The Zealandia Switch: Ice age climate shifts viewed from Southern Hemisphere moraines
The Zealandia Switch: Ice age climate shifts viewed from Southern Hemisphere moraines
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DOI：
10.1016/j.quascirev.2020.106771
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发表时间：
2021-03-12
影响因子：
4
通讯作者：
Strand, Peter D.
中科院分区：
文献类型：
--
作者：
Denton, George H.;Putnam, Aaron E.;Strand, Peter D.
关于冰河时代气候系统的两个基本问题有待满意的解决。首先，如果夏季太阳辐射强度确实控制了末次冰期的轨道特征，那么为什么包括末次冰期在内的主要气候变化是全球同步的？其次，是什么导致了叠加在这个周期上的千年尺度气候振荡？我们解决这些问题，从南半球的角度来看，集中在中纬度山区冰原。我们特别强调末次冰期的终止，它涉及轨道尺度和千年尺度的气候要素，通常具有很好的年代控制。山区冰川的持续退缩，通过详细的南阿尔卑斯山和南安第斯山脉冰川地貌的测绘和年代学记录，标志着末次冰期的结束，开始类似于18 kyrs前，并涉及在一两千年内从冰川到近间冰期大气温度的变化。与18 kyrs前相似，副热带锋快速向极移动，描绘了南大洋的北方边缘，这意味着南半球西风带同时向极移动，并使我们假设最后一次冰川终止的主要阶段起源于南方。再加上半球间的古气候记录和耦合海洋-大气气候模型的结果，这些发现表明，上一个冰河时代的大，快，全球结束，其中南方来源的变暖事件连接了半球。我们认为，在南大洋环流和南西风系统的转变，与南方轨道强迫，通过影响热带热力发动机，从而导致全球气候变暖episode。这个假设的核心，被称为“西兰迪亚开关”，是澳大利亚和西兰迪亚大陆相对于南半球海洋和大气环流的位置。耦合的海洋-大气气候模拟表明，无论是在一个更赤道的位置代表冰川模式的气候，或在一个极移的位置标记间冰期模式的气候，南纬西风的轨迹，有深远的影响海洋和相关的热带太平洋和南大洋之间的大气联系。南西风带的移动会对全球气候产生影响，特别是通过大气中温室气体含量的变化以及从热带太平洋进入北方和南半球的热通量的改变。我们认为，最后一次冰川的终止是一个全球变暖的插曲，导致极端的季节性在北方纬度地区的刺激冲洗融水和冰山进入北大西洋从相邻的冰盖。这些淡水的涌入导致北大西洋海冰大面积蔓延，造成寒冷的北方冬季，从而扩大了热带辐合带和季风雨带每年向南的移动。我们进一步认为，沉默的表现西兰迪亚开关机制负责较小的，反复出现的千年尺度的气候振荡在最后一次冰期周期。(C)2020爱思唯尔有限公司保留所有权利。
Two fundamental questions about the ice-age climate system await satisfactory resolution. First, if summer solar radiation intensity truly controls the orbital signature of the last glacial cycle, then why were major climatic shifts, including the last termination, globally synchronous? Second, what caused the millennial-scale climate oscillations superimposed on this cycle? We address these questions from a Southern Hemisphere perspective focused on mid-latitude mountain ice fields. We put particular emphasis on the last glacial termination, which involved both orbital-scale and millennial-scale climate elements and has generally well-resolved chronological control.Sustained retreat of mountain glaciers, documented by detailed mapping and chronology of glacial landforms in the Southern Alps and southern Andes, marked the termination of the last ice age, beginning similar to 18 kyrs ago and involved a change from glacial to near-interglacial atmospheric temperature within a millennium or two. A rapid poleward shift of the Subtropical Front, delineating the northern margin of the Southern Ocean, similar to 18 kyrs ago implies a concurrent poleward shift of the austral westerlies and leads us to hypothesize a southern origin for the dominant phase of the last glacial termination. Together with interhemispheric paleoclimate records and with results of coupled ocean-atmosphere climate modeling, these findings suggest a big, fast, and global end to the last ice age in which a southern-sourced warming episode linked the hemispheres. We posit that a shift in the Southern Ocean circulation and austral westerly wind system, tied to southern orbital forcing, caused this global warming episode by affecting the tropical heat engine and hence global climate.Central to this hypothesis, dubbed the 'Zealandia Switch', is the location of the Australia and Zealandia continents relative to Southern Hemisphere oceanic and atmospheric circulation. Coupled ocean-atmosphere climate modeling shows that the locus of the austral westerlies, whether in a more equatorward position representing a glacial-mode climate or in a poleward-shifted position marking interglacial-mode climate, has profound effects on oceanic and associated atmospheric linkages between the tropical Pacific and the Southern Ocean. Shifts in the austral westerlies have global climatic consequences, especially through resulting changes in the greenhouse gas content of the atmosphere and altered heat flux from the tropical Pacific into the Northern and Southern Hemispheres. We suggest that the last glacial termination was a global warming episode that led to extreme seasonality in northern latitudes by stimulating a flush of meltwater and icebergs into the North Atlantic from adjoining ice sheets. This fresh-water influx resulted in widespread North Atlantic sea ice that caused very cold boreal winters, thus amplifying the annual southward shift of the Intertropical Convergence Zone and the monsoonal rain belts. We further suggest that muted manifestations of the Zealandia Switch mechanism were responsible for smaller, recurring millennial-scale climate oscillations within the last glacial cycle. (C) 2020 Elsevier Ltd. All rights reserved.