Deuterium record of Vostok ice core

Taking advantage of the fact that the Vostok deuterium (deltaD) record now covers almost two entire climatic cycles, we have applied the orbital tuning approach to derive an age-depth relation for the Vostok ice core, which is consistent with the SPECMAP marine time scale. A second age-depth relation for Vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from Southern Ocean core MD 88-770. Both methods lead to a close correspondence between Vostok and MD 88-770 time series. However, the coherence between the correlated deltaD and insolation is much lower than between the orbitally tuned deltaD and insolation. This reflects the lower accuracy of the correlation method with respect to direct orbital tuning. We compared the ice and marine records, set in a common temporal framework, in the time and frequency domains. Our results indicate that changes in the Antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands. Moreover, the average phase we estimated between the filtered deltaD and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes. The relatively large lag found between Vostok deltaD variations and obliquity-driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies. Finally, in contrast to the cross-spectral analysis method used in previous studies, the method we use here to estimate the phases can reveal errors in cross-correlations with orbitally tuned chronologies.

鉴于沃斯托克（Vostok）冰芯的氘（deuterium，δD）记录现已覆盖近乎完整的两个气候旋回，我们采用轨道调谐（orbital tuning）方法构建了该冰芯的年龄-深度关系，该结果与SPECMAP海洋时间标尺相一致。第二种沃斯托克冰芯年龄-深度关系则通过将冰同位素含量与南大洋岩芯MD 88-770的海表温度估算值进行关联得到。两种方法均使得沃斯托克冰芯与MD 88-770岩芯的时间序列呈现出高度吻合性。然而，经关联得到的δD与日射量（insolation）之间的相干性，远低于轨道调谐后的δD与日射量的相干水平，这反映出相较于直接轨道调谐，关联方法的精度更低。我们将置于统一时间框架下的冰芯与海洋记录，在时域与频域两个维度开展了对比分析。研究结果表明，在黄赤交角（obliquity）与岁差（precession）频段内，南极气温变化明显超前于全球冰量变化。此外，我们在岁差频段下估算得到的滤波后δD与日射量信号间的平均相位显示，南极高纬度表层温度变化，可能由北半球低纬度夏季时段或南半球低纬度冬季时段的日射量变化所驱动。沃斯托克冰芯δD变化与黄赤交角驱动的日射量变化之间存在的较大滞后性表明，当地辐射平衡并非该频段下表层温度变化的唯一驱动机制。最后，与此前研究中使用的交叉谱分析（cross-spectral analysis）方法不同，本文所采用的相位估算方法，可揭示轨道调谐年代序列中存在的互相关（cross-correlation）误差。