The deglaciation of the Pyrenees through the 47 ka record of Pllan d'Están paleolake (Ésera valley)

The last deglaciation in the Pyrenees was a complex period with several glacier advances associated with rapid climate changes which differ in terms of timing and intensity. The 46.7 ka lacustrine sequence of Pllan d’Están paleolake (1,840 m a.s.l.) provides new information about that deglaciation period for the first time in the Ésera valley. The multiproxy analysis (sedimentological, geochemical and biological indicators) constrained with a robust chronological model, enabled the longest reconstruction of the glacier evolution, climate and environmental change made in the Pyrenees to date. This lacustrine sedimentary sequence (4.9 m) is composed of banded to finely laminated silts with few intercalations of massive sections where carbonatic, siliciclastic and organic facies appear from the bottom to the top characterizing environmental changes from a subglacial/proglacial lake to the current peatbog. A cold and glacier-dominated period from 46.7 to 15.9 ka BP was interrupted by a warmer period spanning from 38.2 to 34.8 ka. The vegetation succession determined by the palynological analyses is similar to other Pyrenean valleys but dates the onset of mesophyte expansion at 13.8 ka BP during the Allerød, pointing to a difference with other European sequences where temperate forest development took place earlier, associated with the Bølling period. The colder conditions of the Younger Dryas (13-34 11.7 ka) have been detected from cold tolerant diatom taxa that preceded a peatbog development during the Holocene (11.7 ka BP – present-day). These results, together with previously studied Pyrenean sequences, allow characterizing past environmental changes during last deglaciation phases in southern Europe.

比利牛斯山脉末次冰消期是一段复杂的地质时期，期间多次冰川进退事件均与气候快速变化相关，且这些变化在发生时序与强度上均存在显著差异。位于海拔1840米的埃斯特朗古湖（Pllan d’Están paleolake）的46.7 ka湖相沉积序列，首次为埃塞拉河谷的该冰消期研究提供了全新的实证数据。通过依托稳健年代学框架构建的多代用指标分析（包括沉积学、地球化学与生物学指标），本研究实现了迄今为止比利牛斯山脉地区最长时间尺度的冰川演化、气候与环境变化重建。本次研究的4.9米湖相沉积序列由条带状至细层状粉砂组成，夹少量块状层段；自下而上依次发育碳酸盐岩相、硅质碎屑岩相与有机质相，完整记录了从冰下/冰前湖环境向现今泥炭沼泽环境的连续演化过程。46.7~15.9 ka BP期间为寒冷且以冰川为主导的时期，其间被38.2~34.8 ka BP的暖期短暂打断。通过孢粉分析重建的区域植被演替序列与比利牛斯山脉其他河谷的研究结果具有相似性，但本研究将中生植物扩张的起始时间限定在13.8 ka BP的阿勒罗德暖期，这与欧洲其他沉积序列的结果存在明显差异——后者的温带森林发育更早，且与波令暖期直接绑定。新仙女木期（13~11.7 ka BP）的寒冷气候可通过耐寒硅藻类群得到明确识别，该类群在全新世（11.7 ka BP至今）泥炭沼泽发育之前占据优势群落地位。上述研究结果结合此前已发表的比利牛斯山脉沉积序列数据，得以系统刻画南欧末次冰消期各阶段的古环境变化特征。