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Jin Z.,CAS Institute of Earth Environment | Jin Z.,National Cheng Kung University | You C.-F.,National Cheng Kung University | Wang Y.,Pacific Northwest National Laboratory | Shi Y.,The Bureau of Hydrology and Water Resources of Qinghai Province
Quaternary International | Year: 2010

Water level and chemistry of Lake Qinghai are sensitive to climate changes and are important for paleoclimatic implications. An accurate understanding of hydrological and chemical budgets is crucial for quantifying geochemical proxies and carbon cycle. Published results of water budget are firstly reviewed in this paper. Chemical budget and residence time of major dissolved constituents in the lake are estimated using reliable water budget and newly obtained data for seasonal water chemistry. The results indicate that carbonate weathering is the most important riverine process, resulting in dominance of Ca2+ and DIC for river waters and groundwater. Groundwater contribution to major dissolved constituents is relatively small (4.2 ± 0.5%). Wet atmospheric deposition contributes annually 7.4-44.0% soluble flux to the lake, resulting from eolian dust throughout the seasons. Estimates of chemical budget further suggest that (1) the Buha-type water dominates the chemical components of the lake water, (2) Na+, Cl-, Mg2+, and K+ in lake water are enriched owing to their conservative behaviors, and (3) precipitation of authigenic carbonates (low-Mg calcite, aragonite, and dolomite) transits quickly dissolved Ca2+ into the bottom sediments of the lake, resulting in very low Ca2+ in the lake water. Therefore, authigenic carbonates in the sediments hold potential information on the relative contribution of different solute inputs to the lake and the lake chemistry in the past. © 2009 Elsevier Ltd and INQUA.

Wang Y.J.,CAS Institute of Earth Environment | Wang Y.J.,Nanjing Agricultural University | Jin Z.D.,CAS Institute of Earth Environment | Jin Z.D.,Global University | And 7 more authors.
Science China Earth Sciences | Year: 2014

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-14C ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-14C dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn’t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12±18.50)×10−5) and δ18O ((1.76±1.03)‰) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11±0.41)× 10−5 and δ18O=(−4.82±0.96)‰). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and δ18O ratios than modern Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today’s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km2 during the Ming Dynasty, approximately ∼5% larger than it is today. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg.

Jin Z.,CAS Institute of Earth Environment | Wang S.,CAS Nanjing Institute of Geography and Limnology | Zhang F.,CAS Institute of Earth Environment | Shi Y.,The Bureau of Hydrology and Water Resources of Qinghai Province
Earth Surface Processes and Landforms | Year: 2010

Strontium (Sr) concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the Lake Qinghai basin on the north-eastern Tibetan Plateau. Dissolved Sr and 87Sr/86Sr show ranges of 488-12 240 nmol/l and 0·710497-0·716977, respectively. These data, together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment, were used to determine the contributions of Sr and its isotopic expense to rivers and lakes. Our results demonstrate that the chemical components and 87Sr/86Sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources, with the former contributing 72 ± 18% dissolved Sr to rivers. The difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi-arid condition. Variation in 87Sr/86Sr ratios places constraint on the Sr-isotopic compositions of the main tributaries surrounding Lake Qinghai. The water chemistry of the Buha River, the largest river within the catchment underlain by the late Paleozoic marine limestone and sandstones, dominates Sr isotopic composition of the lake water, being buffered by the waters from the other rivers and probably by groundwater. However, the characteristic chemical composition of the lake itself differs remarkably from the rivers, which can be attributed to precipitation of authigenic carbonates (low-magnesium calcite, aragonite, and dolomite), though this does not impact the Sr isotope signature, which may remain a faithful indicator in paleo-records. Regarding the potential role of groundwater input within the Lake Qinghai systems in the water budget and water chemistry, we have also determined the Sr concentration and 87Sr/S6Sr ratio of groundwater from diverse environments. This has allowed us to further constrain the Sr isotope systematic of this source. A steady-state calculation gives an estimate for the groundwater flux of 0·19 ± 0·03 x 108 m3/yr, accounting for about 8% of contemporary lake Sr budget. © 2010 John Wiley & Sons, Ltd.

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