The Mechanical Impact of the Tibetan Plateau on the Seasonal Evolution of the South Asian Monsoon

The impact of the Tibetan Plateau on the South Asian monsoon is examined using a hierarchy of atmospheric general circulation models. During the premonsoon season and monsoon onset (April–June), when westerly winds over the Southern Tibetan Plateau are still strong, the Tibetan Plateau triggers early monsoon rainfall downstream, particularly over the Bay of Bengal and South China. The downstream moist convection is accompanied by strong monsoonal low-level winds. In experiments where the Tibetan Plateau is removed, monsoon onset occurs about a month later, but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase. During the mature and decaying phase of monsoon (July–September), when westerly winds over the Southern Tibetan Plateau almost disappear, monsoon circulation strength is not much affected by the presence of the Tibetan Plateau. A dry dynamical core with east–west-oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain. In a moist atmosphere, the mechanically driven downstream convergence is expected to be associated with significant moisture convergence. The authors speculate that the mechanically driven downstream convergence in the presence of the Tibetan Plateau is responsible for zonally asymmetric monsoon onset, particularly over the Bay of Bengal and South China

The spatial variation of Asian dust and marine aerosol contributions to glaciochemical signals in central Asia

Short-term (6 months to 17 years) glaciochemical records have been collected from several glacier basins in the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled by the influx of dust from the large expanse of arid and semiarid regions in central Asia. Glaciers in the Northern and Western Tibetan Plateau show elevated concentrations and elevated annual fluxes of calcium, sodium, chloride, sulphate and nitrate due to the influx of desert dust from nearby arid and semi-arid regions. Glaciers in the Southeastern Tibetan Plateau show lower concentrations and lower annual fluxes of major ions due to longer transport distances of dust from the arid and semi-arid regions of Western China. Snow from the Karakoram and Western Himalaya show ion concentrations similar to those in Southeastern Tibetan Plateau, but much higher annual fluxes suggesting that much of the aerosol and moisture transported with the westerly jet stream is removed as it ascends the Southwest margin of the Tibetan Plateau. Snow from the Southern slopes of the Eastern Himalayas shows very low concentrations and very low annual fluxes of major ions, indicating that this region is relatively free from the chemical influence of Asian dust. The glaciochemical data suggest that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the Southeastern Tibetan Plateau, are the ones most likely to contain longer-term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long-range transport of Asian dust

Changes in NDVI and human population in protected areas on the Tibetan Plateau

Understanding the Tibetan Plateau’s role in environmental change has gained increasing scientific attention in light of warming and changes in landmanagement. We examine changes in greenness over the Tibetan Plateau using the Normalized Difference Vegetation Index (NDVI) from the Global Inventory Monitoring and Modeling Study (GIMMS3g) to identify significant changes over the entire plateau, six ecoregions, and protected areas based on a multiyear time series of July imagery from 1982 to 2015. We also test whether there have been changes in human populations in protected areas. There has been relatively little change in mean NDVI over the Tibetan Plateau or ecoregions, however, there were significant changes at the pixel level. There are sixty-nine protected areas on the Tibetan Plateau; sixtytwo protected areas had no significant change in mean NDVI and seven protected areas experienced a significant increase in NDVI. There has been an increase in population within protected areas from 2000 to 2015; however, mean populations significantly increased in two protected areas and significantly decreased in four protected areas. Results suggest a slow greening of the Tibetan Plateau, ecoregions, and protected areas, with a more rapid greening in northern Tibet at the pixel level. Most protected areas are experiencing minor changes in NDVI independent of human population

Late Holocene forcing of the Asian winter and summer monsoon as evidenced by proxy records from the northern Qinghai-Tibetan Plateau

Little is known about decadal- to centennial-scale climate variability and its associated forcing mechanisms on the Qinghai-Tibetan Plateau. A decadal-resolution record of total organic carbon (TOC) and grainsize retrieved from a composite piston core from Kusai Lake, NW China, provides solid evidence for decadal- to centennial-scale Asian monsoon variability for the Northern Qinghai-Tibetan Plateau during the last 3770 yr. Intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance. A number of intensified Asian winter monsoon phases are potentially correlated with North Atlantic climatic variations including Bond events 0 to 2 and more recent subtle climate changes from the Medieval Warm Period to the Little Ice Age. Our findings indicate that Asian monsoon changes during the late Holocene are forced by changes in both solar output and oceanic-atmospheric circulation patterns. Our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid-latitude regions (the Northern Qinghai-Tibetan Plateau)

Sedimentary ancient DNA reveals past ecosystem and biodiversity changes on the Tibetan Plateau: Overview and prospects

Alpine ecosystems on the Tibetan Plateau are being threatened by ongoing climate warming and intensified human activities. Ecological time-series obtained from sedimentary ancient DNA (sedaDNA) are essential for understanding past ecosystem and biodiversity dynamics on the Tibetan Plateau and their responses to climate change at a high taxonomic resolution. Hitherto only few but promising studies have been published on this topic. The potential and limitations of using sedaDNA on the Tibetan Plateau are not fully understood. Here, we (i) provide updated knowledge of and a brief introduction to the suitable archives, region-specific taphonomy, state-of-the-art methodologies, and research questions of sedaDNA on the Tibetan Plateau; (ii) review published and ongoing sedaDNA studies from the Tibetan Plateau; and (iii) give some recommendations for future sedaDNA study designs. Based on the current knowledge of taphonomy, we infer that deep glacial lakes with freshwater and high clay sediment input, such as those from the southern and southeastern Tibetan Plateau, may have a high potential for sedaDNA studies. Metabarcoding (for microorganisms and plants), metagenomics (for ecosystems), and hybridization capture (for prehistoric humans) are three primary sedaDNA approaches which have been successfully applied on the Tibetan Plateau, but their power is still limited by several technical issues, such as PCR bias and incompleteness of taxonomic reference databases. Setting up high-quality and open-access regional taxonomic reference databases for the Tibetan Plateau should be given priority in the future. To conclude, the archival, taphonomic, and methodological conditions of the Tibetan Plateau are favorable for performing sedaDNA studies. More research should be encouraged to address questions about long-term ecological dynamics at ecosystem scale and to bring the paleoecology of the Tibetan Plateau into a new era

Phylogenetic analysis of birne shrimp (Aretemia) in China using DNA barcoding

DNA barcoding is a powerful approach for characterizing species of organisms, especially those with almost identical morphological features, thereby helping to to establish phylogenetic relationships and reveal evolutionary histories. In this study, we chose a 648-bp segment of the mitochondrial gene, cytochrome c oxidase subunit 1 (COI), as a standard barcode region to establish phylogenetic relationships among brine shrimp (Artemia) species from major habitats around the world and further focused on the biodiversity of Artemia species in China, especially in the Tibetan Plateau. Samples from five major salt lakes of the Tibetan Plateau located at altitudes over 4,000m showed clear differences from other Artemia populations in China. We also observed two consistent amino acid changes, 153A/V and 183L/F, in the COI gene between the high and low altitude species in China. Moreover, indels in the COI sequence were identified in cyst and adult samples unique to the Co Qen population from the Tibetan Plateau, demonstrating the need for additional investigations of the mitochondrial genome among Tibetan Artemia populations

The influence of 14C reservoir age on interpretation of paleolimnological records from the Tibetan Plateau

There is a great deal of controversy regarding the fate of glaciers and ice fields on the Tibetan Plateau in the face of continued anthropogenic global warming. Paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the Tibetan Plateau to changing conditions. Specifically, the numerous lakes distributed across the Tibetan Plateau can provide high-resolution (spatial and temporal) climate reconstructions to investigate past changes in the climate system. In this paper, we review the primary limitation to exploiting these valuable paleoclimate archives: errors in radiocarbon-based age models. We review the techniques that have been used to estimate 14C reservoir ages on the Tibetan Plateau and compile the published 14C reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties. Using site-specific evaluations of Bangong Co and Lake Qinghai, we demonstrate that 14C age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records. We also examine 14C-induced uncertainties in the spatial climatic response on the Tibetan Plateau to (1) the termination of the Last Glacial Maximum and (2) the Holocene Thermal Maximum. We conclude with recommendations for reducing uncertainties in future lake-based paleoclimate studies on the Tibetan Plateau

Hydrological impacts of deforestation on the southeast Tibetian plateau

The hydrological impact of forest removal on the southeast Tibetan Plateau during the second half of the last century is investigated in this study using an atmospheric general circulation model. The effects of deforestation are investigated by examing the differences between the forest replacement and control experiments. Model results demonstrate that deforestation of the southeast Tibetan Plateau would influence the local and the remote climate as well. It would lead to decreased transpiration and increased summer precipitation in the deforested area and a wetter and warmer climate on the Tibetan Plateau in summer. This may produce more runoff into the rivers originating from the Tibetan Plateau and worsen flooding disasters in the downstream areas. The numerical experiments also show that deforestation would remotely impact Asian climate, and even global climate, although the statistical significance is small. A strong drought is found at middle and lower reaches of the Yellow River, where livelihoods and economics have suffered from recent droughts. Ecosystem research on the Tibetan Plateau is a relatively new topic and needs further interdisciplinary investigation

No Consistent Evidence for Advancing or Delaying Trends in Spring Phenology on the Tibetan Plateau

Vegetation phenology is a sensitive indicator of climate change and has significant effects on the exchange of carbon, water, and energy between the terrestrial biosphere and the atmosphere. The Tibetan Plateau, the Earth\u27s “third pole,” is a unique region for studying the long‐term trends in vegetation phenology in response to climate change because of the sensitivity of its alpine ecosystems to climate and its low‐level human disturbance. There has been a debate whether the trends in spring phenology over the Tibetan Plateau have been continuously advancing over the last two to three decades. In this study, we examine the trends in the start of growing season (SOS) for alpine meadow and steppe using the Global Inventory Modeling and Mapping Studies (GIMMS)3g normalized difference vegetation index (NDVI) data set (1982–2014), the GIMMS NDVI data set (1982–2006), the Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI data set (2001–2014), the Satellite Pour l\u27Observation de la Terre Vegetation (SPOT‐VEG) NDVI data set (1999–2013), and the Sea‐viewing Wide Field‐of‐View Sensor (SeaWiFS) NDVI data set (1998–2007). Both logistic and polynomial fitting methods are used to retrieve the SOS dates from the NDVI data sets. Our results show that the trends in spring phenology over the Tibetan Plateau depend on both the NDVI data set used and the method for retrieving the SOS date. There are large discrepancies in the SOS trends among the different NDVI data sets and between the two different retrieval methods. There is no consistent evidence that spring phenology (“green‐up” dates) has been advancing or delaying over the Tibetan Plateau during the last two to three decades. Ground‐based budburst data also indicate no consistent trends in spring phenology. The responses of SOS to environmental factors (air temperature, precipitation, soil temperature, and snow depth) also vary among NDVI data sets and phenology retrieval methods. The increases in winter and spring temperature had offsetting effects on spring phenology

Response of Inland Lakes to Climate Change across the Tibetan Plateau Investigated Using Landsat and ICESat Data

The Tibetan Plateau experienced tremendous climate change during the past four decades. Due to the large size, widely distribution of cryosphere, and diverse landforms, different parts of the plateau may experience different climate and cryosphere changing patterns. The changes of inland lakes within the plateau are important indicators of climate change as these lakes are fed by precipitation, permafrost degradation, and glacier melting that are all sensitive to climate change. To examine the spatial and temporal differences of lake variations across the Tibetan Plateau, Landsat images and ICESat/GLAS altimetry data were used to extract the changes in surface areas of 26 lakes selected from six different sub-regions during the 1970s-2010 and the changes in lake elevations of these lakes during 2003-2009. An automated model to extract lake surface area and elevation from Landsat and ICESat data is developed to improve the efficiency of processing the large amount of satellite data. By applying this model, the spatial and temporal changing patterns of selected 26 inland lakes across the Tibetan Plateau during the past four decades are revealed. The lakes from different parts of the Tibetan Plateau show different changing patterns. The lake expansion firstly started from the Central Tibetan Plateau in the 1980s, then moving northward and northwestward; the Northeastern and Northwestern Tibetan Plateau experienced obvious expansion after the late 1990s, and this expansion is still continuing in the northern part, whereas the rapid lake expansion either slowed down or stopped in the central and southern parts of the plateau. The differences in lake changing pattern are caused by diverse climatic regimes and the pattern of the cryospheric distribution in the Tibetan Plateau. For the southern part of the plateau, the change in precipitation and evaporation seems to be the dominating factor to control the lake changes; however, the cryospheric change caused by temperature increase is the most important factor influencing the lake fluctuations in the northern part. These patterns can provide insight into the mechanism of lakes dynamics in response to climate and cryospheric changes; and be applied to assess the potential impacts of climate change on water resources in the Tibetan Plateau