Response of Marine‐Terminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics
Response of Marine‐Terminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics
复制标题
DOI：
10.1029/2018jf004709
复制
发表时间：
2018-09
期刊：
影响因子：
--
通讯作者：
A. Robel;M. Haseloff;G. Roe
中科院分区：
文献类型：
--
作者：
A. Robel;M. Haseloff;G. Roe
最近的观测表明，格陵兰岛和南极洲的许多终止海洋的冰川目前正在退缩和变薄，这可能是由于气候强迫的长期趋势。在这项研究中，我们描述了一个简单的两阶段模型，该模型准确地模拟了在空间扩展模型中模拟的海洋终止冰川对外部强迫的响应。该模型的简单性允许推导出描述海洋终止冰川对强迫响应的解析表达式。我们发现有两个时间尺度表征了冰川对外部强迫的稳定响应，一个是几十年到几百年的快速时间尺度，另一个是几千年的缓慢时间尺度。这两个时间尺度在不同的床坡阈值处变得不稳定，表明海洋冰盖不稳定存在明显的慢速和快速形式。我们推导了稳定冰川对外部强迫响应的近似大小和瞬态演化的简单表达式，这取决于冰川的平衡状态和强迫过程中的非线性强度。海洋终止冰川的缓慢响应速度表明，由于过去的气候强迫，一些冰川目前的变化将在未来几个世纪继续并加速，这些冰川目前的变化程度很可能只是过去气候强迫造成的未来持续变化的一小部分。最后，我们发现改变某些非线性强迫过程（如冰架崩解）的自然波动幅度会改变冰川的平衡状态。
Recent observations indicate that many marine‐terminating glaciers in Greenland and Antarctica are currently retreating and thinning, potentially due to long‐term trends in climate forcing. In this study, we describe a simple two‐stage model that accurately emulates the response to external forcing of marine‐terminating glaciers simulated in a spatially extended model. The simplicity of the model permits derivation of analytical expressions describing the marine‐terminating glacier response to forcing. We find that there are two time scales that characterize the stable glacier response to external forcing, a fast time scale of decades to centuries, and a slow time scale of millennia. These two time scales become unstable at different thresholds of bed slope, indicating that there are distinct slow and fast forms of the marine ice sheet instability. We derive simple expressions for the approximate magnitude and transient evolution of the stable glacier response to external forcing, which depend on the equilibrium glacier state and the strength of nonlinearity in forcing processes. The slow response rate of marine‐terminating glaciers indicates that current changes at some glaciers are set to continue and accelerate in coming centuries in response to past climate forcing and that the current extent of change at these glaciers is likely a small fraction of the future committed change caused by past climate forcing. Finally, we find that changing the amplitude of natural fluctuations in some nonlinear forcing processes, such as ice shelf calving, changes the equilibrium glacier state.