ALBERT

Description: The monthly air temperature in 1153 stations and precipitation in 1202 stations in China and neighboring countries were collected to construct a monthly climate dataset in China on 0.025 ° resolution (approximately 2.5 km) named LZU0025 dataset designed by Lanzhou University (LZU), using a partial thin plate smoothing method embedded in the ANUSPLIN software. The accuracy of the LZU0025 was evaluated from analyzing three aspects: 1) Diagnostic statistics from surface fitting model in the period of 1951-2011, and results show low mean square root of generalized cross validation (RTGCV) for monthly air temperature surface (1.1 °C) and monthly precipitation surface (2 mm1/2) which interpolated the square root of itself. This indicate exact surface fitting models. 2) Error statistics based on 265 withheld stations data in the period of 1951-2011, and results show that predicted values closely tracked true values with mean absolute error (MAE) of 0.6 °C and 4 mm and standard deviation of mean error (STD) of 1.3 °C and 5 mm, and monthly STDs presented consistent change with RTGCV varying. 3) Comparisons to other datasets through two ways, one was to compare three indices namely the standard deviation, mean and time trend derived from all datasets to referenced dataset released by the China Meteorological Administration (CMA) in the Taylor diagrams, the other was to compare LZU0025 to the Camp Tibet dataset on mountainous remote area. Taylor diagrams displayed the standard deviation derived from LZU had higher correlation with that induced from CMA (Pearson correlation R=0.76 for air temperature case and R=0.96 for precipitation case). The standard deviation for this index derived from LZU was more close to that induced from CMA, and the centered normalized root-mean-square difference for this index derived from LZU and CMA was lower. The same superior performance of LZU were found in comparing indices of the mean and time trend derived from LZU and those induced from other datasets. LZU0025 had high correlation with the Camp dataset for air temperature despite of insignificant correlation for precipitation in few stations. Based on above comprehensive analyses, LZU0025 was concluded as the reliable dataset.

Description: The Kongtong Mountain area is a marginal area of the Asian summer monsoon and is sensitive to monsoon dynamics. The sensitivity highlights the need to establishing long-term climate records there and evaluating links with the Asian monsoon. Using "signal-free" methods, we developed a tree-ring chronology based 52 ring-width series from 23 Pinus tabulaeformis and Pinus armandidi trees in the Kongtong Mountain, northern China. Tree growth is highly correlated (0.844) with the Palmer Drought Severity Index (PDSI) from May to July, demonstrating the strength of PDSI in modeling drought conditions in this region. We therefore developed a robust May-July PDSI reconstruction spanning 1615-2009, which explained 71.2% of the instrumental variance for the period 1951-2005. Extremely dry epochs are found in periods of 1723-1727 and 1928-1932, and significant wet conditions are seen from 1696-1700, 1753-1757 and 1963-1969. These persistent dry and wet epochs were also found in northeastern Mongolia, suggesting similar drought regimes between these two regions. The dryness that occurred in the 1920s-1930s was the most severe and was concurrent with a warming period. This warming/drying relationship of the 1920s-1930s may be an analog to the current drying trend in northern China.

Description: High mountains are humid islands in arid central Asia, and alpine vegetation is sensitive to climate change, especially to temperature variations. Here we present a palynological sequence and discuss the past vegetation and climate changes based on core BY10A from the Swan Lake, an alpine lake situated at an inter-montane basin in the central Tienshan Mountains, Xinjiang, northwestern China. We collected 52 modern pollen surface samples at different elevations to aid in the interpretation of fossil-pollen data, which provide a reconstruction of vegetation and climate history for the last 8.5 ka (1 ka = 1000 cal yr BP). Artemisia and Amaranthaceae (= Chenopodiaceae) are the main pollen types in desert steppe zone below 1800 m elevation, while Poaceae and Picea dominate the mid-elevation forest steppe zone (1800-2800 m). Cyperaceae is the main indicator of high alpine meadows (〉 2800 m). From 8.5 to 6.9 ka, the vegetation was steppe meadow suggesting relatively warm climate. From 6.9 to 2.6 ka generally high values of Cyperaceae and peaty sediments indicate a fen environment and cooler, more humid conditions. Interrupting this mid-Holocene period is a 5.5-4.5 ka millennium of lacustrine sediments with lower Cyperaceae, higher Poaceae and Artemisia, and high values of Myriophyllum and Pediastrum indicating higher water levels and warmer temperatures. After 2.6 ka, pollen data indicate alpine steppe and warmer climate. The mid-Holocene pattern of cooler climate interrupted by a warmer period is consistent from other regional records from Xinjiang, including the Guliya ice core and Kesang Cave speleothem record. During the cooler periods, the regional record indicates that a weakened summer Asian monsoon is countered to some extent by a stronger winter monsoon.

Description: The Asian monsoon (AM) played an important role in the dynastic history of China, yet it remains unknown whether AM-mediated shifts in Chinese societies affect earth surface processes to the point of exceeding natural variability. Here, we present a dust storm intensity record dating back to the first unified dynasty of China (the Qin Dynasty, 221–207 B.C.E.). Marked increases in dust storm activity coincided with unified dynasties with large populations during strong AM periods. By contrast, reduced dust storm activity corresponded to decreased population sizes and periods of civil unrest, which was co-eval with a weakened AM. The strengthened AM may have facilitated the development of Chinese civilizations, destabilizing the topsoil and thereby increasing the dust storm frequency. Beginning at least 2000 years ago, human activities might have started to overtake natural climatic variability as the dominant controls of dust storm activity in eastern China.

Description: Pollen-based quantitative reconstructions of past climate variables is a standard palaeoclimatic approach. Despite knowing that the spatial extent of the calibration-set affects the reconstruction result, guidance is lacking as to how to determine a suitable spatial extent of the pollen-climate calibration-set. In this study, past mean annual precipitation (Pann) during the Holocene (since 11.5 cal ka BP) is reconstructed repeatedly for pollen records from Qinghai Lake (36.7 N, 100.5 E; north-east Tibetan Plateau), Gonghai Lake (38.9N, 112.2E; north China) and Sihailongwan Lake (42.3 N, 126.6 E; north-east China) using calibration-sets of varying spatial extents extracted from the modern pollen dataset of China and Mongolia (2559 sampling sites and 168 pollen taxa in total). Results indicate that the spatial extent of the calibration-set has a strong impact on model performance, analogue quality and reconstruction diagnostics (absolute value, range, trend, optimum). Generally, these effects are stronger with the modern analogue technique (MAT) than with weighted averaging partial least squares (WA-PLS). With respect to fossil spectra from northern China, the spatial extent of calibration-sets should be restricted to radii between ca. 1000 and 1500 km because small-scale calibration-sets (〈800 km radius) will likely fail to include enough spatial variation in the modern pollen assemblages to reflect the temporal range shifts during the Holocene, while too broad a scale calibration-set (〉1500 km radius) will include taxa with very different pollen-climate relationships.

Description: Changes in the magnitude of millennial-scale climate variability (MCV) during the Late Pleistocene occur as a function of changing background climate state over tens of thousands of years, an indirect consequence of slowly varying incoming solar radiation associated with changes in Earth’s orbit. However, whether astronomical forcing can stimulate MCV directly (without a change in the background state) remains to be determined. Here we use a comprehensive fully coupled climate model to demonstrate that orbitally driven insolation changes alone can give rise to spontaneous millennial-scale climate oscillations under intermediate glacial conditions. Our results demonstrate that an abrupt transition from warm interstadial to cold stadial conditions can be triggered directly by a precession-controlled increase in low-latitude boreal summer insolation and/or an obliquity-controlled decrease in high-latitude mean annual insolation, by modulating North Atlantic low-latitude hydroclimate and/or high-latitude sea ice–ocean–atmosphere interactions, respectively. Furthermore, contrasting insolation effects over the tropical versus subpolar North Atlantic, exerted by obliquity or precession, result in an oscillatory climate regime, even within an otherwise stable climate. With additional sensitivity experiments under different glacial–interglacial climate backgrounds, we synthesize a coherent theoretical framework for climate stability, elaborating the direct and indirect (dual) control by Earth’s orbital cycles on millennial-scale climate variability during the Pleistocene.

Description: 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.

Description: Bulletin of the American Meteorological Society, Ahead of Print. 〈br/〉