Collaborative Research: NSFGEO-NERC: C-FORCE Carbon-Cycle Feedbacks from Response to Carbon Emissions

古新世-始新世极热期（PETM）是大约5600万年前的一次全球变暖事件。PETM与主要的火山活动同时发生，北大西洋的开放导致北大西洋火成岩省的形成。然而，目前还不清楚，在整个始新世纪，大气中二氧化碳的增加有多少是由火山活动引起的。目前还不清楚碳循环反馈是否影响了二氧化碳的增加。该项目将使用地球物理、地球化学和数值模拟技术来量化PETM的净全球碳循环反馈。该项目的美国参与者将生成详细的海洋化学新记录，并开发新的建模策略。总之，这些将有助于确定火山排放是否可以解释PETM环境变化的幅度和速度。该项目将资助一名加州大学圣克鲁斯分校的博士后研究员，并将为加州大学河滨分校的本科生提供支持和实习研究机会。该项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与本国有关的调查人员提供资金。为了解决全球变暖中碳循环反馈的不确定性，该项目将测量在过去一段由碳基温室气体排放到大气中所导致的全球变暖期间，全球碳循环是如何响应的。古新世-始新世热最大值（PETM）是近6500万年来最大的自然气候变化事件，也是最接近现代全球变暖和碳温室气体排放速率的自然模拟。在PETM期间，最初的全球变暖在几千年的时间里上升了4-5摄氏度，部分原因是由一次异常大规模的火山活动产生的碳排放造成的，随后气候在10多万年的时间里逐渐恢复到原来的状态。该项目将使用一个新的全球碳循环模型来比较火山活动提供的碳与PETM总碳收支；这两种预算之间的差异可归因于碳循环反馈。首先，项目团队将通过测量岩浆产生的过程，对整个始新世纪火山活动向大气提供碳的速率做出新的高分辨率估计。接下来，新的高分辨率海洋酸化记录将限制对大气中导致气候变化的碳排放总量的计算。最后，碳循环模型将允许科学家进行这两套测量有效地结合，以解决全球净碳循环反馈问题。此外，由于地球上的碳储层在同位素组成上有所不同，该项目将确定哪些储层最有可能在始新世纪（PETM）过程中充当碳源或碳汇。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Paleocene-Eocene Thermal Maximum (PETM) was a global warming event roughly 56 million years ago. The PETM coincided with major volcanism, when opening of the North Atlantic Ocean led to the formation of the North Atlantic Igneous Province. However, it is not clear what fraction of the increase in atmospheric carbon dioxide across the PETM was caused by volcanism. It is also unclear whether carbon cycle feedbacks influenced the carbon dioxide increase. This project will use geophysical, geochemical, and numerical modeling techniques to quantify the net global carbon cycle feedbacks across the PETM. The project’s US participants will generate detailed new records of ocean chemistry and develop novel modeling strategies. Together, these will help determine whether volcanic emissions can explain the magnitude and pace of PETM environmental change. This project will support a postdoctoral researcher at UC Santa Cruz and will provide support and internship research opportunities for undergraduate students from UC Riverside. This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.To address uncertainties in carbon cycle feedbacks on a warming planet, the project will measure how the global carbon cycle responded during a past period of global warming that was driven by emissions of carbon-based greenhouse gases to the atmosphere. The Paleocene-Eocene Thermal Maximum (PETM) is the largest natural climate change event of the last 65 million years, and the closest natural analog to the modern rates of global warming and carbon greenhouse gas emissions. During the PETM, initial global warming of 4-5 degrees C over a few thousand years was partially driven by carbon emissions from an unusually massive episode of volcanism, and the climate then gradually recovered to its pre-existing state over more than 100 thousand years. The project will use a novel model of the global carbon cycle to compare the carbon supplied by volcanism with the total PETM carbon budget; the difference between these two budgets can be attributed to carbon cycle feedbacks. First, the project team will make new high-resolution estimates of the rate at which volcanism supplied carbon to the atmosphere throughout the PETM by measuring the processes that generated the magma. Next, new high-resolution records of ocean acidification will constrain calculations of the total budget of carbon emissions to the atmosphere that caused the climate change. Finally, carbon cycle modeling will allow the scientists who make these two sets of measurements to interface effectively to solve the net global carbon cycle feedback problem for the first time. Furthermore, because Earth's carbon reservoirs differ in isotopic composition, this project will fingerprint which reservoirs most likely acted as carbon sources or sinks over the course of the PETM.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.