The offshore sector around Shetland remains one of the least well-studied parts of the former British–Irish Ice Sheet with several long-standing scientific issues unresolved. These key issues include (i) the dominance of a locally sourced ‘Shetland ice cap’ vs an invasive Fennoscandian Ice Sheet; (ii) the flow configuration and style of glaciation at the Last Glacial Maximum (i.e. terrestrial vs marine glaciation); (iii) the nature of confluence between the British–Irish and Fennoscandian Ice Sheets; (iv) the cause, style and rate of ice sheet separation; and (v) the wider implications of ice sheet uncoupling on the tempo of subsequent deglaciation. As part of the Britice-Chrono project, we present new geological (seabed cores), geomorphological, marine geophysical and geochronological data from the northernmost sector of the last British–Irish Ice Sheet (north of 59.5°N) to address these questions. The study area covers ca. 95 000 km², an area approximately the size of Ireland, and includes the islands of Shetland and the surrounding continental shelf, some of the continental slope, and the western margin of the Norwegian Channel. We collect and analyse data from onshore in Shetland and along key transects offshore, to establish the most coherent picture, so far, of former ice-sheet deglaciation in this important sector. Alongside new seabed mapping and Quaternary sediment analysis, we use a multi-proxy suite of new isotopic age assessments, including 32 cosmogenic-nuclide exposure ages from glacially transported boulders and 35 radiocarbon dates from deglacial marine sediments, to develop a synoptic sector-wide reconstruction combining strong onshore and offshore geological evidence with Bayesian chronosequence modelling. The results show widespread and significant spatial fluctuations in size, shape and flow configuration of an ice sheet/ice cap centred on, or to the east of, the Orkney–Shetland Platform, between ~30 and ~15 ka BP. At its maximum extent ca. 26–25 ka BP, this ice sheet was coalescent with the Fennoscandian Ice Sheet to the east. Between ~25 and 23 ka BP the ice sheet in this sector underwent a significant size reduction from ca. 85 000 to <50 000 km², accompanied by several ice-margin oscillations. Soon after, connection was lost with the Fennoscandian Ice Sheet and a marine corridor opened to the east of Shetland. This triggered initial (and unstable) re-growth of a glaciologically independent Shetland Ice Cap ca. 21–20 ka BP with a strong east–west asymmetry with respect to topography. Ice mass growth was followed by rapid collapse, from an area of ca. 45 000 km² to ca. 15 000 km² between 19 and 18 ka BP, stabilizing at ca. 2000 km² by ~17 ka BP. Final deglaciation of Shetland occurred ca. 17–15 ka BP, and may have involved one or more subsidiary ice centres on now-submerged parts of the continental shelf. We suggest that the unusually dynamic behaviour of the northernmost sector of the British–Irish Ice Sheet between 21 and 18 ka BP – characterized by numerous extensive ice sheet/ice mass readvances, rapid loss and flow redistributions – was driven by significant changes in ice mass geometry, ice divide location and calving flux as the glaciologically independent ice cap adjusted to new boundary conditions. We propose that this dynamism was forced to a large degree by internal (glaciological) factors specific to the strongly marine-influenced Shetland Ice Cap.

中文翻译：

---

英国-爱尔兰冰原退缩的模式、风格和时间：设得兰群岛和北海北部地区

设得兰群岛周围的离岸地区仍然是前英国-爱尔兰冰原中研究最少的部分之一，有几个长期存在的科学问题尚未解决。这些关键问题包括 (i) 本地来源的“设得兰冰盖”与入侵的芬诺斯坎迪亚冰盖的主导地位；(ii) 末次盛冰期（即陆地与海洋冰川作用）；(iii) 英国-爱尔兰和芬诺斯坎迪亚冰盖汇合的性质；(iv) 冰盖分离的原因、方式和速度；(v) 冰盖解耦对随后冰川消融速度的更广泛影响。作为 Britice-Chrono 项目的一部分，我们提供了来自最后一个英国 - 爱尔兰冰盖（北纬 59.5°以北）最北端的新地质（海底岩心）、地貌、海洋地球物理和地质年代学数据，以解决这些问题。研究区域涵盖约。95 000 公里²面积与爱尔兰相当，包括设得兰群岛和周围的大陆架、部分大陆坡和挪威海峡的西缘。我们收集和分析来自设得兰群岛陆上和离岸关键横断面的数据，以建立迄今为止这一重要部门的前冰盖冰川消融最连贯的图片。除了新的海底测绘和第四纪沉积物分析外，我们还使用了新同位素年龄评估的多代理套件，包括来自冰川运输巨石的 32 个宇宙成因核素暴露年龄和来自冰消期海洋沉积物的 35 个放射性碳日期，以开发全行业的天气重建将强大的陆上和海上地质证据与贝叶斯时间序列建模相结合。BP。在其最大程度约。26-25 ka BP，这个冰盖与东面的芬诺斯坎德冰盖合并。在大约 25 到 23 ka BP之间，该部门的冰盖从大约 85 000 到 <50 000 km ²，伴随着几次冰缘振荡。不久之后，与 Fennoscandian 冰盖的连接中断，一条海洋走廊在设得兰群岛以东开放。这触发了冰川学上独立的设得兰冰盖的初始（和不稳定）重新生长。21-20 ka BP，在地形方面具有强烈的东西向不对称性。冰块增长之后迅速崩塌，从大约 10 米的区域开始。45 000 公里²至约 15 000 公里²在 19 到 18 ka BP 之间，稳定在大约。2000 km ² by ~17 ka BP。设得兰群岛的最终冰川消融大约发生在。17-15 ka BP，并且可能涉及大陆架现在淹没部分的一个或多个附属冰中心。我们认为 21 到 18 ka BP之间英国-爱尔兰冰盖最北端的异常动态行为– 以大量广泛的冰盖/冰块重新分布、快速损失和流量重新分布为特征——是由冰块几何形状、冰分位置和崩解通量的显着变化驱动的，因为冰川学上独立的冰盖适应了新的边界条件。我们认为，这种活力在很大程度上是受强烈海洋影响的设得兰冰盖所特有的内部（冰川学）因素所迫使的。