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.

地质的过去包含许多与当今的地球气候不同的例子，这些例子是我们对气候系统的理解以及我们对未来气候的预测的出色测试床。在过去的60万年前（KYR）左右，地球的气候定期摇摆，大约每100 kyr，在温暖的“冰间”时期之间的气候与今天的气候相似，而寒冷的“冰川”时期在北美和北欧（有时延伸到Simiizia）时，几公里的冰笼罩了几公里。古代空气中被困在南极冰芯中的古老空气的气泡表明，气候中的这些周期性变化部分是由温室气二氧化碳二氧化碳（CO2）的大气浓度变化驱动的 - 在冰川期间，二氧化碳二氧化碳（CO2）在冰川间期间较低，在间隔期间间隔很高。在每个冰河时代周期中，朝向峰值冰川气候的冷却往往相当慢（占90 kyr），而终止每个冰川时期的变暖往往很快（长度约为10 kyr）。但是，在大约120万年前地球的气候平均温暖之前，大洲的冰更少，气候周期更加规律，对称和较短 - 他们当时跟随了41 kyr轨道的节拍。逐渐在1.2到60万年前，冰川间冰期循环的特征发生了变化，从这些较小的41公斤循环转移到最近较大的100千克周期。数十年来，气候科学家研究了这个重要的间隔，称为更新世过渡（MPT），以了解气候系统的内部运作，但迄今为止的基本原因仍然在争论。尽管具有相反的特征，但这两种类型的气候循环都取决于阳光的量和空间和季节性分布，这是由于地球如何绕阳光绕太阳（称为轨道循环）的定期变化而到达地球表面的空间和季节性分布。令人困惑的是，气候周期的性质的变化发生在这些轨道周期中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变化，尤其是当气候系统受到强迫范围时，某些反馈的行为如何。为了测试哪些可用模型中有哪些充分解释了这种过渡，我们需要重建大陆冰盖的大小以及对大气二氧化碳浓度的了解。虽然冰量的演变相对众所周知，但大气二氧化碳的直接冰核记录仅涵盖了过去的80万年，并且不可能在不久的将来（如果有的话）延伸。因此，我们必须使用其他更间接的方法来重建古代气氛的二氧化碳含量。一种具有验证记录的方法使用了称为有孔虫的钙质微化石的硼（B）同位素组成，该化石随着时间的推移在深海沉积物中稳步积累。在有孔虫的壳中，有两个天然存在的硼同位素，这两个同位素的比率为11b至10b，反映了海洋表面生存时的酸度，因此，当时可以估计大气CO2。该提案的主要目的是使用该方法在过去的130万年中产生二氧化碳记录，该记录与Ice Core CO2记录重叠，然后将其扩展为覆盖更新世中期过渡。以这种方式使我们目前对MPT进行测试的理解有望对气候变化和全球碳循环的耦合有新的见解，从而最终阐明了气候和极地冰盖将如何应对化石燃料的燃烧。

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

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.

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