Abstract The effects of climatic extremes on Alpine ecosystems, such as in the last glacial period, are poorly understood. The recently discovered Nesseltalgraben site is currently the best dated and most complete high-resolution sedimentary sequence in the northern Alps covering the Marine Isotope Stage (MIS) 3 around 59-28 calibrated kiloyears before present (ka cal BP). The MIS 3 is a period with frequent climatic fluctuations known as Dansgaard-Oeschger cycles or Greenland interstadials-stadials. Here, we present pollen assemblages, bryophyte macrofossils, and stable isotopes (δ2H, δ13C, δ18O) from the Nesseltalgraben to elucidate palaeoenvironments and palaeoclimatic variability during that period. In addition to bulk sedimentary cellulose, also cellulose extracted from fossil wood, monocots, and bryophytes was analysed isotopically. Among the terrestrial pollen, Poaceae and arboreal pollen show an antithetic behaviour reflecting interstadial-stadial variations. Arboreal pollen are dominated by Pinus sylvestris-type, with admixtures of Picea, Betula, Alnus, and Salix. The arboreal pollen record exhibits several maxima indicating milder climatic conditions tentatively assigned to Greenland interstadials 17–14, 12/11, 8, and 6. During Heinrich events 5 and 4, the arboreal pollen record shows distinct minima underlining a severe impact of these events on regional climate and vegetation. Bryophyte assemblages show predominant wetland conditions at the site during the entire MIS 3. The sudden occurrence of the bryophyte Drepanocladus turgescens after 31.6 ka cal BP indicates a change from a fen to a frequently drying wetland environment. This habitat change is presumably linked to enhanced glaciofluvial action caused by glaciers approaching the site. Carbon, hydrogen, and oxygen stable isotope records of bulk sedimentary cellulose exhibit comparably stable conditions from 59 until 52 ka cal BP and increased values around 51 ka cal BP followed by a period of almost absent cellulose until 39 ka cal BP. Thereafter, and lasting until 30 ka cal BP, bulk sedimentary cellulose isotope records (δ2H, δ13C, and δ18O) reveal strongly fluctuating values. These isotope variations are interpreted as variable mixtures between terrestrial lignified plants and monocots on the one, and wetland bryophyte sources on the other hand. A strong negative isotope excursion in the bulk sedimentary and the bryophyte cellulose records around 36.4 ka cal BP is contemporaneous with maximum Cyperaceae pollen and best explained by progressively waterlogged soils due to permafrost. The rise in the bryophyte δ18O record thereafter, accompanied by likewise increasing δ13C values, most likely indicates an enhanced evaporation of source waters.

中文翻译：

---

MIS 3期间极端气候对高山生态系统的影响

摘要 气候极端事件对高山生态系统的影响，如末次冰期，知之甚少。最近发现的 Nesseltalgraben 站点是目前北阿尔卑斯山中年代最好、最完整的高分辨率沉积序列，覆盖了大约 59-28 年前（ka cal BP）的海洋同位素阶段 (MIS) 3。MIS 3 是一个气候波动频繁的时期，称为 Dansgaard-Oeschger 循环或格陵兰岛间-体育场。在这里，我们展示了来自 Nesseltalgraben 的花粉组合、苔藓植物大化石和稳定同位素（δ2H、δ13C、δ18O），以阐明该时期的古环境和古气候变化。除了大量沉积纤维素外，还对从化石木材、单子叶植物和苔藓植物中提取的纤维素进行了同位素分析。在陆生花粉中，禾本科和树栖花粉表现出反映间质变化的对立行为。树栖花粉以樟子松型为主，混合有云杉、桦木、桤木和柳树。树栖花粉记录显示出几个最大值，表明暂时分配给格陵兰岛间区 17-14、12/11、8 和 6 的温和气候条件。在海因里希事件 5 和 4 期间，树栖花粉记录显示出明显的最小值，强调了这些事件的严重影响关于区域气候和植被。苔藓植物组合在整个 MIS 3 期间显示该地点的主要湿地条件。苔藓植物 Drepanocladus turgescens 在 31.6 ka cal BP 后突然出现表明湿地环境从沼泽变为经常干燥的湿地环境。这种栖息地变化可能与冰川接近该地点引起的冰川河流作用增强有关。大量沉积纤维素的碳、氢和氧稳定同位素记录显示出从 59 到 52 ka cal BP 的相对稳定的条件，并且在 51 ka cal BP 附近的值增加，然后是一段几乎没有纤维素的时期，直到 39 ka cal BP。此后，一直持续到 30 ka cal BP，大量沉积纤维素同位素记录（δ2H、δ13C 和 δ18O）显示出强烈波动的值。这些同位素变化被解释为陆地木质化植物和单子叶植物之间的可变混合物，另一方面是湿地苔藓植物来源。大块沉积物和苔藓植物纤维素中的强烈负同位素偏移记录在 36 左右。4 ka cal BP 与最大的莎草科花粉同时出现，最好用永久冻土导致的逐渐浸水的土壤来解释。此后苔藓植物 δ18O 记录的增加，伴随着同样增加的 δ13C 值，很可能表明源水蒸发增强。