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Science  26 Mar 2004:
Vol. 303, Issue 5666, pp. 1947
DOI: 10.1126/science.303.5666.1947b

The El Niño-Southern Oscillation (ENSO) is the primary cause of modern interannual variability of tropical climate. Has ENSO always behaved as it does today? Some studies have indicated that its behavior may depend on the background climate state—particularly whether it is a glacial or warm interval—and that its strength, periodicity, and regularity can change. Unfortunately, annually resolved records are scarce.

Using a 350,000-year-old fossil coral from the southwestern tropical Pacific Ocean island of Vanuatu, Kilbourne et al. have measured Sr/Ca and oxygen isotopic anomalies, which are proxies for temperature and salinity changes, and compare them to those of a modern coral from the same location. Although annual sea surface temperature variations recorded in the corals were of the same amplitude, the seasonal salinity variations recorded by the fossil coral were smaller than those seen in the modern one. They also calculate that both the average sea surface temperature and salinity then were probably lower than today. They interpret these results as showing that ENSO or ENSO-like climate variations were in fact already present 350,000 years ago, although the South Pacific Convergence Zone did not migrate as far northward during austral winter then as it does today. — HJS

Paleoceanography 19, 10.1029/2003PA000944 (2004).

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