Palynology on lake sediments from the Pyrenees@en

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.

本次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（multi-proxy palaeoecological investigation），涵盖孢粉（pollen）、植物大化石（plant macrofossil）、放射性碳测年与沉积学分析。通过本次研究，得以重建两项核心内容：(1) 基于5幅孢粉图谱与8组加速器质谱碳14（AMS14C）测年数据，重建该区域的植被演化历史；(2) 基于两处经孢粉分析对比的地层断面的植物大化石、岩性与孢粉分析结果，重建古湖水位变化历史。
该古湖可能形成于新仙女木期（Younger Dryas）之前，彼时湖水位较低，区域植被以寒冷干草原为主。全新世（Holocene）大西洋期中期（约5060±45 b.p.），湖水位升至全新世最高值。冰后森林包括混生栎林（Quercetum mixtum）与冷杉-山毛榉林（Abieto-Fagetum），逐渐在河谷下游发育；而茂密的欧洲弯松（Pinus uncinata）林快速占据了沼泽周边区域，并成为当地优势植被直至今日。晚大西洋期与亚北方期（约5060±45 b.p.至3590±40 b.p.）观测到的湖水位下降，与沼泽的过度发育存在关联。植被受人类活动干扰的首个明确信号记录于大西洋期/亚北方期交界时段，表现为森林组分占比下降，且这一趋势在过去两千年中进一步加剧。