HR: 0800h
AN: PP21A-1556    [Abstracts]
TI: Orbital forcing of continental climate during the Pleistocene: a complete astronomically-tuned climatic record from Lake Baikal, SE Siberia
AU: * Prokopenko, A
EM: sasha@geol.sc.edu
AF: Univ. South Carolina, Dept. Geological Sciences, Columbia, SC 29208 United States
AU: Hinnov, L
EM: hinnov@jhu.edu
AF: Johns Hopkins Univ., Earth and Planetary Sciences, Baltimore, MD 10101 United States
AU: Williams, D
EM: doug@schc.sc.edu
AF: Univ. South Carolina, Dept. Geological Sciences, Columbia, SC 29208 United States
AU: Kuzmin, M I
EM: kuzmin@igc.ru
AF: Institute of Geochemistry, Russian Academy, Siberian Branch, Irkutsk, 6609903 Russian Federation
AB: Baikal was the first ancient rift lake where an ODP-style coring technology was used to recover a spectacular continuous paleoclimate record spanning several million years. Glacial/interglacial diatom productivity cycles recorded as biogenic silica content variations in sediments reveals strong power in Milankovitch frequency bands. By splicing BDP-96-1 and BDP-96-2 drill cores, we generated the new composite BDP-96 BioSi record over the entire Pleistocene. During the Holocene, Lake Baikal biogenic silica (BioSi) proxy response is anti-phased with regional humidity indices. Instead, BioSi closely follows a significant rise in regional annual temperature reflected in palynological records and predicted by GCM simulations around 6 ka (corresponding to September perihelion (SP), 4-5 ka past June insolation maximum). The Holocene-like BioSi timing is confirmed by observations during the last interglacial and around two paleomagnetic reversals constrained by independent dating methods. September perihelia timing during the Pleistocene were used as a tuning target for the BDP-96 composite record. Tuning results in a robust timescale which passes spectral analysis, magnetic reversal and Termination timing tests with a high degree of confidence. Power spectral analysis of the new astronomically tuned BioSi record shows a major improvement compared with previously reported Lake Baikal timescales. Significant power is now aligned into the precession index frequencies (1/(19 kyr), 1/(22 kyr), and 1/(24kyr), testifying to the success of the tuning, as well as to the presence of consistent BioSi signal in the precession band. More importantly, the SP-tuning (which manipulates the record at precession index frequencies only) confines high signal power to a narrow band at the obliquity frequency, at 1/(41 kyr). Two major spectral peaks also occur at 1/(94 kyr) and 1/(75 kyr), which only partly coincide with the predicted orbital eccentricity band (1/(128 kyr) to 1/(95 kyr)). Cross-spectral analysis further confirms SP-tuning efficacy. At the same time, however, an anomaly is observed between the BioSi obliquity component and the obliquity variation. A phasing of -32§+3§ (2? level) points to a possible inherent time-lagged response of BioSi (productivity) and terrestrial vegetation proxies to insolation forcing. The presence of this ca. 4-kyr lag is intriguing because Baikal record is non-marine and not ice volume-driven, and with its continental interior location, highly sensitive to insolation forcing. It suggests that factors other than `slow physics of ice sheets' may have contributed to generating lagged responses to insolation in the northern hemisphere climate proxy records. We suggest the composite BDP-96 Baikal record as a new benchmark correlation target for terrestrial records in continental Eurasia as an alternative to June 65§N insolation and ODP marine oxygen isotope timescales, commonly used as targets for tuning loess/soil sections and palynological records in this part of the world.
DE: 3344 Paleoclimatology (0473, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005