Yang Yuzhong, Guo Xiaoyan, Wu Qingbai, Jin Huijun, Liu Fengjing
State Key Laboratory of Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China; Beiluhe Observation and Research Station on Frozen Soil Engineering and Environment in Qinghai-Tibet Plateau, China.
Key Laboratory of Ecohydrology of Inland River Basin, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China.
Sci Total Environ. 2023 Mar 10;863:160967. doi: 10.1016/j.scitotenv.2022.160967. Epub 2022 Dec 15.
The Source Area of the Yellow River (SAYR) on the Northeastern Qinghai-Tibet Plateau (QTP) stores substantial amounts of ground ice, which plays a significant role in understanding the hydrological processes and past permafrost evolution on the QTP. However, little is known about the initial sources and controlling factors of the ground ice in the SAYR. In this study, for the first time, ground ice stable isotope data (δO, δD, and d-excess) are presented, along with cryostratigraphic information for nine sites is integrated into three cryostratigraphic units (palsa, thermo-gully, and lake-affected sites) in the central SAYR. The ground ice in the nine sites exhibited diverse structures, ice contents, and stable isotopes due to differences in the initial water sources, ice formation mechanisms, soil types, and climate conditions. All of the freezing lines of ground ice are below those of the precipitation, streams, and lakes in most cases, suggesting the freezing of liquid water. The near-surface ground ice (NSGI) originated from precipitation, active layer water, and precipitation-fed springs. The NSGI was formed by quick freezing at the thermo-gully site (TG-1). In contrast, the formation of the NSGI at the palsa site (Palsa-1) experienced a slow segregation process during the permafrost aggradation. The NSGI was formed by quick freezing at the lake-affected sites under colder climate conditions. Conversely, the deep-layer ground ice (DLGI) at the lake-affected sites was fed by isotopically negative water and lake water occurred during a colder climate period. The DLGI at the TG-1 and Palsa-1 formed via similarly slow segregation of supra-permafrost water (mixed with precipitation), but had opposite water migration directions. The stable isotope compositions of the DLGI at the lake-affected sites became gradually more positive with decreasing distance from WL Lake, emphasizing the large influence of the lake changes on the growth of ice. The two end-member mixing model estimated that the contributions of paleo-lake water to the DLGI ranged from 9.8 % to 63.4 % towards the lake at the lake-affected sites, while the meltwater from past permafrost/ground ice contributed 36.6-90.2 % of the total input. A conceptual diagram of the δO trajectories of ground ice was constructed, the water migration patterns and ground ice formation processes between the palsa, thermo-gully, and lake-affected sites were clarified. The results of this study emphasize the influence of lake changes and past permafrost evolution on ground ice growth and improve our understanding of permafrost changes on the QTP.
青藏高原东北部的黄河源区储存着大量的地下冰，这对于理解青藏高原的水文过程和过去的多年冻土演化具有重要作用。然而，关于黄河源区地下冰的初始来源和控制因素却知之甚少。在本研究中，首次呈现了地下冰稳定同位素数据（δO、δD和d值），并将中部黄河源区9个站点的低温地层信息整合为3个低温地层单元（泥炭丘、热融沟和受湖泊影响站点）。由于初始水源、结冰机制、土壤类型和气候条件的差异，9个站点的地下冰呈现出不同的结构、含冰量和稳定同位素特征。在大多数情况下，所有地下冰的冻结线都低于降水、溪流和湖泊的冻结线，表明液态水发生了冻结。近地表地下冰（NSGI）起源于降水、活动层水和降水补给的泉水。热融沟站点（TG-1）的近地表地下冰是由快速冻结形成的。相比之下，泥炭丘站点（Palsa-1）的近地表地下冰在多年冻土堆积过程中经历了缓慢的分凝过程。在较寒冷的气候条件下，受湖泊影响站点的近地表地下冰是由快速冻结形成的。相反，受湖泊影响站点的深层地下冰（DLGI）由同位素负值水和较寒冷气候时期出现的湖水补给。热融沟站点（TG-1）和泥炭丘站点（Palsa-1）的深层地下冰通过类似的多年冻土上水（与降水混合）缓慢分凝形成，但水的迁移方向相反。受湖泊影响站点的深层地下冰的稳定同位素组成随着距WL湖距离的减小而逐渐变得更正，强调了湖泊变化对冰生长的重大影响。双端元混合模型估计，在受湖泊影响的站点，古湖水对深层地下冰的贡献范围为9.8%至63.4%，而过去多年冻土/地下冰的融水占总输入的36.6%至90.2%。构建了地下冰δO轨迹的概念图，并阐明了泥炭丘、热融沟和受湖泊影响站点之间的水迁移模式和地下冰形成过程。本研究结果强调了湖泊变化和过去多年冻土演化对地下冰生长的影响，并增进了我们对青藏高原多年冻土变化的理解。
