The Changjiang Diluted Water (CDW) plays a crucial role in shaping the hydrography and ecosystem dynamics of the East China Sea (ECS), particularly during summer when freshwater discharge enhances stratification and modulates biogeochemical processes. Despite its importance, the detailed progression of CDW and its short‐term impacts remain poorly understood due to the limited availability of high‐resolution observations. Using high‐resolution in situ observations from the Ieodo Ocean Research Station in summer 2020, we examined the sequential evolution of CDW and its effects on the upper‐ocean structure and phytoplankton blooms. CDW evolution was categorized into six distinct phases, characterized by abrupt shifts in salinity and stratification, driven by monsoonal winds, tides, and typhoon‐induced mixing. CDW intrusion formed a persistent barrier layer that suppressed vertical mixing and trapped surface heat, leading to increased sea surface temperatures. Nutrient influx from CDW, enriched in nitrate and phosphate, promoted the proliferation of diatoms relative to picoplankton and dinoflagellates, although all groups increased during the CDW‐influenced period. Internal wave‐induced mixing facilitated nutrient replenishment from deeper layers, partially alleviating phosphate deficiency inherent in CDW and enhancing phytoplankton productivity. Typhoon Bavi disrupted stratification through strong vertical mixing, resulting in a high‐salinity state that differed from preintrusion hydrography. This study provides a time‐resolved view of CDW‐driven variability and demonstrates how episodic freshwater inputs, coupled with physical forcing, regulate stratification, nutrient supply, and ecosystem response in the ECS.

This study investigates the generation and propagation of nonlinear internal waves (NLIWs) in the northeastern East China Sea (ECS), focusing on the impact of time‐varying background stratification. Using satellite imagery and tide‐generating body force, 327 groups of NLIWs were identified from 93 MODIS images collected between 2015 and 2019 and classified into three distinct types based on their propagation directions—Type‐A (∼42%), Type‐B (∼38%), and Type‐C (∼20%)—each originating from different generation sites. Type‐B NLIWs were found to originate from a newly identified site near southwestern Fukue Island reported here for the first time, whereas Type‐A and Type‐C originated from the northern Okinawa Trough and southwestern Jeju Island, respectively. Seasonal variations in NLIW propagation speed using historical CTD data revealed an increase in the speed from winter to spring and fall, peaking in summer due to strong stratification. Although spatial distribution varied by season, propagation was generally faster in the eastern region than in the western region attributed to deeper thermoclines and higher density gradients. During field observation in May 2015, the observed NLIWs had an amplitude of 5–6 m, a characteristic width of 380–450 m, southwestward propagating directions, and a speed of ∼0.54 m s⁻¹. An empirical model, used to track and predict these waves, confirmed their generation locations from southwestern Fukue Island (Type‐B) and indicated fast arrival speeds, influenced by time‐varying stratification conditions during the stratification period. These findings highlight the impacts of varying background conditions on NLIW propagation and would facilitate their prediction.

This study investigates the variability of coastal currents off the east coast of Korea, specifically in the Wangdolcho area of the East/Japan Sea, from June 2021 to October 2022. The observations revealed significant fluctuations in depth-averaged current velocity, with a peak of 0.81 m/s in August 2021 and a minimum of −0.05 m/s in August 2022. These year-to-year variations highlight the complex dynamics of coastal currents influenced by regional wind patterns and mesoscale eddies. In the summer of 2021, the development of offshore eddies, coupled with variable alongshore wind stress, led to increased current velocities and alternating upwelling and downwelling conditions, resulting in abrupt changes in current intensity. Conversely, in the summer of 2022, the negative vorticity in the Korea Strait and negative wind stress curl along the coast likely caused the East Korean Warm Current to shift further offshore, resulting in a weakened southward flow along the coast. This study emphasizes the need for long-term monitoring to better understand the coastal current dynamics and their environmental impacts. The anticipated completion of the Wangdolcho Ocean Research Station is expected to greatly improve monitoring capabilities, providing continuous and comprehensive data that will enhance our understanding of coastal currents and their broader impacts on the marine environment.

The Seychelles-Chagos Thermocline Ridge (SCTR) in the western tropical Indian Ocean is known as a region of off-equatorial upwelling contrasting to equatorial upwelling in the Pacific and Atlantic where the most wide open-ocean upwelling occurs corresponding to ascending branch of one of the meridional overturning cells in the Indian Ocean, yet detailed stratification, upwelling intensity, and dynamics of SCTR upwelling variability are still poorly understood. Here, we present observational results on the SCTR upwelling based on ship-based data collected during April-May 2019 as a part of the Korea-US inDian Ocean Scientific Research Program (KUDOS). The upwelling structure is confirmed from 20 ℃ and 10 ℃ isotherms (D20 and D10) shoaling up in the center of SCTR, from 200 m to 100 m (D20) and from 600 m to 400 m (D10), respectively. Horizonal divergence at the upper 250 m within an 1° by 1° area in the SCTR center (8 °S, 61 °E) estimated from currents measurements along the boundaries (1.0 x 10-3 Sv) supports a mean upwelling intensity of 7.0 x 10-3 m day-1 (1.0 x 10-3 Sv divided by the area). The upwelling intensity generally decreases with depth but shows multiple peaks within the upper water column, yielding the maximum peak (5.0 x 10-2 m day-1) at 60 m and the minimum peak (1.4 x 10-2 m day-1) at 230 m, with negative peaks (downwelling) at depths around 100 and 210 m. Our results on the observed structure and intensity of SCTR upwelling are discussed in comparison to time-varying local wind stress curl-driven Ekman pumping, D20-based Seychelles Upwelling Index (SUI), and Indian Dipole Mode Index (DMI). Detailed observations on the structure and intensity of SCTR upwelling presented here have important implications on time-varying SCTR upwelling (e.g., weakened upwelling peaked in fall 2019) and climate via meridional overturning circulation in the upper Indian Ocean.