Characterizing Holocene environmental transitions using magnetic properties of sediments from the continental shelf of the northern South China Sea

Abstract

Understanding past climate changes during the Holocene epoch, as recorded in continental shelf sediments, is crucial for reconstructing past climate patterns, sea-level fluctuations, and the influence of human activities. To explore Holocene environmental transitions in the northern South China Sea, we analyzed the sedimentary magnetic properties of the continental shelf east of Hainan Island. Our measurements revealed two significant transitions in magnetic mineral composition and grain size: around 7.6 ka and near 2 ka. The early transition around 7.6 ka is attributed to eustatic sea-level changes that altered coastal erosion, fluvial input, and sediment transportation due to the region's shallow shelf dynamics. Conversely, the recent transition near 2 ka is primarily due to the strengthened Atlantic Meridional Overturning Circulation, which influenced the East Asian monsoon regime. This later period coincides with intensified anthropogenic agricultural activities over the last ca. 2 kyr, highlighting interactions between natural and early human intervention. Between these transitions, from ca. 7.6 ka to ca. 2 ka, the magnetic proxy data suggest relatively stable environmental conditions resembling an event similar to a Holocene climatic optimum. This interval is characterized by consistent sedimentary magnetic properties, indicating a period of climatic stability under the monsoonal climate regime.