What caused the Mid Pleistocene Transition? Insights from a new high resolution CO2 record

是什么导致了中更新世过渡？

• 批准号: NE/P011381/1
• 负责人: Gavin Foster
• 金额: $ 63.2万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FP011381%2F1
• 关键词: What; caused; Mid; Pleistocene; Transition

The geological past contains many examples of Earth's climate being different to today and these are excellent test beds for our understanding of the climate system and ultimately our predictions of our future climate. Over the last 600 thousand years (kyr) or so, the Earth's climate has regularly oscillated, roughly every 100 kyr, between warm "interglacial" periods with climates similar to today, and frigid "glacial" periods when several kilometres of ice blanketed North America and northern Europe (at times extending into Siberia). Bubbles of ancient air trapped in ice cores from Antarctica reveal that these cyclical changes in climate were partly driven by changes in the atmospheric concentration of the greenhouse gas carbon dioxide (CO2) - CO2 was low during glacial periods and high during intervening interglacial periods. During each ice age cycle, cooling towards peak glacial climates tended to be rather slow (taking around 90 kyr) whereas the warming that terminates each glacial period tended to be very quick (~10 kyr in length). However, before about 1.2 million years ago Earth's climate was warmer on average, there was less ice on the continents and climate cycles were more regular, symmetric, and shorter - they followed a 41 kyr orbital beat at that time. Gradually between 1.2 and 0.6 million years ago, the character of glacial-interglacial cycles changed, shifting from these smaller 41-kyr cycles to the more recent larger 100-kyr cycles. Climate scientists have studied this important interval, known as the Mid Pleistocene Transition (MPT), for decades to learn about the inner workings of the climate system, but as yet the underlying cause remains debated. Despite their contrasting character, these two types of climate cycle were both paced by subtle variations in the amount and the spatial and seasonal distribution of sunlight reaching the Earth's surface as a result of regular changes in how the Earth orbits the sun (known as orbital cycles). What is puzzling is that the change in the nature of the climate cycles occurred in the absence of any notable change in these orbital cycles. It therefore represents a fundamental change in the way the climate system operates and in particular how certain feedbacks behave when the climate system is subjected to forcing. In order to test which, if any, of the available models adequately explains this transition we need reconstructions of both the size of the continental ice sheets and knowledge of the concentration of atmospheric CO2. While the evolution of ice volume through time is known relatively well, the direct ice core record of atmospheric CO2 only covers the last 800 thousand years and it is unlikely that it can be extended further back in the near future (if at all). We therefore have to use other, more indirect methods to reconstruct the CO2 content of the ancient atmosphere. One approach with a proven track record uses the boron (B) isotopic composition of calcareous microfossils called foraminifera, which steadily accumulate over time in deep-sea sediments. There are two naturally occurring isotopes of boron and the ratio of these two isotopes, 11B to 10B, in the shells of foraminifera reflects the acidity of the ocean surface when they lived, and from this it is possible to estimate atmospheric CO2 at that time. The principal aim of this proposal is to use this method to produce a record of CO2 for the last 1.3 million years that overlaps with the ice core CO2 record but then extends this back to cover the Mid Pleistocene Transition. Putting our current understanding of the MPT to the test in this way promises new insights into the coupling of climate change and the global carbon cycle, thereby also ultimately shedding light on how climate and polar ice sheets will respond to fossil fuel burning.

地质上的过去包含了许多地球气候与今天不同的例子，这些都是我们理解气候系统并最终预测未来气候的极好试验台。在过去60万年左右的时间里，地球的气候在温暖的“间冰期”（类似于今天的气候）和寒冷的“冰期”(有数公里的冰层覆盖北美和北欧（有时延伸到西伯利亚）之间有规律地振荡，大约每100千万年一次。被困在南极冰芯中的古代空气气泡表明，这些气候的周期性变化部分是由大气中温室气体二氧化碳（CO2）浓度的变化驱动的——在冰期CO2浓度低，在间冰期期间CO2浓度高。在每一个冰期周期中，向冰期气候峰值的冷却过程往往相当缓慢（大约需要90千基尔），而结束每一个冰期的变暖过程往往非常快（长度约为10千基尔）。然而，在大约120万年前地球的气候平均变暖之前，大陆上的冰更少，气候周期更规则、对称、更短——当时它们遵循41凯尔的轨道周期。在120万至60万年前，冰期-间冰期旋回的特征逐渐发生变化，从这些较小的41 kyr旋回转变为最近的较大的100 kyr旋回。几十年来，气候科学家一直在研究这个重要的间隔，即中更新世过渡期（MPT），以了解气候系统的内部运作，但其根本原因仍存在争议。尽管这两种气候周期具有截然不同的特点，但由于地球绕太阳公转的规律变化（称为轨道周期），到达地球表面的阳光的数量、空间和季节分布都发生了微妙的变化。令人费解的是，在这些轨道周期没有任何显著变化的情况下，气候周期的性质发生了变化。因此，它代表了气候系统运行方式的根本变化，特别是当气候系统受到强迫时某些反馈的行为。为了测试哪一个可用的模型（如果有的话）能充分解释这种转变，我们需要重建大陆冰盖的大小和大气中二氧化碳浓度的知识。虽然冰量随时间的演变已经比较清楚了，但大气二氧化碳的直接冰芯记录只覆盖了过去80万年，而且在不久的将来（如果有的话）不太可能再延长到更早的时候。因此，我们必须使用其他更间接的方法来重建古代大气中的二氧化碳含量。一种已被证明有迹可循的方法是利用一种叫做有孔虫的钙质微化石的硼(B)同位素组成，这种化石随着时间的推移在深海沉积物中稳步积累。有孔虫的壳中有两种天然存在的硼同位素，这两种同位素的比例，11B和10B，反映了它们生活时海洋表面的酸度，由此可以估计当时大气中的二氧化碳。这项提议的主要目的是利用这种方法产生过去130万年的二氧化碳记录，与冰芯二氧化碳记录重叠，然后将其延伸到中更新世过渡时期。以这种方式测试我们目前对MPT的理解，有望对气候变化与全球碳循环的耦合产生新的见解，从而最终揭示气候和极地冰盖将如何对化石燃料燃烧做出反应。

项目成果

Automation of boron chromatographic purification for d11 B analysis of coral aragonite.

用于珊瑚霰石 d11 B 分析的硼色谱纯化自动化。

• DOI: 10.1002/rcm.8762
• 发表时间: 2020
• 期刊: RCM
• 作者: De La Vega E

Orbital CO 2 reconstruction using boron isotopes during the late Pleistocene, an assessment of accuracy

使用硼同位素重建晚更新世期间的轨道CO 2 ，​​评估准确性

• DOI: 10.5194/cp-2022-93
• 发表时间: 2023
• 作者: De La Vega E

Insensitivity of alkenone carbon isotopes to atmospheric CO<sub>2</sub> at low to moderate CO<sub>2</sub> levels

烯酮碳同位素对大气 CO 的不敏感性

• DOI: 10.5194/cp-2018-152
• 发表时间: 2018
• 作者: Badger M

Causes of ice age intensification across the Mid-Pleistocene Transition.

• DOI: 10.1073/pnas.1702143114
• 发表时间: 2017-12-12
• 期刊: Proceedings of the National Academy of Sciences of the United States of America
• 影响因子: 11.1
• 作者: Chalk TB;Hain MP;Foster GL;Rohling EJ;Sexton PF;Badger MPS;Cherry SG;Hasenfratz AP;Haug GH;Jaccard SL;Martínez-García A;Pälike H;Pancost RD;Wilson PA
• 通讯作者: Wilson PA

Late Miocene cooling coupled to carbon dioxide with Pleistocene-like climate sensitivity

• DOI: 10.1038/s41561-022-00982-7
• 发表时间: 2022-07-25
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: Brown, Rachel M.;Chalk, Thomas B.;Foster, Gavin L.
• 通讯作者: Foster, Gavin L.