A Holistic Paleolimnological Study of North-Central Mongolian Lakes

Concern for environmental degradation in response to recent warming trends is highly relevant for modern Mongolian society. A general lack of high-resolution, long-term information on regional environmental history however, limits any thorough understanding of the potential rate and extent of such ecosystem alteration. Paleoenvironmental methods are thereby required to assess baseline conditions within sensitive ecosystems and thereby evaluate past climate and environmental changes. Here, a detailed paleolimnological study of northern Mongolian lakes is presented in an effort to examine the response of sensitive lake systems to climatic variation during the Holocene. More specifically, eight high-alpine lakes with the Baroon Taiga Mountains of northern Mongolia were identified and studied as part of a broad survey of north/central Mongolian lake systems. The application of diffuse reflectance spectroscopy and standard loss-on-ignition techniques to radiocarbon-dated sediment core samples provides a high-resolution history of late Holocene algal productivity within the basins of Sanjin, Asgat and Ganbold Nuur, and a low-resolution full-Holocene paleoproductivity history for Mustei Nuur. Evidence for a long-term decrease in production rates in response to orbital forcing from 8000 cal yr B.P. is provided by the Mustei Nuur record. Inter-core comparison of high-resolution records provides evidence for regional growing season temperature variations as the dominant mechanism controlling higher frequency aquatic productivity variations during the late Holocene period. Diminished regional aquatic productivity trends are observed during the Little Ice Age (300 - 100 cal yr B.P.). Increased productivity is noted between 900 and 1100 cal yr B.P. (coincident with the so-called Medieval Climatic Anomaly) and from ~ 100 cal yr B.P. to the present, likely in response to 20th century warming trends. A direct comparison of the Sanjin and Ganbold Nuur aquatic productivity records to nearby tree-ring based temperature reconstructions supports the hypothesis that the high-frequency aquatic productivity changes reflect regional temperature variations, and thereby extend the regional temperature reconstructions to 3000 cal yr B.P