Browsing by Author "Lei, Yanbin"
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Item A 2540-year record of moisture variations derived from lacustrine sediment (Sasikul Lake) on the Pamir Plateau(Sage, 2014-05-06) Lei, Yanbin; Tian, Lide; Bird, Broxton W.; Hou, Juzhi; Ding, Lin; Oimahmadov, Ilhomjon; Gadoev, MustafoAlthough the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900, corresponding to the ‘Little Ice Age’ (LIA). More negative values of carbonate δ18O, lower total inorganic carbon (TIC), and sand content during LIA all indicate a relatively wet period with higher lake level. Higher TIC during the ‘Medieval Warm Period’ (MWP; ad 950–1200) reveals a lower lake level relative to the LIA. Low δ18O during this time is probably attributed to changes in the isotopic composition of input water and/or upstream moisture sources. The significant increase in detrital minerals and decrease in carbonate during the LIA provide further evidence for higher allochthonous input during the wet period at Sasikul Lake. The inferred moisture variations are consistent with existing records from regions of the northern Tibetan Plateau and Central Asia that are also influenced by the westerlies, but out-ofphase with those records from the Asian monsoon region, indicating that moisture variations at Sasikul Lake were mainly influenced by the strength and trajectories of the westerlies. The inferred water level at Sasikul Lake decreased significantly during the first half of the 20th century, and then increased in recent decades. This is consistent with the increase in lake area derived from satellite images and the monitoring data of large lake-level changes in Central Asia.Item Contrasting hydrological and thermal intensities determine seasonal lake-level variations – a case study at Paiku Co on the southern Tibetan Plateau(Copernicus Publications, 2021) Lei, Yanbin; Yao, Tandong; Yang, Kun; Lazhu; Ma, Yaoming; Bird, Broxton W.; Earth Sciences, School of ScienceEvaporation from hydrologically closed lakes is one of the largest components of the lake water budget; however, its effects on seasonal lake-level variations remain unclear on the Tibetan Plateau (TP) due to a lack of comprehensive observations. In this study, weekly lake evaporation and its effects on seasonal lake-level variations are investigated at Paiku Co on the southern TP using in situ observations of thermal structure and hydrometeorology (2015–2018). Lake evaporation from Paiku Co was estimated to be 975±142 mm during the ice-free period (May to December), characterized by low values of 1.7 ± 0.6 mm d−1 during the pre-monsoon season (May to June), high values of 5.5±0.6 mm d−1 during the post-monsoon season (October to December), and intermediate values of 4.0±0.6 mm d−1 during the monsoon season (July to September). There was a ∼ 5-month lag between the maximum net radiation (June) and maximum lake evaporation (November). These results indicate that the seasonal pattern of lake evaporation from Paiku Co was significantly affected by the large lake heat storage. Contrasting hydrological and thermal intensities may play an important role in the large amplitude of seasonal lake-level variations at deep lakes like Paiku Co. High inflow from monsoon precipitation and glacier melting and moderate lake evaporation, for instance, drove rapid lake-level increase during the monsoon season. In contrast, high lake evaporation and reduced inflow caused lake level to decrease significantly during the post-monsoon season. This study implies that lake evaporation may play an important role in the different amplitudes of seasonal lake-level variations on the TP.Item An integrated investigation of lake storage and water level changes in the Paiku Co basin, central Himalayas(Elsevier, 2018) Lei, Yanbin; Yao, Tandong; Yang, Kun; Bird, Broxton W.; Tian, Lide; Zhang, Xiaowen; Wang, Weicai; Xiang, Yang; Dai, Yufeng; Lazhu; Zhou, Jing; Wang, Lei; Earth Sciences, School of ScienceSince the late 1990s, lakes in the southern Tibetan Plateau (TP) have shrunk considerably, which contrasts with the rapid expansion of lakes in the interior TP. Although these spatial trends have been well documented, the underlying hydroclimatic mechanisms are not well understood. Since 2013, we have carried out comprehensive water budget observations at Paiku Co, an alpine lake in the central Himalayas. In this study, we investigate water storage and lake level changes on seasonal to decadal time scales based on extensive in-situ measurements and satellite observations. Bathymetric surveys show that Paiku Co has a mean and maximum water depth of 41.1 m and 72.8 m, respectively, and its water storage was estimated to be 109.3 × 108 m3 in June 2016. On seasonal scale between 2013 and 2017, Paiku Co’s lake level decreased slowly between January and May, increased considerably between June and September, and then decreased rapidly between October and January. On decadal time scale, Paiku Co’s lake level decreased by 3.7 ± 0.3 m and water storage reduced by (10.2 ± 0.8) × 108 m3 between 1972 and 2015, accounting for 8.5% of the total water storage in 1972. This change is consistent with a trend towards drier conditions in the Himalaya region during the recent decades. In contrast, glacial lakes within Paiku Co’s basin expanded rapidly, indicating that, unlike Paiku Co, glacial meltwater was sufficient to compensate the effect of the reduced precipitation.Item Lake seasonality across the Tibetan Plateau and their varying relationship with regional mass changes and local hydrology(Wiley, 2017-01) Lei, Yanbin; Yao, Tandong; Yang, Kun; Sheng, Yongwei; Kleinherenbrink, Marcel; Yi, Shuang; Bird, Broxton W.; Zhang, Xiaowen; Zhu, La; Zhang, Guoqing; Department of Earth Sciences, School of ScienceThe recent growth and deepening of inland lakes in the Tibetan Plateau (TP) may be a salient indicator of the consequences of climate change. The seasonal dynamics of these lakes is poorly understood despite this being potentially crucial for disentangling contributions from glacier melt and precipitation, which are all sensitive to climate, to lake water budget. Using in situ observations, satellite altimetry and gravimetry data, we identified two patterns of lake level seasonality. In the central, northern, and northeastern TP, lake levels are characterized by considerable increases during warm seasons and decreases during cold seasons, which is consistent with regional mass changes related to monsoon precipitation and evaporation. In the northwestern TP, however, lake levels exhibit dramatic increases during both warm and cold seasons, which deviate from regional mass changes. This appears to be more connected with high spring snowfall and large summer glacier melt. The variable lake level response to different drivers indicates heterogeneous sensitivity to climate change between the northwestern TP and other regions.Item Late-Holocene Indian summer monsoon variability revealed from a 3300-year-long lake sediment record from Nir’pa Co, southeastern Tibet(Sage, 2017-04) Bird, Broxton W.; Lei, Yanbin; Perello, Melanie; Polissar, Pratigya J.; Yao, Tandong; Finney, Bruce; Bain, Daniel; Pompeani, David; Thompson, Lonnie G.; Earth Science, School of ScienceSedimentological and geochemical results from Nir’pa Co, an alpine lake on the southeastern Tibetan Plateau, detail late-Holocene Indian summer monsoon (ISM) hydroclimate during the last 3300 years. Constrained by modern calibration, elevated silt and lithics and low sand and clay between 3.3 and 2.4 ka and 1.3 ka and the present indicate two pluvial phases with lake levels near their current overflow elevation. Between 2.4 and 1.3 ka, a sharp increase in sand and corresponding decrease in lithics and silt suggest drier conditions and lower lake levels at Nir’pa Co. Hydroclimate expressions in the sedimentological proxies during the Medieval Climate Anomaly (MCA) and ‘Little Ice Age’ (LIA) are not statistically significant, suggesting that these events were minor compared to the millennial scale variability on which they were superimposed. However, decreasing sand and increasing lithics and silt during the MCA between 950 and 800 cal. yr BP may suggest briefly wetter conditions, while increasing sand and reduced lithics and silt from 500 to 200 cal. yr BP suggest potentially drier conditions during the LIA. Similarities with regional records from lake sediment and ice cores and speleothem records from the central and eastern Tibetan Plateau, India, and the Arabian Sea, suggest generally coherent late-Holocene ISM variability in these regions. Increased late-Holocene ISM intensity occurred during times when Tibetan Plateau surface air temperatures were warmer, Indo-Pacific sea surface temperatures were elevated, and the tropical Pacific was in a La Niña–like mean state. Conversely, aridity between 2.4 and 1.3 ka occurred in concert with cooling on the Tibetan Plateau and in the Indo-Pacific with more El Niño–like conditions in the tropical Pacific. Differences with western Tibetan records may reflect a weakened ISM and stronger westerlies in this region during the late-Holocene.Item Stable isotopes of river water and groundwater along altitudinal gradients in the High Himalayas and the Eastern Nyainqentanghla Mountains(Elsevier, 2017-12-01) Florea, Lee; Bird, Broxton W.; Lau, Jamie K.; Wang, Lixin; Lei, Yanbin; Yao, Tandong; Thompson, Lonnie G.; Earth Science, School of ScienceStudy Region This study considers river water and groundwater in seeps and springs collected from the non-monsoon season in the valleys of the Dudh Koshi River in eastern Nepal and the Niyang River of eastern Tibet, both in the Himalaya Mountains. Study Focus Data from this study comprise water samples that provide a single season snapshot of δ18O and δD values that give additional information into the sources of moisture and the altitude lapse rates for the southern flank of the High Himalaya of Nepal and the Eastern Nyainqentanghla Mountains of the Tibetan Plateau. New Hydrological Insights The local water line for Nepal samples, δD=(7.8±0.3) · δ18O + (4.0‰±4.6‰), was moderately lower in slope than for Tibetan Plateau samples, δD=(8.7±0.1) · δ18O + (24.3‰±2.0‰); evaporation has a greater influence on the Nepal samples—consistent with warmer temperatures in Nepal versus Tibet within the same altitude range. Mean d-excess values for Tibet samples (13.1‰±2.0‰) implies that recycled continental moisture has more influence than marine moisture observed for the Nepal samples (7.4‰±4.4‰). Altitude lapse rates of δ18O and δD for Nepal samples (-2.8‰‰km−1 and −24.0‰km−1) do not significantly differ from Tibet samples (−3.1‰‰km−1 and −27.0‰km−1) and regional measurements; the lapse rates are reduced above 4500m and are not influenced by exceptionally high elevations in the Dudh Koshi River watershed.Item Thermal regime, energy budget and lake evaporation at Paiku Co, a deep alpine lake in the central Himalayas(EGU, 2019) Lei, Yanbin; Yao, Tandong; Yang, Kun; La, Zhu; Ma, Yaoming; Bird, Broxton W.; Earth Sciences, School of ScienceEvaporation from hydrologically-closed lakes is one of the largest components of their lake water budget, however, its effects on seasonal lake level changes is less investigated due to lack of comprehensive observation of lake water budget. In this study, lake evaporation were determined through energy budget method at Paiku Co, a deep alpine lake in the central Himalayas, based on three years' in-situ observations of thermal structure and hydrometeorology (2015–2018). Results show that Paiku Co was thermally stratified between July and October and fully mixed between November and June. Between April and July when the lake gradually warmed, about 66.5 % of the net radiation was consumed to heat the lake water. Between October and January when the lake cooled, heat released from lake water was about 3 times larger than the net radiation. Changes in lake heat storage largely determined the seasonal pattern of lake evaporation. There was about a 5 month lag between the maximum lake evaporation and maximum net radiation due to the large heat capacity of lake water. Lake evaporation was estimated to be 975 ± 39 mm between May and December during the study period, with low values in spring and early summer, and high values in autumn and early winter. The seasonal pattern of lake evaporation at Paiku Co significantly affects lake level seasonality, that is, significant lake level decrease in post-monsoon season while slight in pre-monsoon. This study may have implications for the different amplitudes of seasonal lake level variations between deep and shallow lakes.