Holocene environmental variations recorded by organic-related and carbonate-related proxies of the lacustrine sediments from Bosten Lake, northwestern China

Abstract

We reconstructed a multiproxy record of the Holocene climate changes from a 9.53 m core from Bosten Lake in the southern Xinjiang of northwestern China based on a chronology supported by nine AMS 14C dates in the hope that the previous reconstructions can be improved. Our data exhibited three timescales of variation in the water salinity of the lake. First, the upward-increasing parallel trends of major salinity proxies suggest that the salinity has been gradually increasing in the past ~8000 years. This constant increase in the salinity is most likely to have resulted from the shrinking of glacial cover in the central Tianshan Mountains where the inflowing river (i.e. Kaidu River) originated. Second, the C/S ratio and carbonate-based salinity proxies suggest that the lake was formed around ~8060 cal. yr BP and reached its maximum depth around ~7250 cal yr BP. The lake level then declined to the mid- and late-Holocene average level around ~6370 cal. yr BP and has varied drastically around a relatively constant mean during the past ~6370 years. Third, the past ~8060 yr history of the Bosten Lake can be divided into five salinity stages. That is, three high salinity intervals are separated by two low salinity intervals. The two low salinity stages occurred between ~6370 and ~5170 cal. yr BP and between ~3000 and ~2170 cal. yr BP. Each one of the three high salinity stages can be further divided into less saline and more saline substages. Specifically, less saline time intervals are: substage 2-1 (~8060—~7250 cal. yr BP), substage 4-2 (~4370—~3830 cal. yr BP) and substage 6-2 (~1250—~0 cal. yr BP). Also, saltier time intervals are: substage 2-2 (~7250—~6370 cal. yr BP), substage 4-1 (~5170—~4370 cal. yr BP), substage 4-3 (~3830—~3000 cal. yr BP) and substage 6-1 (~2170—~1250 cal. yr BP). It should be stressed that the phase relationships between the carbonate-based salinity proxy and diatom-based temperature proxy suggest that the salinity was mainly controlled by temperature. Finally, the comparison between the Bosten Lake salinity record and the high northern latitudinal climate pattern suggests that the lower salinity and cooler periods in Bosten Lake area correspond with abrupt climatic events (i.e. cooling events) in the high northern latitudes.