Paleosecular Variations During the Last Glacial Period From Tengchong Qinghai Lake, Yunnan Province, China

Abstract

In recent years, the evolution of the magnetic flux lobes in terms of location and intensity has been attributed to paleosecular variation of the geomagnetic field, reflecting outer‐core fluid convection close to the core‐mantle boundary. However, most results were based on observational data for the past 400 years supplemented by sparse archeomagnetic studies with data for approximately 3 kyr. In this paper, we construct a relative paleointensity (RPI) record and an inclination record spanning the past ∼90 kyr based on two cores from Tengchong Qinghai Lake (Yunnan Province, China), a closed crater lake that formed in the late Pleistocene. The evolution of flux lobes and the non‐dipole field can be assessed on a much longer time scale. Although the concentration and domain state of magnetic grains in the cores vary significantly, the RPI record is still representative of geomagnetic field features in the region of Yunnan Province, China. The contrasting trends in RPI with the records for eastern China since the late Holocene indicate the southeastward migration of the Siberian flux lobe. During the last glacial period, the RPI records of Tengchong Qinghai Lake and the North Atlantic Ocean show opposite trends, denoting the diverse and strong influence of the two flux lobe systems. The strong reverse flux lobe in the North Atlantic Ocean strengthened the non‐dipole field, while the weak normal flux lobe in Tengchong weakened the non‐dipole field.

Persistent Influence of Non‐Dipole Geomagnetic Field on East Asia Over the Past 4,000 Years

“…However, the Bohai Sea RPI stack differs significantly from the low-latitude results of Tengchong Qinghai Lake (98.57°E, 25.13°N, Figure 8c; X. Yang et al, 2022) and core OR1-715-21 (121.29°E, 22.7°N, Figure 8d; Huang et al, 2014), particularly during the intervals of ∼700 to 300 BCE and ∼100 to 500 CE, where the low-latitude (Figures 8c and 8d) records are opposite to the mid-latitude records (Figures 8a and 8b).…”

“…Over the past 7,000 years, there have been two or three intense magnetic flux lobes beneath North America, Europe, and Siberia in the Northern Hemisphere (Bloxham et al., 1989; Korte & Holme, 2010). The expansion and intensification of these magnetic flux lobes would influence the behavior of regional magnetic fields (Gallet et al., 2009; X. Yang et al., 2022). Variations in the Bohai Sea RPI may reflect the varying activity of the Siberian surface lobe, which originates from the Siberian flux lobe located on the CMB (Bloxham & Gubbins, 1985; Livermore et al., 2020).…”

“…New publication of archeointensity data in China(Cai et al, 2014(Cai et al, , 2017(Cai et al, , 2020, Japan(Yu, 2012), and Korea(Hong et al, 2013) are respectively indicated by the cyan stars, red circles, and black squares. (c) RPI curve of Tengchong Qinghai Lake (without core top samples, 25.13°N;Yang et al, 2022). (d) Virtual axial dipole moment variations of core OR1-715-21 (22.7°N;Huang et al, 2014).…”

Decoupled Indian Summer Monsoon Intensity and Effective Moisture Since the Last Glaciation in Southwest China

“…(2019) and X. Zang et al. (2022). A total of 679 and 1,068 discrete sediment samples were taken at ∼2.5 and ∼2 cm stratigraphic intervals from the TCQH4 and TCQH17A cores, respectively.…”

“…Here we characterized EM variations over the LGP in Southwest China based on environmental magnetism proxies in two long sediment cores (TCQH4 and TCQH17A) from TCQH Lake (Figure S1c in Supporting Information ). Accelerator mass spectrometry (AMS) 14 C ages, combined with relative paleointensity (RPI) data indicated that the two cores contained material deposited continuously since approximately 90 kyr BP (before present, where present = 1950 A.D.; Z. Yang et al., 2022). Combined with the ISM intensity, which was previously reconstructed by the leaf wax hydrogen isotope (δD wax ) record in the TCQH17A core (Zhao et al., 2021), we provide new insights into the terrestrial EM pattern in Southwest China since the LGP.…”