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Mechanisms of glacial/interglacial changes during the late Oligocene

渐新世晚期冰川/间冰期变化机制

基本信息

批准号：
319899677
负责人：
Professor Dr. Oliver Friedrich
金额：
--
依托单位：
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR)
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/319899677?language=en
关键词：
Mechanisms glacial interglacial changes during

项目摘要

The principal objective of this project is to obtain a mechanistic understanding of the processes that led to the differences in the morphology of glacial/interglacial (G/I) cycles during the Late Oligocene of IODP Site U1406 (off Newfoundland, IODP Expedition 342). An existing sub-orbital resolution benthic foraminiferal oxygen-isotope dataset from this site for the time interval ~25.6 to 23.9 Ma reveals two morphologies of G/I cycles. The prominent morphology is U-shaped ("control interval") and well-known from glacials before the Middle-Pleistocene Transition (MPT). The other morphology is characterized by a slow increase of benthic foraminiferal oxygen isotope values followed by a rapid decrease (“target interval”). This pattern is fundamentally different from the U-like shape of other Oligocene glacial cycles, but conspicuously reminiscent of the sawtooth nature of Late Pleistocene glacial/interglacial cycles. In light of the above, benthic foraminiferal δ18O and Mg/Ca records for the „target“ and "Control" intervals have been generated and used to constrain the magnitudes and durations of ice-volume and sea-level fluctuations for the observed G/IG cycles. For both the "target" and the "Control" intervals, BWT are surprisingly constant, with values that range generally between 2 and 4 °C. Even more surprisingly, both intervals lack a clear G/IG cycle in BWT, which suggests that the contribution of BWT fluctuations to the observed G/IG cycles in the benthic delta18O data is small. This becomes even more evident when the δ18O of seawater is calculated and converted to sea level. The observed difference in sea-level estimates between the two study intervals argues for a substantial ice-volume loss on Antarctica. If compared to obliquity, sea-level/ice-volume change during the "control interval" seems to respond nearly linearly to obliquity. Sea-level/ice-volume change during the “target interval”, in contrast, occurred during a time of weaker obliquity. This suggests a potential non-linear threshold response of Antarctic ice volume to the underlying obliquity forcing during the study interval. Whether such a threshold truly existed and what the exact climatic conditions for this potential threshold behavior were, however, cannot be answered with the records at hand so far. Therefore, it is proposed to expand the new Site U1406 high-resolution records to cover the time interval 26–24.5 Ma (i.e. the time interval characterized by significant "steps" in the available delta18O record. Following the approach successfully employed during the first project phase, this will be achieved via the investigation of benthic foraminiferal Mg/Ca and stable isotopes.

该项目的主要目标是获得一个机械的理解的过程，导致冰川/间冰期（G/I）周期的形态差异在晚渐新世的IODP网站U1406（纽芬兰，IODP远征342）。从该站点获得的时间间隔为~25.6至23.9 Ma的现有亚轨道分辨率底栖有孔虫氧同位素数据集揭示了G/I循环的两种形态。突出的形态是U形（“控制间隔”），并在中更新世过渡（MPT）之前的冰川中众所周知。另一种形态的特点是底栖有孔虫氧同位素值缓慢增加，然后迅速下降（“目标间隔”）。这一模式与其他渐新世冰期旋回的U形有着根本的不同，但却明显地让人联想到晚更新世冰期/间冰期旋回的周期性。鉴于上述情况，已生成了“目标”和“对照”间隔的底栖有孔虫δ 18 O和Mg/Ca记录，并将其用于约束观测到的G/IG周期的冰量和海平面波动的幅度和持续时间。对于“目标”和“对照”间隔，BWT令人惊讶地恒定，其值通常在2 ° C和4 °C之间。更令人惊讶的是，这两个间隔缺乏一个明确的G/IG周期在BWT，这表明，BWT波动的贡献所观察到的G/IG周期在底栖三角洲18 O数据是小的。当计算海水的δ 18 O并将其转换为海平面时，这一点变得更加明显。在两个研究间隔期间观察到的海平面估计值的差异证明南极洲的冰量损失很大。如果与冰度相比，海平面/冰量的变化在“控制间隔”似乎几乎线性响应于冰度。海平面/冰量的变化，在“目标间隔”，相反，发生在一个时间较弱的粘性。这表明在研究期间南极冰量对潜在的倾角强迫存在潜在的非线性阈值响应。然而，这样一个门槛是否真的存在，以及这种潜在门槛行为的确切气候条件是什么，目前还不能用手头的记录来回答。因此，建议扩大新的站点U1406高分辨率记录，以涵盖26-24.5 Ma的时间间隔（即可用的δ 18 O记录中以显著“台阶”为特征的时间间隔）。按照项目第一阶段成功采用的办法，将通过调查底栖有孔虫镁/钙和稳定同位素来实现这一目标。