COLLABORATIVE RESEARCH: Orbital-scale Variability of the West Antarctic Ice Sheet and the Formation of Bottom Water in the Ross Sea during the Pliocene-Pleistocene

合作研究：上新世-更新世期间南极西部冰盖的轨道尺度变化和罗斯海底层水的形成

• 批准号: 2000997
• 负责人: Molly Patterson
• 金额: $ 10.76万
• 依托单位: SUNY at Binghamton
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2000997&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Orbital; scale; Variability; COLLABORATIVE; RESEARCH; Orbital; scale; Variability

Part I: Non-technical description: Predicting how polar ice sheets will respond to future global warming is difficult because all the processes that contribute to their melting are not well understood. This is important because the more ice on land that melts, the higher sea levels will rise. The most significant uncertainty in current estimates of sea-level rise in the coming decades is the potential contribution from the Antarctic Ice Sheet. One way to increase our knowledge about how large ice sheets respond to climate change in response to natural factors is to examine the geologic past. Natural global warming (and cooling) events in Earth’s history provide examples that we can use to better understand processes, interactions, and responses we can’t directly observe today. One such time period, approximately three million years ago (known as the Pliocene), was the last time atmospheric carbon dioxide levels were as high as they are today and, therefore, represents a time period to study to better understand the ice sheet response to a warming climate. Specifically, this project is interested in understanding how ocean currents near Antarctica, which transport heat and store carbon, behaved during these past climate events. The history of past ice sheet-ocean interactions are recorded in sediments that were deposited, layer upon layer, in the deep sea offshore Antarctica. In January-February 2018, a team of scientists and crew set sail to the Ross Sea, offshore west Antarctica, on the scientific ocean drilling vessel JOIDES Resolution to recover such sediment archives. This project focuses on a sediment core from that expedition, which captures the relatively warm Pliocene time interval, as well as the subsequent transition into cooler climates typical of the past two million years. The researchers will analyze the sediment with multiple complementary measurements, including: grain size, composition, chemistry of organic matter, physical structures, microfossil type and abundance, and more. These analyses will be done by the research team, including several students, at their respective laboratories and will then integrated into a unified record of ice sheet-ocean interactions. Ultimately, the results will be used to improve modeled projections of how the Antarctic Ice Sheet could respond to future climate change. Part II: Technical description: Geological records from the Antarctic Ice Sheet (AIS) margin demonstrate that the ice sheet oscillated in response to orbital variations in insolation (i.e., ~400, 100, 41, and 20 kyr), and it appears to be more sensitive to specific frequencies that regulate mean annual insolation (i.e., 41-kyr obliquity), particularly when the ice sheet extends into marine environments and is impacted by ocean circulation. However, the relationship between orbital forcing and the production of Antarctic Bottom Water (AABW) is unconstrained. Thus, a knowledge gap exists in understanding how changing insolation impacts ice marginal and Southern Ocean conditions that directly influence ventilation of the global ocean. The researchers hypothesize that insolation-driven changes directly affected the production and export of AABW to the Southern Ocean from the Pliocene through the Pleistocene. For example, obliquity amplification during the warmer Pliocene may have led to enhanced production and export of dense waters from the shelf due to reduced AIS extent, which, in turn, led to greater AABW outflow. To determine the relationship of AABW production to orbital regime, they plan to reconstruct both from a single, continuous record from the levee of Hillary Canyon, a major conduit of AABW outflow, on the Ross Sea continental rise. To test their hypothesis, they will analyze sediment from IODP Site U1524 (recovered in 2018 during International Ocean Discovery Program Expedition 374) and focus on three data sets. (1) They will use the occurrence, frequency, and character of mm-scale turbidite beds as a proxy of dense-shelf-water cascading outflow and AABW production. They will estimate the down-slope flux via numerical modeling of turbidity current properties using morphology, grain size, and bed thickness as input parameters. (2) They will use grain-size data, physical properties, XRF core scanning, CT imaging, and hyperspectral imaging to guide lithofacies analysis to infer processes occurring during glacial, deglacial, and interglacial periods. Statistical techniques and optimization methods will be applied to test for astronomical forcing of sedimentary packages in order to provide a cyclostratigraphic framework and interpret the orbital-forcing regime. (3) They will use bulk sedimentary carbon and nitrogen abundance and isotope data to determine how relative contributions of terrigenous and marine organic matter change in response to orbital forcing. All of these data will be integrated with sedimentological records to deconvolve organic matter production from its deposition or remobilization due to AABW outflow as a function of the oscillating extent of the AIS. These data sets will be integrated into a unified chronostratigraphy to determine the relationship between AABW outflow and orbital-forcing scenarios under the varying climate regimes of the Plio-Pleistocene.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.

第一部分：非技术描述：预测极地冰盖将如何对未来的全球变暖做出反应是困难的，因为所有促成其融化的过程都不对其进行充分了解。这很重要，因为融化的土地上越多，海平面就会上升。未来几十年，目前对海平面上升的估计值的不确定性是南极冰盖的潜在贡献。提高我们对响应自然因素对气候变化的大型冰淇淋的认识的一种方法是检查地质的过去。地球历史上的自然全球变暖（和冷却）事件提供了我们可以用来更好地了解今天无法直接观察的过程，互动和响应的例子。大约三百万年前（称为上新世）的一个这样的时期是最后一次大气中的二氧化碳水平与今天一样高，因此代表了一个研究时间段，可以更好地了解对气候变暖的冰盖反应。具体而言，该项目有兴趣了解在过去的气候事件中，在热量和储存碳的南极洲附近的洋流如何运输和储存碳。过去的冰片海洋相互作用的历史记录在沉积在深海南极洲的沉积的沉积物中。 2018年1月至2月，一支科学家和船员团队在科学的海洋钻井船上启航到西南极海上的罗斯海，加入了解决这些沉积物档案的解决方案。该项目的重点是该探险队的沉积物核心，该探险队捕捉了相对温暖的上新世时间间隔，以及随后向过去200万年典型的凉爽气候的过渡。研究人员将通过多个完成测量值分析沉积物，包括：晶粒尺寸，组成，有机物化学，物理结构，微化石类型和抽象等等。这些分析将由研究团队（包括几个学生）在各自的实验室中进行，然后将其融入冰盖海洋互动的统一记录中。最终，结果将用于改善南极冰盖如何应对未来气候变化的建模项目。第二部分：技术描述：来自南极冰盖（AIS）边缘的地质记录表明，冰盖响应于轨道上的轨道变化而振荡（即〜400、100、41和20 kyr），它似乎对调节年度冰的特定频率更敏感，即在41-KYR IS的特定频率中（即41- kyrique），尤其是在41- kyr scile中，尤其是在41- kyr yemique时（尤其是kyrique）。通过海洋循环。但是，轨道强迫与南极底水（AABW）的产生之间的关系是不受限制的。这是一个知识差距在理解变化的隔热层如何影响直接影响全球海洋通风的冰块边缘和南部海洋状况的情况下。研究人员假设以Imsolation驱动的变化直接影响了AABW从上新世到更新世向南大洋的生产和出口。例如，由于AIS范围降低，在温暖的上新世期间的倾斜扩增可能导致了从架子上的密集水的产量和出口，这又导致了更大的AABW出口。为了确定AABW生产与轨道政权的关系，他们计划从Ross Sea Sea Continental Rise的Hillary Canyon（AABW Outlet的主要渠道）中从单一连续的记录中重建两者。为了检验他们的假设，他们将分析IODP网站U1524（2018年在国际海洋发现计划探险374年回收）的沉积物，并专注于三个数据集。 （1）他们将使用MM规模的浊度床的发生，频率和特征作为密集的水上级联出口和AABW生产的代理。他们将使用形态学，晶粒尺寸和床厚度作为输入参数来估计斜率通过浊流特性的数值模型来估计下坡通量。 （2）他们将使用晶粒大小的数据，物理特性，XRF核心扫描，CT成像和高光谱成像来指导岩相分析来推断冰川，冰川冰期和冰川间期间发生的过程。统计技术和优化方法将应用于测试沉积包的天文学强迫，以提供环形地层学框架并解释轨道锻造方案。 （3）他们将使用大量的沉积碳和氮丰度和同位素数据来确定陆源和海洋有机物对轨道强迫的相对贡献如何变化。所有这些数据都将与沉积学记录集成，以从其沉积或由于AABW出口而导致的有机物生产，这是AIS振荡范围的函数。这些数据集将被整合到统一的年度地层学中，以确定在Plio-Pleisteene的不同气候状态下AABW插座和轨道锻造场景之间的关系。该奖项反映了NSF的法定任务，并认为通过基金会的知识优点和广泛的criperia criperia criperia criperia criperia criperia criperia criperia criperia rection the precion the precial taunce the奖励。