Climate and Environmental Changes Over the Past 150 years Inferred from Two Alpine Lakes in the Eastern Tibetan Plateau

Abstract:

Current global warming and human activities may exert profound effects on lacustrine environment and ecosystem. However, limited data have been reported to show how lake systems have responded to changes in climate and human disturbances. Here we report multi-proxy climate and environmental data for the past ~150 years from two small alpine lakes with similar size and hydrology at the eastern margin of the Tibetan Plateau, a place influenced by the Indian summer monsoon. One is Jiren Lake (4500 m asl), above the modern tree line and undisturbed by any human activity in history. Another is Cuoqia Lake (3900 m asl), just below the tree line and only experienced an deforestation and reforestation process by human activity over the past centuries. We use hydrogen isotopes of C₂₈-fatty acid and TOC as proxies for changes in monsoon precipitation and lake productivity, respectively. Our data indicate both lakes have experienced similar variations in monsoon precipitation over the past 150 years, resembling the temperature variations in the northern Hemisphere. On the other hand, both lakes show very different changes in lake productivity. Productivity at Jiren Lake was stable before 1920AD and then shifted to an increasing trend, which coincides with our precipitation record and reveals the lake ecosystem being largely controlled by natural climate change. At Cuoqia Lake, the lake productivity gradually decreased until ~1980AD and then increased until now, largely following the local deforestation and reforestation process. Overall, our preliminary data probably indicate that human activities may have a stronger influence than natural climate change on lacustrine ecosystems.