Collaborative Research: The role of the Southern Ocean in Late Miocene climate change

合作研究：南大洋在晚中新世气候变化中的作用

• 批准号: 2226054
• 负责人: Elizabeth Walsh
• 金额: $ 19.28万
• 依托单位: San Jose State University Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-01-15 至 2025-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2226054&HistoricalAwards=false
• 关键词: Collaborative; Research; role; Southern; Ocean

Concern over rising global temperatures makes it important to predict future climate change. However, to predict future climate requires a better understanding of how the climate system works in a warmer world. One way to better understand future warmth is to look at a warm period in the past. The project will explore one of the most recent periods of long-term warmth, the late Miocene, approximately 5 to 8.5 million years ago. The Miocene was characterized by warmer temperatures globally, and particularly in the polar regions. However, currently models are not able to correctly hindcast Miocene temperatures and often underestimate the warming. The ability to predict and understand this warmer world is limited by the availability of observations from the late Miocene. This is particularly true of the Southern Ocean, the area of ocean around Antarctica. This region plays an important role in controlling global temperature changes because it interacts with atmospheric carbon dioxide through physical processes (e.g., ocean mixing) and biological productivity (e.g., photosynthesis). Currently, there are no records of surface ocean temperature or biological productivity from the late Miocene for the Pacific sector of the Southern Ocean. This project will generate records of late Miocene oceanographic conditions in this region, including ocean surface temperature and biological productivity. These data will document how warm the Southern Ocean was during the late Miocene. The data will also provide key insights into how climate in a warmer world responds to changes in atmospheric carbon dioxide. Finally, the study will assess how processes in the Southern Ocean may have contributed to the cooling of the globe at the end of the Miocene. This work will support graduate and undergraduate students in both oceanography and science education. As part of the project, science education MS students and oceanography PhD students will work together to develop expertise in equitable teaching methods and curricular design.The Miocene (23.3 - 5.05 Ma) is critical to understand as it was a period of sustained warmth leading up to the early phase of Northern Hemisphere glaciation. A recent Miocene model comparison study (MioMIP1) indicates that: during the late Miocene the majority of warmth is attributed to atmospheric carbon dioxide (pCO2) forcing; climate sensitivity to pCO2 forcing is state dependent; regional sensitivity to orbital variations in insolation is poorly understood and model-dependent; while a reduced meridional sea surface temperature (SST) gradient is generally a robust feature of warm climates with profound impacts on the hydrologic cycle, it is not well-constrained. One of the largest data-model misfits is in the southern high latitudes where models severely underestimate observed warming. However, this misfit is determined by observations from only a few southern sites, none of which are from the vast region of the central Pacific Southern Ocean (SO). This project will produce the first paleoceanographic records from the late Miocene to early Pliocene (8.3 – 4.0 Ma) in the Central Pacific sector of the SO from a recently drilled site (IODP Expedition 383, Site U1541). These records, covering the Late Miocene Cooling and Late Miocene Carbon Isotopic Shift, will enable the determination of South Pacific meridional SST gradients, an evaluation of long-term climate sensitivity to pCO2 forcing and orbital forcing, an assessment of the links between SST and paleoproductivity variability, and of the evolution of deep-water circulation. The project objectives are to: (a) develop a high-resolution Uk’37-based SST record to constrain the cold southern end member of the meridional SST gradient and to evaluate responses to decreasing pCO2 forcing and potential changes in orbital variability as the mean state changed, and (b) use paleoproductivity proxies to test the hypothesis that enhanced marine productivity during the late Miocene contributed to the removal of atmospheric CO2 leading into the Pliocene. Although not the focus of this project, the study will also use benthic foraminiferal d13C at U1541 to constrain zonal and meridional gradients in deep ocean d13C to inform potential changes in global deep-water circulation. The new late Miocene data from Site U1541, a previously unstudied region, will provide new insight into the workings of the climate system in a warmer climate.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.

对全球气温上升的担忧使得预测未来气候变化变得非常重要。然而，预测未来气候需要更好地了解气候系统在变暖的世界中如何运作，更好地了解未来温暖的一种方法是观察未来的温暖时期。该项目将探索最近的长期温暖时期之一，即大约 5 至 850 万年前的中新世，其特点是全球气温升高，特别是在极地地区。模型无法正确预测中新世温度并经常低估变暖的能力受到中新世晚期观测的限制，对于南极洲周围的南大洋尤其如此。该地区在控制全球温度变化方面发挥着重要作用，因为它通过物理过程（例如海洋混合）和生物生产力（例如光合作用）与大气二氧化碳相互作用。目前，没有来自该地区的表面海洋温度或生物生产力的记录。该项目将生成该地区中新世晚期海洋状况的记录，包括海洋表面温度和生物生产力。这些数据将记录中新世晚期南大洋的温暖程度。最后，这项研究还将评估南大洋的过程如何导致中新世末期的全球变冷。将支持研究生和本科生作为该项目的一部分，科学教育硕士生和海洋学博士生将共同努力发展公平教学方法和课程设计方面的专业知识。中新世（23.3 - 5.05 Ma）对于理解至关重要，因为它是一个最近的中新世模型比较研究（MioMIP1）表明：在中新世晚期，大部分温暖归因于大气中的二氧化碳。 (pCO2) 强迫；气候对 pCO2 强迫的敏感性取决于状态；对日照轨道变化的区域敏感性知之甚少且取决于模型；而经向海面温度 (SST) 梯度的降低通常是温暖气候的一个重要特征。最大的数据模型错误之一是在南部高纬度地区，那里的模型严重低估了观测到的变暖。然而，这种错误仅由少数南部地点的观测结果决定。其中来自南太平洋 (SO) 中部的广阔区域 该项目将通过最近钻探的南太平洋中部区域产生第一批中新世晚期至上新世早期（8.3 – 4.0 Ma）的古海洋记录。这些记录涵盖了晚中新世冷却和晚中新世碳同位素变化，将有助于确定南太平洋经向。海表温度梯度、对 pCO2 强迫和轨道强迫的长期气候敏感性的评估、对海表温度与古生产力变异性之间的联系以及深水环流演化的评估。 项目目标是： (a) 开发一个基于 Uk'37 的高分辨率 SST 记录，用于约束经向 SST 梯度的冷南端成员，并评估随着平均状态变化而减少的 pCO2 强迫和轨道变率的潜在变化的响应，以及 (b) 使用古生产力代理来检验以下假设：中新世晚期海洋生产力的增强有助于去除大气中的二氧化碳，从而进入上新世。尽管这不是本项目的重点，但该研究还将使用 U1541 的底栖有孔虫 d13C 来限制纬向和经向梯度。深海 d13C，以了解全球深水环流的潜在变化，来自站点 U1541 的新中新世晚期数据。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。