Tab. 1+7: Hydrochemical analyses of firn and meltwater from different \"cold\" snow patches

In wide areas of Northern Siberia, glaciers have been absent since the Late Pleistocene. Therefore, ground ice and especially ice wedges are used as archives for paleoclimatic studies. In the present study, carried out on the Bykovsky Peninsula, eastern Lena Delta, we were able to distinguish ice wedges of different genetic units by means of oxygen and hydrogen isotopes. The results obtained by this study on the Ice Complex, a peculiar periglacial phenomenon, allowed the reconstruction of the climate history with a subdivision of a period of very cold winters (60-55 ka), followed by a long stable period of cold winter temperatures (50-24 ka), Between 20 ka and 11 ka, climate warming is indicated in stable isotope compositions, most probably after the Late Glacial Maximum. At that time, a change of the marine source of the precipitation from a more humid source to the present North AtIantic source region was assumed. For the Ice Complex, a continuous age-height relationship was established, indicating syngenetic vertical ice wedge growth and sediment accumulation rates of 0.7 m/ky. During the Holocene optimum, ice wedge growth was probably limited due to the extensive formation of lacustrine environments. Holocene ice wedges in thermokarst depressions (alases) and thermoerosional valleys (logs) were formed after climate deterioration from about 4.5 ka until the present. Winter temperatures were warmer at this time as compared to the cooler Pleistocene. Migration of bound water between ice wedges and segregated ice may have altered the isotopic composition of old ice wedges. The presence of ice wedges as diagnostic features for permafrost conditions since 60 ka, implies that a large glacier extending over the Laptev Sea shelf did not exist. For the remote non-glaciated areas of Northern Siberia, ice wedges were established as a powerful climate archive.

在西伯利亚北部的广大区域，晚更新世（Late Pleistocene）以来便无冰川分布。因此，地下冰（ground ice）尤其是冰楔（ice wedges）被用作古气候研究的天然档案。本研究在勒拿河三角洲东部的别科夫斯基半岛（Bykovsky Peninsula）开展，通过氧同位素与氢同位素分析，得以区分不同遗传成因单元的冰楔。针对冰复合体（Ice Complex）这一特殊冰缘现象（periglacial phenomenon），本研究所得结果实现了古气候历史的重建：将极寒冬季时段（60~55 ka）划分为一段，随后是持续稳定的冷冬季气温时段（50~24 ka）。在20 ka至11 ka期间，稳定同位素组成指示气候变暖，这一变化极有可能发生在末次冰盛期（Late Glacial Maximum）之后。彼时，降水的海洋水汽来源被认为从更为湿润的源区转变为现今的北大西洋源区。本研究为冰复合体建立了连续的年龄-高度关系，表明冰楔以同生垂直方式生长，沉积物沉积速率为0.7米/千年（m/ky）。在全新世适宜期（Holocene optimum），由于湖相环境广泛发育，冰楔的生长可能受到限制。发育于热喀斯特洼地（thermokarst depressions, alases）与热侵蚀河谷（thermoerosional valleys, logs）中的全新世冰楔，形成于约4.5 ka至今的气候恶化阶段。相较于较为寒冷的更新世，该时期的冬季气温更高。冰楔与分凝冰之间的束缚水迁移作用，可能改变了古老冰楔的同位素组成。自60 ka以来，冰楔作为多年冻土（permafrost）条件的标志性特征，意味着拉普捷夫海陆架（Laptev Sea shelf）之上从未存在过大规模冰川。对于西伯利亚北部偏远的无冰川区域，冰楔已被证实为极具价值的气候档案。