Ice streams flowing into Ross Ice Shelf are presently responsible for around 10% of the mass flux from West Antarctica, with the noteworthy exception of Kamb Ice Stream, which stagnated in the late 1800s. The subsequent reduction in ice supply led to grounding-line retreat at the coastal margin where Kamb transitions into the floating Ross Ice Shelf. Grounding-line migration is linked to broader changes in ice-sheet mass balance and sea level, but our understanding of related ice, ocean and seafloor interactions is limited by the difficulty in accessing these remote regions. Here we report in situ observations from an underwater vehicle deployed at Kamb that show how fine-scale variability in ice and ocean structure combine to influence a diversity of ice–ocean interactions. We found a stratified water column within a tenth of a degree of freezing at the ice base and mapped basal crevasses with supercooled water and active marine ice formation. At the seafloor, we interpret parallel ridges as crevasse impressions left as the ice lifted off during grounding-line retreat. These observations from a recently ungrounded sub-shelf environment illuminate both the geomorphological signatures of past grounding-line retreat and the fine-scale sensitivity of ongoing ice–ocean interactions to ice topography.

流入罗斯冰架的冰流目前占南极洲西部质量通量的 10% 左右，值得注意的例外是 Kamb 冰流，它在 1800 年代后期停滞不前。随后的冰供应减少导致 Kamb 过渡到漂浮的罗斯冰架的沿海边缘搁浅线退缩。接地线迁移与冰盖质量平衡和海平面的更广泛变化有关，但我们对相关冰、海洋和海底相互作用的理解因难以进入这些偏远地区而受到限制。在这里，我们报告了部署在 Kamb 的水下航行器的现场观察结果，这些观察结果表明冰和海洋结构的精细变化如何结合起来影响冰-海相互作用的多样性。我们在冰基处发现了一个冰点在十分之一度范围内的分层水柱，并绘制了具有过冷水和活跃海冰形成的基底裂缝。在海底，我们将平行脊解释为冰在接地线撤退过程中升起时留下的裂缝印象。这些来自最近未接地的亚大陆架环境的观察结果阐明了过去接地线后退的地貌特征以及正在进行的冰海相互作用对冰地形的精细敏感性。