After Bakun proposed his hypothesis in 1990 regarding upwelling under climate change, researchers conducted intensive studies to obtain the trends, current status, and future predictions of upwelling. Numerous studies have mainly focused on four major upwelling areas, which are part of the Eastern Boundary Upwelling System (EBUS). However, despite its importance, little attention has been given to the marginal seas upwelling areas such as the South China Sea (SCS), Arabian Sea, Baltic Sea, and other small-scale upwelling locations. Here, we combined several published studies to develop a new synthesis describing climate change impacts on these areas. There had been uncertainty regarding the intensification of upwelling, depending on the locations, data type, and method used. For the SCS, Vietnam and the northern SCS showed intensifying upwelling trends, while the Taiwan Strait showed a decreasing trend. Separate studies in eastern Hainan and the Arabian Sea (Somali and Oman) showed contrasting results, where both increasing and decreasing trends of upwelling had been recorded. Like the SCS, the Baltic Sea showed different results for different areas as they found negative trends along the Polish, Latvian and Estonian, and positive trends along the Swedish coast of the Baltic Sea and the Finnish coast of the Gulf of Finland. While small scales upwelling in La Guajira and southern Java showed increasing and decreasing trends, respectively. All of these limited studies suggest that researchers need to conduct a lot more studies, including the future projection of upwelling, by using climate models to develop a new understanding of how the upwelling in the SCS responds to climate change.

The short- to long-distance dispersal (SDD and LDD) of propagules is critical for the regeneration of mangrove forests. Mark–recapture experiments are considered to be a good tool for assessing such dispersal patterns. However, dense mangrove roots, exposed mudflats, shallow water, etc. often limit the number of recaptured propagules and their implication studies. Therefore, a combination of hydrodynamic and particle tracking models, together with a mark–recapture experiment, were applied to identify the dispersal behavior of Rhizophora mucronata Lamk. propagules in a coastal lagoon of Setiu Wetlands, Malaysia. The transport trajectories revealed that the dispersal of propagules is leptokurtic, with majority of them confined to very-short-distance dispersal (VSDD; 3–5 m) to SDD (1400 m). While higher obstacle density (e.g., mangrove roots) constrained the propagule dispersal, weaker tidal currents that coupled with less upstream discharge increased their retention time and settlement closer to the point of release. Under this scenario, the chances for propagules to exit from the lagoon mouth and their entry into the open waters for LDD are very limited. These results can explain the abundance of Rhizophora spp. in the northern sector of the Setiu Wetlands and be useful for species-level conservation/management.

The Eastern Indian Ocean (EIO) is one of the eastern boundary areas, which control currents circulation and atmospheric dynamics. This research mainly aimed to identify and analyze the water mass transformation in the EIO. The investigated physical properties of the ocean are the temperature, salinity, seasonal temperature–salinity, and water column stability. An extensive amount of in situ data measurements from 1950 to 2018 was downloaded from the global datasets inventory. The visualization and analysis of the data were defined in monthly spatial and vertical profiles. The result showed the mixed layer is shallower during the northwest monsoon relative to the southwest monsoon. The surface water in the EIO is documented to be warmer due to the interaction with the atmosphere. Furthermore, low-salinity surface water around the Java Seas area is caused by a mixing with fresh water from the eastern Indonesia rivers. The data also confirmed that, at latitude 16° S, the maximum salinity occurred at a depth between 150 and 350 m. There are ten types of water masses found in the EIO, which originate from several regions, including the Indonesia Seas, Pacific Ocean, Indian Ocean, and Antarctic. During the northwest and southeast monsoons, a stable layer is found at a depth of 40 to 150 m and 80 to 150 m, respectively. For further research, it is recommended to focus on the coastal region, particularly the Timor Sea and Northwestern Australia, to investigate the dynamics between the Indonesian Throughflow, Holloway Currents, and Leeuwin Currents. Additionally, deep water observations below 800 m are crucial for a comprehensive understanding of the oceanographic variability in the deep layers of the EIO.

Setiu Lagoon experienced shoreline alterations, leading to the opening of a new inlet and the closing of the old one. To evaluate the effects of these alterations on the tidal flow in this shallow and narrow lagoon, a numerical hydrodynamic model was developed. The model-predicted water level and current velocities were validated against field measurements, which yielded a high simulation skill. The transport of particles and residence time under different inlet configurations were also investigated through the implementation of numerical tracers released from R1, R2, and R3, which represent different pollution sources. The results indicated that the particle transport and residence time in Setiu Lagoon varied spatially and temporally depending on the release locations, proximity to the inlet, and tidal current strength. Comparing the scenarios, the flushing efficiency in Setiu Lagoon was improved with the presence of both inlets, resulting in a shorter residence time of less than 50 days. The findings of this research are vital for understanding the water current flow and residence time in this restricted lagoon, while evaluating the possible adverse effects on its water quality. Although this work is case-study based, the output is applicable to other lagoon systems with similar characteristics.