Palynology on lake sediments from the Pyrenees

A multi-proxy palaeoecological investigation including pollen, plant macrofossil, radiocarbon and sedimentological analyses, was performed on a small mountain lake in the Eastern Pyrenees. This has allowed the reconstruction of: (1) the vegetation history of the area based on five pollen diagrams and eight AMS14C dates and (2) the past lake-level changes, based on plant macrofossil, lithological and pollen analysis of two stratigraphical transects correlated by pollen analysis. The palaeolake may have appeared before the Younger Dryas; the lake-level was low and the vegetation dominated by cold steppic grasslands. The lake-level rose to its highest level during the Holocene in the Middle Atlantic (at ca. 5060±45 b.p.). Postglacial forests (Quercetum mixtum and Abieto-Fagetum) developed progressively in the lower part of the valley, while dense Pinus uncinata forests rapidly invaded the surroundings of the mire and remained the dominant local vegetation until present. The observed lowering of the lake levels during the Late Atlantic and the Subboreal (from 5060 ± B.P. to 3590±40 b.p.) was related to the overgrowth of the mire. The first obvious indications of anthropogenic disturbances of the vegetation are recorded at the Atlantic/Subboreal boundary as a reduction in the forest component, which has accelerated during the last two millennia.

本研究针对东比利牛斯山脉的一处小型山地湖泊开展了多代理古生态调查，涵盖孢粉分析、植物大化石分析、放射性碳测年与沉积学分析。通过该调查，得以重建两项内容：(1) 基于5幅孢粉图谱与8次加速器质谱14C（AMS14C）测年结果，重建该区域的植被演化历史；(2) 基于2条经孢粉分析对比的地层剖面的植物大化石、岩性与孢粉分析结果，重建古湖泊水位的历史变化。该古湖泊可能形成于新仙女木期（Younger Dryas）之前，彼时湖泊水位较低，区域植被以寒旱草原群落为主。全新世大西洋期中期（约距今5060±45年），湖泊水位升至全新世最高值。冰后期森林（混合栎林Quercetum mixtum与冷杉-山毛榉林Abieto-Fagetum）逐渐在河谷下游区域发育，而茂密的Pinus uncinata林快速入侵泥炭沼泽周边区域，并成为当地优势植被直至今日。观测到的大西洋晚期至亚北方期（约距今5060±45年至距今3590±40年）湖泊水位下降，与泥炭沼泽的过度发育密切相关。在大西洋期/亚北方期界线处，首次出现了植被受人为干扰的明确迹象：森林组分占比下降，且这一趋势在过去两千年中进一步加剧。