Stable isotopes in bulk carbonates and organic matter in recent sediments of Lake Qinghai and their climatic implications

Multi-proxy indices on annual/decadal scales during the past 600 years were developed from the surface sediments of Lake Qinghai based on Pb-210 and Cs-137 geochronology. The delta C-13(carb), delta O-18(carb), and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature. It is suggested that the strong evaporation contributes in modifying delta O-18 of lake water and delta C-13 of the dissolved inorganic carbon of the surface water, and appears to be responsible for the covariance between delta C-13(carb) and delta O-18(carb). Photosynthesis of the aquatic plants appears to have played a significant role in determining delta N-15 of organic matter. The discrimination of N-14 and N-15 during photosynthesis may have triggered a positive linkage between temperatures and delta N-15(org) (after removal of the stratigraphic trend). Variations of total organic carbon (TOC), C/N ratio, and delta C-13(org) have been ascribed to local precipitation. TOC (after removal of the stratigraphic trend) is positively correlated with the C/N ratio (r = 0.45, alpha < 0.01), and negatively correlated with delta C-13 of organic matter (delta C-13(org)) (r = -0.55, alpha < 0.01); while delta C-13(org) is negatively correlated with the C/N ratio (r = -0.48, alpha < 0.01). The climatic significance of these multi-proxy indices has been verified by comparing with the meteorological records and the climates inferred from tree rings in adjacent regions. (c) 2006 Elsevier B.V. All rights reserved.