 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 p CO 2 . 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.
Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United StatesM. J. Winnick, J. M. Welker, and C. P. Chamberlain
Clim. Past, 9, 903-912, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.