Collaborative research: The role of pCO2 in the astronomically-paced climatic cycles of the Miocene

合作研究：pCO2 在中新世天文气候循环中的作用

• 批准号: 1702913
• 负责人: Andrew Ridgwell
• 金额: $ 7.23万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-15 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1702913&HistoricalAwards=false
• 关键词: Collaborative; research; role; pCO2; astronomically; Collaborative; research; role; pCO2; astronomically

Earth's geologic record is paced by cyclical variations in the geometry of our planet's orbit around the sun, generally called Milankovitch cycles (named for the Serbian mathematician who first predicted the orbital variations). Over the last ~1 million years, these orbital variations caused global climatic oscillations between cold Ice Ages, when large ice sheets covered much of North America, and warmer Interglacial periods with climates similar to today's. Measurements of air bubbles of ancient atmosphere trapped in Antarctic ice cores has shown that these Ice Age cycles coincide with significant swings in atmospheric carbon dioxide (CO2) levels. This suggests that the CO2 greenhouse effect plays a role climate change on orbital timescales. However, estimates of atmospheric CO2 from ice cores cover only the last 800,000 years, leaving open the question of whether atmospheric CO2 played a role in the Milankovitch forcing of climate during earlier times in Earth history. This research aims to fill this major knowledge gap by applying geochemical methods to reconstruct ancient CO2 at unprecedented resolution during a time interval with well-documented Milankovitch cycles ~14 million years ago, when global climate was warmer, and the continents were in different positions compared to today. The resulting high-resolution CO2 record will be coupled to a cutting-edge Earth System model to test hypotheses regarding how Milankovitch cycles control Earth's carbon cycle and climate. Together, new geochemical records and modeling undertaken during this project promise to refine understanding of the role of atmospheric CO2 during warm climates -- an issue of significant societal importance in light of currently increasing atmospheric CO2. Results will be communicated to the scientific community by publications in widely-read scientific journals, and to grade school students through by the creation and distribution of an illustrated book exploring the interaction between atmospheric CO2 and climate in Earth history.More specifically, this project aims to generate the first high-resolution (1 sample per ~5 thousand years) records of atmospheric pCO2 using the foraminiferal boron isotope proxy system coupled with matching proxy records of global temperature and carbon cycle dynamics in the mid-Miocene. This time interval was selected as an example of a warmer-than modern Earth with slightly higher background pCO2, smaller continental ice sheets, and well-defined Milankovitch cycles in climate and carbon cycling. The primary, high-resolution boron isotope record will be generated at Site 926 (Ceara Rise, Atlantic Ocean) with supplementary, lower resolution data generated at Sites 608 (North Atlantic) and 806 (Western Pacific). Boron isotope measurements will include the development and rigorous analytical testing of a new microsublimation method for boron separation from carbonate samples, which offers the prospect of smaller sample sizes and faster throughput. At Site 926, boron isotopes will be complemented by measurements of carbon isotopes (placing constraints on carbon cycling), oxygen isotopes (as a measure of paleotemperature and ice volume) and trace metal concentration including Mg/Ca (a paleotemperature proxy) and B/Ca (an emerging carbonate chemistry proxy) on both planktic and benthic foraminifera. These combined datasets will be used to reconstruct ocean temperatures and carbon cycle dynamics, and by comparison to the boron isotope-based CO2 record, allow estimates of temperature sensitivity to changing CO2 levels on orbital timescales. The new records will be used to guide model simulations of Milankovitch climate forcing in an Earth system model of intermediate complexity (cGENIE), providing quantitative constraints on the mechanisms and feedbacks responsible for the Milankovitch control of climate and carbon cycling. Contrasting mid-Miocene and Pleistocene Milankovitch cycles will enable a direct assessment of the role of large continental ice-sheets in modulating the dynamics, and role, of orbitally-forced pCO2 variations.

地球的地质记录是由我们星球围绕太阳轨道的几何形状的周期性变化所节拍的，通常称为米兰科维奇循环（以塞尔维亚数学家的名字命名，他们首先预测了轨道变化）。在过去的一百万年中，这些轨道变化引起了冷冰年龄之间的全球气候振荡，当时大型冰盖覆盖了北美的大部分地区，以及较暖的冰河间冰川时期，气候与今天的气候相似。被困在南极冰芯中的古老气泡气泡的测量表明，这些冰河时代的周期与大气二氧化碳（CO2）水平的显着波动重合。这表明二氧​​化碳温室效应在轨道时标上起着气候变化的作用。然而，冰芯的大气二氧化碳的估计仅在过去的800，000年中仅覆盖，这一问题是，大气二氧化碳在地球历史上早期的米兰科维奇强迫中是否发挥了作用。这项研究的目的是通过应用地球化学方法在时间间隔内以空前的分辨率重建古代二氧化碳，以填补这一主要知识差距，与今天的全球气候更加温暖，与今天相比，全球气候更加温暖，与当今的米尔兰科维奇周期有据可查。所得的高分辨率二氧化碳记录将与尖端的地球系统模型耦合，以测试有关米兰科维奇周期如何控制地球周期和气候的假设。在此项目中，共同进行的新的地球化学记录和建模有望完善对气候中大气二氧化碳在温暖气候中的作用的了解 - 鉴于目前增加的大气二氧化碳，这是社会重要性的重要问题。结果将通过广泛阅读的科学期刊的出版物传达给科学界，并通过创建和分发一本插图书的创建和分发，探索地球历史上大气中的二氧化碳与气候之间的相互作用。更具体地说，该项目旨在使用第一个高分辨率的高分辨率（每〜5千年的样本）使用大气PCO2的记录，并与Foramifers iSing Ising Ising iSing iSing iSing iSing iSing iSing iSing Ising borore bore rore biore bilory bilory bilory bilory biore nocked。中新世中期全球温度和碳循环动力学的记录。选择此时间间隔作为一个比现代地球较温暖的示例，其背景PCO2稍高，大陆冰盖较小，以及在气候和碳循环中定义明确的Milankovitch循环。主要的高分辨率硼同位素记录将在926（CEARA RISE，大西洋）中产生，并在608（北大西洋）和806（西太平洋）（西太平洋）中产生的补充，较低的分辨率数据。硼同位素测量将包括针对与碳酸盐样品分离的新的微公开方法的开发和严格分析测试，该方法提供了较小的样本量和更快的吞吐量的前景。在第926号站点，将通过测量碳同位素（对碳循环的限制），氧同位素（作为古温率和冰量的量度）和痕量金属浓度（包括mg/ca）（包括mg/ca（包括古emotemple的代理）和b/ca（B/Ca（B/CA）（B/Ca）（ber -ca）（ber）（BB/CA）（be）（be）（BB/CA）（A plank and Ca），将对碳纤维浓度和含量金属（A plank），将对碳纤维浓度（A plank and emersif contrancy croxif），将对碳纤维浓度和金属浓度进行补充。这些组合的数据集将用于重建海洋温度和碳循环动力学，并且与基于硼同位素的CO2记录相比，可以估计温度对轨道时间尺度上二氧化碳水平变化的敏感性。新记录将用于指导米兰科维奇气候强迫在中间复杂性（CGENIE）模型中的模型模拟模拟，从而对负责米兰科维奇气候和碳循环的米兰科维奇控制的机制和反馈提供了定量约束。对比中新世和更新世的Milankovitch周期将可以直接评估大型大陆冰盖在调节椭圆形PCO2变化的动力学和作用中的作用。