A mineral magnetic record in Lake Hovsgol, Mongolia during the past 20,000 years

Mineral magnetic study has been carried out for five gravity cores (HS11, HS12, HS3, HS5 and HS20) obtained from Lake Hovsgol located in northern Mongolia to reconstruct paleoclimatic changes for the past 20,000 years. Various magnetic properties, implying variations in concentration, grain size and composition of magnetic minerals in samples from five cores were measured in laboratory. We found that the major magnetic mineral is low coercive ferromagnetic mineral such as magnetite from the results of stepwise IRM acquisition curves and magnetic phase proxies. We estimate the sedimentation period of each core by comparing results magnetic proxies and AMS radiocarbon ages. The Last Glacial Maximum (LGM) strata are characterized by high magnetic concentration and coarser grain size due to the increase of detrital influx. The Holocene strata are characterized by the low magnetic concentration and finer grain size. The decrease of magnetic mineral concentration during Hococene would be caused by the highest lake level and dilution effect associated with the relatively abundant paramagnetic materials such as diatom. The rise of lake level would also affect the decrease of magnetic grain size because the distance from the source area increased. The magnetic properties of five cores correspond to results of other paleoclimate proxies (sand content, mean grain size and climate index of central Asia). Particularly, it should be noted that the granulometry proxies show some evidences of abrupt climate changes (i.e., cold events) during the Holocene and Deglacial periods. Therefore, it is suggested that the magnetic granulometry proxies can be useful for reconstructing paleoclimate changes in the study area.