Summertime thermally-induced circulations over the Lake Nam Co region of the Tibetan Plateau

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 mountainous environment allows the observation and tracking of abiotic and biotic feedback mechanisms. Closed lake systems, such as the Nam Co on the central TP represent important natural laboratories for tracking past and recent climatic oscillations, as well as geobiological processes and interactions within their respective catchments. This review gives an interdisciplinary overview of modern and paleoenvironmental changes, focusing on Nam Co as model system. In the catchment area, the steep rise in air temperature forced glaciers to melt, leading to a rise in lake levels 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 decades. The enhanced 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 a significant effect on CO2 fluxes, with moderate grazing enhancing belowground allocation of carbon while adversely affecting the C-sink potential through reduction of above- 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 have 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 geo- and biodiversity and their interplay in the Lake Nam Co, which acts as a case study for potentially TP-wide processes that are currently shaping the earth’s future.

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Surface ozone at Nam Co (4730 m a.s.l.) in the inland Tibetan Plateau: variation, synthesis comparison and regional representativeness

10.5194/acp-2017-175 ◽

2017 ◽

Cited By ~ 1

Author(s):

Xiufeng Yin ◽

Shichang Kang ◽

Benjamin de Foy ◽

Zhiyuan Cong ◽

Jiali Luo ◽

...

Keyword(s):

Tibetan Plateau ◽

Surface Ozone ◽

Early Morning ◽

Photochemical Reactions ◽

Transport Processes ◽

The Tibetan Plateau ◽

Nam Co ◽

Mixing Ratios ◽

Northern Tibetan Plateau ◽

Ozone Levels

Abstract. Ozone is an important pollutant and greenhouse gas, and tropospheric ozone variations are generally associated with both natural and anthropogenic processes. As one of the most pristine and inaccessible regions in the world, the Tibetan Plateau has been considered as an ideal region for studying processes of the background atmosphere. Due to the vast area of the Tibetan Plateau, sites in the southern, northern and central regions exhibit different patterns of variation in surface ozone. Here, we present long-term measurements for ~ 5 years (January 2011 to October 2015) of surface ozone mixing ratios at Nam Co Station, which is a regional background site in the inland Tibetan Plateau. An average surface ozone mixing ratio of 47.6 ± 11.6 ppb was recorded, and a large annual cycle was observed with maximum ozone mixing ratios in the spring and minimum ratios during the winter. The diurnal cycle is characterized by a minimum in the early morning and a maximum in the late afternoon. Nam Co Station represents a background region where surface ozone receives negligible local anthropogenic emissions. Surface ozone at Nam Co Station is mainly dominated by natural processes involving photochemical reactions and potential local vertical mixing. Model results indicate that the study site is affected by the surrounding areas in different seasons and that air masses from the northern Tibetan Plateau lead to increased ozone levels in the summer. In contrast to the surface ozone levels at the edges of the Tibetan Plateau, those at Nam Co Station are less affected by stratospheric intrusions and human activities which makes Nam Co Station representative of vast background areas in the central Tibetan Plateau. By comparing measurements at Nam Co Station with those from other sites in the Tibetan Plateau and beyond, we aim to expand the understanding of ozone cycles and transport processes over the Tibetan Plateau. This work may provide a reference for model simulations in the future.

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Atmospheric processes of persistent organic pollutants over a remote lake of the central Tibetan Plateau: Implications for regional cycling

10.5194/acp-2016-989 ◽

2016 ◽

Author(s):

Jiao Ren ◽

Xiaoping Wang ◽

Chuanfei Wang ◽

Ping Gong ◽

Tandong Yao

Keyword(s):

Tibetan Plateau ◽

Organic Pollutants ◽

Persistent Organic Pollutants ◽

Secondary Source ◽

The Tibetan Plateau ◽

Lake Area ◽

Nam Co ◽

Surface Exchange ◽

Atmospheric Processes ◽

Water Gas

Abstract. Atmospheric processes (air-surface exchange, and atmospheric deposition and degradation) are crucial for understanding the global cycling and fate of persistent organic pollutants (POPs). However, such assessment over the Tibetan Plateau (TP) remains uncertain. More than 50 % of the Chinese lakes are located on the TP, which exerts a remarkable influence on the regional water, energy, and chemical cycling. In this study, air and water samples were simultaneously collected in Nam Co, a large lake on the TP, to test whether the lake is a "secondary source" or "sink" of POPs. Lower concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were observed in the atmosphere and lake water of Nam Co, while the levels of polycyclic aromatic hydrocarbons (PAHs) were relatively higher. Results of fugacity ratios and chiral signatures both suggest that the lake acted as the net sink of atmospheric hexachlorocyclohexanes (HCHs), following their long-range transport driven by the Indian Monsoon. Different behaviors were observed in the PAHs, which primarily originated from local biomass burning. Acenaphthylene, acenaphthene, and fluorene showed volatilization from the lake to the atmosphere; while other PAHs were deposited into the lake due to the integrated deposition process (wet/dry and air-water gas deposition) and limited atmospheric degradation. As the dominant PAH compound, phenanthrene exhibited a seasonal reversal of air-water gas exchange, which was likely related to the melting of the lake ice in May. The annual input of HCHs from air to the entire lake area (2015 km2) was estimated as 1.9 kg year−1, while those estimated for PAHs can potentially reach up to 550 kg year−1. This study highlights the significance of PAH deposition on the regional carbon cycling in the oligotrophic lakes of the TP.

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Air-Lake Interaction Features Found in Heat and Water Exchanges over Nam Co on the Tibetan Plateau

SOLA ◽

10.2151/sola.2009-044 ◽

2009 ◽

Vol 5 ◽

pp. 172-175 ◽

Cited By ~ 47

Author(s):

Shigenori Haginoya ◽

Hideyuki Fujii ◽

Tsuneo Kuwagata ◽

Jianqing Xu ◽

Yasushi Ishigooka ◽

...

Keyword(s):

Tibetan Plateau ◽

The Tibetan Plateau ◽

Nam Co

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Spatial and temporal variations in water temperature in a high-altitude deep dimictic mountain lake (Nam Co), central Tibetan Plateau

Journal of Great Lakes Research ◽

10.1016/j.jglr.2018.12.005 ◽

2019 ◽

Vol 45 (2) ◽

pp. 212-223 ◽

Cited By ~ 8

Author(s):

Junbo Wang ◽

Lei Huang ◽

Jianting Ju ◽

Gerhard Daut ◽

Yong Wang ◽

...

Keyword(s):

Tibetan Plateau ◽

Water Temperature ◽

High Altitude ◽

Temporal Variations ◽

Spatial And Temporal Variations ◽

Mountain Lake ◽

Nam Co ◽

Central Tibetan Plateau ◽

Lake Nam Co

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Observed and Simulated Lake Effect Precipitation Over the Tibetan Plateau: An Initial Study at Nam Co Lake

Journal of Geophysical Research Atmospheres ◽

10.1029/2018jd028330 ◽

2018 ◽

Vol 123 (13) ◽

pp. 6746-6759 ◽

Cited By ~ 10

Author(s):

Yufeng Dai ◽

Lei Wang ◽

Tandong Yao ◽

Xiangyu Li ◽

Lingjing Zhu ◽

...

Keyword(s):

Tibetan Plateau ◽

Initial Study ◽

The Tibetan Plateau ◽

Nam Co ◽

Lake Effect ◽

Nam Co Lake

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Carbon and water fluxes in an alpine steppe ecosystem in the Nam Co area of the Tibetan Plateau during two years with contrasting amounts of precipitation

International Journal of Biometeorology ◽

10.1007/s00484-020-01892-2 ◽

2020 ◽

Vol 64 (7) ◽

pp. 1183-1196

Author(s):

Yuyang Wang ◽

Zhikun Zhu ◽

Yaoming Ma ◽

Ling Yuan

Keyword(s):

Tibetan Plateau ◽

The Tibetan Plateau ◽

Water Fluxes ◽

Nam Co ◽

Alpine Steppe ◽

Steppe Ecosystem

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Response of δD values of sedimentary n-alkanes to variations in source water isotope signals and climate proxies at lake Nam Co, Tibetan Plateau

Quaternary International ◽

10.1016/j.quaint.2010.12.006 ◽

2011 ◽

Vol 236 (1-2) ◽

pp. 82-90 ◽

Cited By ~ 19

Author(s):

F. Günther ◽

I. Mügler ◽

R. Mäusbacher ◽

G. Daut ◽

K. Leopold ◽

...

Keyword(s):

Tibetan Plateau ◽

Source Water ◽

Nam Co ◽

Lake Nam Co ◽

Climate Proxies ◽

Water Isotope

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What are the key drivers of regional differences in the water balance on the Tibetan Plateau?

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-4271-2015 ◽

2015 ◽

Vol 12 (4) ◽

pp. 4271-4314 ◽

Cited By ~ 5

Author(s):

S. Biskop ◽

F. Maussion ◽

P. Krause ◽

M. Fink

Keyword(s):

Tibetan Plateau ◽

Water Balance ◽

Hydrological Modeling ◽

Integrated Approach ◽

Water Levels ◽

The Tibetan Plateau ◽

Nam Co ◽

Water Balance Components ◽

South Central ◽

Lake Basins

Abstract. Lake-level fluctuations in closed basins on the Tibetan Plateau (TP) indicate climate-induced changes in the regional water balance. However, little is known about the region's key hydrological parameters, hampering the interpretation of these changes. The purpose of this study is to contribute to a more quantitative understanding of these controls. Four lakes in the south-central part of the TP were selected to analyze the spatiotemporal variations of water-balance components: Nam Co and Tangra Yumco (indicating increasing water levels), and Mapam Yumco and Paiku Co (indicating stable or slightly decreasing water levels). We present the results of an integrated approach combining hydrological modeling, atmospheric-model output and remote-sensing data. The hydrological model J2000g was adapted and extended according to the specific characteristics of closed lake basins on the TP and driven with "High Asia Refined analysis (HAR)" data at 10 km resolution for the period 2001–2010. Our results reveal that because of the small portion of glacier areas (1 to 7% of the total basin area) the contribution of glacier melt water accounts for only 14–30% of total runoff during the study period. Precipitation is found to be the principal factor controlling the water-balance in the four studied basins. The positive water balance in the Nam Co and Tangra Yumco basins was primarily related to larger precipitation amounts and thus higher runoff rates in comparison with the Paiku Co and Mapam Yumco basins. This study highlights the benefits of combining atmospheric and hydrological modeling. The presented approach can be readily transferred to other ungauged lake basins on the TP, opening new directions of research. Future work should go towards increasing the atmospheric model's spatial resolution and a better assessment of the model-chain uncertainties, especially in this region where observational data is missing.

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