Driving mechanisms of monthly ocean front variations in a typical mariculture bay: insight from quantitative analysis of dual water isotopes.

The ocean front in the estuary plays a key role in regulating the transport of terrestrial pollutants into the ocean. It also significantly impacts the eco-environment of coastal and estuary waters. This study conducted monthly investigations of hydrology and dual water isotopes in Zhanjiang Bay spanning from January to December 2019, quantifying the contributions of various water masses in the region and exploring the mechanisms behind changes in frontal intensity. The results showed that the salinity front began to strengthen in the early rainy season and peaked in August, while its intensity was generally weaker in the dry season. This seasonal variation is attributed to the increased contribution of riverine freshwater input during the rainy season, rising from less than 5 % in the dry season to approximately 15 % in the rainy season. Importantly, the strengthening of the ocean front may lead to the accumulation of land-based pollutants, such as nutrients, within the bay, thereby deteriorating water quality.