Mineral magnetism and other characteristics of sediments from a sub-alpine lake (3080 m a.s.l.) in central east China and their implications on environmental changes for the last 5770 years

Abstract

A sediment sequence (SQC07) was recovered from Sanqing Chi, a small sub-alpine lake (3080 m a.s.l.) on Taibai (3767 m a.s.l.), the highest mountain in east mainland China (east of 105°). The Mountain is also the highest part and central massif of the Qinling Mountain Range functioning as the boundary between the warm temperate climate zone to the north and sub-tropical climate zone to the south in east China. Soils and debris were also sampled from the catchment of Sanqing Chi. SQC07 was AMS 14C dated. Mineral magnetism was measured for the sediment sequence and catchment samples. Particle-size, TOC and TN analysis were undertaken on SQC07, while pollen analysis was made for the sediment sequence and surface-soil samples. With the mineral magnetism of the catchment materials, the magnetic and other characteristics of SQC07 indicate the environmental changes occurring on the high altitudes of Taibai Mountain during the past 5770 years. Environments were still moderately warm and wet over 5770–5100 cal. yr BP around this sub-alpine lake. Then cold and dry conditions persisted in the period of 5100–4000 cal. yr BP. Local environments began to ameliorate from 4000 cal. yr BP onwards and were thus generally warm and wet over 4000–1200 cal. yr BP. The warmth and wetness culminated in 1200–800 cal. yr BP. During the period of 800–400 cal. yr BP, cold and arid conditions again predominated. Environments have subsequently become warm and humid since ∼400 cal. yr BP. The overall trend of the changes is coincident with what have been identified at several other sites in east mainland China and Taiwan. Presumably, the deterioration over 5100–4000 cal. yr BP marks the termination of the Holocene optimum, corresponds to or encompasses Holocene event 3, while the deterioration occurring in 800–400 cal. yr BP may correspond to LIA cooling. However, they appear to have commenced earlier than the aforementioned sites at relatively low altitudes in east mainland China or even higher altitudes but far southeast in Taiwan. These differences are possibly caused partly by uncertainties and/or errors of chronologies. Nevertheless, they also could be attributed to the spatial variability of East Asian monsoon and/or earlier responses of local landscapes around Sanqing Chi to larger-scale climate-deterioration.