季节性海冰驱动的冰期北大西洋“电容器”效应  

The Glacial North Atlantic “Capacitor” effect controlled by seasonal sea ice change

作　　者：张旭 张炜晨 王振乾 郑凯 邓凤飞 ZHANG Xu;ZHANG Weichen;WANG Zhenqian;ZHENG Kai;DENG Fengfei(Key Laboratory of Western China’s Environmental Systems(Ministry of Education),College of Earth and Environmental Science,Lanzhou University,Lanzhou 730000,China;Group of Alpine Paleoecology and Human Adaptation(ALPHA),Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101,China;State Key Laboratory of Tibetan Plateau Earth System,Resources and Environment(TPESRE),Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101,China)

机构地区：[1]兰州大学资源环境学院,西部环境教育部重点实验室,甘肃兰州730000 [2]中国科学院青藏高原研究所古生态与人类适应团队,北京100101 [3]中国科学院青藏高原研究所,青藏高原地球系统与资源环境国家重点实验室,北京100101

出　　处：《地学前缘》2022年第5期334-341,共8页Earth Science Frontiers

基　　金：国家自然科学基金项目(42075047);国家重点研发项目(2020YFA0608902)。

摘　　要：第四纪冰期的千年尺度气候突变事件——Dansgaard-Oeschger Event (D-O事件),一直是古气候学领域关注的重点。近年来,数值模拟的研究发现,北大西洋副极地地区年际-年代际气候变率的振幅在D-O事件中的冰阶冷期远大于间冰阶暖期,这一现象为理解该区域海温代理指标的气候学意义提供了重要参考价值,但其动力机制尚不清晰。本文利用海气耦合气候模型(COSMOS),通过模拟氧同位素(MIS)3阶段的一个典型D-O事件过程,探讨了冰阶冷期北大西洋气候变率的放大机制。结果显示,北大西洋副极地海域的季节性海冰通过调控海气间热量交换,影响当地气候变率的幅度。冰阶期,热带暖水向北输送导致海洋次表层逐渐升温,削弱了表层-次表层海水的密度层结,有利于次表层暖水上涌,促进海冰融化及海表温度升高。这将激发出海平面气压的负异常,引起气旋式风切变,并通过Ekman抽吸作用加速表层-次表层海水的垂直混合,进一步促进次表层暖水的上涌。这一正反馈机制造成海洋次表层热量的迅速释放,海表温度快速升高。当次表层热量释放结束后,海表将无暖水补充,导致海表温度下降,海冰增多。该过程激发的海表气压正异常(即反气旋式风切变)将抑制垂直混合发生,促进次表层热量积累,为下一次放热过程提供条件。在间冰阶暖期,随着北大西洋季节性海冰消失,海气间热交换不再受海冰变化影响,海洋次表层与大气间的热交换始终处于准平衡态,气候变率的振幅显著下降。本研究结果显示,北大西洋季节性海冰的存在可以调控海洋次表层热量积累-释放的过程,产生“电容器”效应,这对理解冰期年际-年代际气候变率放大现象有重要启示意义。Millennium-scale climate fluctuations,known as Dansgaard-Oeschger(D-O)events during the last glacial cycle,have been a hot topic in paleoclimatology research.Previous modeling studies show that during the cold DO-stadials the amplitude of interannual-interdecadal climate variability in the subpolar North Atlantic is greater than during the warm DO-interstadials.This phenomenon provides valuable implications for interpreting temperature proxies during D-O events,yet its dynamic mechanism remains unclear.Here,via simulation of a typical D-O event during marine isotope stage 3(MIS 3)using a fully coupled atmosphere-ocean general circulation model,we explore the mechanism behind the amplitude change in interannual-interdecadal climate variability.We find that subpolar seasonal sea-ice in the northern North Atlantic plays an important role by regulating atmosphere-ocean heat exchange.During stadials,sea subsurface gradually warms up due to the northward transport of tropical warm water masses,weakening the density stratification between sea surface and subsurface,which eventually leads to upwelling of the subsurface warm water masses,promoting sea ice melting and sea surface warming.In turn,the sea level pressure lowers and the associated cyclonic wind stress anomaly accelerates the vertical mixing by Ekman suction,which further promote local upwelling.This positive feedback mechanism results in the rapid release of sea subsurface heat and rapid sea surface warming.As the heat release gradually ceases,surface warming is deaccelerated and even paused,allowing sea ice to regrow.This weakens the low-pressure system and stimulates anti-cyclonic wind anomaly,which in turn reduces the vertical mixing.Consequently,sea temperature drops quickly,meanwhile heat starts accumulating in sea subsurface until the vertical stratification is broken again.During interstadials,with the disappearing of seasonal sea ice in the key convection sites of the North Atlantic,the atmosphere-ocean heat exchange is no longer affected by sea ice.Th

关 键 词：年际-年代际气候变率 冰期气候变率发大现象 冰海气相互作用 千年气候事件 

分 类 号：P43[天文地球—大气科学及气象学] P467P731.15