Dynamics of the Late Oligocene Antarctic Ice Sheet
Dynamics of the Late Oligocene Antarctic Ice Sheet
复制标题
渐新世晚期南极冰盖的动力学
DOI：
10.11588/heidok.00030687
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Brzelinski
中科院分区：
文献类型：
--
作者：
Brzelinski
渐新世(33.9-23.03 Ma)叠加了从古近纪暖期到新近纪冷期的全球长期降温趋势，代表了新生代气候演化的过渡期。这标志着新生代冰屋的开始，人们认为这座冰屋始于南极洲大冰盖的形成。虽然渐新世南极冰盖(AIS)的长期演化在过去20年中已经得到了很好的证实，但其短期动力学还没有被很好地理解。此外，现有的关于晚渐新世的替代记录显示了关于南极冰量变率的步调和大小的相反信号，这阻碍了对晚渐新世冰量和气候动力学的全面和机械性的理解。这篇论文旨在解决这一悖论，并有助于更深入地理解晚渐新世气候和冰冻圈动力学。因此，高分辨率底栖和浮游有孔虫替代记录是根据在U1406号站点(大西洋西北部)综合大洋钻探计划(IODP)考察342的框架内钻探的深海沉积物生成的。这些记录为研究晚渐新世期间在轨道时间尺度上冰盖减弱和融化的基本过程和机制提供了足够的保真度。在本文的第一部分，对AIS波动的短期过程和机制提出了前所未有的新颖见解。本论文的研究证明，晚渐新世AIS在轨道时间尺度上具有高度的动力学特征。AIS通常在两种冰川状态之间转换，即现代冰量的一半到略大于现代全球冰量的一半，以及小于现代全球冰量的一半。太阳辐射强迫被认为是调节AIS范围和动力学变化的关键因素：当AIS体积较小时，偏心周期的影响较大，而较大的冰量对倾角的变化更敏感。地球自转轴上非常大的天使会引起严重的冰川消融脉冲。本文的第二部分探讨了这些AIS动态的潜在后果。首次报道了北大西洋高原(U1406站位)的高分辨率浮游有孔虫代理记录。探讨了晚渐新世南半球冰川动力学对表层海洋特征的潜在变化。结果表明，北大西洋洋流(NAC)在晚渐新世期间的经向位置和强度随南半球冰川动力学的变化而变化。有迹象表明，NAC的变异性导致了营养物质浓度的变化和向北输送的热量的变化，这对环北大西洋区域的气候具有更广泛的影响。
Superimposed on a global long-term cooling trend from the warm conditions of the Paleogene into the colder Neogene, the Oligocene epoch (33.9–23.03 Ma) represents a transitional phase of Cenozoic climate evolution. It marks the onset of the Cenozoic “icehouse” that is thought to have commenced with the initiation of large ice sheets on Antarctica. While the long-term evolution of the Oligocene Antarctic Ice Sheet (AIS) has been well established over the last two decades, its short-term dynamics are not well understood. Furthermore, available proxy records of the Late Oligocene show opposing signals regarding the pacing and magnitude of Antarctic ice-volume variability, which hampers a full and mechanistic understanding of Late Oligocene ice-volume and climate dynamics. This thesis aims to address this paradox and contribute to a more sophisticated understanding of the Late Oligocene climate and cryosphere dynamics. Therefore, high-resolution benthic and planktic foraminiferal proxy records are generated based on deep-sea sediments drilled within the framework of the Integrated Ocean Drilling Program (IODP) Expedition 342 at Site U1406 (northwestern Atlantic). These records provide adequate fidelity to study the fundamental processes and mechanisms underlying ice-sheet waning and waxing on orbital timescales during the Late Oligocene. In the first part of this thesis, novel and unprecedented insights into short-term processes and mechanisms of AIS fluctuations are presented. Investigations of this thesis evidence that the Late Oligocene AIS was highly dynamic on orbital timescales. The AIS generally shifted between two states of glaciation, i.e., volumes of half the modern to slightly bigger than modern global ice-volumes, and smaller than to half the modern global ice volume. Insolation forcing is identified as a key player in modulating changes in the extent and dynamics of the AIS: The influence of eccentricity periodicities is higher when AIS volumes are smaller, whereas bigger ice-volume react more sensitively to changes in obliquity. Very large angels of the Earth’s spin axis are shown to cause severe deglaciation pulses. Potential consequences of those AIS dynamics are explored in the second part of this thesis. The first high-resolution planktic foraminiferal proxy record from the high Northern Atlantic (Site U1406) is presented. Potential changes in surface ocean characteristics in response to glacial dynamics of the Southern Hemisphere during the Late Oligocene are explored. It is shown that the meridional position and strength of the North Atlantic Current (NAC) during the Late Oligocene has varied as a function of glacial dynamics of the Southern Hemisphere. There are indications that the NAC variability caused changes in nutrient concentrations and alterations in the amount of northward heat transport, which has broader implications for the climate in the circum-North Atlantic region.