HR: 1340h
AN: PP23A-1073    [Abstracts]
TI: Atmospheric Circulation Changes During the Little Ice Age in NW China: a Late Holocene Oxygen Isotope Record From Lake Qinghai, NE Tibetan Plateau
AU: * Henderson, A C
EM: ahenders@life.uiuc.edu
AF: Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Llandinan Building, Penglais Campus, Aberystwyth, Ceredigion, SY23 3DB, United Kingdom
AU: * Henderson, A C
EM: ahenders@life.uiuc.edu
AF: Environmental Change Research Centre, Department of Geography, University College London, Pearson Building, Gower Street, London, WC1E 6BT, United Kingdom
AU: Holmes, J A
EM: j.holmes@ucl.ac.uk
AF: Environmental Change Research Centre, Department of Geography, University College London, Pearson Building, Gower Street, London, WC1E 6BT, United Kingdom
AU: Leng, M J
EM: mjl@nigl.nerc.ac.uk
AF: NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom
AU: Leng, M J
EM: mjl@nigl.nerc.ac.uk
AF: School of Geography, University of Nottingham, Nottingham, NG7 2RD, United Kingdom
AB: We present a decadal-scale δ ¹⁸O record from lake sediment carbonates spanning the last 1500 years from Lake Qinghai (37°N, 100°E), a large, hydrologically closed, brackish lake on the NE Tibetan Plateau. Specifically, we focus on the Little Ice Age (LIA), which has been widely recognized as a cold period in the Northern Hemisphere between ~ AD 1550 and 1850, but it's causes, timing and climatic manifestation within the monsoon domain remain unclear. Lake Qinghai presently lies near the modern limit of the East Asian monsoon, but the Siberian High and westerly storm flow also influence it. Based on the conventional interpretation of changes in δ ¹⁸O in closed basin lakes, as a balance between precipitation and evaporation (P/E), the depletion of ¹⁸O in the δ ¹⁸O record from AD 1300 to 1825 implies an increase in precipitation during a period synonymous with the LIA, suggesting increased monsoon intensity at this time. However, we argue that this observed trend during the LIA is a result of changes in atmospheric circulation rather than monsoon strengthening. The timing of these more negative δ ¹⁸O values coincide with a period of decreases in reconstructed monsoon rainfall based on a δ ¹⁸O stalagmite record from Dongge Cave in central China, as well as occurring during a well-documented southward displacement of the inter-tropical convergence zone. Together, this suggests that the influence of the East Asian monsoon was greatly reduced. Therefore changes observed in the δ ¹⁸O record during the LIA must be controlled by other factors. Comparison of our record with variations in δ ¹⁸O from the nearby Dunde ice core demonstrate that during the LIA there were significant changes in the δ ¹⁸O of precipitation. This would have led to changes in the δ ¹⁸O of lake water, suggesting that variability in the composition of input waters (in particular precipitation) was a key control. The δ ¹⁸O of precipitation is, in turn, controlled by moisture source and air temperature, indicating changes in atmospheric circulation during the LIA is the primary cause of δ ¹⁸O variability observed in the Lake Qinghai record, with a switch to more westerly- dominated climate.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 9320 Asia
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting