Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes ¹⁰Be in natural stratified archives. It provides scientific data for further study of solar activity change history, which is an important external forcing factor of earth's climate change.

However, there are few reports on the reconstruction of Holocene solar activity history recorded by 10Be in low-latitude regions.

A research team led by Prof. ZHOU Weijian from Institute of Earth Environment(IEE), Chinese Academy of Sciences reported a new high-resolution Holocene ¹⁰Be record from Huguangyan Maar Lake in subtropical-tropical South China, aimed to detect the atmospheric 10Be production signal in low-latitude regions.

After minimizing climatic effects by regression analyses between 10Be concentration and climatic proxies from the same archive, they successfully distinguished variations in geomagnetic field intensity and solar activity using 2000-yr low and high-pass filtering, respectively, of the residual ¹⁰Be record (a proxy of the atmospheric 10Be production rate).

The resulting ¹⁰Be-derived record of geomagnetic field intensity was generally comparable with geomagnetic models, and the solar-modulated ¹⁰Be signal showed significant correlations with solar activity proxies. The preservation of ¹⁰Be production signal in the sediments of this low-latitude maar lake highlighted the largely unexplored potential as well as limitations of ¹⁰Be as a tool to reconstruct variations in solar activity and geomagnetic field intensity.

The study, published in Geophysical Research Letters, was was jointly supported by Key Research Program of Frontier Sciences, CAS, Grant No. QYZDY-SSW-DQC010, the MOST special fund for State Key Laboratory of Loess and Quaternary Geology. X. Wang further acknowledges support from NSFC (grant 41672178) and China Geological Survey (DD20160306).

Fig.1 Time series of ¹⁰Be concentration and paleoenvironmental proxies from Huguangyan Maar Lake since 10 ka. (Image by Tang et al.)

 Fig.2 10Be production rate, comparisons of ¹⁰Be-based geomagnetic intensity and solar activity with geomagnetic dipole field model and recent solar activity reconstructions. (Image by Tang et al.)