Documentation of sediment cores@en

The presence of a complex bedform arrangement on the sea-floor of the continental shelf in the western Amundsen Sea Embayment, West Antarctica, indicates a multi-temporal record of flow related to the activity of one or more ice streams in the past. Mapping and division of the bedforms into distinct landform assemblages reveals their time-transgressive history, which implies that bedforms can neither be considered part of a single down-flow continuum nor a direct proxy for palaeo-ice velocity, as suggested previously. A main control on the bedform imprint is the geology of the shelf, which is divided broadly between rough bedrock on the inner shelf, and smooth, dipping sedimentary strata on the mid-to-outer shelf. Inner shelf bedform variability is well preserved, revealing information about local, complex basal-ice conditions, meltwater flow, and ice dynamics over time. These details, which are not apparent at the scale of regional morphological studies, indicate that past ice streams flowed across the entire shelf, at times, and often had onset zones that lay within the interior of the Antarctic Ice Sheet today. In contrast, highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice-stream flow, and may be a truer representation of fast palaeo-ice flow in these locations. A revised model for ice streams on the shelf captures complicated multi-temporal bedform patterns associated with an Antarctic palaeo-ice stream for the first time, and confirms a strong substrate control on this ice stream system that drained the West Antarctic Ice Sheet during the Late Quaternary.

西南极洲阿蒙森海海湾（Amundsen Sea Embayment）大陆架（continental shelf）海底发育的复杂床形地貌（bedform）组合，指示了过去与一处或多处冰流（ice streams）活动相关的多期水流记录。通过对床形地貌进行制图并划分为独立的地貌组合（landform assemblages），可揭示其穿时（time-transgressive）演化历史，这表明床形地貌既不能被归为单一顺流连续体的组成部分，也无法如既往研究所言，直接作为古冰流速（palaeo-ice velocity）的代用指标。床形地貌分布的主要控制因素为大陆架地质特征：陆架内侧以粗糙基岩为主，中-外陆架则分布着平缓倾斜的沉积地层。陆架内侧的床形地貌变异特征保存完好，可揭示随时间演化的局地复杂底冰（basal-ice）条件、融水流（meltwater flow）过程与冰动力学（ice dynamics）信息。这类细节在区域尺度的地貌学研究中往往难以被捕捉，表明过去的冰流曾在不同时期覆盖整个大陆架，且其启动带时常位于现今南极冰盖的内部区域。与之相对，中-外陆架沉积地层上发育的高度拉长型冰下床形地貌（subglacial bedform），代表了冰流末次活动的瞬时快照，或可更真实地反映这些区域的古冰快速流动特征。本研究首次构建了适用于陆架冰流的修正模型，该模型还原了与西南极洲古冰流相关的复杂多期床形地貌格局，并证实晚第四纪（Late Quaternary）期间排泄西南极冰盖的该冰流系统受到强烈的基底（substrate）控制。