The evolution of the chemical composition of lake waters is determined by the inflow waters and subsequent evaporative concentration and the precipitation of minerals. In closed-basin lakes, evaporative concentration is mostly determined by changes in aridity, as a result of regional climate change. However, the interactions among lake water and groundwater chemistries, lake sediment geochemistry, and environmental change have not been studied over short or long time scales, and seldom using multidisciplinary approach. Intellectual merits. This pilot study is to investigate paired chemically-contrasting lakes (fresh and saline) in the arid northeastern Tibetan Plateau. These lakes are likely to be ideal sites for the study of water isotopic and elemental evolution, and the interactions of environmental change and lacustrine geochemical processes. The overarching objective of the proposed study is to understand hydrochemical evolution and how it interacts with various environmental controls at different time scales. The added bonus for undertaking such a study in this climate-sensitive region near the northern limit of the East Asian monsoon is to improve our ability to read the lacustrine sediment record of this region to better understand the past environmental changes. We propose to use a multidisciplinary approach to investigate at regional and watershed scales, the modern processes in these two lakes, history of solute and water flux from mineralogy and chemical and isotopic composition of authigenic and biogenic minerals, and from species assemblage of ostracodes and the history of climate and environmental change from such records of landscape processes as pollen, plant macrofossils, and environmental magnetism. The results from this project will provide insights into understanding the pathways and mechanisms of lake solute evolution and water flux and how they affect the sedimentary record of past environmental changes. This is the first study to employ a multidisciplinary approach to address the lake-climate interactions in Central Asia. A key feature of this project is in its use of paired limnologically- and chemically-contrasting lakes in order to unravel the interactions between lacustrine hydrologic and hydrochemical processes and environmental (and climatic) changes. The study of modern responses of the dilute lake (Keluke Lake) with a saline Lake (Toson Lake) will enable comprehensive and robust reconstructions of paleohydrochemistry. Also, the multiple techniques used in the proposed study will provide independent records of regional climate change, watershed stability and vegetation, as well as changes in lake chemistry. Integration of these records will allow us to focus on the complex interactions and feedbacks between these processes at different temporal scales (from present-day to interglacialglacial cycles). Broader impacts. Our interdisciplinary research will advance the understanding of complex interactions in these systems under different climate regimes. Understanding the lake and watershed responses to climate change of the past will contribute to our ability to predict the environmental consequences of climate (especially monsoon) variations and variability. Our approach of using contrasting hydrochemistries of paired fresh and saline lakes is not commonly employed but we believe is a very instructive one with a large pay-off. Understanding the hydrological dynamics will benefit the people in this remote arid part of China in adapting to the potential future changes in climate and hydrological cycles. The results will be compared with the response of lakes in the semi-arid northern Great Plains to climate and hydrololgic changes and shared with the state geological surveys and water commissions. Once past the pilot-stage, graduate and undergraduate students will be more fully involved in the project and will benefit from interacting with an international multidisciplinary research team. The project will facilitate collaborations, especially with our Chinese colleagues, who are having increased impacts in the international scene of science and technology.
