Assessing changes in temperature, ice volume and ice sheet dynamics across the Middle Pleistocene Transition

评估中更新世过渡期间温度、冰量和冰盖动态的变化

• 批准号: NE/H009930/1
• 负责人: David Hodell
• 金额: $ 32.01万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH009930%2F1
• 关键词: Assessing; changes; temperature; ice; volume

Earth's climate for the last 2.5 million years has been characterized by the waxing and waning of large continental ice sheets in the Northern Hemisphere. Prior to about a million years ago, the glacial and interglacial cycles marched to the beat of the tilt of Earth's rotational axis (i.e., obliquity), which varied with a cycle of 41,000 years. About a million years ago, the length of glacial-interglacial cycles became longer, averaging about 100,000 years. This change, known as the Middle Pleistocene Transition (MPT), represents an important unsolved problem in paleoclimatology. Why did the frequency of glacial-interglacial cycles suddenly shift in the middle Pleistocene from 41- to 100-kyrs? The size of the ice sheets became larger across the MPT, thereby allowing individual domes of the North American ice sheet to coalesce to form a massive ice sheet. The great volume and thickness of this ice made it less sensitive to changes in boreal summer insolation, thereby lengthening the glacial cycle as the ice sheets survived through insolation maxima and deglaciation began skipping precessional (~21 kyr) and/or obliquity (~41 kyr) cycles. One of the hindrances to furthering our understanding of the MPT is the lack of a quantitative estimate of the change in ice volume that occurred across the MPT. This shortcoming results largely because the benthic oxygen isotope record reflects both temperature and ice volume changes. Using Mg/Ca of infaunal benthic species, we aim to deconvolve the benthic d18O signal and provide a quantitative estimate of changes in the d18O of seawater that is related to global ice volume. As the North American Ice Sheet increased in volume and thickness following the MPT, the dynamical behavior of the ice sheet may have changed. During the last glacial period, Laurentide Ice Sheet dynamics was dramatically expressed by so-called Heinrich layers, which consist of sediment rich in ice rafted debris (IRD) deposited in the North Atlantic stretching from Labrador to Portugal. Heinrich layers represent massive discharges of icebergs from surging of the Laurentide Ice Sheet in the region of Hudson Strait in northern Canada. Although Heinrich events have been studied for the last glacial cycle, little is known about their occurrence in older glaciations of the Pleistocene. At Site U1308 in the central North Atlantic, we found that the first Heinrich layer occurred at 650 ka coinciding with the onset of the 100-kyr cycle. It is not known, however, whether this represented the initiation of surging of the Laurentide Ice Sheet via the Hudson Strait Ice Stream or was it the first time icebergs produced by this process survived the transport to Site U1308. The former interpretation implies a fundamental change in Laurentide ice sheet dynamics before and after the MPT, whereas the latter interpretation indicates a change in atmospheric and/oror surface water conditions that changed the location of iceberg melting. Were Heinrich events limited to the 100-kyr world or did they also occur prior to the MPT? We will address this question by examining Site U1304 located to the north and west of Site U1308. Site U1304 should record Heinrich layers if they were produced prior to the MPT because the IRD belt was probably displaced to higher latitude when ice sheets were smaller and North Atlantic SST was warmer than late Pleistocene glaciations.

过去 250 万年地球气候的特点是北半球大型大陆冰盖的盛衰。大约一百万年前，冰期和间冰期周期随着地球自转轴倾斜（即倾角）的节拍进行，以 41,000 年为一个周期变化。大约一百万年前，冰期-间冰期循环的长度变得更长，平均约为10万年。这种变化被称为中更新世过渡（MPT），代表了古气候学中一个重要的未解决问题。为什么冰期-间冰期循环的频率在更新世中期突然从 41 公里转变为 100 公里？ MPT 上冰盖的尺寸变得更大，从而使北美冰盖的各个圆顶合并形成一个巨大的冰盖。这些冰的巨大体积和厚度使其对北方夏季日照的变化不太敏感，从而延长了冰川周期，因为冰盖在日照最大值中幸存下来，并且冰消作用开始跳过进动（~21 kyr）和/或倾角（~41 kyr） ）循环。进一步了解 MPT 的障碍之一是缺乏对 MPT 上发生的冰量变化的定量估计。这一缺点很大程度上是因为底栖氧同位素记录反映了温度和冰体积的变化。使用动物底栖物种的 Mg/Ca，我们的目标是对底栖 d18O 信号进行去卷积，并提供与全球冰量相关的海水 d18O 变化的定量估计。随着 MPT 后北美冰盖体积和厚度的增加，冰盖的动力学行为可能发生了变化。在末次冰期期间，劳伦泰冰盖动态通过所谓的海因里希层显着地表现出来，该层由沉积在从拉布拉多到葡萄牙的北大西洋中富含冰筏碎片（IRD）的沉积物组成。海因里希层代表加拿大北部哈德逊海峡地区劳伦泰德冰盖汹涌澎湃的冰山大量排放。尽管人们对最后一个冰川周期的海因里希事件进行了研究，但人们对它们在更新世较古老的冰川期中的发生情况知之甚少。在北大西洋中部的 U1308 站点，我们发现第一个海因里希层发生在 650 ka，与 100 kyr 周期的开始时间一致。然而，目前尚不清楚这是否代表劳伦太德冰盖通过哈德逊海峡冰流涌动的开始，或者是否是该过程产生的冰山首次在运输到 U1308 站点的过程中幸存下来。前一种解释意味着在 MPT 之前和之后劳伦太德冰盖动力学发生了根本性变化，而后一种解释表明大气和/或地表水条件的变化改变了冰山融化的位置。海因里希事件仅限于 100 kyr 世界还是也发生在 MPT 之前？我们将通过检查位于站点 U1308 北部和西部的站点 U1304 来解决这个问题。如果海因里希层是在 MPT 之前产生的，则站点 U1304 应该记录海因里希层，因为当冰盖较小且北大西洋海表温度比晚更新世冰川更温暖时，IRD 带可能会移动到更高的纬度。

项目成果

Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition.

中更新世气候转变期间海洋温度和冰量的演变。

• DOI: http://dx.10.1126/science.1221294
• 发表时间: 2012
• 期刊: Science (New York, N.Y.)
• 作者: Elderfield H

Local and regional trends in Plio-Pleistocene d 18 O records from benthic foraminifera

上里欧-更新世 d 18 O 底栖有孔虫记录的局部和区域趋势

• DOI: http://dx.10.1002/2014gc005297
• 发表时间: 2014
• 期刊: Geochemistry, Geophysics, Geosystems
• 作者: Bell D

Oceanic heat pulses fueling moisture transport towards continental Europe across the mid-Pleistocene transition

海洋热脉冲推动了更新世中期过渡时期水分向欧洲大陆的输送

• DOI: 10.1016/j.quascirev.2017.11.009
• 发表时间: 2024-09-14
• 期刊: Quaternary Science Reviews
• 影响因子: 4
• 作者: A. Bahr;S. Kaboth;D. Hodell;C. Zeeden;J. Fiebig;O. Friedrich
• 通讯作者: O. Friedrich

ODP Site 1063 (Bermuda Rise) revisited: Oxygen isotopes, excursions and paleointensity in the Brunhes Chron

• DOI: 10.1029/2011gc003897
• 发表时间: 2012-02-01
• 期刊: Geochemistry
• 影响因子: 3.7
• 作者: J. Channell;D. Hodell;J. Curtis
• 通讯作者: J. Curtis

Earth and Life Processes Discovered from Subseafloor Environments - A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP)

从海底环境中发现的地球和生命过程 - 综合海洋钻探计划 (IODP) 十年的科学成就

• DOI: http://dx.10.1016/b978-0-444-62617-2.00014-1
• 发表时间: 2014
• 作者: Channell J