Recent climate changes recorded by sediment grain sizes and isotopes in Erhai Lake

By careful sampling and accurate analysis of recent sediments, the time series of sediment grain sizes and 6" 1B0, S 13C of carbonates in recent 700 years are successfully established, based on which the evolutionary history of the regional climate and environment in Erhai Lake is reconstructed. The results show that the climatic succession type in the region of Erhai Lake is warm-dry and cold-humid alternatively, and there exist 200 and 400 years of quasi-periodical changes in temperature and 100, 200 and 400 years of quasi-periodical changes in aridity/humidity regime. The two coldest periods in recent 700 years occurred in the 14th century and the duration of 1550—1800 AD. The latter period may be the imprint left of the Little Ice Age.     

Pollen evidence of early human activities in Erhai basin, Yunnan Province

The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sediment core in the lake, northwest Yunnan Province. The chronologic sequence based on AMS ^14C data made it possible for pollen results to compare with archaeological records and historical documents. The preliminary deforestation started from the selective clearance at about 5500 ^14C a BP, marked by the loss of vertically distributed montane forest and the expansion of second pine woodland across the catchment. The deforestation resulted in the increase of surface runoff and the enhanced erosion in the catchment. The increased herbs of pasture and crop suggested the primitive agriculture and stockbreeding in study region. With the limited human activity, as well as the suitable climatic condition, second pine forest expanded quickly, resulting in the weakened soil erosion around the basin. The strong forest clearance inferred from pollen occurred since 2160 ^14C a BP, paralleling to the first dense immigration of population, when Yeyu County was first set up around west coast of Erhai Lake, documented in historic record. The development of agriculture led to the steady enhancement of soil erosion from farming land, increasing the input of fine materials and nutrients to the lake. Moreover, the serious deforestation by human activity stressed the vulnerability in ecosystem of the landscape. The time of primary anthropologic impact recorded from pollen is earlier than that of the oldest archaeological record by 1500 a (^14C year).     

Paleosandstorm characteristics and lake evolution history deduced from investigation on lacustrine sediments——The case of Hongjiannao Lake, Shaanxi Province

Sediment cores from desert lakes serve as good records of the frequency and intensity of sandstorms in history. By multi-proxy analysis of grain-size, magnetic susceptibility, TOC and Rb/Sr ratio, the paleosandstorm characteristics and lake evolution history in Yulin Area for the past 80 years, are discussed in this article. It is revealed that Hongjiannao Lake formed in about 1928 A.D. and in its initial stage sandstorms were prevalent with three extremes taking place in 1936 A.D., 1939 A.D. and 1941 A.D.. During the expansion period of 1952-1960 A.D., inflow waters to the lake increased sharply and a lot more weathered materials were carried into the lake. The frequency and intensity of sandstorms have reduced a lot since 1960s and the ＂double peaks＂ feature of the grain-size frequency curve has changed into the ＂single peak＂ feature. Study on the catchment ecology of the lake shows that the occurrence of sandstorms has been effectively restrained by the forest plantation and water and soil conservation.     

近300年来岱海流域气候干湿变化与人类活动的湖泊响应

根据岱海60cm柱状岩芯的磁化率、孢粉、粒度等环境指标的分析结果,对历史时期岱海气候干湿变化和人类活动的湖泊记录进行探讨,岱海湖泊沉积记录近300年来的气候干湿变化可划分七个阶段,与历史记载有较好的一致性;频率磁化率高值段对应气候偏湿阶段,低值对应气候偏干阶段,人类活动特别是人口增加和土地开垦,加剧流域水土流失,导致湖泊沉积物中细颗粒组分增加,频率磁化率升高;孢粉Ulmus的变化受流域人口增加的影响。频率磁化率和孢粉是反映岱海历史时期干湿变化和人类活动的重要环境指标。     

Sediment resuspension in the Lake Taihu, China

The Lake Taihu is a large shallow lake in eastern China, with a surface area of 2338 km2, catchments of 36500 km2 and mean depth of 1.9-2.0 m [1]. It is fre-quently influenced by winds and therefore wind-gen- erated waves. The bottom sediment can be resus…     

Climatic changes documented by stable isotopes of sedimentary carbonate in Lake Sugan, northeastern Tibetan Plateau of China, since 2 kaBP

Lake Sugan at the northern edge of the Qaidam Basin was selected as the research object. The temporal sequence of sedimentary cores retrieved from Lake Sugan since 2 kaBP was reconstructed using the ^210Pb, AMS 14C and conventional 14C dating methods. Carbon and oxygen isotopes of carbonate in the fine-grained lake sediments were analysed. Combined with the changes of 8180 values of surface water and air temperature observation data in the study area, it might be thought that the δ^18O value of the carbonate indicates effective moisture, and the changes in δ^13C values are related to annual freeze-up duration of the lake and indirectly indicate air temperature changes in winter half year. From the above, the sequence of climatic changes in the region since 2 kaBP was established. The climatic changes experienced five stages： Warm-dry climate during 0-190 AD： cold-dry climate during 190-580 AD; warm-dry climate during 580-1200 AD （MWP）; cold-wet climate during 1200-1880 AD （LIA）; cold-dry climate during 1880-1950 AD： and climate warming since 1950s. The air temperature changes in winter half year reflected by carbon isotope since 2 kaBP are in good agreement with the historical literature records and other geologic records, which shows that the climate changes recorded by the stable isotopes from Lake Sugan since 2 kaBP are of universal significance.     

Environmental changes during early-middle Holocene from the sediment record of the Chaohu Lake,Anhui Province

A typical lake sediment core is obtained from the Chaohu Lake in the lower reaches of the Yangtze River,Anhui Province,China.The timing scale is constrained by AMS 14 C dating method.Climate proxies such as pollen and grain size in the core are analyzed to reconstruct the environment changes at this site approximately between 9870 and 2170 cal.a BP.The results indicate that at the research area, the climate in the early-middle Holocene had evolved through 3 stages.From 9870 to 6040 cal.a BP, proxy records show a warm and dry climate with low water levels after the late-glacial period.During this stage,cool and dry events occurred at about 8910 and 6060-6030 cal.a BP.Then,between 6040 and 4860 cal.a BP,the climate was humid and vegetation was more flourishing in the Chaohu Lake Valley.The Holocene Optimum occurred at 5840-5500 cal.a BP in the Chaohu Lake,showing the best condition of water and heat.Elm Decline occurred at the period of 5380-4930 cal.a BP.Since 4860 cal.a BP,the climate was warm and dry through 2170 cal.a BP as shown in both pollen spectrum and grain-size histories.Two obvious dry events occurred in 3760 and 2170 cal.a BP,respectively.At 2170 cal.a BP,the water level of the Chaohu Lake reached the lowest as the lakebed possibly exposed. Such lake sediment observations are consistent with the historical records in this area.     

Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake,Shanxi, North China

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the and S 300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.     

137Cs tracing of lacustrine sediments in the Dalian Lake, Qinghai Province, China

Based upon the analysis of Cs and grain-size parameters, the total amounts of ¹³⁷Cs deposition by wind and water in the Dalian Lake of Gonghe Basin, Qinghai Province are defined. The vertical profile of ¹³⁷Cs in the lacustrine sediments exhibits three ¹³⁷Cs activity maxima and one minimum. The major maximum corresponds to the global ¹³⁷Cs fallout in 1963; the two secondary maxima correspond to the leakage of the Chernobyl reactor in 1986 and complete desiccation of the lake in 1994, respectively. The minimum corresponds to aeolian deposition caused by extensive reclamation in the late 1980s and early 1990s. The 137Cs data set was used to evaluate average sedimentation rate of the Dalian Lake since 1963. The deposition was stable in 1963-1986 and 1994-1998, and it was rapid during 1986-1994. This preliminary study reveals that l37Cs has the same potential to trace environmental changes introduce by human interference in arid/semiarid regions as in humid regions.     

Spatio-temperial variations of the bacterioplankton community composition in Chaohu Lake, China

Despite considerable attention paid to Chaohu Lake in China, the dynamics of bacterioplankton community composition （BCC） on spatial and seasonal scales are poorly understood. In this study, water samples were collected from autumn 2006 to summer 2007 at five positions in Chaohu Lake with different trophic status. BCC of these samples was determined by both the PCR amplification of the 16S rDNA gene and the denaturing gradient gel electrophoresis （DGGE）. The abundance and diversity of bacterioplankton communities at different sampling positions showed similar seasonal patterns. The BCCs in the samples varied substantially, and the pattern of changes indicated that the seasonal difference might have a significant impact on the BCC＇s structure in the lake. Canonical correspondence analysis （CCA） on the DGGE patterns and physicochemical parameters indicated that the temperature and the levels of 5-d biochemical 02 demand （BODs）, NH3-N, CODMn, total nitrogen, total phosphorous, and dissolved oxygen significantly influenced the BCC, and four of the seven variables were related to the level of eutrophication. Our results indicate that eutrophic status and season are the most influ- ential factors in determining BCC in Chaohu Lake.     

Carbon isotopic record of foraminifers in surface sediments from the South China Sea and its significance

Since the 1990s, the papers and data involved withthe South China Sea (SCS) have been emerging in largenumbers in the world as people pay more attention to thepaleoceanography of the SCS. There have been more than100 cores mentioned in papers containing p…     

云南轮藻植物研究

云南共有轮藻植物５属４８种（包括变种和变型）．在种类组成中，丽藻属最多，轮藻属次之，其它３属的种类较少分布特点具有热带、亚热带性质；区系属于印度一马来西亚，但鸟巢藻属、拟丽藻属、松藻属的地理分布带有地中海沿岸区系的成分。云南轮藻某些种类在形态上存在的差异显示了系统发育的间断性，同时，它们在形态上所具有的一些共同点，反映了在其进化过程中的连续性．     

Dynamics of sediment resuspension and the conceptual schema of nutrient release in the large shallow Lake Taihu,China

On the basis of investigations in situ, it was found that mass exchange on the water-sediment interface occurred chiefly on the superficial sediment within 5-10 cm. The spatial physicochemical character of sediment was distributed uniformly. The observation of lake currents and waves indicated that the dynamic sources, which act on the interface of water and sediment, came mainly from waves under strong wind forcing, while the critical shear stresses     

Relative paleointensity of the geomagnetic field during the past 0.8 Ma from Nihewan Basin,Hebei Province,China

We conducted a detailed rock magnetic study on upper 80 m of Jing抏rwa core from the Nihewan basin. The results indicate that the sediments from Jing抏rwa core are suitable for relative paleointensity study, and anhyster-etic remanent magnetization (ARM) can be used as the nor-malization parameter of the natural remanent magnetization (NRM). Our relative paleointensity data of upper 80 m of Jing抏rwa core provide a continuous record of the intensity variation during the last 0.8 Ma, which correlates well with the results from marine sediments cores in the Pacific Ocean. This means that the sediments records are reliable for rela-tive paleointensity of Earth抯 magnetic field, and suggests that these sediments have recorded the real changes of geo-magnetic field, which would provide a new method for re-gional stratigraphic correlation.     

Vegetation and climate changes during the last 8660 cal. a BP in central Mongolia, based on a high-resolution pollen record from Lake Ugii Nuur

Based on modern pollen studies and reliable chronology of nine AMS 14C dates, a detailed history of vegetation and climate changes during the past 8660 cal. a BP was reconstructed by a high-resolution pollen record from Ugii Nuur in central Mongolia. Poaceae-steppe dominated the study area and the climate was mild and semi-humid before 7800 cal. a BP with a noticeable cool and humid interval at 8350―8250 cal. a BP. Xerophytic plant increased and the climate became warm and dry gradually since 7800 cal. a BP...     

Southwest monsoon changes indicated by oxygen isotope of ostracode shells from sediments in Qinghai Lake since the late Glacial

The δ 18O records of ostracode shells in sediments of core QH-2000 from Qinghai Lake can be used as a better proxy to reflect monsoon changes. Low monsoon precipitation between 17.5 and 11 cal. ka BP is indicated by positive δ 18O values averaging 2.37‰. A fast shift in δ 18O from positive at 11 cal. ka BP to negative at 10 cal. ka BP indicates sharp increase of monsoon precipitation. An interval of generally high monsoon precipitation is observed between 10 and 6 cal. ka BP with δ 18O values averaging -2.15‰. Decrease of monsoon precipitation between 6 and 2.5 cal. ka BP is indicated by positive δ 18O values. δ 18O keeps positive values averaging 3.0‰ between 2.5 and 0 cal. ka BP suggesting low high monsoon precipitation. The climatic changes indicated by δ 18O records of ostracode shells in sedi- ments of core QH-2000 from Qinghai Lake and our broader regional comparison show that the climate in Qinghai Lake since the late Glacial is probably controlled by southwest monsoon other than southeast monsoon.     

High-precision measurement of mercury isotope ratios of atmospheric deposition over the past 150 years recorded in a peat core taken from Hongyuan,Sichuan Province,China

High-precision 210Pb dating technology was applied to a peat core with a time span of about 150 years that was taken from Hongyuan, Sichuan Province, China. The concentrations of total mercury (Hg) and stable isotope compositions of mercury in the peat core were measured using a LUMEX 915 instrument and multi-collector inductively coupled plasma mass spectrometer, respectively. Total mercury (Hg) concentrations in the peat core had a clearly increasing trend from the bottom to top of the core while δ 202Hg ...