Pliocene El Niño

Closing of the Indonesian Seaway and El Niño teleconnections and tropical anomalies as a blueprint for pre-Ice Age climates

Supported solely through patient encouragement from family and friends

Collaborators (recent past and present)

• Mark Cane, Lamont-Doherty Earth Observatory, Columbia University
• Katherine Dayem, CIRES and Department of Geological Sciences, University of Colorado
• David Noone, CIRES and Program in Atmospheric and Ocean Sciences, University of Colorado

Work of Bill Chaisson, Christina Ravelo, Kira Lawrence, Tim Herbert, and their collaborators has shown that before continental ice sheets formed in Canada and Fennoscandia, sea-surface temperatures in the Pacific showed little east-west variability, as they do during El Niño events (Fig. 1). In addition differences between pre-Ice Age and present-day climates in a number of regions resemble those El Niño teleconnections, as we might expect if the atmosphere responded to a permanent El Niño state [Molnar and Cane, 2002]. Further analysis (in progress) extends this synthesis to suggest that the El Niño of 1997-98 represents the pre-Ice Age equatorial Pacific sea-surface temperature distribution better than that of other El Niño events.

The apparent permanent El Niño state in pre-Ice Age times poses the question of what process destroyed that state. We are pursuing two variants on the theme that the closing of the Indonesian Seaway and the conversion of a largely maritime region into the Maritime Continent both blocked warm water to help form the warm pool in the western equatorial pacific [Cane and Molnar, 2001] and increased precititation over the expanding Maritime Continent that strengthened the Walker Circulation, whose easterly winds along the equator sustain the warm pool.

Sea surface temperatures and ODP sites from the equatorial Pacific. The top map shows mean winter (January-March) sea surface temperature for the period 1972-2000, and the bottom map shows the mean sea surface temperature (in °C) for January through March of the El Niño year 1998. In the El Niño year high temperatures extend into the eastern Pacific, eliminating the climatological cold tongue. The image was obtained using the NCEP data [Kalnay et al., 1996] provided by the NOAA-CIRES Climate Diagnostics Center, Boulder Colorado on their Web site at http://www.cdc.noaa.gov/. Site numbers beside the white circles indicate the locations of ODP sites used.

References

Molnar, P., and M. A. Cane (2002), El Niño's tropical climate and teleconnections as a blueprint for pre-Ice Age climates, Paleoceanography, 17 (2), 10.1029/2001PA000663.

Cane, M. A., and P. Molnar (2001), Closing of the Indonesian seaway as a precursor to east African aridification around 3–4 million years ago, Nature, 411, 157-162.