Landscape evolution and volcanic activity in the Eifel reconstruction from maar sediments of the last 70.000 years

Laminated sediment records from several maar lakes and dry maar lakes of the Eifel (Germany) reveal the history of climate, weather, environment, vegetation, and land use in central Europe during the last 60,000 years. The time series of the last 30,000 years is based on a continuous varve counted chronology, the MIS3 section is tuned to the Greenland ice - both with independent age control from 14C dates. Total carbon, pollen and plant macrofossils are used to synthesize a vegetation-stack, which is used together with the stacks from seasonal varve formation, flood layers, eolian dust content and volcanic tephra layers to define Landscape Evolution Zones (LEZ). LEZ 1 encompasses the landscape dynamics of the last 6000 years with widespread human influence. The natural oak and hazel forests of the early Holocene back to 10,500 b2k define LEZ 2. LEZ 3, the late glacial between 10,500 and 14,700 b2k, shows the development of a boreal forest with abundant grass and shallow water biomass in the lakes. The maximum of the last glaciation (LEZ 4: 14,700-23,000 b2k) was characterized by sparse vegetation of moss and characeae. These sediments are generally devoid of clay and sand and reveal no indication of snow-meltwater events. Accordingly, the Last Glacial Maximum (LGM) must have been extremely arid in central Europe. The sediments of the subsequent LEZ 5 from 23,000-28,500 b2k preserve distinct layers of clay and coarse sand, which indicates running water with clay in suspension and ephemeral coarse-grained fluvial sediment discharge. Abundant Ranunculaceae macroremains (used for 14C dating), insects, moss and fungi sclerotia reflect a tundra environment during a time of frequent strong snowmelt events. Total carbon content, Betula-Pinus pollen and diatoms reach increased concentrations during Marine Isotope Stage (MIS) 3 interstadials that occurred between 28,500 and 36,500 b2k (LEZ 6). The entire MIS3 interstadials are well documented in the organic carbon record from the Auel dry maar. The main paleobotanical indicators of MIS3 are, however, grass pollen and heliophytes, which indicate a steppe environment with scattered/patchy trees during the interstadials. The stadial phases inferred during LEZ 6 reveal initiation of eolian dust deflation. The change of the early MIS 3 forested landscape to a steppe occurred with the LEZ 7-LEZ 6 transition. This is when modern man spread in central Europe. The principle vegetation change to a steppe at 36,500 b2k must have favoured the spread of horses, an important hunting prey of modern humans. We propose accordingly that the migration of the modern humans into central Europe might have been at least partly driven by climate and associated vegetation change. The LEZ 7 encompassed the time interval 36,500 to 49,000 b2k and was characterized by a boreal forest with high abundance of pine, birch, as well as spruce during the interstadial events. Abundant charcoal fragments indicate that this taiga was under frequent drought stress with regular burning. The most unexpected finding, but corroborated by all our maar records is the dominance of thermophilous tree taxa from 49,000 to 55,000 b2k (LEZ 8). Greenland interstadials 13 and 14 were apparently the warmest of MIS 3 according to the Eifel pollen records. The preceeding LEZ 9 from 55,000 to 60,000 b2k is also dominated by spruce, but thermophilous trees were sparse. A warm early MIS3 appears plausible, because summer insolation (at 60° N) was higher in the early MIS 3 than today, ice cover was low in Scandinavia and sea-surface temperatures of the North Atlantic were almost comparable to modern values during GI-14.

来自德国埃菲尔地区多个玛珥湖（maar lake）与干玛珥湖（dry maar lake）的层积沉积物记录，揭示了过去60000年以来中欧地区气候、天气、环境、植被与土地利用的演化历史。过去30000年的时间序列基于连续纹泥计数定年，海洋同位素阶段3（Marine Isotope Stage, MIS3）剖面则与格陵兰冰芯进行了旋回校准，二者均通过¹⁴C测年获得独立年代控制。研究采用总有机碳、孢粉与植物大化石重建了植被序列，并将其与季节性纹泥沉积、洪水层、风尘含量以及火山灰层的序列相结合，划定了景观演化带（Landscape Evolution Zones, LEZ）。

LEZ 1涵盖了过去6000年受人类广泛影响的景观动态过程。LEZ 2对应全新世早期至10500 b2k的天然栎林与榛木林。LEZ 3为10500至14700 b2k的晚冰期阶段，彼时湖泊中发育以丰富草本与浅水生物量为特征的寒温带针叶林。末次冰盛期（Last Glacial Maximum, LGM）对应LEZ 4（14700~23000 b2k），其植被以稀疏的苔藓与轮藻群落为典型特征。此类沉积物通常不含黏土与砂质组分，且无融雪径流事件的迹象，据此推断中欧地区末次冰盛期气候极端干旱。

后续LEZ 5（23000~28500 b2k）的沉积物保存有清晰的黏土与粗砂层，指示当时存在悬浮黏土的流水环境与间歇性粗粒河流沉积物输入。大量毛茛科（Ranunculaceae）大化石（用于¹⁴C测年）、昆虫、苔藓与真菌菌核，反映了频发强融雪事件时期的苔原环境。在28500~36500 b2k的海洋同位素阶段3（MIS3）间冰阶（LEZ 6）中，总有机碳含量、桦木-松属（Betula-Pinus）孢粉与硅藻浓度均出现升高。整个MIS3间冰阶的有机碳记录在奥厄干玛珥湖沉积物中得到了完整记录。不过MIS3的主要古植物指示物为草本孢粉与阳生植物，指示间冰阶时期为散布有零星树木的草原环境。LEZ 6推断的冰阶阶段显示风尘吹蚀作用开始发育。

MIS3早期森林景观向草原的转变发生在LEZ7向LEZ6的过渡时期，这一阶段也是现代人类在中欧扩散的时期。36500 b2k时植被向草原的根本性转变，可能促进了马的扩散——而马是现代人类重要的狩猎猎物。据此我们推测，现代人类向中欧的迁徙可能至少部分受到气候与伴随的植被变化的驱动。LEZ7对应36500~49000 b2k的时段，其特征为间冰阶事件中发育以丰富松、桦以及云杉为代表的寒温带针叶林。大量炭屑碎片指示此类泰加林频繁遭受干旱胁迫并伴有周期性火烧。

最出人意料但经所有玛珥湖记录证实的发现是：在49000~55000 b2k（LEZ8）时期，嗜暖树木类群占据主导地位。根据埃菲尔地区的孢粉记录，格陵兰间冰阶13与14为MIS3阶段最为温暖的时期。此前的LEZ9（55000~60000 b2k）同样以云杉为主导，但嗜暖树木较为稀少。MIS3早期整体偏暖的推论合理，因为彼时北纬60°的夏季日照量高于现代，斯堪的纳维亚地区冰盖覆盖率较低，且格陵兰间冰阶14（GI-14）时期北大西洋海表温度几乎与现代值相当。