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《极地计划办公室》的南极地质和地球物理学计划提供，支持一个项目，以调查南塔斯曼崛起中海洋钻井计划中的中新世气候过渡。了解强迫气候变化的机制是地球科学的主要挑战。中新世中期（〜13-15 Ma（百万年前））地质记录描述了与南极冰裂层扩张相吻合的重要全球海洋/大气冷却，并且缺乏明显的北半球冰盖。这表明南极气候和冰冻圈的演化在周末的新生代气候发展中起着核心作用。鉴于传统代理的复杂性（例如D18O），存在有关驱动中新世冰量和温度变化的幅度，平差和过程的基本问题。该项目的主要目标是更好地理解：1）在此间隔内，整​​体冷却和南极冰圈扩展的幅度和相分； 2）此时迫使南极气候/冰冻圈进化的过程； 3）在轨道时期（大约40、100和40万年），南极冰裂层扩展和日益稳定的南极冷冻层的影响。最近开发的地球化学古温代理（mg/ca）应解除中新世D18O温度和冰量信号。来自ODP站点1171个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植物。该项目将集成高分辨率（2-6 KYR（千年））浮游生物和底栖有孔虫MG/CA，D18O，D13C和动物记录以解决这些目标。这种新型的多核方法将测试有关中新世南极中期冰冻圈进化和全球冷却的假设。进一步的询问将解决：1）迫使中新世气候变化的过程，以及2）整个转变中气候反馈的动态影响。研究将：i）评估西南太平洋/南方海洋水文对这种气候变化的反应，ii）评估使用记录的记录涉及的可能的过程/反馈，年龄分辨率约为2-6 kyr，以区分40和100 kyr轨道周期性，以及III），以及III），表征了Orbital Time-Scales calliens-miocene clindition clindition clindition clindition clinciention clindition clindition clindition clindition clindition clindition clindition clinciention calliess calliend calliend cliendsine。为了实现提出的目标，将在一对（ODP地点1170和1171）上进行高分辨率（〜2-6 kyr）多型地球化学和动物的研究，对中年时代中期的异常高质量的海上CACO3序列（〜16.8至12 MA）的序列（〜16.8至12 MA）的序列（〜16.8至12 MA）的序列（STR）在prep（STR）中的繁殖（STR）稀有（ODP）在ODE（STR）r的序列（ODP）稀有。中新世全球气候变化在高纬度地区的敏感海洋界面处。在中新世中期，STR位于亚热带太平洋循环和南极循环电流的近端。 STR标志着东澳大利亚电流的南部范围，这是一种敏感的西部边界电流，向高南部的高纬度地区供应热量和水分。地点1170和1171的特征是高质量的CACO3保存，相对较高的深海沉积率（〜6 cm/kyr）和80％的回收率。这项研究的主要智力优势在于，它将提供一个前所未有的机会，以检查影响中新世南极中期冰冻圈中间的大小，阶段和过程，以及在轨道时间表上的全球冷却。这项研究将重点关注新生代气候演化的观点，包括影响地球系统在主要气候过渡的过程中的过程和反馈。南极洲发生的巨大变化，可能与观察到的热带太平洋变异性（ENSO）有关，强调了对反馈的理解的必要性，这些反馈会影响南极冰圈的发展，程度和稳定性对长期（数千至数百万年至百万年）和（对千年）时代的时间。这项研究的影响很广，因为它解决了与南极冰冻圈的演变有关的主要问题及其对社会至关重要的气候重组的反应。更广泛的影响是在研究过程中将完成的学生培训。