The Mid-Pleistocene Enigma
The Mid-Pleistocene Enigma
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DOI：
10.5670/oceanog.2020.216
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发表时间：
2020-06
期刊：
影响因子：
2.8
通讯作者：
H. Ford;T. Chalk
中科院分区：
文献类型：
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作者：
H. Ford;T. Chalk
地球轨道的变化会影响入射的太阳辐射，并引导过去的冰川-间冰期振荡。这些日照的节律性变化被称为米兰科维奇周期。大约90万年前，地球的气候起搏器跳过了一拍，从早更新世的41，000年偏心率（地球的轴向倾斜）起搏切换到晚更新世的约100，000年偏心率（地球绕太阳轨道的圆形）起搏。这种从冰川到间冰期的转变，被称为中更新世过渡（MPT），仍然是第四纪和古海洋学领域最持久的谜团之一。最近对大气和海洋过程的重建以及对它们之间的动态联系的研究为更详细地了解这种气候转变和整个地球气候系统铺平了道路。应用于海洋沉积物岩心研究的地球化学技术的进步，通过科学的海洋钻探恢复，使重建更高分辨率的古气候记录的大气CO2，海洋蒸发碳含量，海洋环流变化，冰量。我们现在了解到，冰川间冰期变化的特征时间尺度主要与海洋及其与冰盖相互作用所调制的动力学过程有关-特别是，我们对南大洋在调节地球气候及其特征节拍方面的作用有了更多的了解。MPT至少分两步进行（图1和图2）。第一次是海洋同位素第一阶段（MIS）22附近的“900 kyr事件”，当时出现了准偏心率信号。第二次是MIS 16，当过渡完成时。第一步对海洋碳循环和（可能）对大气碳的影响最大。早更新世具有对称的冰期周期，冰川-间冰期大气CO2约为240-285 μatm（Yan等人，2019年，以及参考文献）。在MIS 22-MIS 16之间，存在着弱间冰期和日益严重的冰期。在MIS 16，
Variations in Earth’s orbit affect incoming solar radiation and have guided past glacialinterglacial oscillations. These rhythmic changes in insolation are known as Milankovitch cycles. Approximately 900,000 years ago, Earth’s climate pacemaker skipped a beat and switched from the 41,000-year obliquity (Earth’s axial tilt) pacing of the Early Pleistocene to ~100,000-year eccentricity (circularity of Earth’s orbit around the sun) pacing of the Late Pleistocene. This glacial-tointerglacial shift, called the Mid-Pleistocene Transition (MPT), remains one of the most enduring mysteries of the Quaternary and in the field of paleoceanography. Recent reconstructions of atmospheric and oceanic processes and studies of the dynamic linkages between them have paved the way for a more detailed mechanistic understanding of this climatic transition and of Earth’s climate system at large. Advances in geochemical techniques applied to studies of ocean sediment cores recovered by scientific ocean drilling enable reconstruction of higher-resolution paleo climatic records of atmospheric CO2, ocean remineralized carbon content, ocean circulation change, and ice volume. We now understand that the characteristic timescales of glacialinterglacial variability are primarily linked to dynamical processes modulated by the ocean and its interaction with ice sheets—in particular, we understand much more about the Southern Ocean’s role in moderating Earth’s climate and its characteristic beats. The MPT occurred in at least two steps (Figures 1 and 2). The first was the “900 kyr event” around Marine Isotope Stage1 (MIS) 22, when the quasi-eccentricity signal emerged. The second was MIS 16 when the transition was complete. The first step had the largest impact on ocean carbon cycling and (likely) on atmospheric carbon. The Early Pleistocene had symmetrical ice age cycles and a glacialtointerglacial atmospheric CO2 of ~240–285 μatm (Yan et al., 2019, and references within). Between MIS 22 and MIS 16, there were weak interglacial and increasingly severe glacial periods. At MIS 16,