Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake, Shanxi, North China

Abstract

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the  and S 300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910-1220), which is supported by pollen evidence. Furthermore, this 3-6-year resolution environmental magnetic record indicates a dry event around AD 980-1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.Gonghai Lake, lacustrine sediments, magnetic parameter, Medieval Warm Period, humid climate

Weakening of the East Asian summer monsoon at 1000–1100 A.D. within the Medieval Climate Anomaly: Possible linkage to changes in the Indian Ocean‐western Pacific

“…Similarly, the variation of precipitation reconstructed from historical documents from the Central Plains of China [ Shi , ] indicates a drought episode at 1010–1100 A.D., which implies a fall in summer monsoon rainfall at this time (Figure j). In the sediments of Gonghai Lake, decreased values of magnetic susceptibility and S ratio, mainly controlled by the degree of pedogenesis in the lake drainage basin, also suggest a fall in summer monsoon rainfall at 990–1120 A.D. against a background of an overall strong summer monsoon (Figures g and h) [ Liu et al ., ]. In addition, a decadal‐resolution precipitation index record for north central China, which was synthesized from both documentary and speleothem data from different regions close to the present East Asian summer monsoon limit, indicates a significant decrease in summer monsoon rainfall during 1000–1100 A.D. relative to the overall strong monsoon rainfall during the MCA [ Tan et al ., ] (Figure a).…”

“…In addition, results from a full‐physics coupled climate model demonstrate that a slight warming of the tropical Indian and western Pacific Oceans can induce a broad range of the medieval (900–1350 A.D.) circulation and climate changes indicated by proxy data [ Yang et al ., ; Graham et al ., ]. To investigate if this forcing factor might have influenced the climatic perturbations recorded in this study, we compared Indian Ocean‐western Pacific SST records [ Stott et al ., ; Oppo et al ., ; Dang et al ., ] (Figures 4c–4e) with East Asian summer monsoon records reconstructed from Gonghai Lake [ Liu et al ., ] (Figure b) and with the oxygen isotope record of speleothems from Wangxiang Cave [ Zhang et al ., ] (Figure a). Both sites are sensitive to EASM changes because of their location on the modern EASM margin (Figure ).…”

“…At Gonghai Lake on the Chinese Loess Plateau, the dominant magnetic minerals in the sediments are magnetite mainly originating from pedogenic processes in the lake drainage basin. Post‐depositional effects on the detrital magnetic minerals are minimal, and thus, the high magnetic susceptibility and “ S ratio” values of the sediments, reflecting increases in the content and proportion of ferrimagnetic minerals, respectively, reflect strong pedogenesis in the lake catchment, which in turn is largely a function of the amount of precipitation delivered by the East Asian summer monsoon [ Liu et al ., ]. At Huguangyan maar Lake, South China, the concentration of sedimentary carbonate has been used as a proxy for precipitation, with higher carbonate concentration representing a weaker summer monsoon and dryer conditions [ Chu et al ., ].…”

“…However, previous reviews of monsoon variability have tended to focus on determining how and why the Asian monsoon varies on either interannual or multicentury timescales [e.g., Liu et al ., ; Tan et al ., ; Zhou et al ., ]. Previous results have shown that summer precipitation increased significantly over North China during the MCA, indicating a generally strong EASM at that time [ Zhang et al ., ; Yang and Tan , ; Liu et al ., , ]. However, there is still a dearth of studies which address the issue of whether or not significant decadal‐centennial‐scale precipitation variability occurred during the MCA, and in particular whether there is evidence for a centennial‐scale weakening in the EASM over East Asia.…”

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

“…Subsequently, Guo et al (1996) further documented this climate teleconnection through analyzing chemical weathering indices of Chinese loess and extended this behavior into the penultimate glaciation. Recently, several highresolution enviromagnetic records on lake sediments in the semi-arid East Asia depicted climate fluctuations during the last deglaciation and Holocene (Chen et al, 2013;Liu et al, 2011Liu et al, , 2015Tang et al, 2015). Given their locations at the East Asian summer monsoon limit, these lakes are highly sensitive to climate changes.…”