Collaborative Proposal: Tectonic degassing as a possible solution to the Miocene climate enigma

合作提案：构造脱气作为解决中新世气候之谜的可能方法

• 批准号: 2202760
• 负责人: Weimin Si
• 金额: $ 54.35万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2202760&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Tectonic; degassing; possible

About 20 million years ago, the Earth was much warmer than today and the Antarctic was nearly ice-free. However, a mysterious climatic transition happened around 14 million years ago and the Earth went through a series of cooling events since then. The persistent cooling over millions of years ultimately led to the emergence of the bi-polar icehouse climate of today. Scientists have long been puzzled about what processes could have caused the cooling. One idea is that the rise of the Himalayas mountains may have sped up erosion and increased the rate of chemical weathering, a process that draws down atmospheric carbon dioxide. Other scientists suggest that the cooling may have been caused by a slowdown in the supply of carbon dioxide from deep inside the earth. The idea is that the formation rate of oceanic crustal rocks decelerated about 14 million years ago. That would have caused a decrease in the release of carbon dioxide from the Earth's interior into the atmosphere. The decrease in the supply of that greenhouse gas then led to the decrease in global temperatures. This study will help address this cooling mystery by providing improved estimates of past global temperatures. Those estimates will come from analyses of organic molecules preserved in deep-sea sediments and from climate model simulations. The new global temperature reconstruction will help determine the relative contributions of mountain building and carbon dioxide release from the Earth's interior to changes in the carbon cycle. The study will provide a better picture of how tectonic processes on Earth, both on land and at the sea floor, influence long-term global climate. The project broader impacts include support for a postdoctoral researcher at both institutions, support for a graduate student and undergraduate researchers at Brown University, and support for K-12 focused outreach activity through an existing program at Brown University.Beginning in the Middle Miocene (~14 Ma), the Earth experienced sustained cooling of 10-12 degrees C that ended the generally warm climate that had prevailed since the Mesozoic. A major enigma about this Miocene climate transition is whether it is driven by reduced carbon dioxide degassing (source) or enhanced weathering removal (sink). Assuming a relatively constant seafloor spreading rate over time, previous studies suggest that the carbon dioxide drawdown (and the global cooling) was caused by enhanced chemical weathering. That could have been due to either the uplift of the Himalayas or the emergence of the tropical maritime continent, which exposed easily weathered volcanic material in one of the warmest, wettest areas of the world. Recent sea surface temperature reconstructions, however, reveal that the Middle Miocene was much warmer than previously thought, raising the puzzle of whether reduced weathering alone is sufficient to sustain the large warming; an enhanced carbon dioxide flux is probably required to balance the expected weathering sink of carbon dioxide under warm Middle Miocene conditions. This study is motivated by a challenge to the weathering hypothesis based on recent evidence of a ~30% reduction in global crustal production rate since 15 Ma. This project will generate new biomarker sea surface temperature estimates with global coverage for the Miocene, filling temporal and spatial gaps of current datasets. Along with proxy analysis, the study will also develop new Miocene climate simulations sampling a wide range of model physics and boundary conditions to reproduce the Miocene large-scale temperature and hydrological cycle. The model simulations will be used to probe source/sink configurations compatible with Miocene temperatures and mass balance in the carbon cycle. By synthesizing the model-data information, the project will develop an improved reconstruction of the Miocene climate which will ultimately allow for estimation of the relative contribution of different source-sink terms (i.e., the Himalayas, the maritime continent, and the carbon dioxide degassing associated with seafloor spreading) in driving the Miocene temperature and atmospheric carbon dioxide evolution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大约2000万年前，地球比今天温暖得多，南极几乎没有冰。但是，一个神秘的气候过渡发生了大约1400万年前，从那以后，地球经历了一系列的冷却事件。数百万年前的持续冷却最终导致了当今双极冰屋气候的出现。长期以来，科学家对哪些过程可能导致冷却感到困惑。一个想法是，喜马拉雅山山的兴起可能已经加剧了侵蚀并增加了化学风化的速度，这一过程吸引了大气中的二氧化碳。其他科学家认为，冷却可能是由于地球内部二氧化碳供应的放缓而引起的。这个想法是，大约1400万年前，海洋地壳岩石的形成速率下降了。这将导致从地球内部释放二氧化碳释放到大气中。然后，该温室气体的供应减少导致全球温度的降低。这项研究将通过改进过去全球温度的估计来帮助解决这一冷却之谜。这些估计将来自对深海沉积物中保存的有机分子和气候模型模拟的分析。新的全球温度重建将有助于确定从地球内部释放山地建筑和二氧化碳对碳循环变化的相对贡献。这项研究将更好地了解地球上的构造过程，无论是在陆地还是在海底上都影响了长期的全球气候。该项目更广泛的影响包括对两家机构的博士后研究人员的支持，对布朗大学的研究生和本科研究人员的支持，以及通过布朗大学的现有计划来支持K-12的集中范围外展活动。在中新世中期（〜14 MA），地球上经验丰富的10-12级持续冷却，这是10-12摄氏度的持续冷却。关于中新世气候过渡的主要谜团是它是由二氧化碳脱气（源）降低或增强的风化去除（接收器）驱动的。假设随着时间的流逝，海底散布率相对恒定，先前的研究表明，二氧化碳缩水（和全球冷却）是由化学风化增强引起的。这可能是由于喜马拉雅山脉的升高或热带海洋大陆的出现，在世界上最温暖，最潮湿的地区之一，易于风化的火山材料暴露了风化的火山材料。然而，最近的海面温度重建表明，中新世中部比以前想象的要温暖得多，这增加了是否仅仅降低风化就足以维持大型变暖。在温暖中新世条件下，可能需要增强的二氧化碳通量来平衡二氧化碳的预期风化水槽。这项研究是基于最近的证据表明，自从15 MA以来，全球地壳生产率降低了约30％的证据，这项研究的挑战是为了挑战。该项目将通过中新世的全球覆盖范围产生新的生物标志物海面温度估计，从而填补当前数据集的时间和空间间隙。除了代理分析外，该研究还将开发新的中新世气候模拟，对广泛的模型物理和边界条件进行采样，以重现中新世的大规模温度和水文循环。该模型模拟将用于探测与中新世温度兼容的源/接收器配置和碳循环中的质量平衡。通过综合模型数据信息，该项目将建立重新印度气候的重建，最终将允许估算不同源链接项的相对贡献（即，喜马拉雅山脉，海上大陆，海上大陆，是与二氧化碳dioxide de diosing seafors in the Seafore dios dios dio carbone dio carbone vios dios dio dio dio dio dio dio dio dio dios dio dio dios dio dio dios dios dio dios dios diof serviense viocy dio dios dios dios dios dio diof。法定任务，并被认为是值得通过基金会的智力优点和更广泛影响的审查标准来评估的值得支持的。

项目成果

Very high Middle Miocene surface productivity on the U.S. mid-Atlantic shelf amid glacioeustatic sea level variability

在冰川海平面变化的情况下，美国大西洋中部大陆架的中中新世表面生产力非常高

• DOI: 10.1016/j.palaeo.2022.111249
• 发表时间: 2022
• 期刊: Palaeoecology
• 作者: Robinson, Marci M.;Dowsett, Harry J.;Herbert, Timothy D.
• 通讯作者: Herbert, Timothy D.