IODP Exp 361 SAFARI Moratorium: Glacial terminations of the Plio-Pleistocene

最近500万年左右见证了全球显著的变冷和约100 kyr的冰期/间冰期旋回的发展。中更新世过渡期（MPT; ~1250- 700 ka）标志着从以重力强迫为主的冰川旋回（“40 kyr世界”）向晚更新世的更大振幅旋回的转变。所谓的“100 kyr问题”源于这样一个事实，即轨道强迫在~ 100 kyr（偏心率）太弱，无法解释观测到的冰川周期性。此外，整个MPT的日射强迫没有明显的变化，这可以解释从40 kyr到100 kyr的周期性变化。最近的研究表明，次轨道气候振荡对晚更新世冰川终止的时间和幅度产生了影响。在这里，我们打算测试过去500万年来与冰川终止有关的亚轨道尺度事件的存在和幅度。具体来说，我们将重点关注Agulhas泄漏的作用（从印度洋进入大西洋的温暖和咸沃茨）在冰消过渡期间传播大西洋盆地内间冰期模式环流的恢复。我们将采用综合方法，使用多种测量技术和核心站点。我们的方法是在取样之前根据船上测量和XRF岩心扫描结果确定冰川终止。然后，我们将在选定的终端上进行高分辨率测量（例如，XRF扫描，有孔虫稳定同位素和浮游有孔虫动物群计数），以评估千年尺度扰动的幅度及其时间，相对于所讨论的特定终端（由底栖有孔虫d18 O确定）。我们还将调查每个冰消期序列（即前冰期和随后的间冰期）的条件，以评估千年尺度扰动幅度与终止本身之间的潜在联系。将把（有孔虫动物区系的）表面温度重建结果与X射线荧光光谱法扫描的Fe/Ti/Al/Ca替代河流径流数据进行比较，以评估与海洋环流突变相关的锋面运动的复合效应。底栖有孔虫d13 C将被用来评估与我们重建的表面变化相关的海洋环流的相应变化。要调查的冰川终止将包括T2，5和7以及一系列早期过渡。在航行期间，随着材料的收集和初步筛选/年龄模型的开发，将确定具体的终止。

The last 5Myr or so witnessed significant global cooling and the development of ~100kyr glacial/interglacial cyclicity. The Mid-Pleistocene transition (MPT; ~1250-700ka) marks a shift from glacial cycles dominated by obliquity forcing (the '40kyr world') to the much larger amplitude cycles that characterise the Late Pleistocene. The so-called '100kyr problem' stems from the fact that orbital forcing at ~100kyr (eccentricity) is too weak to explain the observed glacial cyclicity. Furthermore there was no apparent change in insolation forcing across the MPT that could explain the change from 40kyr to ~100kyr periodicity. Recent studies have implicated the influence of sub-orbital climate oscillations in the timing and amplitude of glacial terminations during the Late Pleistocene. Here we propose to test for the presence and amplitude of sub-orbital scale events associated with glacial terminations over the past 5 Myr.Specifically, we will focus on the role of the Agulhas Leakage (warm and salty waters entering the Atlantic Ocean from the Indian Ocean) in propagating the recovery of interglacial mode circulation within the Atlantic basin during deglacial transitions.We will employ an integrated approach, using multiple measurement techniques and core sites. Our approach will be to identify glacial terminations based on ship-board measurements and the results of XRF core scanning prior to the sampling party. We will then perform high resolution measurements (e.g. XRF scans, foraminiferal stable isotopes and planktonic foraminiferal faunal counts) across a selection of terminations to assess the magnitude of millennial-scale perturbations and their timing, relative to the specific termination in question (as determined by benthic foraminiferal d18O). We will also investigate conditions bracketing each deglacial sequence (i.e. the preceding glacial and subsequent interglacial intervals) in order to assess potential linkages between the magnitudes of millennial-scale perturbations and the termination itself. Surface temperature reconstructions (from foraminiferal fauna) would be compared with XRF scans of Fe/Ti/Al/Ca to proxy riverine runoff, in order to assess the compound effects of frontal movements associated with abrupt changes in ocean circulation. Benthic foraminiferal d13C will be employed to assess corresponding changes in ocean circulation associated with the surface changes we reconstruct.Glacial terminations to be investigated will include T2, 5 and 7 and a selection of earlier transitions. Specific terminations will be identified during the cruise as material is collected and initial screening / age model development proceeds.