A Holocene climatic record from arid northwestern China

The history of climatic changes during the interval 8500-3000 cal. yr B.P. has been reconstructed from stratigraphical and chronological studies and the results of Total Organic Carbon (TOC), Total Inorganic Carbon (TIC), element composition, pollen, and stable isotope analyses of a section along the Hongshui River, in the southern Tengger Desert, NW China. The record suggests that from 8450 (bottom of the studied section) to 7500 yr B.P., the climate was characterized by instability. From 7500 to 5070 yr B.P., the climatic conditions improved and can be divided into two parts: a warm-humid sped between 7290 and 6380 yr B.P., during which the average temperature was 3-4 degrees C higher than that of today, and a warm-dry spell lasting from 5950 to 5720 yr B.P. The climate deteriorated between 6380 and 5950 yr B.P. From 5720 to 5070 yr B.P., the temperature decreased, but humidity increased. An abrupt temperature drop occurred between 5340 and 5290 yr B.P. that indicated the decline of the warmer and humid Mid-Holocene climate. From 5070 yr B.P. onward, the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070-4670 yr B.P., 4300-3740 yr B.P. and 3410-3230 yr B.P. (top of the section), respectively. The climatic fluctuations recorded in the southern Tengger Desert appear in-phase with climatic changes recognized in the Tibetan Plateau, suggesting that the period between 7290 and 6380 yr B.P. was the most warm-humid spell. One extremely dry event occurred at ca. 3000 yr B.P., and subsequently the fluvial-lacustrine depositional process terminated and wind action prevailed in the area; both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation, which are closely connected with global changes. (C) 2000 Elsevier Science B.V. All rights reserved.