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: 2226055
• 负责人: Ana Ravelo
• 金额: $ 24.02万
• 依托单位: University of California-Santa Cruz
• 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=2226055&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.

对全球温度升高的关注使预测未来气候变化至关重要。但是，要预测未来的气候，需要更好地了解气候系统在温暖的世界中的运作方式。更好地了解未来温暖的一种方法是看过去一个温暖的时期。该项目将探索大约5至850万年前的中新世晚期长期温暖的最新时期之一。中新世的特征是全球温度较高，尤其是在极地地区。但是，目前的模型无法正确地缩放中新世的温度，并且经常低估了变暖。预测和理解这个温暖的世界的能力受到中新世晚期观察结果的可用性的限制。南方海洋地区的南大洋地区尤其如此。该区域在控制全球温度变化中起着重要的作用，因为它通过物理过程（例如海洋混合）和生物产物（例如光合作用）与大气二氧化碳相互作用。目前，南大洋太平洋地区的中新世晚期尚无表面海洋温度或生物生产力的记录。该项目将在该区域中产生中新世晚期海洋学条件的记录，包括海面温度和生物学生产力。这些数据将记录中新世晚期在南大洋的温暖。数据还将提供有关温暖世界中气候如何应对大气二氧化碳变化的关键见解。最后，该研究将评估南洋的过程如何在中新世结束时促进地球的冷却。这项工作将支持海洋学和科学教育的毕业生和本科生。作为该项目的一部分，科学教育的MS学生和海洋学博士生将共同努力开发公平的教学方法和当前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，因为这是持续的温暖时期，直到北半球冰川的早期。中新世模型比较研究（MIOMIP1）表明：在中新世晚期期间，大多数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。对轨道上的轨道变化的敏感性对显得很差，并且依赖于模型。虽然子午海表温度（SST）梯度的降低通常是温暖气候的强大特征，对水文循环产生了深远的影响，但它并未得到很好的约束。最大的数据模型型不适板之一是在南部高纬度地区，模型严重低估了观察到的变暖。但是，该级别的属性是由仅几个南部地点的观察结果决定的，没有一个来自中太平洋南部大洋地区（SO）的广阔地区。该项目将产生从中新世晚期到上新世早期（8.3 - 4.0 mA）的首个古射记录，该项目是在SO的中太平洋部门从最近钻探的地点（IODP Expedition 383，Site U1541）。这些记录涵盖了中新世晚期冷却和中新世晚期碳同位素转移，将能够确定南太平洋子午线SST梯度，评估长期气候对PCO2强迫和轨道强迫的敏感性，评估SST和古生物可变性之间的链接和深层循环循环的链接。 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 production during the late Miocene contributed to the removal of atmospheric CO2 leading into the上新世。尽管不是该项目的重点，但该研究还将在U1541上使用底栖有孔虫D13C来限制深海D13C中的区域和子午梯度，以告知全球深水循环的潜在变化。以前未研究的地区U1541的新中新世数据将在温暖的气候下为气候系统的运作提供新的见解。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和广泛的审查标准通过评估来通过评估来获得的支持。