Chronological framework for Lake Baikal and Lake Elgygytgyn drill cores and orbital forcing of continental climate in the Northern Hemisphere during the past 3.6 Ma
Final Report Abstract
A detailed regional paleoclimate record from continental interior Asia was constructed for the late Pliocene - early Pleistocene interval 3.7‐1.8 Ma by analyzing biogenic silica content in two overlapping sediment cores from the archive of the Lake Baikal Drilling Project (BDP) and by accurately splicing these two new records to produce a continuous new composite record 102 meters long. Supplementing the previously available 70‐meter Baikal paleoclimate record of the past 1.8 Ma, the new record now extends back in time beyond the Gauss/Gilbert geomagnetic polarity reversal and fully covers the time interval represented in the Lake Elgygygtgyn drill core record. This new study resolved the issues of an incomplete recovery of the Pliocene to early Pleistocene sediment in individual Lake Baikal drill cores; with over 5,000 individual measurements at 1‐2 cm increments the new record is now continuous with an outstanding resolution of 200 to 500 years. The new spliced BDP record also made possible to accurately merge several independently obtained data sets of paleomagnetic measurements into a single composite stratigraphic record, thereby improving both the resolution and accuracy of assigning geomagnetic event/reversal boundaries of the Pliocene. Estimated sedimentation rates in both studied Baikal drill core records are remarkably stable in the mid‐Pliocene, they increase somewhat and become more variable on glacial‐interglacial scale after the initiation of the Northern Hemisphere glaciations at ca. 2.8 Ma. The originally stated goal of developing a continent‐based orbital time scale for the Pliocene, independent of peak‐to‐peak correlation with marine oxygen isotope template, was successfully met in the project. New results show that biogenic silica proxy for higher diatom production in Lake Baikal during warmer (interglacial) periods faithfully recorded the orbital cycles of obliquity and precession not only in the Pleistocene but in the Pliocene as well, making the development of an orbitally‐tuned timescale a reasonably straightforward task. Similar to the record of the mid‐late Pleistocene, the newly studied Pliocene to early Pleistocene portion of the Lake Baikal record allows clearly distinguishing the continental equivalents of each of the marine oxygen isotope stages; in addition, it offers implications for modifying the orbital alignment of the marine global stratigraphic template around Olduvai and Reunion subchrons and around the prominent M2 glacial at the base of the Mammoth subchron. The apparent phasing of the Lake Baikal biogenic silica proxy response in the Pliocene is similar to that of the mid‐late Pleistocene: peak proxy response occurs at a time of high obliquity and aligns with the Northern Hemisphere September perihelion, lagged by roughly 5 kyr relative to June insolation maxima of orbital precession cycles. A significant novel finding is that of a prominent variability in Lake Baikal biogenic silica signal on sub‐orbital timescale during the Pliocene portion of the record, including the ‘PRISM time slab’ period of a sustained warm global climate ca. 3.26‐3.03 Ma, which is often regarded a possible analog of the warmer global climate of the future. Two Baikal archive drill cores studied in the project are from different sites, yet they revealed a strongly coherent pattern of sub‐orbital variations in the proxy response. Given the absence of substantial cryosphere components in the Baikal region during the Pliocene, the observed variability in the new biogenic silica record points to a substantial variability of regional hydroclimate in a warmer greenhouse world of the Pliocene.
Publications
- (2016). Interglacials of the last 800,000 years, Rev. Geophysics, 54, 162-219
A. Berger, ... A.A. Prokopenko, ... N. Vazquez Riveiros
(See online at https://doi.org/10.1002/2015RG000482)
