NOAA/WDS Paleoclimatology - Lake Baikal Composite BDP-96 Pleistocene Biogenic Silica Data

A new composite BDP-96 biogenic silica record over the entire Pleistocene was generated by splicing BDP-96-1 and BDP-96-2 drill cores from Lake Baikal, crosschecked against a similar record from a nearby BDP-98 drill core. A new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of September perihelia. This target is derived from analysis of regional climate proxy responses during the Holocene, the last interglacial and around paleomagnetic reversals. By resolving virtually every precessional cycle during the Pleistocene, the new age model represents a major improvement compared with previously reported Lake Baikal timescales. The astronomically tuned ages of the Pleistocene paleomagnetic reversals are consistent with published dates.The minimal tuning approach we used (precession only) has also aligned high signal power in a narrow obliquity band, confirming the strong presence of orbital forcing. There are also strong ca 100-ka scale cycles, but these are not aligned with the orbital eccentricity. Despite the location of Lake Baikal in a continental interior that is highly sensitive to insolation forcing, the tuned biogenic silica record reveals a consistent phase difference of -32° (ca 4 ka) relative to insolation in the obliquity band. An inherent lag embedded in a continental proxy record, not driven by global ice volume, is an intriguing finding. Another new observation is that long-term changes in sedimentation rates in Lake Baikal appear to be related to the amplitude of orbital forcing; both amplitudes and sedimentation rates undergo significant changes during MIS 24-MIS 19 interval corresponding to the Middle Pleistocene Transition. With potential for linking continental and marine climato-stratigraphies, the new Baikal record serves a new benchmark correlation target in continental Eurasia, as an alternative to June 65°N insolation and ODP-correlated timescales.

本研究通过拼接贝加尔湖BDP-96-1与BDP-96-2钻孔岩芯，构建了覆盖整个更新世（Pleistocene）的全新复合BDP-96生物硅（biogenic silica）记录，并利用附近BDP-98钻孔的相似记录对该记录进行交叉验证。本研究基于生物硅峰值与九月近日点（September perihelia）时刻的对应关系，提出了全新的天文调谐年龄模型（astronomically tuned age model）。该年龄模型的构建依托于全新世（Holocene）、末次间冰期（last interglacial）以及古地磁倒转（paleomagnetic reversal）事件前后的区域气候代用指标（climate proxy）响应分析。通过近乎完整解析更新世时期的每一个岁差周期（precessional cycle），该全新年龄模型相较已发表的贝加尔湖年代标尺实现了显著改进。更新世古地磁倒转事件的天文调谐年龄与已发表的测年结果一致。我们采用的仅基于岁差的最小调谐方法（minimal tuning approach），同时实现了窄幅黄赤交角频段（obliquity band）内高信号功率的对齐，证实了轨道强迫（orbital forcing）的显著作用。记录中同时存在显著的约10万年尺度旋回，但这些旋回并未与轨道偏心率（orbital eccentricity）周期对齐。尽管贝加尔湖位于对日照辐射（insolation）强迫极为敏感的大陆内部区域，但经天文调谐的生物硅记录仍显示，在黄赤交角频段内，其与日照辐射存在稳定的-32°（约4千年）相位差。该大陆代用记录中存在不受全球冰量（global ice volume）驱动的固有滞后效应，这是一项颇具研究价值的发现。另一项全新观测结果显示，贝加尔湖沉积速率（sedimentation rate）的长期变化似乎与轨道强迫振幅相关：在对应中更新世转型（Middle Pleistocene Transition）的MIS 24至MIS 19区间（MIS即海洋同位素阶段Marine Isotope Stage）内，轨道强迫振幅与沉积速率均发生了显著变化。该全新贝加尔湖记录具备连接大陆与海洋气候地层（climato-stratigraphy）的潜力，可作为欧亚大陆区域的全新基准对比目标，用以替代北纬65°六月日照辐射以及与ODP（Ocean Drilling Program，海洋钻探计划）关联的年代标尺。