Quantifying West Antarctic mantle viscosity via precise GPS measurement of Earth's response to surface mass balance anomalies

冰盖变化的卫星测量对于理解和帮助预测海平面上升是必要的，但是受到了冰川均衡调整（GIA）现象的影响。GIA是一种持续的固体地球变形形式，是对先前冰盖质量变化的响应。原则上，它可以在任何我们接近基岩的地方测量，但南极洲的大部分地区都不是这样，因此（也出于实用性的原因）我们需要基于物理的GIA数学模型。这些模型必须经过校准和验证，这可以通过使用位于基岩上的连续GPS接收器对地球变形进行精确测量来完成。因此，连续的GPS数据对于确定南极洲过去和现在的冰质量变化以及量化冰动力学和固体地球变形之间的反馈至关重要。在这类研究中必须量化的一个基本特性是固体地球的流变性（它对作用于它的力的变形响应）。地幔在较长的时间尺度上表现出粘性行为，但在短期内表现出弹性行为（如通过地震波的传播观察到的），这种现象被称为粘弹性。最近的研究表明，整个南极洲的地幔粘度存在很大的空间变化，但目前这种变化的幅度尚不清楚。我们建议开创一种新的方法来确定空间可变的地幔粘度，包括分析固体地球对南极洲幕式表面质量平衡（SMB）异常的粘弹性响应。我们的方法利用了这样一个事实，即在表面质量变化幅度众所周知的地区，对伴随的固体地球响应的观测允许对地球的流变特性进行量化。为了实现我们的目标，我们需要获得高精度、长时间的GPS记录。幸运的是，南极洲西部已经有了一个广泛的GPS网络，尽管它是通过一系列nerc资助的项目（以及同等的海外资助）零零碎碎地建立起来的，但现在有可能在未来几年内提供这样的记录。因此，我们建议彻底检修现有的GPS网络，该网络位于英国在南极洲的后勤支持范围内；我们将在现有站点的一个战略子集上延长时间序列，并通过卫星将所有数据传输到开放访问服务器。由此产生的精度和数据可及性的阶梯式变化将使我们能够实现我们的科学目标，同时也将使国际科学界受益：为西南极洲提供开放获取的GPS时间序列将有助于新兴的数据反演活动，并使数百万美元的重力恢复和气候实验（GRACE）后续任务提供的地面真实冰质量平衡估计成为可能，该任务将于2017年发射。

Satellite measurements of ice sheet change are necessary to understand and help predict sea level rise, but are contaminated by a phenomenon known as Glacial Isostatic Adjustment (GIA). GIA is a form of ongoing solid Earth deformation in response to previous ice sheet mass changes. It can in principle be measured wherever we have access to bedrock, but this is not the case for much of Antarctica and therefore (and also for reasons of practicability) we require physically-based mathematical models of GIA. These models must be calibrated and validated, which can be done with the aid of precise measurements of Earth deformation made using continuous GPS receivers sited on bedrock.Continuous GPS data are therefore crucial to the determination of past and present ice mass change across Antarctica and the quantification of feedbacks between ice dynamics and solid Earth deformation. A fundamental property that must be quantified in such studies is the rheology of the solid Earth (its deformational response to forces acting on it). The Earth's mantle shows viscous behaviour over longer timescales but behaves elastically in the short term (as observed e.g. by the passage of seismic waves), a phenomenon known as viscoelasticity. Recent studies have demonstrated that there are large spatial variations in mantle viscosity across Antarctica, but at present the magnitude of such variations is not known. We propose to pioneer a new approach to determining spatially-variable mantle viscosity that involves analysing the viscoelastic response of the solid Earth to episodic surface mass balance (SMB) anomalies across Antarctica. Our approach makes use of the fact that in regions where the magnitude of surface mass change is well known, observations of the accompanying solid Earth response allow the quantification of the rheological properties of the Earth.In order to achieve our goal we require access to high-precision, long-duration GPS records. Fortunately there is already an extensive GPS network in West Antarctica, which although erected piecemeal via a series of NERC-funded projects (and equivalent overseas grants), now has the potential to deliver such records over the next few years. We therefore propose to overhaul the existing GPS network that lies within the remit of UK logistical support in Antarctica; we will extend the time series at a strategic subset of the existing sites, and transmit all data to open access servers via satellite. The resulting step change in precision and data accessibility will enable us to achieve our scientific goals and at the same time will benefit the international scientific community: the provision of open access GPS time series for West Antarctica will contribute to emerging data inversion activities and make it possible to ground-truth ice mass balance estimates delivered by the multi-million-dollar Gravity Recovery and Climate Experiment (GRACE) Follow-on mission, which is due for launch in 2017.