A reference time scale for the study of Pleistocene orbital and millennial-scale climate variability: IODP Site U1385 ("Shackleton site")

我们在了解地球气候系统方面的未来进展将取决于我们能否将来自海洋、冰芯和陆地序列的高分辨率沉积档案联系起来，并在新的地球系统建模方法的背景下解释这些记录。世界上很少有地方可以做到足够详细和明确的海洋-冰-陆地联系。伊比利亚西部边缘就是这样一个位置，为恢复海洋-冰-陆地对比所需的关键序列提供了难得的机会。在第339次考察中，我们在U1385遗址(“沙克尔顿遗址”)钻了5个孔，最大深度为166.5 Mcd，恢复了全新世至1.42 Ma(海洋同位素46期)的连续半洋沉积记录，平均沉积速率为~10 cm Kyr-1。已经获得的高分辨率岩心测井、颜色和XRF数据表明，该站点在轨道和亚轨道时间尺度上研究更新世气候变化历史方面具有巨大潜力。然而，在充分利用这些记录之前，必须为U1385遗址制定一份有充分依据的年表。在这里，我们建议制定这样一个详细的参考时间尺度，以供未来对U1385遗址的所有研究参考。一个稳健的时间尺度尤其重要，因为沙克尔顿遗址很可能成为全球对比的“海洋参考区”，其他气候记录将不可避免地与之进行比较。一旦建立了年龄模型，就可以将其转移到我们已经收集的各种时间序列(例如，磁化率、密度、NGR、扫描XRF和颜色)，以及本项目将产生的时间序列(浮游和底栖d18O和d13C，底栖镁钙比)和我们的项目合作伙伴(烷烃和有孔虫海洋表面温度估计)。时间序列分析将被用来解决有关更新世轨道和亚轨道气候变异性在不断变化的轨道和冰川边界条件下的共同演化的几个基本问题：轨道：在米兰科维奇频率上替代气候变量的相位是什么，它们告诉我们关于气候系统的不同组成部分对太阳辐射强迫的反应是什么？观察到的相位与Imbrie等人提出的系统模型相比如何。(1992)详细描述了当地对日照强迫的响应的地理进程？在更新世，当平均气候状态演变为普遍较冷的条件和更大的冰盖，气候变率的光谱特征从主要的41年转变为100年时，这种阶段性是否发生了变化？亚轨道：在过去1.4 Ma的冰期中，千年尺度变率的频率和步调是如何变化的？千禧年变化的幅度和/或频率是否与冰量阈值有关？地球轨道几何形状是否影响亚轨道气候变化的性质(幅度和/或频率)(例如，通过频率调制)？在中更新世过渡时期，千禧年尺度的气候变异性是如何变化的？千禧年尺度的气候振荡是引发冰川终止的原因之一，还是主要由轨道驱动？该项目的成果将使在U1385站点工作的IODP 339考察队的许多科学家受益，为这一重要的海洋参考区段建立一个年代地层学基础。

Future advances in our understanding of the Earth's climate system will rely on our ability to link high-resolution sedimentary archives from the oceans, ice-cores and terrestrial sequences, and to interpret these records in the context of novel Earth system modeling approaches. Few places exist in the world where sufficiently detailed and unambiguous marine-ice-terrestrial linkages are possible. The western Iberian Margin represents such a location, and provides a rare opportunity for recovering key sequences needed to for marine-ice-terrestrial correlation. During Expedition 339, we drilled five holes at Site U1385 ("Shackleton site") to a maximum depth of 166.5 mcd, and recovered a continuous record of hemipelagic sedimentation from the Holocene to 1.42 Ma (Marine Isotope Stage 46) with average sedimentation rates of ~10 cm kyr-1. The high-resolution core logging, colour, and XRF data already obtained demonstrate the great potential of this site for studying the history of Pleistocene climate change on orbital and suborbital time scales. Before these records can be fully exploited, however, a well-founded chronology must be developed for Site U1385. Here we propose to develop such a detailed reference time scale to which all future studies of Site U1385 will refer. A robust time scale is particularly important as the Shackleton site is likely to become a "marine reference section" for global correlation and against which other climate records will inevitably be compared.. Once the age model has been established, it can be transferred to the various time series we have already collected (e.g., magnetic susceptibility, density, NGR, scanning XRF, and colour) and those that will be produced by this project (planktonic and benthonic d18O and d13C, benthic Mg/Ca) and our project partners (alkenone and foraminiferal sea surface temperature estimates). Time series analysis will be used to address several fundamental questions regarding the coevolution of Pleistocene orbital and suborbital climate variability under changing orbital and glacial boundary conditions:Orbital: What are the phasings of proxy climate variables at Milankovitch frequencies and what do they tell us about the response of different components of the climate system to insolation forcing? How do the observed phasings compare with the system model proposed by Imbrie et al. (1992) detailing the geographic progression of local responses to insolation forcing? Has the phasing changed through the Pleistocene when the average climate state evolved toward generally colder conditions with larger ice sheets, and the spectral character of climate variability shifted from dominantly 41 to 100 kyrs?Suborbital: How does the frequency and pacing of millennial-scale variability vary among glacial periods of the last 1.4 Ma? Is the amplitude and/or frequency of millennial variations related to an ice volume threshold? Does Earth's orbital geometry influence the nature (magnitude and/or frequency) of suborbital climate variability (e.g., through frequency modulation)? How did millennial-scale climate variability change across the Middle Pleistocene transition? Do millennial-scale climatic oscillations play a role in initiating glacial terminations or are they principally orbitally driven?The results of this project will benefit the many scientists of IODP Expedition 339 working on Site U1385 by establishing a chronostratigraphic foundation for this important marine reference section.