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The Role of the Southern Ocean in Abrupt Transitions and Hysteresis in Glacial Ocean Circulation

机译：南海在冰川海洋循环中突然转型和滞后的作用

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High-latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard-Oeschger events, which were recorded in Greenland ice cores as shifts in the oxygen isotopic composition of the ice. These shifts in inferred Northern Hemisphere high-latitude temperature have been linked to changes in Atlantic meridional overturning strength. The response of ocean overturning circulation to forcing is nonlinear and a hierarchy of models have suggested that it may exist in multiple steady state configurations. Here, we use a time-dependent coarse-resolution isopycnal model with four density classes and two basins, linked by a Southern Ocean to explore overturning states and their stability to changes in external parameters. The model exhibits hysteresis in both the steady state stratification and overturning strength as a function of the magnitude of North Atlantic DeepWater formation. Hysteresis occurs as a result of two nonlinearities in the model-the surface buoyancy distribution in the Southern Ocean and the vertical diffusivity profile in the Atlantic and Indo-Pacific basins.We construct a metric to assess circulation configuration in the model, motivated by observations from the Last Glacial Maximum, which show a different circulation structure from the modern.We find that circulation configuration is primarily determined by North Atlantic DeepWater density. The model results are used to suggest how ocean conditions may have influenced the pattern of Dansgaard-Oeschger events across the last glacial cycle.
机译：在最后一次冰川期间的高纬度北半球气候的特点是一系列突然的气候变化，称为Dansgaard-Oeschger事件，这些活动被记录在格陵兰冰核中，如冰的氧同位素组成。这些转变在推断的北半球高度高度温度与大西洋经络倾覆强度的变化有关。倾覆循环到强制的海洋的响应是非线性的，模型的层次建议表明它可能存在于多个稳态配置中。在这里，我们使用具有四个密度类和两个盆地的时间依赖性粗分辨率等级模型，由南海联系，探索推翻状态及其对外部参数变化的稳定性。由于北大西洋深水形成的函数，该模型在稳态分层和倾覆强度的延迟强度上表现出滞后。由于模型中的两个非线性 - 南海的表面浮力分布和大西洋和印度 - 太平洋盆地的垂直扩散曲线的表面浮力分布所发生的滞后。我们构建了一个指标，以评估模型中的循环配置，通过观察最后的冰川最大值显示出来自现代的不同循环结构。我们发现循环配置主要由北大西洋深水密度决定。模型结果用于建议海洋状况如何影响最后冰川周期的丹塔德 - 核心事件的模式。

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