School of Geographical Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China.
Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, MI 48109, USA.
Sci Total Environ. 2023 Oct 1;893:164641. doi: 10.1016/j.scitotenv.2023.164641. Epub 2023 Jun 4.
The bulk nitrogen isotope composition of lacustrine sediments can be a useful proxy of past climatic and environmental changes. We previously reconstructed paleoenvironmental histories recorded in sediments of Lake Ximencuo and Lake Ngoring, both located on the eastern Qinghai-Tibetan Plateau (QTP), using a suite of biogeochemical paleoclimate proxies that included the sedimentary δN values. We have revisited the different patterns of δN variations in the two lakes and now conclude that their isotopic trends over the last millennium have been controlled by multiple factors. Regional temperature evidently is one potential factor affecting the sedimentary δN values, indicating that the lake ecosystems respond to regional temperature changes on a sub-millennial timescale but in indirect and lake-specific ways. The processes involved in the sedimentary δN changes appear to be more strongly influenced by the shapes of lake basins and associated hydrologic characteristics that control the origins of nitrogen-containing compounds in the lakes. To help understand the dynamics of nitrogen cycling and nitrogen isotope records in the QTP lakes, we identified two patterns - a terrestrial nitrogen-controlled pattern (TNCP) that is observed in deeper, steep-walled glacial-basin lakes and an aquatic nitrogen-controlled pattern (ANCP) that is observed in shallower, tectonic-basin lakes. We also considered the influences of the "amount effect" and the "temperature effect" on sedimentary δN values and their possible operative mechanisms in these montane lakes. We postulate that both patterns are applicable to the QTP lakes, including both glacial and tectonic lakes, and probably to lakes in other regions that have also not experienced significant human disturbance.
湖泊沉积物的氮同位素组成可以作为过去气候和环境变化的有用指标。我们之前曾使用包括沉积δN 值在内的一系列生物地球化学古气候代用指标，重建了位于青藏高原东部的西门错湖和纳木错湖沉积物中记录的古环境历史。我们重新研究了这两个湖泊中不同的δN 变化模式，现在得出的结论是，它们在过去一千年中的同位素趋势受到多种因素的控制。区域温度显然是影响沉积δN 值的一个潜在因素，这表明湖泊生态系统在亚千年时间尺度上对区域温度变化做出响应，但方式是间接的且具有湖泊特异性。沉积δN 变化所涉及的过程似乎受到湖泊盆地形状和相关水文特征的强烈影响，这些特征控制了湖泊中含氮化合物的来源。为了帮助理解青藏高原湖泊中氮循环和氮同位素记录的动态，我们确定了两种模式——一种是在较深、壁陡的冰川盆地湖中观察到的陆地氮控制模式（TNCP），另一种是在较浅、构造盆地湖中观察到的水生氮控制模式（ANCP）。我们还考虑了“数量效应”和“温度效应”对沉积δN 值的影响及其在这些山地湖泊中可能的作用机制。我们假设这两种模式都适用于青藏高原湖泊，包括冰川湖和构造湖，可能也适用于其他地区的湖泊，这些湖泊也没有经历过显著的人为干扰。
