Sedimentary record of the western Amundsen Sea Embayment@en

The Amundsen Sea Embayment (ASE) drains approximately 35% of the West Antarctic Ice Sheet (WAIS) and is one of the most rapidly changing parts of the cryosphere. In order to predict future ice-sheet behaviour, modellers require long-term records of ice-sheet melting to constrain and build confidence in their simulations. Here, we present detailed marine geological and radiocarbon data along three palaeo-ice stream tributary troughs in the western ASE to establish vital information on the timing of deglaciation of the WAIS since the Last Glacial Maximum (LGM). We have undertaken multi-proxy analyses of the cores (core description, shear strength, x-radiographs, magnetic susceptibility, wet bulk density, total organic carbon/nitrogen, carbonate content and clay mineral analyses) in order to: (1) characterise the sedimentological facies and depositional environments; and (2) identify the horizon(s) in each core that would yield the most reliable age for deglaciation. In accordance with previous studies we identify three key facies, which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments. These facies are: i) subglacial, ii) proximal grounding-line, and iii) seasonal open-marine. In addition, we incorporate ages from other facies (e.g., glaciomarine diamictons deposited at some distance from the grounding line, such as glaciogenic debris flows and iceberg rafted diamictons and turbates) into our deglacial model. In total, we have dated 78 samples (mainly the acid insoluble organic (AIO) fraction, but also calcareous foraminifers), which include 63 downcore and 15 surface samples. Through careful sample selection prior to dating, we have established a robust deglacial chronology for this sector of the WAIS. Our data show that deglaciation of the western ASE was probably underway as early as 22,351 calibrated years before present (cal 44 yr BP), reaching the mid-shelf by 13,837 cal yr BP and the inner shelf to within c.10-12 km of the present ice shelf front between 12,618 and 10,072 cal yr BP. The deglacial steps in the western ASE broadly coincide with the rapid rises in sea-level associated with global meltwater pulses 1a and 1b, although given the potential dating uncertainty, additional, more precise ages are required before these findings can be fully substantiated. […]阿蒙森海盆（Amundsen Sea Embayment, ASE）汇水覆盖约35%的西南极冰盖（West Antarctic Ice Sheet, WAIS），是冰冻圈中变化最迅速的区域之一。为预测未来冰盖行为，建模人员需要获取长期的冰盖消融记录，以约束模拟结果并提升模拟的可信度。本文呈现了ASE西部3条古冰流支槽的详细海洋地质与放射性碳数据，旨在建立末次盛冰期（Last Glacial Maximum, LGM）以来西南极冰盖冰消作用时间的关键信息。我们对岩芯开展了多指标分析，涵盖岩芯描述、抗剪强度、X光影像、磁化率、湿容重、总有机碳/总氮、碳酸盐含量及黏土矿物分析，以实现两大目标：（1）刻画沉积相与沉积环境；（2）确定各岩芯中可提供最可靠冰消作用年龄的层位。与既往研究一致，我们识别出3种关键沉积相，它们通过记录从接地冰盖到开阔海洋环境的转变，为冰消作用定年提供了最可靠的地层序列，这三种相分别为：i）冰下相，ii）近接地带相，iii）季节性开阔海相。此外，我们将来自其他沉积相的定年数据（例如在距接地带有一定距离处沉积的冰海混积岩，如冰源性碎屑流、冰山筏运混积岩及浊积岩）纳入冰消作用模型。本次研究共对78个样品进行了定年，主要为酸不溶有机质（acid insoluble organic, AIO）组分，同时也包含钙质有孔虫，其中63个为岩芯深部样品，15个为表层样品。通过定年前的精心样品筛选，我们为该西南极冰盖区域建立了可靠的冰消年代学框架。研究数据显示，阿蒙森海盆西部的冰消作用可能早在距今22351个校准年前（cal 44 yr BP）就已启动，至13837个校准年前时冰退已推进至陆架中部，并在12618至10072个校准年前抵达现今冰架前缘约10-12公里范围内的陆架内侧。阿蒙森海盆西部的冰消阶段大致与全球融水脉冲1a和1b对应的海平面快速上升阶段相吻合，但考虑到定年结果存在潜在不确定性，在完全证实该结论前还需获取更多更精确的定年数据。[…]