Earth’s spin axis slowly moves relative to the crust over time. A 120-year-long record of this polar motion from astronomical and more modern geodetic measurements displays interannual and multidecadal fluctuations of 20 to 40 milliarcseconds superimposed on a secular trend of about 3 milliarcseconds per year. Earth’s polar motion is thought to be driven by various surface and interior processes, but how these processes operate and interact to produce the observed signal remains enigmatic. Here we show that predictions made by an ensemble of physics-informed neural networks trained on measurements to capture geophysical processes can explain the main features of the observed polar motion. We find that glacial isostatic adjustment and mantle convection primarily account for the secular trend. Mass redistribution on the Earth’s surface—for example, ice melting and global changes in water storage—yields a relatively weak trend but explains about 90% of the interannual and multidecadal variations. We also find that core processes contribute to both the secular trend and fluctuations in polar motion, either due to variations in torque at the core–mantle boundary or dynamical feedback of the core in response to surface mass changes. Our findings provide constraints on core–mantle interactions for which observations are rare and global ice mass balance over the past century and suggest feedback operating between climate-related surface processes and core dynamics.

随着时间的推移，地球的自转轴相对于地壳缓慢移动。来自天文和更现代的大地测量的长达 120 年的极移记录显示，年际和数十年的波动为 20 至 40 毫角秒，叠加在每年约 3 毫角秒的长期趋势上。地球的极移被认为是由各种表面和内部过程驱动的，但这些过程如何运作和相互作用以产生观测到的信号仍然是个谜。在这里，我们表明，通过测量数据训练的一组物理信息神经网络做出的预测可以捕获地球物理过程，可以解释观测到的极移的主要特征。我们发现冰川均衡调整和地幔对流主要解释了长期趋势。地球表面的大规模重新分配（例如冰融化和全球水储存变化）产生的趋势相对较弱，但可以解释约 90% 的年际和数十年变化。我们还发现，地核过程对极移的长期趋势和波动都有贡献，这要么是由于地核-地幔边界处扭矩的变化，要么是地核响应表面质量变化的动态反馈。我们的研究结果提供了对过去一个世纪罕见的地核-地幔相互作用和全球冰质量平衡的限制，并提出了与气候相关的表面过程和地核动力学之间的反馈作用。