DF2021 chronology and Dome Fuji gas data (O2/N2, d15N, CH4) (0 - 207 kyr BP)

Precise ice-core chronologies are essential for identifying the timing and duration of polar climatic changes as well as their phasing with the changes in other parts of the globe. However, existing ice-core chronologies beyond the last 60 kyr show relatively large disagreements with each other and with U-Th chronologies of speleothems. Here, we constructed new ice and gas age scales for the Dome Fuji (DF) core (DF2021) over the last 207 kyr by combining a Bayesian dating model and firn densification model, constrained by various types of chronological and glaciological information including new O2/N2 age markers, precise synchronization to other high-quality chronologies (volcanic, cosmogenic, and CH4 signals), and high-resolution d15N of N2 (reflecting past firn thickness). The new chronology is tightly constrained by synchronization to other well-dated records for the last 60 kyr, whereas it is independent from other chronologies for the older period. For the last 60 kyr, the DF2021 chronology agrees with the layer-counted ice core chronologies (GICC05 and a part of WD2014) and U-Th chronologies of speleothems within ~200 years. For the period 60 -130 kyr BP, the timing of all Dansgaard-Oeschger warming events on DF2021 agree with those of corresponding events in the U-Th dated Chinese or European speleothems mostly within 1 kyr (well within 2sigma uncertainty of DF2021). The excellent agreement suggests high accuracy of our chronology, and supports the assumption of negligible phasing between the past local summer solstice insolation and O2/N2 fractionation at bubble close-off (the basis for constructing the O2/N2 age markers). Between 130 and 207 kyr BP (penultimate glacial period), there is a lower degree of similarity between the variations in atmospheric CH4 and speleothem calcite d18O than in the last glacial period, making the age comparison challenging. The comparison of DF2021 with 9 U-Th dates at 7 abrupt events shows the mean difference of -0.2 +- 0.8 kyr, which is within the DF2021 uncertainty (on the order of 1.5 kyr). The DF2021 chronology agrees with the AICC2012 chronology within 2 kyr except between ~103 and 128 kyr BP where AICC2012 is likely too young by up to ~4 kyr. By analyzing the lag between d18O of O2 (d18Oatm) on DF2021 and 65N summer solstice insolation, the relatively large error in AICC2012 is found to originate in three d18Oatm age markers assuming a constant lag, which are off by more than 3 kyr. The phasing between d18Oatm and orbital forcing identified in this study may be useful for future ice core dating, especially where other age constraints are weak or lacking.精准的冰芯年代学（ice-core chronologies）是识别极地气候变化的发生时间与持续时长，以及其与全球其他区域气候变化相位关系的核心依据。然而，现有针对距今6千年（kyr）以外的冰芯年代学结果，彼此之间以及与石笋的铀钍（U-Th）年代学结果均存在较大分歧。本研究结合贝叶斯定年模型（Bayesian dating model）与雪层压实模型（firn densification model），依托多种年代学与冰川学约束信息——包括全新的氧氮比（O2/N2）年龄标记、与其他高质量年代学记录（火山、宇宙成因信号与甲烷（CH4）信号）的精准同步，以及高分辨率的氮气氮15同位素比值（d15N of N2，反映过往雪层厚度）——构建了过去20.7万年（207 kyr）富士冰穹（Dome Fuji, DF）岩芯（DF2021）的全新冰龄与气体年龄标尺。全新年代学框架在过去6万年区间内，通过与其他定年精确的记录进行同步得到严格约束；而在更早的时段，则独立于其他年代学体系。在过去6万年中，DF2021年代学与层序计数型冰芯年代学（GICC05与WD2014的部分序列）以及石笋铀钍年代学结果的偏差均在约200年以内。在距今6万至13万年（BP, Before Present）的时段内，DF2021记录中所有丹斯果-奥什格尔（Dansgaard-Oeschger）升温事件的发生时间，与经铀钍定年的中国或欧洲石笋对应事件的时间基本吻合，偏差大多在1千年以内（远小于DF2021的2σ不确定性范围）。这种极佳的吻合性证明了本年代学框架的高精度，同时验证了一个关键假设：气泡封闭时，当地过去的夏至日日照与氧氮比分馏之间的相位偏差可忽略不计——这也是构建氧氮比年龄标记的核心基础。在距今13万至20.7万年的倒数冰期（penultimate glacial period），大气甲烷浓度变化与石笋方解石氧18同位素比值的相关性，相较于末次冰期有所降低，使得年龄对比颇具挑战。通过对比DF2021与7次突变事件对应的9个铀钍定年数据，我们得到平均偏差为-0.2±0.8千年，该值处于DF2021的不确定性范围（约1.5千年）以内。DF2021年代学与AICC2012年代学的偏差基本在2千年以内，仅在距今约10.3万至12.8万年的区间例外——该区间内AICC2012的年代结果可能偏年轻多达约4千年。通过分析DF2021记录中的大气氧18同位素比值（d18Oatm）与北纬65度夏至日日照量之间的滞后关系，我们发现AICC2012的较大误差源于三个采用固定滞后量的大气氧18年龄标记，这些标记的偏差超过了3千年。本研究揭示的大气氧18同位素比值与轨道强迫之间的相位关系，可为未来的冰芯定年工作提供参考，尤其是在其他年龄约束条件薄弱或缺失的场景中。