Simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation
Simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation
复制标题
模拟末次冰期海洋反馈对轨道强迫的放大
作者：
Myriam Khodri;Y. Leclainche;Gilles Ramstein;P. Braconnot;O. Marti;E. Cortijo
根据米兰科维奇理论，大约 115,000 年前高纬度地区夏季日照量较低，使得冬雪持续整个夏季，导致冰盖堆积和冰川作用。但是，仅在日照变化的情况下，使用全球大气模型模拟末次冰期的尝试未能产生这一结果。这些结果表明反馈效应（例如通过植被或海洋环流的变化）对于放大太阳强迫的重要性。在这里，我们提出了末次冰期的完全耦合的海洋-大气模型，该模型在此期间在已知的冰盖位置上形成了常年积雪。我们表明，海洋反馈导致北部高纬度地区变冷，同时大气水分从赤道到两极的输送增加。这些变化与现有的地质数据一致，并且共同导致向北部高纬度地区的降雪量增加。我们提出的机制解释了冰川作用的发生——植被的变化会加剧冰川作用——以响应弱轨道强迫。
According to Milankovitch theory, the lower summer insolation at high latitudes about 115,000 years ago allowed winter snow to persist throughout summer, leading to ice-sheet build-up and glaciation. But attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only. These results point towards the importance of feedback effects—for example, through changes in vegetation or the ocean circulation—for the amplification of solar forcing. Here we present a fully coupled ocean–atmosphere model of the last glaciation that produces a build-up of perennial snow cover at known locations of ice sheets during this period. We show that ocean feedbacks lead to a cooling of the high northern latitudes, along with an increase in atmospheric moisture transport from the Equator to the poles. These changes agree with available geological data and, together, they lead to an increased delivery of snow to high northern latitudes. The mechanism we present explains the onset of glaciation—which would be amplified by changes in vegetation—in response to weak orbital forcing.