Coastal upwelling usually brings cold and nutrient-rich water up to the surface, changes the nutrient structures and induces high primary production. The Zhejiang Coastal Upwelling (ZCU) occurs in the coast of the East China Sea in summer when the southerly monsoon prevails. The satellite-derived sea surface temperature and the sea surface concentration of chlorophyll in the past ten years indicated obvious interannual variations of ZCU. In this study, the year of 2013 and 2012 were chosen to represent the strong and weak year of the intensity of ZCU, respectively. A 3-D physical and biogeochemical coupled model was used to simulate the vertical velocities, nutrient concentrations and phytoplankton biomasses in the upwelling region. After validating the model results by observations, the results of the two years were compared. In the strong year of ZCU (2013), average upward vertical velocity was 7 times larger than that in 2012. Nutrients were transported across 60m isobath into ZCU region in 2013 while out of the region in 2012. The surface diatom biomass in 2013 was about twice than that in 2012. Based on the simulation of the weak year, a group of numerical experiments were carried out by changing four forcings to those in 2013, respectively. The results showed that the two main factors were the wind field and the open boundary conditions. In the strong year, upwelling-favorable winds pumped more nutrients up to the surface and induced high phytoplankton biomasses. Different southern open boundary conditions represented the intrusion of the Kuroshio. In 2012, stronger intrusion of Kuroshio increased the nutrient concentrations at the bottom in the offshore regions, but weaker upwelling-favorable wind did not pump up the rich bottom nutrients to the euphotic layer and led to a low primary production in the ZCU region.

Ports located in estuaries are always faced with problems of the sediment accumulation in the port from river. The entrance to the North Port, located in Incheon, Korea, is an area where sediment deposits more severely than other ports nearby. Thus, dredging is conducted periodically to maintain the navigation channel. To find out the cause of the sedimentation, the Community Sediment-Transport Modelling System (CSTMS) coupled with the unstructured-grid Finite Volume Community Ocean Model (FVCOM) was applied to the North Port. The port is developed nearly perpendicular to the main channel, where sea water by tides with the range over 9 m meets fresh water discharges from the north. To analyze effects of the mixture of seawater and fresh water in the port on the sedimentation, we set x-z cross section from the main channel to the innermost North Port and analyzed tidally averaged salinity, current, and suspended sediment (SS) fields. During flood tide, fresh water flowing into the port at the surface was trapped, so the averaged salinity in the port was always lower than that that in the main channel. Once, the saltier water intruded into the port, then formed the salt stratification like salt wedge. By this stratification, the averaged currents were strengthened in the direction of inflow near the bottom and outflow near the surface. A large amount of sediment suspended by strong currents around the main channel flowed into the port along the seawater intrusion and was deposited in the port. In case of a simply straight channel with river discharge, it is general that the bottom residual currents flow upstream. However, in the North Port without direct river discharge, averaged salinity was lower than that in the main channel with direct river discharge. This made extra density-driven currents near the bottom resulting in intensive sedimentation.

The topography of the seafloor is essential to determine physical phenomena such as ocean currents, favorable habitats for marine organisms, optimal vessel navigation, exploration of undersea resources, etc. Prevailing currents and waves, as well as associated shear stresses acting on the ocean floor, are responsible for formation of typical topographic features including sea caldrons and sandbanks through erosion of bedrocks and sediments and their deposition processes. In the Seto Inland Sea (SIS), the most extensive semi-enclosed estuary in Japan, tidal currents affect pronouncedly the formation of seafloor topographic features, yet having not been fully studied in particular from a hydrodynamic viewpoint. This study aims at understanding bathymetric formation under predominance of tidal currents in the SIS. A 3-D high-resolution SIS circulation model based on the JCOPE2-ROMS system in a double nested configuration were utilized to examine detailed hydrodynamic processes for the topography formations. A high correlation between the bottom shear stress and the scour depth of the erosive areas is observed to demonstrate that local tidal forcing has continuously been exerted on the seafloor to be eroded. A diagnostic sediment budget analysis was then conducted for sediments typical in the SIS, i.e., gravel, sand and clay, using the modeled flow field. Horizontal divergence of the residual flows indicates consistency between divergence (convergence) and erosion (deposition); the divergent outflow occurs on the eroded terrains, while the convergent inflow is prevailed on the deposited terrains frequently appeared in the vicinity of the eroded terrains. The sediment budget model also exhibits that sediments are generally transported from deep to shallow areas in the eroded terrains to form the deposited terrains fringing the eroded terrains, whereas sedimentation tendency differs largely from location to location.

In recent years, coral bleaching has occurred extensively over the world ocean due primarily to high water temperatures. Mesophotic corals that inhabit in intermediate depth at about 30-150m depth are expected to survive during bleaching events and to reseed shallow water corals afterward. In particular, in Okinawa, Japan, mesophotic coral ecosystems (MCEs) have been reported to serve as a refuge to preserve genotypic diversity of bleaching-sensitive corals (Sinniger et al,. 2017). Connectivity of larval populations between different habitats has been a key element that determines the area to be conserved for desirable coral ecosystems. Coral larvae generally behave passively to the surrounding currents and are transported by the advective and dispersive effects of ambient ocean currents. Thus, numerical ocean circulation models enable us to quantity connectivity with more detailed spaciotemporal network structures than genetic approaches. This study aims at quantifying short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. Because both short-distance and vertical larval transports are influenced pronouncedly by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we develop a quadruple nested high-resolution synoptic ocean modeling at a lateral spatial resolution of 50m based on the JCOPE2-ROMS downscaling system (Kamidaira et al., 2017), coupled with an offline 3-D Lagrangian particle-tracking mode that mimics coral larval transport. After validations of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments was conducted for identifying vertical coral migration and 3-D connectivity required for preservation of MCEs.

Berau estuary is a complex coastal area located in Berau regency, East Kalimantan, Indonesia. The river mouth is directed to Makassar Strait, where Indonesian throughflow passes. The eddying current generated by this throughflow is one of the important factors affecting the river plume direction in addition to the wind force. The river discharge carries turbid water mass, which is the result of palm-oil farming and mining activities. The land-use conversion along the river increases the sediment input to the river. In the offshore side, there are some islands constituting the barrier-reef system where seagrass and coral reef can be found. The biodiversity and health of the corals are high despite its proximity to Berau river mouth which carries a lot of nutrients and sediments. A comprehensive study is needed to understand this complex condition of the coastal area under the possible influences of the regional-scale circulation. This study describes the Berau River plume conditions in two different seasons based on the observation data and a multi-nested ocean circulation model using Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system (Warner et al. 2010) coupled with Soil and Water Assessment Tool Plus (SWAT+) to reproduce the river discharge patterns. To assess the river plume patterns, several loggers and sensors were deployed to measure the water quality and physical parameters in certain locations to capture the possible spreading. The turbidity, temperature, and salinity data suggest that different spreading patterns exist between the seasons. 

Understanding the estuarine biogeochemical cycling of many TEIs has implications for their oceanic budgets crucial for interpreting their marine sedimentary records. Although barium (Ba) is widely used as a tracer of many contemporary as well as past oceanic processes, it's seasonal cycling in Indian estuaries is still debated. In this study, dissolved Ba concentrations have been measured in the surface and subsurface estuarine waters of the two major west-flowing Indian rivers (Narmada and Tapi) collected along salinity gradients during 4 different seasons of 2016–2017. Dissolved Ba concentrations in the riverine endmembers (salinity <0.3) reflect different lithologies in the Narmada and the Tapi river basins. The low-salinity Ba removal from the water column of both these estuaries along with its mid-to-high salinity release is evident during all seasons indicating the major role of sediment–water interactions. The relatively higher Ba abundances in the subsurface waters indicate its benthic flux most probably by sediment diagenesis rather than in situ particle release in the water column. The most elevated Ba concentrations in these monsoonal estuaries of western India are found during the post-monsoon as compared to those reported in the Ganga estuary (Hooghly) during the pre-monsoon (Samanta and Dalai, 2016). The high freshwater/sediment fluxes of the Ganga River could be a reason for this time delay in the Ba release. Thus, benthic Ba release seems to control the Ba abundances in Indian estuaries.