Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations
Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations
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DOI：
10.1002/2014jf003239
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发表时间：
2015-07-01
影响因子：
3.9
通讯作者：
Williams, C. Rosie
中科院分区：
文献类型：
--
作者：
Arthern, Robert J.;Hindmarsh, Richard C. A.;Williams, C. Rosie
为了预测全球海平面，需要有精确的南极冰盖动力学模型，并仔细确定初始条件和校准良好的流变参数。通过调整以前使用的电阻抗断层成像的逆方法，我们推断现今的流速内的冰盖。这种反演使用卫星观测的表面速度，积雪积累率，和表面高程的变化率来估计的基础阻力系数和冰的刚度参数，影响粘度。我们代表内部冰运动的不可压缩斯托克斯流的垂直积分近似。该模型代表了冰内的垂直剪切和由水平拉伸和剪切引起的膜应力。结合观测和模型，我们恢复显着的地理变化的基础阻力系数。基底剪应力的相对变化较小。没有一个简单的滑动定律能充分地把基底剪应力表示为滑动速度的函数。低基底剪切应力在东南极洲中部占主导地位，那里厚的绝缘冰允许底部的液态水润滑滑动。较高的剪切应力发生在南极洲东部沿海地区，那里更有可能形成冻床。对斯韦茨冰川进行更详细的研究表明，最慢的滑动往往与升高的基底地形相吻合。我们的研究结果和类似的伴随反演之间的差异表明，反演或正则化方法可以影响恢复的参数缓慢滑动和更精细的尺度，在更广泛的尺度上，我们恢复了类似的模式，低基底阻力下的主要冰流和广泛的地区在南极洲东部移动的基底滑动。
Accurate dynamical models of the Antarctic ice sheet with carefully specified initial conditions and well-calibrated rheological parameters are needed to forecast global sea level. By adapting an inverse method previously used in electric impedance tomography, we infer present-day flow speeds within the ice sheet. This inversion uses satellite observations of surface velocity, snow accumulation rate, and rate of change of surface elevation to estimate the basal drag coefficient and an ice stiffness parameter that influences viscosity. We represent interior ice motion using a vertically integrated approximation to incompressible Stokes flow. This model represents vertical shearing within the ice and membrane stresses caused by horizontal stretching and shearing. Combining observations and model, we recover marked geographical variations in the basal drag coefficient. Relative changes in basal shear stress are smaller. No simple sliding law adequately represents basal shear stress as a function of sliding speed. Low basal shear stress predominates in central East Antarctica, where thick insulating ice allows liquid water at the base to lubricate sliding. Higher shear stress occurs in coastal East Antarctica, where a frozen bed is more likely. Examining Thwaites glacier in more detail shows that the slowest sliding often coincides with elevated basal topography. Differences between our results and a similar adjoint-based inversion suggest that inversion or regularization methods can influence recovered parameters for slow sliding and finer scales; on broader scales we recover a similar pattern of low basal drag underneath major ice streams and extensive regions in East Antarctica that move by basal sliding.