HR: 1340h
AN: PP23A-1396    [Abstracts]
TI: Early Onset and Origin of 100-kyr Cycles in a Tropical Pleistocene SST Record
AU: * Liu, Z
EM: Zhonghui\_Liu\@brown.edu
AF: Brown University, Dept. of Geological Sciences 324 Brook Street, Providence, RI 02912 United States
AU: Herbert, T D
EM: Timothy\_Herbert\@brown.edu
AF: Brown University, Dept. of Geological Sciences 324 Brook Street, Providence, RI 02912 United States
AB: The large 100-kyr cycles evident in most late-Pleistocene paleoclimatic records still lack a satisfactory explanation. Many climatic records show that the period of Pleistocene glacial cycles changed from 41-kyr, dictated by orbital obliquity, to 100-kyr during the mid-Pleistocene transition (MPT). Careful documentation and consideration of how this transition occurred may help resolve the puzzle of late Pleistocene 100-kyr cycles. One hypothesis is that strengthened semi-precession cycles (about 10-kyr) originating in the tropics propagated to high latitudes around 1.5 Ma and triggered the sustained 100-kyr glacial cycles. A 2-Myr SST record from ODP Site 846 in the eastern equatorial Pacific (EEP) indicates that an early onset of 100-kyr cycles did occur in the tropics. However, the record also provides an alternative view of the MPT. Substantial spectral power near the 100-kyr period occurs in early Pleistocene tropical, but not extra-tropical SST records. This spectral power is derived from the subharmonics (multiple integers, about 120-kyr and 80-kyr) of obliquity cycles. In addition, as shown in evolutionary SST spectra, the two subharmonics converge into the late-Pleistocene pseudo 100-kyr period. Therefore, we argue that the subharmonics of obliquity cycles in the early Pleistocene represent a ­rprototype­_ of the late Pleistocene 100-kyr cycles, and that the pseudo 100-kyr cycles are a nonlinear response to orbital obliquity forcing. This view can potentially resolve some existing Pleistocene climate puzzles: (1) the transition from 41-kyr to 100-kyr periodicity during the MPT, (2) the dominance of late-Pleistocene 100-kyr cycles, and (3) weakened late Pleistocene 41-kyr power in some climate records, despite the expected ice-albedo amplification of high latitude insolation forcing.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1045 Low-temperature geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting