High-resolution enviromagnetic records of the last deglaciation from Dali Lake, Inner Mongolia

Abstract

Detailed paleoclimate records during the last deglaciation are highly valuable for understanding rapid climatic changes and mechanisms during extremely variable conditions. High-resolution paleoclimate research in the semi-arid East Asian interior is essential due to its sensitivity to climate variability and importance for human inhabitance. A high-resolution environmental magnetic investigation has been performed on a sedimentary sequence from Dali Lake in central Inner Mongolia, which covers the period of 15.90-11.46 ka. Variable magnetic mineral sources are identified based on integrated rock magnetic analysis of both core sediments and catchment samples, complemented by scanning electron telescope and transmission electron telescope observation and Xray diffraction analysis. The studied core is magnetically divided into four units: Magnetic minerals in Unit 1 (11.83-11.5 m, 15.90-15.32 ka) are mainly sourced from bedrock erosion of basalts in the catchment. This period corresponds to rapid climate fluctuations after the Last Glacial Maximum. In Unit 2 (11.50-9.50 m, 15.32-12.67 ka) and Unit 3 (9.50-8.59 m, 12.67-11.56 ka), pseudo-single domain magnetites from erosion of surface soils are the main magnetic carriers. These two units coincide within time error with the Bølling-Allerød warm period and the Younger Dryas cold period, respectively, and can be correlated with stalagmite and ice core records. Our findings reflect contrasting erosion processes during cold and warm periods in the lake catchment, which were ultimately controlled by climate changes during the last deglaciation.

Nonlagged Response of Vegetation to Climate Change During the Younger Dryas: Evidence from High‐Resolution Multiproxy Records from an Alpine Lake in Northern China

“…In addition to the quantitative precipitation reconstruction record from Lake Gonghai (Figure a), on the northern limit of modern EASM area, a humidity record from Moon Lake (Figure b; Wu et al, ), and an environmental magnetic record from Dali Lake (Figure c; Liu et al, ), all clearly indicate decreased summer monsoon precipitation and drier conditions (and thus a weakened EASM) during the YD. Moreover, the quantitative monsoon precipitation record of Chen, Lu, et al (), from northern China, also reveals a weakened EASM during the YD (Figure d).…”

“…Over the past two decades, many palaeoclimatic records from northern China, focused on the evolution of the EASM, have been published. The archives include lake sediments (Chen, Xu, et al, ; Liu et al, ; Tang et al, ; Wu et al, ), loess‐sand sequences (An et al, ; Chen, Lu, et al, ; Zhao et al, ; Zhou et al, ), peat deposits (Hong et al, , ), and speleothems (Dong et al, ). However, within these studies there are large disparities in sample resolution and age control and in the fidelity of the proxies used.…”

“…At Moon Lake, a closed crater lake on the northern limit of the modern EASM, the vegetation evolution can be expected to capture regional monsoon variations in response to large amplitude climate changes, and thus, the ratio of arboreal pollen to the pollen of steppe taxa is regarded as a moisture index that reflects the intensity of the EASM (Wu et al, ). Given the location of Dali Lake, in central Inner Mongolia, on the modern limit of the EASM, sedimentary processes should be highly sensitive to monsoon variability, and the magnetic record of the Dali Lake sediments are regarded as representing monsoonal variations during the last deglaciation (Liu et al, ). Based on the relationship between monsoon precipitation and the carbon isotopic composition of modern soils, with a minor modification, Chen, Lu, et al () presented the first quantitative estimate of monsoon precipitation during the late glacial‐Holocene in a loess‐sand sequence from the Zhenbeitai section on the margin of Mu Us sandy land.…”

Measuring, processing, and analyzing hysteresis data

“…The shape factor (Fabian,555 2003) of the loop is 1.47. This is indicative of extremely wasp-waited behavior and the presence of 556 a high coercivity component, which is not seen in isothermal remanent magnetization acquisition 557 data and does not fit with the geological context of the specimen (Liu et al, 2015;Liu et al, 2016). 558…”

Measuring, Processing, and Analyzing Hysteresis Data

“…The shape factor (Fabian, ) of the loop is 1.47. This is indicative of extremely wasp‐waited behavior and the presence of a high‐coercivity component, which is not seen in isothermal remanent magnetization acquisition data and does not fit with the geological context of the specimen (Liu et al, , ). An upper branch correction fails to reduce the loop closure error and symmetric averaging exaggerates the high‐coercivity lobes yielding a loop shape factor of 1.67.…”