米兰科维奇冰期旋回理论中的“4万年周期问题”:回顾与展望  

The"40000-year problem"in the Milankovitch Theory of Pleistocene glacial cycles:Retrospect and prospect

作　　者：颜余真 YAN Yuzhen(State Key of Laboratory of Marine Geology,Tongji University,Shanghai 200092;School of Ocean and Earth Science,Tongji University,Shanghai 200092)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092 [2]同济大学海洋与地球科学学院,上海200092

出　　处：《第四纪研究》2023年第6期1722-1729,共8页Quaternary Sciences

基　　金：中央高校基本科研业务费专项项目(批准号:同济大学22120230112)资助。

摘　　要：米兰科维奇理论认为地球轨道的天文周期调控北半球高纬地区夏季接收太阳辐射的强度,进而驱动第四纪地表的冰期-间冰期旋回。20世纪60年代以来,米兰科维奇理论预测的天文周期在第四纪海洋沉积物中得到了印证,看似证明了该理论的正确性。但大量新记录的出现给经典米兰科维奇理论带来了挑战,早更新世的“4万年周期问题”——即为何早更新世的冰期旋回中没有岁差周期——就是其中之一。目前对于该问题的两种回答包括:1)南、北半球冰盖分别受当地夏季太阳辐射强度的驱动;2)早更新世冰期受北半球夏季累积太阳辐射量驱动。不难发现,这两种假说均默认了米兰科维奇理论中“高纬地区是驱动地球气候演变关键区域”的假设,争议的点仅在于岁差是否影响了高纬度冰盖的变化,这或许是“4万年周期问题”至今悬而未决的原因。未来要解决早更新世乃至整个第四纪冰期旋回的问题,或许目光要跳出高纬地区,考虑低纬过程以及高-低纬之间的相互作用。Milankovitch's Theory posits that variations in Earth's orbit around the Sun modulate the intensity of insolation received by the high-latitude region of the Northern Hemisphere,thereby driving the Pleistocene ice age cycles.The predicted cycles corresponding to orbital variabilities have been found in deep sea sediments obtained since the 1960s and they appear to support Milankovitch's Theory.However,the emergence of a large number of new records has brought challenges to the Milankovitch Theory,one of which pertains to the lack of precession cycles in the 40,000-year glacial cycles during the Early Pleistocene(known as the"40,000-year problem").There are currently two leading hypotheses to account for the absence of precession.The first one is that summer insolation in northern and southern hemispheres is out-of-phase on precession frequencies,and therefore global ice volumes lacked precession cycles in the Early Pleistocene when northern and southern hemisphere responded to local summer insolation.The other theorizes that it was the 65°N integrated summer insolation(ISI)above 275 W/m2,which has little periodicity related to precession,that paced Early-Pleistocene glacial cycles.A series of studies have provided pieces of indirect information about the Early-Pleistocene glacial cycles and it appears that precession forcing was indeed present in various high-latitude climate records such as lake and ocean sediments and polar ice cores.Yet,there are no direct records of individual ice volume dating back to the Early Pleistocene,due to the difficulty in reconstructing past volumetric changes of individual ice sheets.Furthermore,insolation rarely leaves a direct imprint in geologic records and,in turn,has to be determined from the age of the record.The accurate dating of geologic records without orbital tuning poses another layer of challenge.After reviewing the progress and difficulties in addressing the"40,000-year problem",it should be emphasized that both hypotheses implicitly acknowledge the assumption in the

关 键 词：米兰科维奇理论 轨道周期 岁差 斜率 低纬过程 

分 类 号：P534.6[天文地球—古生物学与地层学] P512.6[天文地球—地质学]