Northeastern Qinghai-Xizang Plateau Research Articles

Mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau, China

Mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau, China

Relationship between environmental evolution and human activities in the northeastern Qinghai-Xizang Plateau throughout the past millennium and its implications for the onset of the Anthropocene

AbstractIn current research on the Anthropocene, assessing the impact of human activities via stratigraphic records of sediments and demarcating the Anthropocene epoch globally are critical scientific issues that urgently need to be addressed. The northeastern Qinghai-Xizang Plateau (QXP), where humans first settled permanently in large numbers in the QXP, has varying sedimentary environments that are extremely sensitive to human activities. In contrast to other regions of the QXP, the northeastern sector boasts a richer array of climatic and environmental reconstruction sequences. This distinctive feature renders it an exemplary locale for investigating the stratigraphic boundary of the Anthropocene. Through in-depth analysis and integration of existing paleoclimate and paleoenvironment sequences in the northeastern QXP, we draw the following conclusions: (1) Throughout the past millennium, the impact of human activities on the environment of the northeastern QXP has become increasingly significant, especially in the past 200–300 years, gradually overshadowing climatic factors. (2) Since AD 1950, multiple physicochemical indicators related to human activities in the northeastern QXP have shown exponential growth, forming a distinct peak within the past millennium and clearly depicting the global “Great Acceleration” phenomenon and its development process. (3) Intensified human activities have driven swift environmental shifts and “decoupled” the interplay between climatic variations and the ecological environment, propelling the northeastern QXP into the “Early Anthropocene” from the “Late Holocene”. On the basis of the above findings, we construct a model suitable for identifying the stratigraphic boundary of the Anthropocene in the northeastern QXP and note that since the ecological environment in the northeastern QXP has entered the “Early Anthropocene”, the climate signals of certain physicochemical indicators in sediments are gradually becoming weaker, whereas the signals of human activities are becoming stronger.

Warming and Humidification of Climate on the Northeastern Qinghai-Xizang Plateau Over the Past 60 Years：Evidence from Hydroclimatic Records of Delingha

Warming and Humidification of Climate on the Northeastern Qinghai-Xizang Plateau Over the Past 60 Years：Evidence from Hydroclimatic Records of Delingha

Trends in precipitation recycling over the Qinghai–Xizang Plateau in last decades

Summary This study calculated the annual and inter-annual variations in the precipitation recycling ratio (PRR) on the Qinghai–Xizang Plateau (QXP); and by using water mass balance equation; we evaluated the estimated evaporation in the area. The results indicate that the estimated evaporation relate strongly to surface air temperature, relative humidity and wind speed. As temperatures on the QXP increase, the changes of PRR vary by regions within the plateau. Between 1979 and 2008, the PRR decreased in the western QXP, which is an arid area, but it increased in the other areas. The strongest increasing PRR trend is 3.1%/10 a in the northeastern QXP, but a decreasing trend, ranging downward to −2.5%/10 a, was observed in the western QXP. There is a significant seasonal change in precipitation recycling (PR) over QXP. The PR peak values occurred in July in all regions, and PR was very low (approaching 0.0) in winter half-year period. The monthly maximum PRR reached 0.62, which occurred in July over the southeastern QXP, where is a rich center of precipitation. These results imply that there is remarkable change of moisture resource of precipitation in last decades. On the QXP, large-scale moisture advances decrease with increased temperature, and the local moisture cycle is reinforced in wet regions.

Seismic Tomographic Imaging of the Crust and Upper Mantle Beneath the Northeastern Edge of the Qinghai‐Xizang Plateau and the Ordos Area

AbstractWe investigate the P‐wave velocity structure of the crust and upper mantle down to depth 400km beneath the Ordos region and northeastern Qinghai‐Xizang plateau using the seismic tomographic technique. The data used are taken from the record by the regional network and a passive seismic observation profile across the investigated area, respectively. Our results show clear lateral variations of the crust and upper mantle velocity structure along the profile, which exist not only between different blocks, but also inside blocks. The average P‐wave velocity of the crust and upper mantle beneath the northeastern margin of the Qinghai‐Xizang plateau is lower, and that beneath the Ordos block is higher than the global model. Our observations are coincident with the tectonic activities of these two blocks. Between the northeastern Qinghai‐Xizang and Ordos block exists a transition zone about 200km wide, which on the surface corresponds to the region between Lanzhou and Haiyuan. This transition zone in the upper mantle appears as a stripe with a slope of about 45‐ tilting eastward. Its main feature appears as a mixture of high‐ and low‐velocity media. The strike of this stripe in the upper mantle seems to be controlled by the high‐velocity body beneath the Ordos block. This implies that the stable Ordos block plays a role in resisting the eastward movement of the Qinghai‐Xizang plateau. The upper mantle velocity structure beneath the Qaidam basin in the Qinghai‐Xizang plateau has a low average velocity and that beneath the Qilian block has a high average velocity. The difference between both reaches about 8%. We also find the intrusive low‐velocity bodies in uppermost mantle beneath Zêkog, Lanzhou and Haiyuan areas, respectively. The high seismicity in the north‐south seismic zone should be related closely to the medium heterogeneity and very special deep dynamic environment.

The paleo-environmental significance of Sr and Ca contained in acid-soluble fraction of plateau loess deposits in Xining Basin

The Xining Basin, located on northeastern Qinghai-Xizang Plateau, is adjacent to the Qaidam Basin and Gobi-desert. Therefore, thick, integrated deposits of loess or paleo-sol sequence were well developed. As is well known, there is much paleo-environmental information recorded in loess and paleo-sol. So if we deal with paleo-environmental index from different angles, especially from loess geochemistry, some important and detailed paleo-environmental evolutional information will be acquired. Based on this, the authors determined the contents of Sr and Ca contained in acid-soluble fraction from the bottom to the top of the Panzishan section. This section was obtained through making a well about 17 m in depth, including S1 paleo-sol that was developed during the last interglacial period. According to the results, it is found that variations in contents of Sr and Ca are well correlated with conversion of loess and paleo-sol. In loess deposits, the contents of Sr and Ca are higher than those in paleo-sol deposits. It is known that loess was deposited under cold-dry climate conditions and paleo-sol was developed during warm-humid climate episodes. It is concluded that due to their mobile behaviors, under cold-dry climate conditions, Sr and Ca are stagnant during weak weathering, but under warm-humid climate conditions, Sr and Ca are easily leached and transported in aqueous solution. Therefore, they can be utilized as indicators of climate changes. Moreover, variations in contents of Sr and Ca are more sensitive than susceptibility. The mobile behaviors of Sr and Ca contained in acid-soluble fraction can serve as a new quantitative index to evaluate paleo-environmental changes on the plateau.

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

Characteristics of present-day tectonic movement in the northeastern margin of Qinghai-Xizang plateau (Tibetan) are studied based on earthquake data. Evidence of earthquake activity shows that junctures between blocks in this area consist of complicated deformation zones. Between the Gansu-Qinghai block and Alxa block there is a broad compressive deformation zone, which turns essentially to be a network-like deformation region to the southeast. The Liupanshan region, where the Gansu-Qinghai block contacts the Ordos block, is suffering from NE-SW compressive deformation. Junction zone between the Ordos and Alxa block is a shear zone with sections of variable trend. The northwestern and southeastern marginal region of the Ordos is under NNW-SSE extension. The above characteristics of present-day tectonic deformation of the northeastern Qinghai-Xizang plateau may be attributed to the northeastward squeezing of the plateau and the resistance of the Ordos block, as well as the southeastward extrusion of the plateau materials.

Compositions of δ18O and δ13C in various carbonates of core RM in the Zoigê Basin and climatic significance

The hole RM, the deepest one fully obtained core in the Qinghai-Xizang Plateau, situated in the depositional center of the Zoige Basin (33°57′N; 102° 21′E) in the northeastern Qinghai-Xizang Plateau with a depth of 310.46 m. From 14C dating and paleomagnetic stratigraphic study, the core RM can date back to 900 ka B.P.. In this paper we analyzed the compositions of δ18O and δ13C in various carbonates can date (snail, obstrode, chemical carbonate) in core RM and discussed preferably the paleoclimatic record by the proxies of δ18O and δ13C of chemical carbonate (authicarbonate) from core RM in the past 140 ka. The results showed that the values of δ18O in various carbonates are generally identical, and the values of δ13C in it are inconsistent, while there exist better relativity. The studies also demonstrated that there was a negative correlation between δ18O and δ13C of authicarbonate in core RM in the past 140 ka, showing that the changes of δ18O values were mainly relative to the water temperature. According to above, the climatic evolutionary sequence were rebuilt in the past 140 ka in the region.

Source process of the 1990 Gonghe, China, earthquake and tectonic stress field in the northeastern Qinghai-Xizang (Tibetan) plateau

The M s = 6.9 Gonghe, China, earthquake of April 26, 1990 is the largest earthquake to have been documented historically as well as recorded instrumentally in the northeastern Qinghai-Xizang (Tibetan) plateau. The source process of this earthquake and the tectonic stress field in the northeastern Qinghai–Xizang plateau are investigated using geodetic and seismic data. The leveling data are used to invert the focal mechanism, the shape of the slipped region and the slip distribution on the fault plane. It is obtained through inversion of the leveling data that this earthquake was caused by a mainly reverse dip-slipping buried fault with strike 102°, dip 46° to SSW, rake 86° and a seismic moment of 9.4 × 1018 Nm. The stress drop, strain and energy released for this earthquake are estimated to be 4.9 MPa, 7.4 × 10−5 and 7.0 × 1014 J, respectively. The slip distributes in a region slightly deep from NWW to SEE, with two nuclei, i.e., knots with highly concentrated slip, located in a shallower depth in the NWW and a deeper depth in the SEE, respectively.