Climatic significance of n-alkanes and their compound-specific δD values from lake surface sediments on the Southwestern Tibetan Plateau

The content and hydrogen isotope ratios of n-alkanes extracted from recent lake surface sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed. Values were compared with n-alkanes in plants from lake drain- ages, and δD values of meteoric water, lake water, and mean annual precipitation. The results showed that n-C23 was predominantly derived from aquatic plants, and n-C27- n-C33 from terrestrial higher plants. The average carbon chain length of n-C27-n-C33 （ACL27-33） was positively correlated with the mean annual precipitation. δD values of the long-chain n-alkanes n-C29 and n-C31 of terrestrial origin （varying between -214‰ and -169 ‰, and-226 ‰ and -185 ‰, respectively） were inversely correlated with mean annual precipitation; but in accordance with the average annual variations in δD （OIPC）, δD values of n-C31 were strongly related to the δD values of growing season meteoric water （R2 = 0.74）. The large difference between δD values of n-C23 of aquatic origin and n-C31 （an average of about 27 ‰） demonstrates the enrichment of the lake water δD compared to precipitation, caused by strong evaporation in the semiarid-arid areas of the southwestern Tibetan Plateau. Average value of εn-c25- 31/p （-95 ‰） is evidently higher than the value observed in European wet regions （-128 ‰）; besides, εn-C31 （about -116 ‰） is constant along the study transect （SD = 9）, which indicates that n-C31 is a useful proxy for the environment.     

Analysis of aerodynamic and thermodynamic parameters on the grassy marshland surface of Tibetan Plateau

The aerodynamic roughness z0m' the thermodynamic roughness zoh and the excess resistance to heat transfer kB are analyzed with the data obtained from Global Energy and Water Cycle Experiment ( GEWEX) Asian Monsoon Experiment on Tibetan Plateau (GAME/Tibet) in the Intensive Observation Period (IOP). 1998. Some new concepts on the aerodynamic and thermodynamic parameters over the grassy marshland surface of the Tibetan Plateau are proposed.     

Recent temperature increase recorded in an ice core in the source region of Yangtze River

Interests on climate change in the source region of Yangtze River have been raised since it is a region with the greatest warming over the Tibetan Plateau (TP). A 70-year history of precipitation δ~(18)O has been recovered using an ice core record retrieved in a plat portion of the firn area in the Guoqu Glacier (33°34′37.8″N, 91°10′35.3″E, 5720 m a.s.l.), Mt. Geladaindong (the source region of Yangtze River), in November, 2005. By using a significant positive relationship between ice core δ~(18)O record and summer air temperature (July to September) from the nearby meteorological stations, a history of summer air temperature has been reconstructed for the last 70 years. Summer temperature was relatively low in 1940s and high in 1950s to the middle of 1960s. The lowest temperature occurred in the middle of 1970s. Temperature was low in 1980s and dramatically increased since 1990s, keeping the trend to the begin-ning of the 21st century. The warming rate recorded in the ice core with 0.5℃/10 a since 1970s is much higher that that in the central TP and the Northern Hemisphere (NH), and it becomes 1.1℃/10 a since 1990s which is also higher than these from the central TP and the NH, reflecting an accelerated warm-ing and a more sensitive response to global warming in the high elevation region.     

New evidence for human occupation of the northern Tibetan Plateau, China during the Late Pleistocene

The described stone artifacts are recovered from the 70 m-high terrace (4600 m a.s.l.) at the southeastern shore of the Siling Co on the northern Tibetan Plateau. The terrace was formed during the Interstadial period before the LGM, ca. 40-30 ka B.P. based on paleoenvironmental research. The Paleoliths from the Siling Co provide evidence for early human occupation of the northern Tibetan Plateau. They show technological and typological affinities with the European Middle Paleolithic suggesting that the early human occupation here might relate to migratory waves during the Late Pleistocene that dispersed humans across the Old World.     

Climatic significance of δ18O records from precipitation on the western Tibetan Plateau

Analysis of daily precipitation samples for stable oxygen isotopes （δ^18O） collected at the Shiquanhe and Gerze （Gaize, Gertse） stations in the Ngari （Ali） region on the western Tibetan Plateau indicates that air temperature affects the δ^18O variations in precipitation at these stations. In summer, Shiquanhe and Gerze show strongly similar trends in precipitation δ^18O, especially in simultaneous precipitation events. Moreover, both stations experienced low δ^18O values in precipitation during the active monsoon period, resulting from the southwest monsoon （the summer phase of the Indian monsoon）. However, during the break monsoon period （during the summer rainy season, when the monsoon circulation is disrupted）, δ^18O values in summer precipitation remain relatively high and local moisture recycling generally controls the moisture sources. Air temperature correlations with δ^18O strengthen during the non-monsoon period （January--June, and October--December） due to continental air masses and the westerlies. In addition, evaporation also influences the δ^18O variations in precipitation. The observed temporal and spatial variations of δ^18O in precipitation on the western Tibetan Plateau and adjacent regions show that the late May and early June-the late August and early September time frame provides an important period for the transportation of moisture from various sources on the Tibetan Plateau, and that the region of the West Kunlun-Tanggula Ranges acts as a significant climatic divide on the Plateau, perhaps for all of western China.     

Indian monsoon influences altitude effect of δ~(18)O in precipitation/river water on the Tibetan Plateau

The δ^18O variation in precipitation acquired from 28 stations within the network of Tibetan Observation and Research Platform （TORP） is studied, with the focus on the altitude effect of δ^18O in river water during monsoon precipitation in an effort to understand the monsoon influence on isotopic composition in annual river water. It is found that δ^18O in precipitation on the Plateau is influenced by different moisture sources, with significant Indian monsoon influence on δ^18O composition in plateau precipitation and river water. The δ^18O of water bodies in the monsoon domain is generally more depleted than that in the westerly domain, suggesting gradual rainout of southwesterly borne marine moisture in the course of long-distance transportation and lifting over the Himalayas. The lapse rate of δ^18O in river water with altitude is the largest during monsoon precipitation, due to the increased temperature vertical gradient over the southern Plateau region controlled by monsoon circulation. The combination of δ^18O in river water in monsoon （wet） and non-monsoon （dry） seasons shows a larger lapse rate than that in non-monsoon （dry） season alone. As the altitude effect of δ^18O in precipitation and river water on the Tibetan Plateau results from the combined effect of monsoon moisture supply and westerly moisture supply, the δ^18O composition and its altitude effect on the Plateau during monsoon seasons should be considered in the reconstruction of paleoelevation of the Tibetan Plateau.     

Study of altitudinal lapse rates of δ18O in precipitation/river water with seasons on the southeast Tibetan Plateau

Seasonal δ^18O variation in water on the southeast Tibetan Plateau has been studied, showing the consistent variation pattern of δ^18O with altitude indicative of relevant atmospheric circulation processes. Study shows a similar variation pattern of fixed-site river water δ^18O with that of the precipitation δ^18O in southeast Tibet. δ^18O in regional rivers in southeast Tibet demonstrates a gradual depletion with increasing altitude, though the rates vary seasonally. The most depleted river ^18O occurs during the monsoon period, with the lowest δ^18O/altitude lapse rate. The river ^18O during the westerly period is also depleted, together with low δ^18O/altitude lapse rate. The pre-monsoon rivers witness the most enriched ^18O with least significant correlation coefficient with the linear regression, whilst the postmonsoon rivers witness the largest δ^18O/altitude lapse rate. Different coherence of seasonal δ^18O variation with the altitude effect is attributed to different moisture supplies. Though sampling numbers vary with seasons, the δ^18O-H linear correlation coefficients all reach the 0.05 confidence level, thus witnessing the variation features of δ^18O in seasonal river water due to the influence of atmospheric general circulation and land surface processes revealed from the altitudinal lapse rates.     

Environmental changes reflected by n-alkanes of lake core in Nam Co on the Tibetan Plateau since 8.4 kaB.P.

The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon (TOC), total nitrogen (TN) and carbonate are used to elu- cidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holo- cene environment performs three stages in the lake area. In the stage of 8.4―6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7― 5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P. to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600―400 aB.P., the environmental feature was the reflection of "Little Ice Age".