Planimetric ice-flow convergence and flow-orthonormal strain rate across the Antarctic Ice Sheet, with links to model result files

Fast-flowing ice streams discharge most of the ice from the interior of the Antarctic Ice Sheet coastward. Understanding how their tributary organisation is governed and evolves is essential for developing reliable models of the ice sheet's response to climate change. Despite much research on ice-stream mechanics, this problem is unsolved, because the complexity of flow within and across the tributary networks has hardly been interrogated. Here I present the first map of planimetric flow convergence across the ice sheet, calculated from satellite measurements of ice surface velocity, and use it to explore this complexity. The convergence map of Antarctica elucidates how ice-stream tributaries draw ice from the interior. It also reveals curvilinear zones of convergence along lateral shear margins of streaming, and abundant convergence ripples associated with nonlinear ice rheology and changes in bed topography and friction. Flow convergence on ice-stream tributaries and their feeding zones is markedly uneven, and interspersed with divergence at distances of the order of kilometres. For individual drainage basins as well as the ice sheet as a whole, the range of convergence and divergence decreases systematically with flow speed, implying that fast flow cannot converge or diverge as much as slow flow. I therefore deduce that flow in ice-stream networks is subject to mechanical regulation that limits flow-orthonormal strain rates. These properties and the gridded data of convergence and flow-orthonormal strain rate in this archive provide targets for ice- sheet simulations and motivate more research into the origin and dynamics of tributarization.快速流动的冰流（ice stream）将南极冰盖（Antarctic Ice Sheet）内陆的绝大多数冰体向海岸输送。明晰其支流网络的调控机制与演化规律，对构建可靠的冰盖气候变化响应模型至关重要。尽管学界已对冰流力学开展大量研究，但该问题仍未得到解决——这是因为支流网络内部及跨网络的流动复杂性几乎未被深入探究。本文基于冰面速度卫星测量数据，构建了首幅南极冰盖全域平面流动汇聚分布图，并以此解析该流动复杂性。这幅南极汇聚分布图阐明了冰流支流如何从内陆汲取冰体。该图还揭示了沿冰流侧向剪切边界分布的曲线型汇聚带，以及大量与冰的非线性流变学（ice rheology）、床面地形（bed topography）与摩擦力变化相关的汇聚波纹。冰流支流及其补给区的流动汇聚现象显著不均，在数公里尺度范围内与发散现象交错分布。针对单个流域（drainage basins）乃至整个冰盖而言，汇聚与发散的强度范围随流动速度升高呈系统性降低趋势，这表明快速流动的冰体无法像慢速流动冰体那样产生显著的汇聚或发散。据此本文推断，冰流网络内的流动受到力学调控机制的约束，该机制会限制流动正交应变率（flow-orthonormal strain rates）。本数据集存档中的上述特征，以及汇聚现象与流动正交应变率的网格化数据，可为冰盖模拟研究提供参考靶点，并推动学界开展更多关于冰流支流形成起源与动力学机制的研究。