HR: 1340h
AN: PP23A-1391    [Abstracts]
TI: A Mechanism For Amplifying Obliquity Forcing In Low-Latitude Oceans During The Pleistocene
AU: * Lee, S
EM: shihyu@umich.edu
AF: Department of Geological Science University of Michiagn, 2534 C. C. Little Building, 425 East University, Ann Arbor, MI 48109
AU: Poulsen, C
EM: poulsen@umich.edu
AF: Department of Geological Science University of Michiagn, 2534 C. C. Little Building, 425 East University, Ann Arbor, MI 48109
AB: Since the introduction of Milankovitch's astronomical theory of the Ice Ages, Earth's orbital fluctuations have been suspected of driving Pleistocene climate variability. All three orbital parameters, eccentricity, obliquity, and precession, are directly linked to climate change through their influence on the solar insolation received by Earth. By altering the annual meridional distribution of insolation on Earth, obliquity is potentially important to the climate system. In comparison to times of low obliquity (i.e., axial tilt of 22.2ø), at times of high obliquity (i.e., axial tilt of 24.5ø) mean-annual insolation at high latitudes is 1.5% greater at 65ø and 0.4% less at the equator. Despite the very small change in insolation at low latitudes, early Pleistocene climate indices of low-latitude eastern Pacific sea-surface temperature and total alkenone abundance demonstrate a 41 k.y. cyclicity. Using a coupled ocean-atmosphere model (the Fast Ocean-Atmosphere Model), we have identified an oceanic mechanism that amplifies the obliquity signal in the low-latitude Pacific. In response to an increase in axial tilt, subsurface waters in the eastern equatorial Pacific increase by up to 1 øC in the model. Using a Lagrangian transport model, we determine that ventilation of warm subtropical waters, heated by enhanced insolation during periods of high axial tilt, is the primary cause of the low-latitude subsurface warming. In contrast to subsurface waters, sea-surface temperature changes are consistent with variations in local insolation; surface temperatures cool at low-latitudes and warm at high latitudes. This subsurface ocean mechanism is consistent with early Pleistocene proxy data and explains the anti-phase relationship between obliquity insolation forcing and seawater temperature in the eastern tropical Pacific.
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1620 Climate dynamics (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting