Grain-size and magnetic properties of surface sediments from Huguangyan Maar Lake: an integrated assessment of controlling factors and implications for Recent Asian monsoon evolution

Huguangyan Maar Lake (HML) has long been recognized as a critical repository for reconstructing paleoenvironmental changes in southern China. However, interpretations regarding the dynamics of the Asian monsoon system derived from this site have been diverse and, at times, contradictory. To better understand the sediment source-to-sink processes and associated magnetic characteristics, this study investigates grain-size and rock-magnetic properties based on 56 lake-surface sediments from various water depths, as well as 23 topsoil and 4 volcanic rock samples from the HML catchment. Our findings reveal that the lake sediments are sourced predominantly from the surrounding catchment and transported into the lake via surface runoff. The lake sediment consists mainly of silt and sand, with its distribution decreasing toward the lake center and being strongly influenced by water depth. However, the relationship between grain size and water depth is complex, with a threshold depth of about five meters marking the effective limit of wave-induced sediment reworking. Lake sediment magnetic minerals consist mainly of stable single-domain and superparamagnetic magnetite, like those in local topsoil and volcanic rocks, but different from winter monsoon-transported eolian dust (Chinese loess). The concentration of magnetic minerals is largely source-dependent, with higher values observed near magnetite-rich coastal zones. Additionally, water depth exerts a notable influence on it, likely due to greater transport distance from source areas and dissolution under anoxic conditions. The magnetic record in HML sediments likely reflects intensity variations in the Asian summer monsoon, which controls weathered material and organic-matter supply, as well as water depth.