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.

地质过去包含许多地球气候与今天不同的例子，这些是我们了解气候系统以及最终预测未来气候的极好试验台。在过去 60 万年（kyr）左右的时间里，地球气候有规律地波动，大约每 100 kyr，在气候与今天相似的温暖“间冰期”和寒冷“冰河期”之间波动，当时数公里的冰覆盖了北美和北欧（有时延伸到西伯利亚）。南极洲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——二氧化碳在冰期期间较低，而在间冰期期间较高。在每个冰河期周期中，到达冰川气候高峰期的冷却往往相当缓慢（大约需要 90 kyr），而每个冰川期结束时的变暖往往非常快（长度约为 10 kyr）。然而，在大约 120 万年前，地球气候平均变暖，大陆上的冰较少，气候周期更加规则、对称且较短——当时它们遵循 41 kyr 的轨道节拍。在 1.2 至 60 万年前之间，冰期-间冰期循环的特征逐渐发生了变化，从这些较小的 41 kyr 循环转变为最近的较大 100 kyr 循环。气候科学家几十年来一直在研究这个被称为中更新世转变（MPT）的重要时期，以了解气候系统的内部运作，但迄今为止其根本原因仍然存在争议。尽管它们的特征截然不同，但这两种类型的气候周期的节奏都是由于地球绕太阳运行的方式发生定期变化（称为轨道周期）而导致到达地球表面的阳光数量以及空间和季节分布的微妙变化。令人费解的是，气候周期性质的变化是在这些轨道周期没有任何显着变化的情况下发生的。因此，它代表了气候系统运行方式的根本性变化，特别是当气候系统受到强迫时某些反馈的行为方式。为了测试哪些可用模型（如果有的话）能够充分解释这种转变，我们需要重建大陆冰盖的大小和大气二氧化碳浓度的知识。虽然冰体积随时间的演变相对清楚，但大气二氧化碳的直接冰芯记录仅涵盖过去 80 万年，并且在不久的将来不太可能进一步延伸（如果有的话）。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。一种经过验证的方法使用了被称为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定积累。有两种天然存在的硼同位素，有孔虫壳中这两种同位素 11B 与 10B 的比率反映了它们生活时海洋表面的酸度，由此可以估算当时大气中的二氧化碳浓度。该提案的主要目的是利用这种方法生成过去 130 万年的二氧化碳记录，该记录与冰芯二氧化碳记录重叠，但随后将其延伸至更新世中期过渡期。以这种方式检验我们目前对 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响应化石燃料燃烧。

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.