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 ∼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, ∼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.

关于冰河时期气候系统的两个基本问题正在等待令人满意的解决。首先，如果夏季太阳辐射强度真正控制了最后一个冰川周期的轨道特征，那么为什么包括最后一个终止在内的主要气候变化在全球范围内是同步的？其次，是什么导致千禧年尺度的气候振荡叠加在这个周期上？我们从南半球着眼于中纬度山区冰原的角度来解决这些问题。我们特别强调了最后一次冰川终结，它涉及轨道规模和千禧年规模的气候要素，并且在时间顺序上通常得到了很好的解决。

南阿尔卑斯山和安第斯山脉南部冰川地形的详细制图和年代学记录表明，高山冰川持续退缩，标志着最后一个冰河时代的终结，始于约18吉尔，始于冰期到近冰期之间的大气温度变化。一千年。副热带锋的快速极移，描绘了南洋洋北缘，距今约18吉尔，这意味着南风西风同时发生极移，使我们假设最后一个冰川终结的主导相为南方原点。连同半球间的古气候记录以及海洋-大气气候模拟的结果，这些发现表明，到上一个冰期已经结束了一个大的，快速的和全球性的终结，在该冰期中，南半球源于南半球。

这个假说的核心，被称为“ Zealandia Switch”，是相对于南半球海洋和大气环流的澳大利亚和西兰西亚大陆的位置。耦合的海洋-大气气候模型表明，无论是在赤道位置代表冰川模式气候还是在极地偏移位置标志着冰河模式气候，南半球西风的位置都会对海洋和相关的大气联系产生深远的影响。热带太平洋和南大洋。南极西风的转变具有全球气候后果，特别是通过导致大气中温室气体含量的变化以及从热带太平洋到北半球和南半球的热通量的改变而引起的。我们认为，最后一次冰川消融是一次全球变暖事件，它通过刺激冰水融化和冰山从邻接的冰盖进入北大西洋而导致了北纬极端季节性。淡水的涌入导致北大西洋海冰的大量散布，导致北方冬季非常寒冷，从而加剧了热带辐合带和季风雨带的年度南移。我们进一步建议，在过去的冰川周期内，Zlandia Switch机制的减弱表现是导致较小的，反复发生的千禧年规模气候振荡的原因。淡水的涌入导致北大西洋海冰的大量散布，导致北方冬季非常寒冷，从而加剧了热带辐合带和季风雨带的年度南移。我们进一步建议，Zlandia Switch机制的无声表现是最后一个冰川周期内较小的，反复发生的千禧年规模气候振荡的原因。淡水的涌入导致北大西洋海冰的大量散布，导致北方冬季非常寒冷，从而加剧了热带辐合带和季风雨带的年度南移。我们进一步建议，Zlandia Switch机制的无声表现是最后一个冰川周期内较小的，反复发生的千禧年规模气候振荡的原因。