Sedimentological investigations and age model on profile PS58/254@en

Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5-6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial-interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424-374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial-interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15-MIS 13 (621-478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15-MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15-MIS 13. Some of these anomalies are observed in the pelagic Southern Ocean and the South Atlantic and might originate in major ice-sheet drawdown in Antarctica, but further research is required to test this hypothesis.当代全球变暖大概率会引发未来地球极地冰盖的消融，进而可能导致海平面大幅上升。仅西南极冰盖（West Antarctic Ice Sheet, WAIS）的崩塌就可能使全球海平面上升5至6米，该冰盖因主体坐落于海平面以下而被认为极易受到影响。尽管西南极冰盖对全球海平面变化至关重要，但学界对其响应第四纪冰期-间冰期旋回的机制仍约束不足。此外，关于西南极冰盖在过去约75万年的某个时段（可能发生于海洋同位素阶段（Marine Isotope Stage, MIS）11，即42.4万至37.4万年前）发生解体的地质证据仍存在歧义。本研究报道了采自阿蒙森海西南极大陆边缘的一套冰海沉积序列的物理性质、古地磁、地球化学及黏土矿物学数据，该序列的沉积时间跨度超过100万年。在该沉积序列中，生物生产力代用指标（如生物成因蛋白石与钡/铝比值）以及来自西南极内陆的陆源碎屑供给代用指标（如冰筏碎屑与黏土矿物）均呈现出与第四纪冰期-间冰期旋回相匹配的周期性波动。一套显著的沉积异常层位覆盖了海洋同位素阶段15至13（62.1万至47.8万年前）。生物生产力与陆源沉积物供给的代用指标显示，该层位具备单一、长期的间冰期特征。尽管没有任何代用指标显示当时的环境条件与现代存在显著差异，但本研究得出结论：若西南极冰盖在过去80万年中发生过崩塌，那么海洋同位素阶段15至13便是最有可能的时段。显然，间冰期环境的持续时长而非其强度，是控制西南极冰盖消退的关键因素。通过与全球各地各类海洋与陆地气候档案进行对比，研究证实海洋同位素阶段15至13期间确实存在异常的环境条件。南大洋远洋区与南大西洋中也观测到了这类异常信号，其可能源自南极地区大规模冰盖消退，但该假说仍需进一步研究加以验证。