ENSO-Scale Variability in the Eocene Greenhouse Recorded by Fossil Bivalves and Wood from Antarctica

IVANY L. C.,; BREY T.,; HUBER M.,; BUICK D.,; LOMOVASKY BETINA J.,; SCHONE B. R.,

San Francisco

Conferencia; American Geophysical Union, Fall Meeting; 2009

American Geophysical Union

Quasi-periodic variation in sea surface temperature and air pressure in the equatorial Pacific known as the El Niño - Southern Oscillation (ENSO) is the primary driver of interannual change in global climate. Despite a reasonably good understanding of the mechanisms behind ENSO today, there is much uncertainty about how its primary drivers will respond to global warming. Will climate oscillations in the roughly 2-7 year ENSO band persist as our planet warms, or will the Earth move toward one or the other end-member state? Published data from Plio-Pleistocene warm intervals suggest a shift toward either dominantly La Niña or El Niño conditions, both implying that the Bjerknes feedback that gives rise to instability in the tropical Pacific will be affected so as to produce more constant (but cooler or warmer, respectively) conditions. Despite these studies, most climate models still predict the persistence of ENSO variation in the warmer world. Necessary to test this prediction are long continuous records of annual climate conditions from a time when the planet was significantly warmer than today and from a region where the ENSO signal is expected to be strong. Growth increment sequences from the accretionary skeletons of long-lived organisms preserved in the fossil record offer such an archive, as annual growth is controlled in large part by environmental conditions. Multi-annual records of climate derived from fossil bivalve shells and co-occurring driftwood from the greenhouse conditions of the early Eocene, when global average temperature was ~6 degrees higher than today, demonstrate the presence of inter-annual variation consistent with ENSO. Periodicities from both bivalves and wood are consistent with each other, and with those predicted by a coupled ocean-atmosphere climate model tuned for the Eocene. The presence of ENSO variation during this markedly warmer interval argues for its persistence in our future greenhouse world, in contrast to suggestions of a shift toward a permanent El Niño or La Niña state. That these fossils are from the Antarctic Peninsula demonstrates that today’s strong teleconnections to the region were present in the Eocene as well.