Reviews and syntheses: How do abiotic and biotic processes respond to climatic variations in the Nam Co catchment (Tibetan Plateau)?

Abstract

Abstract. The Tibetan Plateau (TP) is the largest alpine plateau on Earth and plays an important role in global climate dynamics. On the TP, climate change is happening particularly fast, with an increase in air temperature twice the global average. The particular sensitivity of this high mountain environment allows observation and tracking of abiotic and biotic feedback mechanisms. Closed lake systems, such as Nam Co on the central TP, represent important natural laboratories for tracking past and recent climatic changes, as well as geobiological processes and interactions within their respective catchments. This review gives an interdisciplinary overview of past and modern environmental changes using Nam Co as a case study. In the catchment area, ongoing rise in air temperature forces glaciers to melt, contributing to a rise in lake level and changes in water chemistry. Some studies base their conclusions on inconsistent glacier inventories, but an ever-increasing deglaciation and thus higher water availability have persisted over the last few decades. Increasing water availability causes translocation of sediments, nutrients and dissolved organic matter to the lake, as well as higher carbon emissions to the atmosphere. The intensity of grazing has an additional and significant effect on CO2 fluxes, with moderate grazing enhancing belowground allocation of carbon while adversely affecting the C sink potential through reduction of above-surface and subsurface biomass at higher grazing intensities. Furthermore, increasing pressure from human activities and livestock grazing are enhancing grassland degradation processes, thus shaping biodiversity patterns in the lake and catchment. The environmental signal provided by taxon-specific analysis (e.g., diatoms and ostracods) in Nam Co revealed profound climatic fluctuations between warmer–cooler and wetter–drier periods since the late Pleistocene and an increasing input of freshwater and nutrients from the catchment in recent years. Based on the reviewed literature, we outline perspectives to further understand the effects of global warming on geodiversity and biodiversity and their interplay at Nam Co, which acts as a case study for potentially TP-level or even worldwide processes that are currently shaping high mountain areas.

Rock glacier inventory of the western Nyainqêntanglha Range, Tibetan Plateau, supported by InSAR time series and automated classification

“…Annual precipitation is higher on the southern side of the mountain range with 460 mm in Damxung from 1971 to 2000 compared to 406 mm at Nam Co Monitoring and Research Station for Multisphere Interactions (NAMORS) from 2006 to 2017 (Figure 2). 54,55 A meteorological station at Zhadang Glacier recorded an annual precipitation between 487 and 568 mm from 2009 to 2011 56 . The mean annual air temperatures at those meteorological stations during the same time periods were 1.6, −0.6, and −5.9°C respectively.…”

“…The study of permafrost and associated periglacial landforms in the western Nyainqêntanglha Range has received much less attention compared to glaciers and lakes 55 . InSAR time series analysis display seasonal heave–thaw cycles with an amplitude of up to 2.5 cm near water bodies 64,65 .…”

High‐throughput identification of non‐marine Ostracoda from the Tibetan Plateau: Evaluating the success of various primers on sedimentary DNA samples

“…Sediment samples were collected in Nam Co, a lake located in the monsoon‐influenced transition zone between semi‐humid and semi‐arid areas of the Tibetan Plateau. The mean annual air temperature measured at the Nam Co Monitoring and Research Station for Multisphere Interactions (NAMORS) between 2006 and 2017 was −0.6°C, and the annual precipitation ranged from 291 to 568 mm (mean =405 mm) with most of the precipitation occurring during the monsoon season from May to September (Anslan et al, 2020). The precipitation rates are subject to spatial variations due to the >7,000 m high Nyainqêntanglha mountain range which represents the southern border of the Nam Co catchment.…”

Rock Glacier Characteristics Under Semiarid Climate Conditions in the Western Nyainqêntanglha Range, Tibetan Plateau

“…In semiarid and highly elevated mountain ranges, like the northern part of the western Nyainqêntanglha range (Anslan et al., 2020; Bolch et al., 2010), the extent of the source areas for moisture and sediment of the rock glacier might be limited (Blöthe et al., 2020; Humlum, 2000; Janke & Frauenfelder, 2008). In general, the moisture of rock glacier ice can originate from precipitation, snow or glacial melt, as well as debris‐covered glacial remnants.…”