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，我们必须知道过去气候是如何变化的。关于过去气候的最大未知之一是全球冷暖循环中大气二氧化碳（CO2）变化的来源。该项目将通过关注表层海洋施肥效率的变化，以及这种变化如何与深海变化相关，以及是否与之相关，来解决大气二氧化碳变化的潜在原因。此外，该研究将调查二氧化碳“如何”与“在哪里”变化，即东赤道太平洋（EEP），这是世界海洋的一个重要区域，今天，大量的二氧化碳被呼入大气，浮游植物的生长速度最快。该项目将有助于增进对全球气候变化和与热带太平洋有关的重要地球系统的了解。在最广泛的层面上，了解地球碳循环的过去动态对于在二氧化碳不断增加的世界中为社会决策提供信息和指导至关重要。该项目将支持研究生和本科生的教育和专业发展，其成果将纳入本科和研究生课程。此外，还将制作一系列YouTube视频，旨在传达过去气候变化如何告诉我们未来气候变化及其对我们生活的潜在影响的重要性。该项目旨在回答以下问题：1)在千年的时间尺度上，大气中的二氧化碳在哪里以及如何从大气中被隔离，或如何从海洋中被通风；2)这些碳动态是如何与末次冰川期、去冰川期和全新世的大气和海洋环流变化相关的。为了实现这些目标，将在先前从EEP收集的两个高堆积率沉积物岩心中测量一套综合的多个代理。这些代理包括：自生铀代表底水氧合作用，底栖有孔虫放射性碳年龄代表EEP深水年龄变化，231Pa/230Th比值和过量Ba通量代表生产力，过量230衍生232Th通量代表尘埃通量，浮游有孔虫B/Ca比值代表地表水碳酸盐离子浓度。Nd和Pb同位素比值可作为沉积物碎屑组分粉尘来源的代表，从而作为热带辐合带迁移的指标。通过研究末次冰期寒冷时期（即约71000年至14000年前）深海中呼吸碳库的储存，同时探索这种储存与出口生产和潜在铁施肥的变化之间的关系，该研究将揭示海洋（分层/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改变。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。

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.