Paleoenvironmental Evolution of Small Tropical Estuary with Sea Level Rising in the Holocene, Chanthaburi, Thailand

Sea level changes are closely linked to the global climate system and play a critical role in shaping coastal and estuarine environments. The Gulf of Thailand (GOT) is a climatically sensitive, low-latitude region with limited high-resolution Holocene records, making it an ideal location to investigate climate-driven sea level and estuarine environmental evolution. This study investigates the paleoenvironmental evolution of a small tropical estuary along the Chanthaburi coast, Gulf of Thailand. Six sediment cores collected perpendicular to the coastline were analyzed using sedimentological, geochemical, mineralogical, micropaleontological, and chronological methods. The results reveal four distinct stages of relative sea level (RSL) evolution: from 8.3 to 7.2 cal ka BP, a low sea level period was associated with a flat landform and high fluvial input; Between 7.2 and 5.5 cal ka BP, due to the warm climate triggered a rapid RSL rise, leading to the formation of sandbars and enclosed lagoons; From 5.5 to 1 cal ka BP, a decline in the RSL under colder, drier climate conditions resulted in lagoon contraction and estuarine morphological changes; Since 1 cal ka BP, the RSL has gradually risen to its present level. This study demonstrates that in tectonically stable coastal settings, closure depth combined with Sr/Ba ratios serves as an effective proxy for paleo-sea level reconstruction. Overall, this study demonstrates the impact of climate-driven paleo-sea level changes on the evolution of small tropical estuaries, offering crucial insights into past environmental changes and providing a valuable reference for future coastal and estuarine evolution reconstructions in tropical regions.