Collaborative Proposal: Miocene Climate Extremes: A Ross Sea Perspective from IODP Expedition 374 and DSDP Leg 28 Marine Sediments

目前，由于地球大气和南大洋变暖，南极洲的冰川正在融化。关于南极洲冰盖如何应对目前和未来的变暖，我们知之甚少，但这些知识很重要，因为随着南极洲冰盖的持续融化，全球海平面可能会大幅上升。随着时间的推移，泥浆在南极洲周围的海底积聚，这些泥浆由海洋微生物的骨骼和碎片以及邻近大陆的沉积物组成。随着这些泥浆的沉积，它创造了过去环境和生态变化的记录，包括海洋深度、冰川进退、海洋温度、海洋环流、海洋生态系统、海洋化学和大陆风化。科学家们有兴趣了解南极洲的冰川和冰盖如何对持续的变暖做出反应，他们可以对这些泥浆档案进行各种物理、生物和化学分析，以确定泥浆沉积的时间，以及过去地球气候变暖期间冰盖、海洋和海洋生态系统的反应。在这个项目中，来自南佛罗里达大学、马萨诸塞大学和北伊利诺伊大学的研究人员将重建1700万至1300万年前罗斯海中部的深度、海洋温度、风化和营养输入以及海洋生态系统，当时温暖的中新世气候最佳过渡到一个更冷的间隔，有更广泛的冰盖。记录将由国际海洋发现计划（IODP）第374次探险期间回收的新沉积物和20世纪70年代深海钻探计划期间回收的遗留序列产生。结果将被整合到冰盖和气候模型中，以提高预测的准确性。该研究通过一个多机构REU项目为三名研究生和七名本科生提供了经验，该项目专注于增加南极地球科学的多样性。深海沉积物揭示了中新世气候最适期（MCO）是最近~20 Ma最温暖的气候期，与全球碳循环变化和冰生长有关，并紧随中中新世气候过渡期（MMCT; ~14 Ma），这是南极冰扩张和全球变冷的三大期之一。需要进行冰近端研究，以评估：冰生长的地点和时间、冰盖范围、大陆架几何形状、高纬度的热量和水分供应、海洋和/或大气温度对冰动力学的影响、区域海冰范围、融水输入和底部水形成区域。现有的研究表明，在~17 ~ 13.5 Ma之间，冰多次扩展到横贯南极山脉之外，并延伸到推进的罗斯海大陆架上。然而，这些记录要么太近冰/陆地，不足以充分评估海洋与冰的相互作用，要么研究不足。为了解决这一数据缺口，本工作将：1)从现有的罗斯海海相沉积序列中生成海洋和大气温度、水深、海洋环流和古生产力的微古生物学和地球化学记录；2)利用这些代理记录来验证MCO期间罗斯海板块的动态冰川扩张是由气候敏感性增强期间向高纬度输送热量和水分驱动的假设。下岩心地球化学和微古生物学研究将集中于在罗斯海大陆架上钻探的IODP站点U1521的一个扩展（120 m/ mi）早至中新世中期（~17-16 Ma）含硅藻/富泥岩/硅藻土单元。裂孔（~16 ~ 14.6 Ma）表明MMCT期间冰膨胀，其次是晶岩到泥岩单元，表明MMCT之前轻微退缩（14.6 ~ 14 Ma）。来自U1521站点的数据将与DSDP Leg 28（1972/73）和RISP J-9（1978-79）的有孔虫地球化学和微古生物学数据相结合，利用以前处理过有孔虫的遗留岩心材料，建立一个MCO到中新世晚期海洋-冰盖相互作用的区域视图。这一综合记录将：1)记录中新世中晚期在前进的罗斯海陆架上冰川进退的时间和范围；2)提供轨道尺度的古温度重建（TEX86, Mg/Ca, δ18O, MBT/CBT），以建立极端高纬度温暖间隔期间大气-海洋-冰的相互作用；3)提供轨道尺度的营养/古生产力，海洋环流。以及评估中新世南极冰盖和全球气候系统发展相关的气候反馈所需的古环境数据。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。

Nontechnical abstractPresently, Antarctica’s glaciers are melting as Earth’s atmosphere and the Southern Ocean warm. Not much is known about how Antarctica’s ice sheets might respond to ongoing and future warming, but such knowledge is important because Antarctica’s ice sheets might raise global sea levels significantly with continued melting. Over time, mud accumulates on the sea floor around Antarctica that is composed of the skeletons and debris of microscopic marine organisms and sediment from the adjacent continent. As this mud is deposited, it creates a record of past environmental and ecological changes, including ocean depth, glacier advance and retreat, ocean temperature, ocean circulation, marine ecosystems, ocean chemistry, and continental weathering. Scientists interested in understanding how Antarctica’s glaciers and ice sheets might respond to ongoing warming can use a variety of physical, biological, and chemical analyses of these mud archives to determine how long ago the mud was deposited and how the ice sheets, oceans, and marine ecosystems responded during intervals in the past when Earth’s climate was warmer. In this project, researchers from the University of South Florida, University of Massachusetts, and Northern Illinois University will reconstruct the depth, ocean temperature, weathering and nutrient input, and marine ecosystems in the central Ross Sea from ~17 to 13 million years ago, when the warm Miocene Climate Optimum transitioned to a cooler interval with more extensive ice sheets. Record will be generated from new sediments recovered during the International Ocean Discovery Program (IODP) Expedition 374 and legacy sequences recovered in the 1970’s during the Deep Sea Drilling Program. Results will be integrated into ice sheet and climate models to improve the accuracy of predictions. The research provides experience for three graduate students and seven undergraduate students via a multi-institutional REU program focused on increasing diversity in Antarctic Earth Sciences. Technical AbstractDeep-sea sediments reveal that the Miocene Climatic Optimum (MCO) was the warmest climate interval of the last ~20 Ma, was associated with global carbon cycle changes and ice growth, and immediately preceded the Middle Miocene Climate Transition (MMCT; ~14 Ma), one of three major intervals of Antarctic ice expansion and global cooling. Ice-proximal studies are required to assess: where and when ice grew, ice sheet extent, continental shelf geometry, high-latitude heat and moisture supply, oceanic and/or atmospheric temperature influence on ice dynamics, regional sea ice extent, meltwater input, and regions of bottom water formation. Existing studies indicate that ice expanded beyond the Transantarctic Mountains and onto the prograding Ross Sea continental shelf multiple times between ~17 and 13.5 Ma. However, these records are either too ice-proximal/terrestrial to adequately assess ocean-ice interactions or under-studied. To address this data gap, this work will: 1) generate micropaleontologic and geochemical records of oceanic and atmospheric temperature, water depth, ocean circulation, and paleoproductivity from existing Ross Sea marine sedimentary sequences, and 2) use these proxy records to test the hypothesis that dynamic glacial expansion in the Ross Sea sector during the MCO was driven by heat and moisture transport to the high latitudes during an interval of enhanced climate sensitivity. Downcore geochemical and micropaleontologic studies will focus on an expanded (120 m/my) early to middle Miocene (~17-16 Ma) diatom-bearing/rich mudstone/diatomite unit from IODP Site U1521, drilled on the Ross Sea continental shelf. A hiatus (~16-14.6 Ma) suggests ice expansion during the MCO, followed by diamictite to mudstone unit indicative of slight retreat (14.6 -14 Ma) immediately preceding the MMCT. Data from Site U1521 will be integrated with foraminiferal geochemical and micropaleontologic data from DSDP Leg 28 (1972/73) and RISP J-9 (1978-79) to develop a MCO to late Miocene regional view of ocean-ice sheet interactions using legacy core material previously processed for foraminifera. This integrated record will: 1) document the timing and extent of glacial advances and retreats across the prograding Ross Sea shelf during the middle and late Miocene, 2) provide orbital-scale paleotemperature reconstructions (TEX86, Mg/Ca, δ18O, MBT/CBT) to establish atmosphere-ocean-ice interactions during an extreme high-latitude warm interval, and 3) provide orbital-scale nutrient/paleoproductivity, ocean circulation, and paleoenvironmental data required to assess climate feedbacks associated with Miocene Antarctic ice sheet and global climate system development.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.