We quantify the magnitude of millennial-scale glacial erosion at Engabreen, a temperate glacier in coastal northern Norway, using the in situ cosmogenic nuclides carbon-14 (14C) and beryllium-10 (10Be) in bedrock exposed recently by glacial retreat. Nuclide concentrations show no dependence on distance down or across the valley. As such, resulting Holocene erosion depths along two transects perpendicular to glacier flow are highly variable with no systematic distribution, ranging from 0.10 to 2.95 m. We observed 14C–10Be ratios elevated above the production ratio in samples of abraded bedrock, which is counter to the expectation for surfaces covered during the Holocene and exposed only recently. Muon reactions produce nuclides at greater depths than do spallation reactions and 14C at production rates at higher than those of 10Be, resulting in 14C–10Be ratios that increase with depth. Therefore, elevated 14C–10Be ratios indicate that sampled sites were deeply plucked during recent cover, the Little Ice Age in this case, and then rapidly abraded prior to retreat. Our results suggest that, while glacial erosion can generate a u-shaped valley profile over long periods of time (e.g., 105–107 years), the discontinuous nature of glacial plucking produces spatially variable patterns of erosion over shorter millennial timescales.

中文翻译：

---

挪威Engabreen千年时间尺度上冰下侵蚀的分布和幅度

我们使用原位宇宙成因核素碳 14 (14C）和铍10（10是）在最近被冰川退缩暴露的基岩中。核素浓度不依赖于向下或穿过山谷的距离。因此，沿垂直于冰川流动的两个横断面产生的全新世侵蚀深度变化很大，没有系统分布，范围从 0.10 到 2.95 m。我们观察到14C-10Be 比率高于磨损基岩样品中的生产比率，这与全新世期间覆盖并仅在最近才暴露的表面的预期相反。μ子反应比散裂反应产生更深的核素，14C 的生产率高于10是，导致14C-10是随深度增加的比率。因此，升高14C-10Be 比率表明采样地点在最近的覆盖期间被深度采摘，在这种情况下是小冰河时代，然后在撤退前迅速磨损。我们的研究结果表明，虽然冰川侵蚀可以在很长一段时间内（例如，105–107年），冰川采摘的不连续性在更短的千年时间尺度上产生了空间可变的侵蚀模式。