HR: 14:55h
AN: PP53A-06    [Abstracts]
TI: Holocene ENSO Variability in the Equatorial Pacific From D/H Ratios in Alkenones
AU: * Pahnke, K
EM: kpahnke@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 42-44 Carleton Street, Cambridge, MA 02139 United States
AU: Sachs, J
EM: jsachs@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 42-44 Carleton Street, Cambridge, MA 02139 United States
AU: Keigwin, L
EM: lkeigwin@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, McLean Lab., Woods Hole, MA 02543 United States
AB: In the equatorial west Pacific and the tropics of northwestern South America, extreme phases of the El Niño-Southern Oscillation (ENSO) are associated with a coherent pattern of hydrological anomalies. While El Niño leads to reduced rainfall and river runoff, La Niña causes extreme maxima in precipitation and river discharge to the Pacific and Atlantic Oceans. Paleo-records of rainfall and runoff variations from these areas will therefore aid understanding of past ENSO behavior. In a novel approach, we utilize the hydrogen isotopic (D/H) signature of alkenones from equatorial Pacific Ocean margin sites that reflects variations in isotopically depleted runoff to the Pacific Ocean to reconstruct past ENSO variability. We observe maximum D/H changes off the Colombian coast of around 18‰ ( vs. VSMOW) over the past three centuries with a marked increase from the mid-1960s to the 1980s, suggesting a decrease in river runoff and hence more frequent or more intense El Niño conditions. A subsequent drop to more depleted D/H values implies an increase in precipitation and freshwater influx into the ocean, reminiscent of conditions typical for La Niña phases. These patterns are consistent with instrumental records of ENSO variability and confirm this new proxy as highly valuable tool for the reconstruction of past changes in tropical climate.
DE: 1055 Organic and biogenic geochemistry
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4922 El Nino (4522)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005