Holocene environmental changes as recorded by mineral magnetism of sediments from Anguli-nuur Lake, southeastern Inner Mongolia Plateau, China

Two cores, one 1141-cm long (An-S) and the other 885-cm long (An-A), were retrieved from Anguli-nuur Lake (41°18′-24′N, 114°20′-27′E, ∼ 1315 masl), one of the largest lakes in the transition zone between a semi-humid and semi-arid climate parallel to the present limit of the southeast monsoon along the southeastern Inner Mongolia Plateau in north China. Mineral-magnetic parameters (χlf, ARM, IRM300mT, SIRM and IRM− 300mT) were measured on An-S and two additional parameters (χARM and HIRM) and four inter-parametric ratios (χARM/SIRM, IRM300mT/SIRM, IRM− 300mT/SIRM and SIRM/χlf) were calculated. Potential sources of these lake sediments (catchment soils and dune materials close to the lake and in a distant sand plain) were sampled, and the magnetic properties of the surface-material specimens were measured. A chronological model was developed for An-S by comparing and combining AMS14C dates of An-S with 137Cs, 210Pb and AMS14C dates of An-A. With the help of surface-material magnetism, the magnetic data of An-S in combination with particle size, TOC and C/N and pollen analyses indicate the environmental changes during the last ∼ 10,000 years around this lake. Conditions began to ameliorate at 10,900 cal. yr BP (9600 14C yr BP) and thus relatively wet and warm environments prevailed during 10,900-8900 cal. yr BP (9600-8000 14C yr BP). The Holocene optimum or the wettest and warmest conditions, was during 8900-7400 cal. yr BP (8000-6500 14C yr BP). The environment began to deteriorate from 7400 cal. yr BP (6500 14C yr BP) and the driest and coolest conditions occurred during 2200-480 cal. yr BP. There may have been a minor amelioration after 480 cal. yr BP. The inferred changes in palaeoenvironmental conditions around Anguli-nuur Lake are broadly in agreement with those around most other sites on the Inner Mongolia Plateau.