Abstract
A high resolution multi–proxy (pollen, grain size, total organic carbon) record from a small mountain lake (Lake Khuisiin; 46.6°N, 101.8°E; 2270 m a.s.l.) in the south–eastern Khangai Mountains of central Mongolia has been used to explore changes in vegetation and climate over the last 1200 years. The pollen data indicates that the vegetation changed from dry steppe dominated by Poaceae and Artemisia (ca AD 760–950), to Larix forest steppe (ca AD 950–1170), Larix–Betula forest steppe (ca AD 1170–1380), meadow dominated by Cyperaceae and Poaceae (ca AD 1380–1830), and Larix–Betula forest steppe (after ∼ AD 1830). The cold-wet period between AD 1380 and 1830 may relate to the Little Ice Age. Environmental changes were generally subtle and climate change seems to have been the major driver of variations in vegetation until at least the early part of the 20th century, suggesting that either the level of human activity was generally low, or the relationship between human activity and vegetation did not alter substantially between AD 760 and 1830. A review of centennial–scale moisture records from China and Mongolia revealed that most areas experienced major changes at ca AD 1500 and AD 1900. However, the moisture availability since AD 1500 varied between sites, with no clear regional pattern or relationship to present–day conditions. Both the reconstructions and the moisture levels simulation on a millennium scale performed in the MPI Earth System Model indicate that the monsoon–westerlies transition area shows a greater climate variability than those areas influenced by the westerlies, or by the summer monsoon only.
Highlights
The past millennium is one of the most important periods for studying environmental changes, as it covers both naturallye driven environmental changes and changes resulting from human influences (Buttler et al, 1996)
Many researchers have assumed that the Mongolia and northern China region was arid during the early Holocene (Grunert et al, 2000; Herzschuh et al, 2004; Wang et al, 2004; Feng et al, 2005; Chen et al, 2008; Liu et al, 2008; Yang and Scuderi, 2010; Yang et al, 2011; Zhang et al, 2012), and a wet early Holocene has been suggested by some records from that region (Prokopenko et al, 2007; Rudaya et al, 2009; Murakami et al, 2010; Xu et al, 2010)
Some studies suggest that temperatures decreased during the Little Ice Age (LIA), reconstructed and modeled moisture levels and hydrological conditions do not show consistent variations across different parts of Mongolia and northern China (Wang et al, 2003; Liu et al, 2004; Mayewski et al, 2004)
Summary
The past millennium is one of the most important periods for studying environmental changes, as it covers both naturallye driven environmental changes and changes resulting from human influences (Buttler et al, 1996). In addition to the yeareround influence of the westerlies, the winter climate is primarily controlled by the intense Siberian high pressure system and the summer climate by north part of the Asian low pressure system (Gong et al, 2001; Tudhope et al, 2001; Wang et al, 2009). These complex climatic systems render Mongolia a climatically sensitive area, as has been confirmed through climateeproxy studies on various time scales (D’Arrigo et al, 2000; Pederson et al, 2001; Fowell et al, 2003; An et al, 2008). The complex spatial differences in climatic variations during the history of the Asian mid-latitude region on centennial to decadal time scales is only poorly understood, which means that the future effects of climate change on Mongolian ecosystems cannot be reliably projected and indicates the urgent need for further research into spatial variations in climate patterns
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