A long-term drift in polar motion (PM) has been observed for more than a century, and Glacial Isostatic Adjustment (GIA) has been understood as an important cause. However, observed PM includes contributions from other sources, including contemporary climate change and perhaps others associated with Earth’s interior dynamics. It has been difficult to separate these effects, because there is considerable scatter among GIA models concerning predicted PM rates. Here we develop a new method to estimate GIA PM using data from the GRACE mission. Changes in GRACE degree 2, order 1 spherical harmonic coefficients are due both to GIA and contemporary surface mass load changes. We estimate the surface mass load contribution to degree 2, order 1 coefficients using GRACE data, relying on higher-degree GRACE coefficients that are dominantly affected by surface loads. Then the GIA PM trend is obtained from the difference between observed PM trend (which includes effects from GIA and surface mass loads) and the estimated PM trend mostly associated with surface mass loads. A previous estimate of the GIA PM trend from PM observations for the period 1900–1978 is toward 79.90° W at a speed of 3.53 mas/year (10.91 cm/year). Our new estimate for the GIA trend is in a direction of 61.77° W at a speed of 2.18 mas/year (6.74 cm/year), similar to the observed PM trend during the early twentieth century. This is consistent with the view that the early twentieth-century trend was dominated by GIA and that more recently there is an increasing contribution from contemporary surface mass load redistribution associated with climate change. Our GIA PM also agrees with the linear mean pole during 1900–2017. Contributions from other solid Earth process such as mantle convection would also produce a linear trend in PM and could be included in our GIA estimate.

一个多世纪以来，人们一直观察到极地运动 (PM) 的长期漂移，冰川等静压调整 (GIA) 被认为是一个重要原因。然而，观察到的 PM 包括来自其他来源的贡献，包括当代气候变化以及可能与地球内部动力学相关的其他来源。很难区分这些影响，因为 GIA 模型之间关于 PM 预测率的差异很大。在这里，我们开发了一种使用 GRACE 任务数据估算 GIA PM 的新方法。GRACE 2 次、1 阶球谐系数的变化是由于 GIA 和当代表面质量载荷变化造成的。我们使用 GRACE 数据估计表面质量负载对 2 阶系数的贡献，依赖于主要受表面载荷影响的更高阶 GRACE 系数。然后，根据观察到的 PM 趋势（包括 GIA 和表面质量负载的影响）与主要与表面质量负载相关的估计 PM 趋势之间的差异，获得 GIA PM 趋势。根据 1900 年至 1978 年期间的 PM 观测结果，先前对 GIA PM 趋势的估计是以 3.53 质量/年（10.91 厘米/年）的速度向 79.90° W 移动。我们对 GIA 趋势的新估计是以 2.18 质量/年（6.74 厘米/年）的速度沿 61.77° W 方向发展，类似于在二十世纪初观察到的 PM 趋势。这与 20 世纪早期趋势由 GIA 主导并且最近与气候变化相关的当代地表质量重新分配的贡献越来越大的观点一致。我们的 GIA PM 也同意 1900-2017 年期间的线性平均极点。来自其他固体地球过程（如地幔对流）的贡献也会产生 PM 的线性趋势，并且可以包含在我们的 GIA 估计中。