Wang Naiang

The sand wedges of the last ice age in the Hexi Corridor, China: paleoclimatic interpretation

Abstract Sand wedges, formed mainly in a Late Pleistocene alluvial gravel in the Hexi Corridor are described in detail in this paper. 14C ages of the infilling eolian sand indicate that the sand wedges were products of the Last Ice Age. During the period of formation, the mean annual air temperature in the Hexi Corridor was about −5.3 °C, i.e. 12.6–14.6 °C lower than that of the present day. This estimated value is coincident with the fall in mean air temperature of 13 °C, which is predicated from a mirabilite (Na2SO4·10H2O) sedimentary layer, and also agrees with research on the estimated amplitude of air temperature lowering in middle and high latitudes of the Northern Hemisphere during the last glacial period. The annual precipitation in the Western Hexi Corridor at that time was probably 100–200 mm, about 100 mm more than at present.

Mid-Holocene Climate Variations Recorded by Palaeolake in Marginal Area of East Asian Monsoon: A Multi-proxy Study

Traditionally, the mid-Holocene in most parts of China was thought to be warmer with higher precipitation, resulting from a strong Asian summer monsoon. However, some recent researches have proposed a mid-Holocene drought interval of millennial-scale in East Asian monsoon margin areas. Thus whether mid-Holocene was dry or humid remains an open issue. Here, Zhuyeze palaeolake, the terminal lake of the Shiyang River Drainage lying in Asian monsoon marginal areas, was selected for reconstructing the details of climate variations during the Holocene, especially mid-Holocene, on the basis of a sedimentological analysis. Qingtu Lake (QTL) section of 6.92m depth was taken from Zhuyeze palaeolake. Multi-proxy analysis of QTL section, including grain size, carbonate, TOC, C/N and δ13C of organic matter, was used to document regional climatic changes during 9–3 cal ka B.P. The record shows a major environmental change at 9.0–7.8 cal ka B.P., attributed to a climate trend towards warmth and humidity. This event was followed by a typical regional drought event which occurred during 7.8–7.5 cal ka B.P. And a warm and humid climate prevailed from 7.5 to 5.0 cal ka B.P., attributed to the warm/humid Holocene Optimum in this region. After that, the climate gradually became drier. Moreover, comparison of the climate record from this paper with the summer insolation at 30°N indicates that the climate pattern reflecting the Asian monsoon changes was caused by insolation change.

The age of sand wedges and its environmental significance at the southeast edge of Badain Jaran Desert

Sand wedge is a product of permafrost in cold climate, and it is of great significance to restore paleoclimate and paleoenvironment. Since the early 20th century, periglacial landforms such as sand, ice, and soil wedges and glacial mud have been intensively studied in North America, Europe, and Russia. Nevertheless, the distribution of desert areas in the permafrost regions after the last glacial period is still debated in academia. Particularly, in China, it has been argued that desert areas were not the parts of ancient permafrost regions. Moreover, the studies of ancient sand wedges are mostly limited to the last glacial period. In recent years, several groups of ancient sand wedges and glacial mud have been recognized in the Badain Jaran Desert. This filled the gap in the Chinese literature regarding ancient permafrost and proved that desert region belonged to the scope of permafrost regions during the last glacial period. The newly discovered sand wedges in the southeast Badain Jaran Desert comprise sand and gravel layers. Optically stimulated luminescence dating of the filler in the sand wedges suggests that they formed during the last glacial period and the late glacial maximum, in particular. The annual average temperatures in the Badain Jaran Desert during the last glacial period were approximately −3–−6°C, and it is 12–15°C cooler than present. The filler in sand wedges was mainly poorly sorted fine sand that was not transported from afar but from nearby sand dunes. According to the sand wedge groups of the last glacial period in the desert and seasonal frozen soil, we can infer that the Badain Jaran Desert was a part of the permafrost that may have been continuous and widespread. The extent and distribution of the Badain Jaran Desert in the last glacial period was probably different than today, reflecting the dynamic nature of sand dunes. According to the law of sand dunes’ movement in the Badain Jaran Desert, combining with the characteristics of aeolian sand of the desert’s ancient permafrost wedge can indirectly infer that three large desert areas of the Alxa Plateau were connected more than ten thousand years ago when the entire Alxa Plateau was part of the permafrost; furthermore, the desert hinterland and the surrounding sand dunes would have been frozen and the movement and development of the sand dunes would have been suppressed. Surface landscape and the kinetics of the sand and landform need to be studied further. While the Badain Jaran Desert was likely a part of the cryosphere climate zone during the last glacial period, whether the Chinese northern desert belonged to the frozen earth region is still questionable.

Luminescence dating of Holocene lacustrine sediments from the southeastern Mu Us sandy land: Comparison of quartz OSL and K-feldspar pIRIR_(150) ages

In the current study,we collected three samples from lacustrine sequences at southeast Mu Us sandy land. For each of these samples,both quartz and K-feldspar fractions were extracted for luminescence dating using small aliquot( 2 mm) technique.The single aliquot regenerative-dose( SAR) protocol was applied to measure the equivalent dose( De) of quartz samples( at preheat temperature of 260℃). Dose recovery tests and luminescence characteristics of quartz suggest that the quartz SAR protocol is suitable and the samples were well bleached before deposition,and the resultant ages of quartz fraction are reliable. For K-feldspar fraction,a new post-IR IRSL protocol measured at 150℃( p IRIR150) was used to determine the De. Dose recovery tests and luminescence characteristics of K-feldspar meet the requirement well. A set of tests,such as residual test and fading test,was carried out. Residual doses of p IRIR150 signal are between-0. 2 and 0. 026 Gy,which can be considered negligible for the Holocene sediments. The g-values of p IRIR150signal( 0. 55 1. 71( % / decade)) are much lower,comparing with that of IRSL50 signal,or even negligible. Thus,we propose that the use of p IRIR150 signal is able to reduce anomalous fading to a negligible level. Subsequently,the K-feldspar p IRIR150 ages are not corrected for anomalous fading. For the three samples,the quartz ages are 11. 3 ±0. 9,6. 5 ± 0. 6 and 2. 7 ± 0. 2 ka BP,respectively,and the K-feldspar ages are 10. 0 ± 0. 7,6. 9 ± 0. 5 and 2. 4 ± 0. 2 ka BP,respectively. Both ages from the two methods agree with each other within the error ranges. Therefore,K-feldspar p IRIR150 protocol can be applied for dating the Holocene lacustrine sediments from southeast Mu Us sandy land. Our research found a method to date the samples that their luminescence signal intensity of quartz is too low to be detected,and a geochronology to support for environmental changes in the Holocene,especially in the historical period( past 2000 years).

Long-term effects of fertilization on aggregates distribution and total nitrogen stock in a reddish paddy soil of subtropical China

Fertilization greatly influences soil structure and nutrients accumulation in soil aggregates. In this study, the effects of long-term fertilization on aggregates composition and total nitrogen stock in a reddish paddy soil in the subtropical area of China were investigated. The fertilization treatments included CK(without fertilization), NK(nitrogen and potassium fertilizer application), NPK(balanced application of nitrogen, phosphorous,and potassium fertilizers), LOM(combined application of NPK and 30% organic manure fertilizers) and HOM(combined application of NPK and 60% organic manure fertilizers). Undisturbed soil samples in two layers were collected and then separated into five aggregate-size classes(5 mm, 2~5 mm, 0.5~2 mm, 0.25~0.5 mm, 0.25mm) by the dry sieving method. The amount and storage of nitrogen in each aggregate fraction were measured.The results indicate that the 5 mm blocky fraction was the dominant aggregates component, accounting for65.7%~83.4% of dry soil mass in the two layers. It sequestrated 63.1%~82.7% of the total nitrogen in the soils and is considered the major carrier of soil nitrogen. Deeper in the soil, the content of 5 mm blocky fraction increased, while the percentages of the other aggregate-size groups decreased. For each soil layer, the contents of soil total nitrogen in different sizes of soil aggregates were significantly different and increased in the order of 5mm, 2~5 mm, 0.5~2 mm, 0.25~0.5 mm, and decreased from 0.25~0.5 mm to 0.25 mm. However, the total nitrogen storage value first decreased and then increased and the minimum value occurred in the size group of 0.25~0.5 mm. Compared to the CK treatment, long-term fertilization was in favor of increasing the proportion of aggregates in the size group of 0.25~5 mm, while reducing the aggregate fractal dimensions. Moreover, the total soil nitrogen contents and storages in 0.25~5 mm aggregates and in the whole soils were increased significantly(P0.05) after fertilizer application and the effects show an increasing sequence of NKNPKLOMHOM.There was a significant positive correlation between the contents of 2~5 mm aggregates and total nitrogen storages in the soils, suggesting that the newly enriched organic nitrogen mostly appeared in 2~5 mm aggregates. Overall, in comparison with the plow pan, the amounts and total nitrogen contents of different aggregates in the plough layer were more sensitive to fertilization. The NPK fertilizers mixed with organic manure application greatly(P0.05) promoted the total nitrogen storages in the plow pan and the whole soil layers when compared to single chemical fertilizer application and can be considered the best fertilization mode for improving soil structure and nitrogen fertility and that can be widely applied in the reddish paddy soil distrribution areas in subtropical China.

Detection of Ecological Environment in Qinghai Lake Basin by Remote Sensing and GIS

Qinghai Lake, the largest inland saline lake in China, one of seven famous international wetlands, lies in the northeast of Qinghai Province and the northeast of Qinghai-Xizang (Tibetan) Plateau. The eco-environmental changes in water bodies, desertified land and grassland in Qinghai Lake basin were detected for the period from 1975 to 2000 based on remote sensing and GIS. From 1975 to 2000, the lakeshore shape had changed much, especially in the west shore near the Bird Island and Buha River, in the north shore near Shaliu River and in the east shore near Sha Island and Haiyan Bay. The area of Qinghai Lake decreased by 150.36km(2), the water body about 100km(2) being separated from Qinghai Lake and water level dropped about 2m. The famous Bird Island was connected to the land in the 1970s. Desertified land had kept a sustainable developing situation, increased by 778.65km(2)

The Study on Urban Climate of Lanzhou

Based on the meteorological data sequence of Lanzhou city and circumjacent regions, and experimental data in urban area, data of climate factors were analyzed. The results are as follows: Temperature variation is divided into three stages in near 70 years; the early 1950s and the early 1980s are the jump points of Lanzhou urban climate during this period. The urban climate effect was analyzed by the difference of each climate factor between Lanzhou city and suburb. According to statistical data, three types of temperature differences show ascending trend from 1960 to 2000. These indicate that urban heat island effect becomes strong gradually. Annual precipitation difference decrease gradually from 1980, there is no rain island effect. Relative humidity in urban area declines gradually, and appears urban dry island effect from 1978. The overlap-add and weakening effects of mountain - valley breeze and heat island circumfluence affect wind speed in Lanzhou. It also displays that the thermodynamic property of urban underlying surface and the urban anthropologic heat have played an important role in urban climate effect.