Earth's Isostatic and Dynamic Topography—A Critical Perspective
Earth's Isostatic and Dynamic Topography—A Critical Perspective
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地球的均衡和动态地形--一个批判的视角
DOI：
10.1029/2021gc009740
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发表时间：
2022-08
期刊：
影响因子：
3.7
通讯作者：
A. Forte;D. Rowley
中科院分区：
文献类型：
--
作者：
A. Forte;D. Rowley
地球的地形是均衡和动力作用的线性叠加。均衡贡献反映了覆盖在静态、非对流地幔上的地壳的厚度和密度分布。我们认为，均衡地形应限于地壳，从而划定所有来源的莫霍面以下的动态地形。动态地形是由作用于莫霍面上的正应力产生的地形的组成部分，该正应力使均衡地形偏离地壳均衡平衡，这主要是地幔流动动力学的结果。这些正应力来自对流地幔中径向流的压力变化和垂直梯度。动态地形的最佳估计是从剩余地形，这是观测地形和地壳均衡地形之间的差异。动态和剩余地形是相同的。很明显，如果地幔没有对流，板块运动水平平流的热异常就不存在，因此它们对地形的贡献在起源上是内在动态的。包含所有非地壳浮力源的动态地形的全球积分被证明等于零。因此，地幔对流不能改变地球的平均半径或平均海拔。由于海洋平均深度的变化导致的海盆体积的变化是动态地形的固有组成部分，因此要求大陆高程也必须变化，因此这些扰动的全球积分也必须等于零。这一限制对全球长期海平面和地层记录以及受地球动态地形变化影响的地球系统的其他特征具有重要意义。
Earth's topography arises from the linear superposition of isostatic and dynamic contributions. The isostatic contribution reflects the distribution of thickness and density of the crust overlying a static, non‐convecting mantle. We argue that isostatic topography should be limited to the crust, thereby delimiting all sources for dynamic topography below the Moho. Dynamic topography is the component of the topography produced by normal stresses acting on the Moho that deflect the isostatic topography away from crustal isostatic equilibrium largely as a consequence of mantle flow dynamics. These normal stresses arise from pressure variations and vertical gradients of the radial flow in the convecting mantle. The best estimate of dynamic topography is from the residual topography, which is the difference between observed topography and crustal isostatic topography. Dynamic and residual topography are the same. It is clear that thermal anomalies horizontally advected by plate motions would not exist if the mantle were not convecting, therefore their contribution to topography is inherently dynamic in origin. The global integral of dynamic topography that encompasses all non‐crustal buoyancy sources is demonstrated to be equal to zero. It follows that mantle convection cannot change the mean radius or mean elevation of the Earth. Since changes in ocean basin volume driven by changes in mean depth of the oceans are inherently part of dynamic topography, thereby requiring that continental elevations must also change, such that the global integral of these perturbations must also be equal to zero. This constraint has important implications for global long‐term sea level and the stratigraphic record, among other features of the Earth system impacted by changes in Earth's dynamic topography.