Terrestrial responses to millennial and sub-millennial climate variability in the Early Glacial and implications for the hydrological cycle

陆地对早冰期千禧年和亚千禧年气候变化的响应及其对水文循环的影响

• 批准号: NE/I017534/1
• 负责人: Polychronis Tzedakis
• 金额: $ 6.7万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2011
• 资助国家: 英国
• 起止时间: 2011 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FI017534%2F1
• 关键词: Terrestrial; responses; millennial; sub; climate

While much work has focused on glacial terminations, less is known about the transitions from warmer to cooler climate states. As such, the transition from the Last Interglacial Complex to the Early Pleniglacial, 67-85 thousand years ago (ka), represents an important case study for gaining insights into the interaction of orbital and short-term climate variability and ice sheet growth. This interval is characterized by a series of millennial-scale climate oscillations, while sea level fell by about 50m, reflecting the expansion of ice sheets in northern high latitudes. For ice sheets to expand a supply of warm, moist air to cold regions is required, so that ice accumulation exceeds ablation. Reconstructed Greenland temperatures show a series of warm events (interstadials) during this period, but corresponding changes in atmospheric methane concentration are subdued, pointing to reduced emissions and a weakening of the hydrological cycle. In parallel, new evidence from ice cores has revealed the presence of centennial oscillations in Greenland temperatures during this interval. These are accompanied by variations in atmospheric methane concentrations, underlining the large geographical extent of these climate changes. This project aims to deliver better constraints on changes in terrestrial environments and the hydrological cycle and on links between key parameters in the climate system during the interval 67-85 ka. This will be achieved by generating a high-resolution pollen record, linked with sedimentological and palaeoceanographic proxies within the same reference marine sequence from the S Portuguese margin. In recent years, the S. Portuguese margin has emerged as a critical area for tracing millennial-scale variability and linking marine and terrestrial records. A key aspect is the geographical setting of the area where the combined effects of the Tagus River and a narrow continental shelf lead to the rapid delivery of terrestrial material, including pollen, to the deep-sea environment. Joint pollen, sediment and palaeoceanographic proxy analysis within the same sequence allows a direct comparison between ocean and terrestrial changes, bypassing timescale and correlation uncertainties. More specifically, the project aims to establish: (1) the strength of the hydrological cycle at mid-to-low latitudes during interstadials: given that changes in vegetation in southern Europe are mainly controlled by variations in the continental hydrological balance, a pollen record for this interval will provide an independent index of changes in the strength of the hydrological cycle, which can be compared with that inferred from the atmospheric methane record. (2) the response of vegetation to sub-millennial events and impact on erosion: while work on the Portuguese margin has established the immediate response of vegetation to millennial-scale variability, sub-millennial variations have not been previously documented. A new ultra high-resolution record of changes in sediment composition in the reference marine core has now revealed the presence of sub-millennial events, coeval with variations in ice core records. By increasing the resolution of the pollen record during these events, the project will investigate whether the oscillations in sediment composition were accompanied by vegetation changes. This, in turn, will test the hypothesis that the rapid changes in sediment composition reflect variations in the terrigenous supply from the Tagus River, which are ultimately controlled by the interplay of the hydrological balance and extent of vegetation cover. The results will have implications for understanding moisture sources for ice sheet growth during transitions into full glacial conditions and the response of terrestrial environments to short-term climate variability.

虽然许多工作都集中在冰川终止，但对从温暖到凉爽的气候状态的转变知之甚少。因此，从末次间冰期复合体到6.7 - 8.5万年前（ka）的早期Pleniglacial的过渡是深入了解轨道和短期气候变化与冰盖生长相互作用的重要案例研究。这段时间的特点是一系列千年尺度的气候振荡，而海平面下降了约50米，反映了北方高纬度地区冰盖的扩张。为了使冰盖膨胀，需要向寒冷地区提供温暖潮湿的空气，因此冰的积累超过了消融。重建的格陵兰温度显示了一系列温暖的事件（interstadials）在此期间，但相应的大气甲烷浓度的变化是温和的，指出减少排放和水文循环减弱。与此同时，来自冰芯的新证据显示，在这段时间内，格陵兰气温存在百年振荡。这些变化伴随着大气甲烷浓度的变化，突出表明这些气候变化的地理范围很广。该项目旨在更好地限制陆地环境和水文循环的变化，以及67-85 ka期间气候系统关键参数之间的联系。这将通过生成一个高分辨率的花粉记录，与沉积学和古海洋学代理内相同的参考海洋序列从葡萄牙南部边缘。近年来，S.葡萄牙边缘已成为追踪千年尺度变化和连接海洋和陆地记录的一个关键领域。一个关键方面是该地区的地理环境，塔霍河和狭窄的大陆架的综合影响导致包括花粉在内的陆地物质迅速进入深海环境。联合花粉，沉积物和古海洋学代用品分析在同一个序列允许直接比较海洋和陆地的变化，绕过时间尺度和相关性的不确定性。更具体地说，该项目旨在确定：（1）在海际期间中低纬度水文循环的强度：考虑到南欧植被的变化主要受大陆水文平衡变化的控制，这段时间的花粉记录将提供水文循环强度变化的独立指数，这可以与从大气甲烷记录中推断的结果进行比较。(2)植被对千年以下事件的反应和对侵蚀的影响：虽然在葡萄牙边缘的工作已经确定了植被对千年尺度变化的直接反应，但千年以下的变化以前没有记录。一个新的超高分辨率记录的参考海洋岩芯中沉积物成分的变化，现在已经揭示了亚千年事件的存在，与冰芯记录的变化同期。通过提高这些事件期间花粉记录的分辨率，该项目将调查沉积物成分的波动是否伴随着植被的变化。反过来，这将测试的假设，即沉积物成分的快速变化反映了从塔霍河，这是最终控制的水文平衡和植被覆盖范围的相互作用的陆源供应的变化。这些结果将对了解冰盖生长在过渡到完整的冰川条件和陆地环境对短期气候变率的反应的水分来源产生影响。