Understanding the recent history of Thwaites Glacier, and the processes controlling its ongoing retreat, is key to projecting Antarctic contributions to future sea-level rise. Of particular concern is how the glacier grounding zone might evolve over coming decades where it is stabilized by sea-floor bathymetric highs. Here we use geophysical data from an autonomous underwater vehicle deployed at the Thwaites Glacier ice front, to document the ocean-floor imprint of past retreat from a sea-bed promontory. We show patterns of back-stepping sedimentary ridges formed daily by a mechanism of tidal lifting and settling at the grounding line at a time when Thwaites Glacier was more advanced than it is today. Over a duration of 5.5 months, Thwaites grounding zone retreated at a rate of >2.1 km per year—twice the rate observed by satellite at the fastest retreating part of the grounding zone between 2011 and 2019. Our results suggest that sustained pulses of rapid retreat have occurred at Thwaites Glacier in the past two centuries. Similar rapid retreat pulses are likely to occur in the near future when the grounding zone migrates back off stabilizing high points on the sea floor.

了解思韦茨冰川的近期历史，以及控制其持续退缩的过程，是预测南极对未来海平面上升的贡献的关键。特别值得关注的是，冰川接地带在未来几十年内可能会如何演变，并由海底测深高度稳定下来。在这里，我们使用部署在 Thwaites Glacier 冰锋的自主水下航行器的地球物理数据，记录过去从海床海角撤退的海底印记。我们展示了在 Thwaites Glacier 比今天更先进的时候，由潮汐抬升和沉降机制每天形成的后退沉积脊模式。在 5.5 个月的时间里，Thwaites 接地带以 >2 的速度后退。每年 1 公里——是 2011 年至 2019 年间卫星在接地带后退最快部分观测到的速度的两倍。我们的结果表明，在过去两个世纪中，思韦茨冰川发生了持续的快速后退脉冲。类似的快速撤退脉冲可能在不久的将来发生，当接地带从海底稳定的高点后退时。