Ice Dynamics and Palaeoclimate, British Antarctic Survey, Cambridge CB3 0ET, United Kingdom;
School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston B15 2TT, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Mar 5;116(10):4099-4104. doi: 10.1073/pnas.1807261116. Epub 2019 Feb 13.
Greenland ice cores provide excellent evidence of past abrupt climate changes. However, there is no universally accepted theory of how and why these Dansgaard-Oeschger (DO) events occur. Several mechanisms have been proposed to explain DO events, including sea ice, ice shelf buildup, ice sheets, atmospheric circulation, and meltwater changes. DO event temperature reconstructions depend on the stable water isotope ([Formula: see text]O) and nitrogen isotope measurements from Greenland ice cores: interpretation of these measurements holds the key to understanding the nature of DO events. Here, we demonstrate the primary importance of sea ice as a control on Greenland ice core [Formula: see text]O: 95% of the variability in [Formula: see text]O in southern Greenland is explained by DO event sea ice changes. Our suite of DO events, simulated using a general circulation model, accurately captures the amplitude of [Formula: see text]O enrichment during the abrupt DO event onsets. Simulated geographical variability is broadly consistent with available ice core evidence. We find an hitherto unknown sensitivity of the [Formula: see text]O paleothermometer to the magnitude of DO event temperature increase: the change in [Formula: see text]O per Kelvin temperature increase reduces with DO event amplitude. We show that this effect is controlled by precipitation seasonality.
格陵兰冰芯为过去突然的气候变化提供了极好的证据。然而，人们尚未形成关于这些 Dansgaard-Oeschger（DO）事件如何以及为何发生的普遍共识。已有几种机制被提出以解释 DO 事件，包括海冰、冰架积聚、冰盖、大气环流和融水变化。DO 事件的温度重建取决于从格陵兰冰芯中测量的稳定水同位素（[Formula: see text]O）和氮同位素：对这些测量的解释是理解 DO 事件性质的关键。在这里，我们证明了海冰作为控制格陵兰冰芯 [Formula: see text]O 的主要因素的重要性：格陵兰南部 95%的 [Formula: see text]O 变化可归因于 DO 事件中海冰的变化。我们使用一个通用环流模型模拟的一系列 DO 事件准确地捕捉到了 DO 事件突然开始时 [Formula: see text]O 富集的幅度。模拟的地理变化与现有冰芯证据基本一致。我们发现了一个迄今未知的 DO 事件温度升高对 [Formula: see text]O 古温度计敏感性：每升高 1 开尔文时 [Formula: see text]O 的变化量随 DO 事件幅度的增加而减少。我们表明，这种效应受降水季节性的控制。
