HR: 08:15h
AN: U21F-02    [Abstracts]
TI: Orbital forcing of continental climate during the Pleistocene: a complete astronomically-tuned climatic record from Lake Baikal, SE Siberia
AU: * Prokopenko, A A
EM: sasha@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, United States
AU: Hinnov, L A
EM: lhinnov1@jhu.edu
AF: Department of Earth and Planetary Sciences, John Hopkins University, Baltimore, MD 21218, United States
AU: Williams, D F
EM: dr.doug@sc.rr.com
AF: Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, United States
AU: Kuzmin, M I
EM: makhom@igc.irk.ru
AF: Institute of Geochemistry, Favorskogo Street 1a, Irkutsk, 664033, 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 . 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 a composite BDP-96 BioSi record over the entire Pleistocene. During the present interglacial, Lake Baikal biogenic silica (BioSi) proxy response is anti-phased with the early Holocene 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. In terms of orbital configuration, this time corresponds 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 and magnetic reversal tests with a high degree of confidence. Power spectral analysis 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° 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 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. Long-term changes in sedimentation rates in Lake Baikal at the hemipelagic drill site suggest a significant orbital forcing of sedimentation process (both biogenic and clastic) in this rift basin. The Middle Pleistocene Transition in the Lake Baikal record is associated with significant changes in average sedimentation rates, with a particularly high rate during glacial MIS 24 (880-900 ka) in contrast with rather low rates over MIS 23-19.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: 1600 GLOBAL CHANGE
DE: 1630 Impacts of global change (1225)
DE: 1637 Regional climate change
SC: Union [U]
MN: 2007 Fall Meeting