Jin Zhangdong

Weak chemical weathering during the Little Ice Age recorded by lake sediments

Low magnetic susceptibility, low Sr content and hence high Rb/Sr ratio in the lake sediment sequence indicate a weak chemical weathering process under arid and cold climate of the Little Ice Age in a single closed lake watershed. According to different geochemical behavior between rubidium and strontium in earth surface processes, variation of Rb/Sr ratios in the lake sediment sequence can be used as an effective geochemical proxy with definite climatic significance of chemical weathering in watershed. Unlike chemical weathering process in tropic zone and modern temperate-humid climate, concordant changes in both Sr content and magnetic susceptibility with δ18O values of Dunde ice core suggest that the weak chemical weathering was controlled by air temperature during the Little Ice Age maximum. After the Little Ice Age, chemical weathering intensity was controlled also gradually by precipitation with increasing in temperature.

Human influence on heavy metal distribution in the Upper Lake Nansi sediments, Shandong Province, China

Core and surface sediment samples were collected from three sub-lakes (Lake Nanyang, Lake Dushan and Lake Zhaoyang) in the Lake Nansi Basin, Shandong Province. In order to reveal the characteristics of spatial and historical distribution of heavy metals in different sublakes of the Upper Lake Nansi, heavy metal (As, Cr, Cu, Hg, K, Mn, Ni, Pb, Zn, Al, Fe, Ti and V) concentrations of sediment samples were investigated. Based on the activity of137Cs in the sediments, the modern accumulation rate of Lake Nansi sediments is 3.5 mm/a. Our results show that the whole Upper Lake Nansi has been already polluted by heavy metals, among which Lake Nanyang has been polluted seriously by mercury, as well as by lead and arsenic, while Lake Dushan has been most seriously polluted by lead and arsenic. Historical variation of heavy metal (Cr, Cu, K, Ni, Zn, Al, Fe, Ti and V) concentrations shows an abrupt shift in 1962, resulting in a division of two periods: from 1957 to 1962 when metal enrichment increased with time, and from 1962 to 2000 when it decreased with time, while that of some anthropogenic elements such as Hg, Pb and Mn tend to increase toward the surface. However, the variation trend of As in the sediments is different from that of Hg, Pb and Mn, with its maximum value appearing in 1982. Since 1982 the concentrations of As have decreased due to the forbidden use of arsenite pesticides. This variation trend revealed changes in manner of human activity (coal combustion, waste discharges from both industries and urban sewage) within the catchment during different periods.Core and surface sediment samples were collected from three sub-lakes (Lake Nanyang, Lake Dushan and Lake Zhaoyang) in the Lake Nansi Basin, Shandong Province. In order to reveal the characteristics of spatial and historical distribution of heavy metals in different sublakes of the Upper Lake Nansi, heavy metal (As, Cr, Cu, Hg, K, Mn, Ni, Pb, Zn, Al, Fe, Ti and V) concentrations of sediment samples were investigated. Based on the activity of137Cs in the sediments, the modern accumulation rate of Lake Nansi sediments is 3.5 mm/a. Our results show that the whole Upper Lake Nansi has been already polluted by heavy metals, among which Lake Nanyang has been polluted seriously by mercury, as well as by lead and arsenic, while Lake Dushan has been most seriously polluted by lead and arsenic. Historical variation of heavy metal (Cr, Cu, K, Ni, Zn, Al, Fe, Ti and V) concentrations shows an abrupt shift in 1962, resulting in a division of two periods: from 1957 to 1962 when metal enrichment increased with time, and from 1962 to 2000 when it decreased with time, while that of some anthropogenic elements such as Hg, Pb and Mn tend to increase toward the surface. However, the variation trend of As in the sediments is different from that of Hg, Pb and Mn, with its maximum value appearing in 1982. Since 1982 the concentrations of As have decreased due to the forbidden use of arsenite pesticides. This variation trend revealed changes in manner of human activity (coal combustion, waste discharges from both industries and urban sewage) within the catchment during different periods.

Characteristics of an early Holocene climate and environment from lake sediments in Ebinur region, NW China

The characteristics of climatic environment in the early Holocene epoch were studied through analyzing environmental proxies from the sediments in the Ebinur Lake-a closed one in the arid region. The pollen assemblage and other geochemical indices showed that, the temperature was somewhat low in the period (8.0–11.5 cal kaBP) as a whole, but in the early period (11.5-10.6 cal kaBP) the temperature was higher, in company with more precipitation. In the conversion period from the early Holocene epoch to the middle Holocene epoch (8.9-8.0 cal kaBP) the climate fluctuated remarkably. Particularly the three layers of peat sediment revealed the strong instability of climate in the early Holocene epoch in the Ebinur region. All information on the development of peat and the experimental data of pollen and stable isotopes implied that, the climatic condition at 8.2, 8.6 and 10.5 cal kaBP was characterized by noticeable cold and humidness, and could be regarded as three cold and humid events in the early Holocene epoch.

Dust-storm Events in Daihai Lake Area, Inner Mongolia During the Past 400 Years: Evidence from Grain size Analysis of Lake Sediments

A 400 year dust storm history in Daihai Lake area, Inner Mongolia, Northern China, was reconstructed on the basis of high resolution grain size analysis of the lake sediments, in combination with reconstructed historical data of regional precipitation from tree ring, frequency of dust storms in China and historical documentary records. The Daihai Lake is located at a climatically transitional zone between semi arid and semi humid where front position and intensity of the East Asian summer monsoon and winter monsoon chiefly control the climate change. Both the median grain size and coarse grain content indicate that dust storm events were controlled mainly by the intensity of the summer and winter monsoon in the past 400 years. Major dust fall events are generally associated with dry and cold climate during the Little Ice Age, when the median grain size of the lake sediments is larger with high contents of coarse grain (100μm). At time of warm conditions after the Little Ice Age, dust storm events were limited, both the contents of coarse grain (100μm) and the median grain size also decreased. During the last one to two decades, however, dust storm events increased gradually, related partly with more desertificated soil by human activity.

Element Distribution in Chemical Fractions of Lake Sediments Determined by Sequential Extraction:the Case of Lake Daihai (Northern China)

Environmental interpretation of geochemical proxies of lake/ocean sediments largely depends on an understanding of where elements are from and of how elements bound to various fractions in the sediments. Fourteen samples from Lake Daihai, Inner Mongolia , located in semiarid zone, were carried out a sequential extraction experiment and analyzed eighteen elements concentration by ICP-AES or AAS in each chemical fractions defined as follows: soluble, exchangeable, bound to carbonate, bound to Fe-Mn-ox-ides, bound to organic matter and residual. Our results indicate that weak chemical weathering was proceeded under climate conditions in the Lake Daihai watershed, resulting that most of the elements determined are in residual due to little activation during weathering, except Ca and Sr, by combining with detrital minerals of predominantly plagioclase. Meanwhile, controlled by element affinity and lake water physicochemical conditions, leached both Sr and Ca are in the same fractions with good correlation, whereas other activated elements including Pb, Be, Co, Cu, K, Mn, Fe etc are predominantly associated with the fractions of bound to carbonate and/or organic matter. Consequently, element distribution in various chemical fractions provides a useful experimental evidence for selection and interpretation of some geochemical proxies.

The Medieval Warm Period and Little Ice Age in the Daihai Area, North China

Rb/Sr ratio, CaCO3 content, organic carbon ( Corg) concentration, magnetic susceptibility and clay mineralogy of 4. 0 m sediments samples recovered from Daihai Lake, northern China, are presented in the paper. Weathering and paleoclimatic change history during the last 2300 years is reconstructed in terms of the variations of Rb/Sr ratios in the sediment sequence, including the Little Ice Age and Medieval Warm Period. Our results suggest that the evolution processes of weathering and paleoclimate can be rebuilt in terms of the variations of Rb/Sr ratios in the lake sediment sequence, in combination with magnetic susceptibility, Corg, CaCO3 contents and clay mineralogy.

Oxygen and strontium isotope markers ofLake Qinghai naked carp otoliths and their implication for fish migratorypattern

As the dominant and unique species in Lake Qinghai, the naked carp Gymnocypris przewalskii (Kessler) is characterized by upstream migration to spawn during late spring and summer in each year and back lake to live during the remaining seasons, but little is known about its migratory pattern. The migratory pattern of the naked carp is significant in understanding its living habitat and in protecting this precious fish. Otoliths are paired biogenic carbonates in the inner ear of teleost fish and grow layer by layer throughout the fish life. Owing to its metabolically inert without involvement in metabolic processes after deposition, chemical compositions of daily and annual growth increments in otoliths record the water elements of the ambient waters where the fish encountered during its life history. Therefore, microchemistry variation of otoliths has been used widely to trace migration pattern of fish and to reconstruct water chemistry and environmental conditions in the past.