Solving the Oligocene icehouse conundrum

解决渐新世冰室难题

• 批准号: NE/V018361/1
• 负责人: Bridget Wade
• 金额: $ 176.6万
• 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: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV018361%2F1
• 关键词: Solving; Oligocene; icehouse; conundrum

Today there is a major ice sheet on Antarctica, but this was not always the case. The Antarctic ice sheet formed around 34 million years ago, ushering in the dawn of the "icehouse world". Over the next 11 million years, the climate swung between cooler and warmer states, with sea level falling and rising as ice sheets grew and collapsed. To simulate changes in sea level and climate of this size, computer models require massive fluctuations in CO2. However, we have no evidence of CO2 change of this magnitude, and little idea of how such changes could be accomplished. Furthermore, the existing CO2 reconstructions from this time interval present another major puzzle, as they show a long-term decrease, which appears to be decoupled from long-term climate. These mysterious interactions between CO2, climate, and ice sheets are the "Oligocene icehouse conundrum" that this project aims to solve.Past changes in climate can be reconstructed using chemical fingerprints in fossil shells of foraminifera - sand-sized organisms that live throughout the ocean - the chemistry of these organisms records the environmental conditions at the time they grew, allowing us to reconstruct how environments have changed in the past. The main reason the climate of the Oligocene (~34-23 million years ago) remains such a mystery is because of a previous lack of sedimentary material containing well-preserved foraminifera from this time interval. Previously acquired records are sparse or biased by poor preservation, leaving us with a limited and confused understanding of how the Oligocene climate system operates. Now, for the first time, we have identified sites with abundant and well-preserved foraminifera, thus overcoming a major obstacle in Oligocene climate reconstruction. We will analyse foraminifera to reconstruct critical aspects of the Oligocene climate, such as the temperature, global ice volume, sea level, ocean acidity (pH), atmospheric carbon dioxide and the strength of the biological pump. These kinds of analyses are increasingly used to help determine both how climate has changed in the past and how it might change in the future, including "climate sensitivity", the amount of warming expected due to rising CO2. We have built a team and strategy that poises the project for success. Principal Investigator (PI) Wade is one of the world's foremost experts on the foraminifera of the Oligocene, and so is perfectly placed to figure out which species best record temperatures and atmospheric CO2. Having identified the best species and sites, we will make the first reconstructions of CO2 from this time using the chemistry of boron. This exciting method has seen extensive development in recent years by Co-PI Rae and Co-Investigator Foster, and we will apply the latest methods to determine past pH and CO2. To explore why CO2 may have changed, we will create new records of the biological pump of carbon to the deep ocean. And to evaluate the impact of CO2 on global climate, we will make new records of temperature, using foraminifera and organic molecules, and sea level, using foraminifera from the sea floor. Armed with these new reconstructions of key components of Oligocene climate, we will use a variety of modelling approaches to integrate and interpret them in a global context. A model of how carbon cycles between different reservoirs will allow us to test mechanisms of CO2 change. Simulations of physical climate and ice sheets will be combined in an exciting new way to explore the stability of major ice sheets. We will transform the understanding of CO2 and climate change in the Oligocene, providing insights into the fundamentals of climate sensitivity and ice sheet stability.The new understanding of Oligocene climate and the carbon cycle that will result from our research will resolve the long-standing Oligocene icehouse conundrum, and improve understanding of climate and ice sheet sensitivity in a warmer world.

今天，南极洲上有一个主要的冰盖，但这并不总是如此。南极冰盖形成于大约3400万年前，迎来了“冰屋世界”的曙光。在接下来的1100万年里，气候在较冷和较暖的状态之间摇摆，随着冰盖的增长和崩溃，海平面下降和上升。为了模拟这种规模的海平面和气候变化，计算机模型需要二氧化碳的巨大波动。然而，我们没有证据表明二氧化碳的变化如此之大，也不知道这种变化是如何实现的。此外，从这一时间间隔的现有CO2重建提出了另一个主要的难题，因为它们显示出长期的减少，这似乎与长期气候脱钩。二氧化碳、气候和冰盖之间的这些神秘的相互作用是这个项目旨在解决的“渐新世冰室难题”。过去的气候变化可以通过有孔虫化石外壳中的化学指纹来重建--有孔虫是一种沙子大小的生物，生活在整个海洋中--这些生物的化学成分记录了它们生长时的环境条件，让我们能够重建过去环境的变化。渐新世（约3400 - 2300万年前）的气候仍然是一个谜的主要原因是因为以前缺乏包含保存完好的有孔虫的沉积物。以前获得的记录是稀疏的或有偏见的保存不善，让我们有限和混乱的了解渐新世气候系统如何运作。现在，我们第一次确定了有孔虫数量丰富且保存完好的地点，从而克服了渐新世气候重建的一个主要障碍。我们将分析有孔虫，以重建渐新世气候的关键方面，如温度，全球冰量，海平面，海洋酸度（pH值），大气二氧化碳和生物泵的强度。这类分析越来越多地用于帮助确定气候在过去如何变化以及未来可能如何变化，包括“气候敏感性”，即由于二氧化碳上升而预期的变暖量。我们已经建立了一个团队和战略，使项目取得成功。首席研究员（PI）韦德是世界上最重要的渐新世有孔虫专家之一，因此完全可以找出哪些物种最能记录温度和大气二氧化碳。在确定了最好的物种和地点之后，我们将利用硼的化学性质对这一时期的二氧化碳进行首次重建。这种令人兴奋的方法近年来得到了共同PI Rae和共同研究员Foster的广泛发展，我们将应用最新的方法来确定过去的pH值和CO2。为了探索二氧化碳变化的原因，我们将创造生物向深海输送碳的新记录。为了评估二氧化碳对全球气候的影响，我们将用有孔虫和有机分子来记录温度，用海底的有孔虫来记录海平面。有了这些对渐新世气候关键组成部分的新重建，我们将使用各种建模方法在全球背景下整合和解释它们。不同储层之间碳循环的模型将使我们能够测试CO2变化的机制。物理气候和冰盖的模拟将以一种令人兴奋的新方式结合起来，探索主要冰盖的稳定性。我们将改变对渐新世二氧化碳和气候变化的理解，深入了解气候敏感性和冰盖稳定性的基本原理。我们的研究将产生对渐新世气候和碳循环的新理解，这将解决长期存在的渐新世冰库难题，并提高对气候和冰盖敏感性的理解在一个更温暖的世界。

项目成果

Climate Evolution Through the Onset and Intensification of Northern Hemisphere Glaciation

• DOI: 10.1029/2022rg000793
• 发表时间: 2023-07
• 期刊: Reviews of Geophysics
• 影响因子: 25.2
• 作者: E. McClymont;S. L. Ho;H. L. Ford;I. Bailey;M. Berke;C. Bolton;S. Schepper;G. Grant;J. Groeneveld;G. Inglis;C. Karas;M. O. Patterson;G. Swann;K. Thirumalai;S. M. White;M. Alonso-García;P. Anand;B. Hoogakker;K. Littler;B. Petrick;B. Risebrobakken;J. Abell;A. J. Crocker;F. D. Graaf;S. Feakins;J. C. Hargreaves;C. L. Jones;M. Markowska;A. S. Ratnayake;C. Stepanek;D. Tangunan