Thermohaline Dynamics in the Northern Continental Slope of the South China Sea: A Case Study in the Qiongdongnan Slope

Understanding the marine hydro-thermohaline environment is essential for terrestrial meteorology and the coastal ecosystem. Here, we provide insight into the hydro-thermohaline environment at the Qiongdongnan continental slope of the northern South China Sea and the mechanism controlling it, with focus on its short-term characteristics. We employ a well-validated three-dimensional unstructured-grid-based Finite Volume Coastal Ocean Model (FVCOM) to analyze the spatial-temporal behavior of its hydro-thermohaline structures and to quantify the transport fluxes over a full tidal period. The analysis reveals a two-layer flow structure with directionally oppositely moving layers in the along-isobaths direction. Furthermore, transport patterns undergo periodic changes. During the spring tide, the downslope (along-isobaths) transport of water/heat/salt is approximately 119%/70%/120% higher (62%/62%/62% lower) than during the neap tide. From analyzing the different terms in the thermohaline balance equation, we find that the main dynamic factors controlling heat transport over a tidal period are the gravitational convention and the mean flow, while the salt transport is only dominated by the mean flow. The data of the short-term thermohaline evolution of the QDNS provided in this study may be of use for future studies of the northern SCS, including its marine ecology and marine fisheries.