The Middle Miocene Antarctic Climate Transition: Investigating Magnitude, Phasing, and Processes Involving Cryosphere Expansion and Global Cooling

中新世南极气候转变：调查涉及冰冻圈扩张和全球变冷的幅度、阶段和过程

• 批准号: 0229898
• 负责人: James Kennett
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-03-01 至 2006-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229898&HistoricalAwards=false
• 关键词: Middle; Miocene; Antarctic; Climate; Transition

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a project to investigate the Miocene climate transition as recorded in Ocean Drilling Program cores from the South Tasman Rise. Understanding mechanisms that force climate change is a major challenge in Earth Sciences. Middle Miocene (~13-15 Ma (million years ago)) geologic records describe significant global ocean/atmosphere cooling coincident with Antarctic cryosphere expansion and a lack of appreciable Northern Hemisphere ice sheets. This suggests that Antarctic climate and cryosphere evolution played a central role in late Cenozoic climate development. Given the complexity of traditional proxies (e.g. d18O), fundamental questions exist concerning the magnitude, phasing, and processes driving mid-Miocene ice volume and temperature change. The primary objectives of this project are to better understand: 1) magnitude and phasing of global cooling and Antarctic cryosphere expansion across this interval; 2) processes that forced Antarctic climate/cryosphere evolution at this time; and 3) effects of an expanding and increasingly stable Antarctic cryosphere on climate feedbacks at orbital periods (about 40, 100, and 400 thousand years). Recently developed geochemical paleotemperature proxies (Mg/Ca) should deconvolve mid-Miocene d18O temperature and ice volume signals. New data from ODP Site 1171 Miocene foraminifers suggest that Mg/Ca will yield paleotemperatures necessary to evaluate ice volume and temperature changes. This project will integrate high-resolution (2-6 kyr (thousand year)) planktonic and benthic foraminifer Mg/Ca, d18O, d13C, and faunal records to address these objectives. This novel multi-proxy approach will test hypotheses regarding mid-Miocene Antarctic cryosphere evolution and global cooling. Further inquiry will address: 1) processes forcing the mid-Miocene climate shift, and 2) dynamic influences of climate feedbacks across this shift. The research will: i) assess the southwest Pacific/Southern Ocean hydrographic response to this climate shift, ii) evaluate possible processes/feedbacks involved in cryospheric expansion using records with age resolution of ~2-6 kyr to distinguish 40 and 100 kyr orbital periodicity, and iii) characterize the evolution of the climate spectrum at orbital time-scales through the mid-Miocene climate transition. To achieve the proposed objectives, high-resolution (~2-6 kyr) multi-proxy geochemical and faunal investigations will be conducted on a pair (ODP Sites 1170 and 1171) of unusually high quality marine CaCO3 sequences of mid-Miocene age (~16.8 to 12 Ma) drilled on the South Tasman Rise (STR) during ODP Leg 189. STR sequences provide a rare opportunity to study the mid-Miocene global climate shift at a sensitive oceanographic interface in the high southern latitudes. In the mid Miocene, the STR was situated proximal to the confluence of subtropical Pacific circulation and the Antarctic Circumpolar Current. The STR marks the southern extent of the East Australian Current, a sensitive western boundary current supplying heat and moisture to high southern latitudes. Sites 1170 and 1171 are marked by superb-quality CaCO3 preservation, relatively high deep-sea sedimentation rates (~6 cm/kyr), and 80% recovery. The primary intellectual merit of this research is that it will provide an unprecedented opportunity to examine the magnitude, phasing, and processes influencing middle Miocene Antarctic cryosphere expansion and global cooling at orbital timescales. This research will focus the view of Cenozoic climate evolution, including processes and feedbacks influencing Earth's systems across a major climate transition. Dramatic changes occurring in Antarctica, which may be linked to observed tropical Pacific variability (ENSO), underscore the need to improve understanding of feedbacks influencing the development, extent, and stability of the Antarctic cryosphere on both long (tens of thousands to millions of years) and short (decadal to millennial) timescales. The impact of this research is broad, as it addresses major issues related to the evolution of the Antarctic cryosphere and its response to climate reorganizations that is of vital interest to society. Further broader impacts are the student training that will be accomplished during the course of the research.

该奖项由极地方案办公室南极地质和地球物理方案提供，支持一个项目，调查南塔斯曼海隆海洋钻探方案岩心记录的中新世气候转变。了解气候变化的机制是地球科学的一个重大挑战。中新世中期（约13-15 Ma（百万年前））的地质记录描述了与南极冰冻圈扩张和缺乏明显的北方半球冰盖相一致的显著的全球海洋/大气冷却。这表明，南极气候和冰冻圈的演变在晚新生代气候发展中发挥了核心作用。由于传统的代理（如d18 O）的复杂性，基本问题存在的规模，相位和过程驱动中中新世冰量和温度变化。该项目的主要目标是更好地了解：1）全球冷却和南极冰冻圈扩张的幅度和阶段; 2）此时迫使南极气候/冰冻圈演变的过程; 3）南极冰冻圈扩张和日益稳定对轨道周期（约40，100和40万年）气候反馈的影响。最近开发的地球化学古温度代理（镁/钙）应去卷积中新世中期d18 O温度和冰量信号。ODP站点1171中新世有孔虫的新数据表明，Mg/Ca将产生评估冰量和温度变化所需的古温度。该项目将整合高分辨率（2-6 kyr（千年））浮游和底栖有孔虫Mg/Ca，d18 O，d13 C和动物群记录，以实现这些目标。这种新的多代理方法将测试假设中中新世南极冰冻圈的演变和全球变冷。进一步的调查将解决：1）迫使中新世中期气候转变的过程，以及2）气候反馈在这一转变中的动态影响。该研究将：i）评估西南太平洋/南大洋水文对这种气候变化的响应，ii）使用年龄分辨率为2-6 kyr的记录来评价冰冻圈扩张中可能涉及的过程/反馈，以区分40 kyr和100 kyr的轨道周期，iii）描述通过中中新世气候过渡的轨道时间尺度上气候谱的演变。为实现拟定目标，将对ODP第189航次期间在南塔斯曼海隆（STR）钻探的一对（ODP站点1170和1171）中中新世（~16.8至12 Ma）异常高质量的海洋CaCO 3层序进行高分辨率（~2-6 kyr）多代地球化学和动物群调查。STR序列提供了一个难得的机会，研究中中新世全球气候变化在一个敏感的海洋界面在南高纬度地区。中新世中期，STR位于副热带太平洋环流和南极绕极流交汇处附近。STR标志着东澳大利亚海流的南部范围，这是一个敏感的西部边界流，为南部高纬度地区提供热量和水分。1170号和1171号地点的特点是保存了优质的碳酸钙，深海沉积速率相对较高（约6厘米/千年），回收率为80%。这项研究的主要智力价值是，它将提供一个前所未有的机会，以审查影响中新世中期南极冰冻圈扩张和全球冷却的轨道时间尺度的幅度，阶段和过程。这项研究将侧重于新生代气候演变的观点，包括在重大气候转变中影响地球系统的过程和反馈。南极洲发生的剧烈变化可能与观测到的热带太平洋变率（ENSO）有关，这突出表明需要更好地了解影响南极冰冻圈长期（数万至数百万年）和短期（十年至千年）发展、范围和稳定性的反馈。这项研究的影响是广泛的，因为它解决了与南极冰冻圈演变及其对气候重组的反应有关的重大问题，这对社会至关重要。更广泛的影响是学生的培训，将在研究过程中完成。