Collaborative Research: Linking Atmospheric CO2 to Millennial Changes in Atmospheric and Oceanic Circulation in the Eastern Equatorial Pacific Ocean over the Past 100 kyr

要了解未来的气候变化，我们必须知道过去的气候是如何变化的。关于过去气候的最大未知数之一是全球冷暖循环期间大气二氧化碳(CO2)变化的来源。该项目将侧重于表层海洋肥化效率的变化，以及这种变化如何以及是否与深海变化有关，从而解决大气二氧化碳变化的潜在原因。此外，这项研究将调查二氧化碳随“地点”变化的“方式”，即东赤道太平洋(EEP)，这是世界海洋的一个重要区域，今天有大量二氧化碳排放到大气中，浮游植物的生长速度最快。该项目将有助于更好地了解全球气候变化和与热带太平洋有关的重要地球系统。在最广泛的层面上，了解地球碳循环过去的动态对于在二氧化碳日益增加的世界中提供信息和指导社会决策具有至关重要的意义。该项目将支持研究生和本科生的教育和专业发展，并将成果纳入本科生和研究生班的课程。此外，还将制作一系列YouTube视频，旨在交流过去的气候变化如何告知我们未来气候变化及其对我们生活的潜在影响的重要性。该项目试图回答与以下问题有关的问题：1)在千年时间尺度上，大气中的二氧化碳在哪里以及如何从大气中隔离或从海洋中排出，2)这些碳动态与上一次冰期以及进入去冰期和全新世的大气和海洋环流的变化有何关系。为了实现这些目标，将在以前从EEP收集的两个高累积速率沉积物岩心中测量一套综合的多个替代指标。这些指标包括：自生铀作为底水氧化作用的替代指标和底栖有孔虫放射性碳年龄作为EEP深水年龄变化的替代指标、231Pa230th比值和过剩的Ba通量作为生产力的替代指标、过量232Th通量作为尘埃通量的替代指标、浮游有孔虫中的B/Ca比值作为地表水碳酸盐离子浓度的替代指标、以及Nd和Pb同位素比值作为沉积物碎屑组分的尘源来源的替代，因此是热带辐合带迁移的一个指标。通过调查最后一次冰川时期(即约71,000至14,000年前)寒冷时期深海中呼吸碳库的储存情况，结合探索这种储存如何与出口产量的变化和潜在的铁肥有关，这项研究将阐明海洋(层化/通风)和大气(风带移动)环流之间的机制联系以及大气二氧化碳水平的变化。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智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

To understand future climate change, we must know how climate varied in the past. One of the biggest unknowns about past climate is the origin of atmospheric carbon dioxide (CO2) variability over global warm-cold cycles. This project will address potential causes of the varying atmospheric carbon dioxide by focusing on changes in the efficiency of fertilization of the surface ocean, and how, and if, that is related to changes in the deep-ocean. Furthermore, the research will investigate both the "how" of varying carbon dioxide with the "where", namely the Eastern Equatorial Pacific (EEP), an important region of the world ocean where, today, significant CO2 is exhaled to the atmosphere and the greatest rates of phytoplankton growth are found. The project will contribute to an improved understanding of global climate change and important Earth systems connected to the tropical Pacific Ocean. On the broadest of levels, understanding the past dynamics of Earth's carbon cycle is of fundamental importance to inform and guide societal policy-making in an increasing CO2 world. The project will support the educational and professional development of graduate and undergraduate students and results will be incorporated into the curriculum of undergraduate and graduate classes. In addition, a series of YouTube videos will be developed that are aimed at communicating the importance of how past climate variability informs us about climate's future variability and its potential impact on our lives.The project seeks to answer questions related to: 1) where and how atmospheric carbon dioxide was sequestered from the atmosphere, or ventilated from the ocean, on millennial timescales, and 2) how these carbon dynamics are related to both changes in atmospheric and oceanic circulation over the last glacial period and into the deglacial and Holocene. To address these objectives, an integrated suite of multiple proxies will be measured in two high accumulation rate sediment cores previously collected from the EEP. These proxies include: authigenic uranium as a proxy for bottom water oxygenation and radiocarbon ages of benthic foraminifera as a proxy for changes in the age of deep water in the EEP, 231Pa/230Th ratios and excess Ba fluxes as proxies for productivity, excess 230Th-derived 232Th flux as a proxy for dust flux, B/Ca ratios in planktonic foraminifera as a proxy for carbonate ion concentration of surface water, and Nd and Pb isotope ratios as a proxy for the provenance of the dust source of the detrital component of the sediment and, therefore, an index of Intertropical Convergence Zone migration. By investigating the storage of a respired carbon pool in the deep ocean during cold periods of the last glacial period (i.e., from ~71,000 to 14,000 years ago), in conjunction with probing how this storage relates to changes in export production and potential iron fertilization, the research will shed light on the mechanistic links between ocean (stratification/ventilation) and atmospheric (wind belt shifts) circulation and the modification of atmospheric CO2 levels.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.