As potential mineral resources, rare earth elements (REY) and yttrium enriched sediments in the deep sea have attracted a lot of attention in recent years. It has been shown by studies that the enrichment process of REY is most likely to occur at the sediment-water interface (SWI), however studies on the early diagenetic processes in REY-enriched sediments are in general lacking. In this paper, we collected two short sediment cores in REY-enriched sediments in the Southeast Pacific Ocean, then we had conducted an in-depth analysis on the early diagenesis process of REY at SWI and its influence on the enrichment mechanism of REY in deep-sea sediment. The low Fe, Mn concentration and high Mo, U and V concentration in pore-water indicated that the sediment cores were in oxic environment. Compared to the REY in overlying water column, the dissolved REY in pore-water characterized by a middle rare earth elements (MREE). In sediment, phosphate phase is the main phase of REY, while the distribution pattern of REY in pore-water may be controlled by the phosphate content in sediments. Our results show that during the early diagenetic processes, the REY initially combined with Fe/Mn phase and other phases re-released into the pore-water, which is subsequently adsorbed by and eventually buried with the phosphate phase. Therefore, the early diagenetic process is an important mechanism of REY enrichment in deep sea sediments.

Based on the satellite altimeter observation data from 1993 to 2022, this paper analyzes the temporal and spatial characteristics of the multi frequency seasonal variation signal of sea surface height in the Sulawesi sea, and gives the dynamic interpretation by using Rossby standard mode theory. The spectral analysis shows that there is a strong intra-seasonal signal of 30–90 days in the sea surface height variation of Sulawesi sea, and its average power spectral density is 13 times of the average power spectral density of the signal in half a year. These seasonal signals have discrete and discontinuous spectral peak periods, and the peaks of 54.0 d and 64.4 d are the largest, which are 28 times and 23 times of the signal of 30–90 days, respectively. The theoretical analysis shows that the existence of Rossby standard modes in the nearly closed Sulawesi deep-sea basin. The seasonal variation observed by satellite altimeter is consistent with the two-dimensional spatial structure evolution, period and westward propagation velocity of Rossby standard mode results, the superposition of Rossby standard mode solutions presents a variance distribution similar to the sea surface height variation field. This shows that the inherent oscillation of Sulawesi Sea basin is one of the important mechanisms that contribute to its intra-seasonal variation.

In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K₁ tidal amplitude increased significantly, while the M₂ tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.

Study on the coral reef canopy hydrodynamics not only provides guidance for the health of coral reef ecosystem and the ecological restoration project, but also supports the decision-making process for the reef coast hazard prevention and mitigation under extreme wave events such as the typhoons. Meanwhile, it also has significant value for predicting the sediment transport over the reef and the reef coast evolution. This paper reviews the state-of-the-art research on reef canopy hydrodynamics, and systematically summarize the research progress from three aspects: the flows inside and outside of reef canopy, the characteristics of canopy resistance as well as the simulation of canopy resistance. This paper finally proposes the further research directions as follows: future study can focus on the hydrodynamics under more severe wave condition or under combined action of wave and current. It should also fully consider the anisotropy of canopy skeleton. Moreover, it can solve the Navier-Stokes equations directly to reproduce the finer flow field at the canopy scale.

Beach is a common and vulnerable coastal ecosystem with huge ecological service functions. Due to the multiple impacts of climate change and human activities, beach ecosystem has been seriously damaged. Beach nourishment is an effective approach to prevent coastal erosion and improve the beach environment by using sand replenishment to restore beach morphology. Previous nourishments have often neglected the impacts on beach ecosystem. Many studies show that beach nourishment have multifaceted, multi-scale and complex impacts on beach ecosystem. Based on reviewing previous researches, the compositions, characteristics and functions of beach ecosystem are summarized. The basic characteristics of beach ecological damage, the impact process and mechanism of beach nourishment on beach ecosystem at various scales are analyzed. Then, some adaptive measures for beach nourishment are suggested from the perspective of reducing negative ecological impacts, which would support coastal management and sustainable utilization of beach.

Manganese (Mn) is an essential trace element for the marine ecosystem. As the transitional zone between rivers and oceans, estuaries have a significant effect on dissolved Mn and its terrigenous input. In this study, the distribution of dissolved Mn, investigated in the surface water of Changjiang River Estuary and its adjacent area during September 2019 (autumn), March 2021 (spring) and July 2021 (summer), was analyzed by automatic solid phase extraction and inductively coupled plasma mass spectrometry. The results indicated that the average concentration and estuarine behaviors of dissolved Mn showed seasonal variations between the three cruises: the maximum average concentration occurred in summer and dissolved Mn was removed firstly and then added with the increase of salinity; the medium average concentration occurred in autumn and dissolved Mn was mainly removed with the increase of salinity; the minimum average concentration occurred in spring and dissloved Mn was mainly conservative with the increase of salinity. The results of significance test indicated that only in the season when the fresh water had high concentrations, dissloved Mn carried by the Changjiang River had significant influence on the distribution of dissolved Mn in the Changjiang River Estuary and its adjacent area; the distribution of dissolved Mn was co-dominated by a variety of biogeochemical processes in the season when the concentrations were low in the fresh water. The high suspended particulate matter concentrations were the important factor of the removal of dissolved Mn in the Changjiang Estuary’s water with medium-low salinity. And the addition mechanism of dissolved Mn in water with high salinity needs further vestigation.

Based on the comprehensive fishery survey in the Chongming Island adjacent waters in November 2020, January 2021, April 2021, and August 2021, we used an open-source program Rpath to build a mass balance model containing 22 functional groups for this area. The ecosystem structure and characteristics in this sea area were then studied. Results showed that the trophic level for these 18 functional groups ranged from 1 to 4.32, with the highest trophic level of bottom carnivorous fish. The ecological transfer efficiency of small benthic organisms is the lowest (0.01), suggesting a bottleneck in their energy transfer to higher trophic levels and indicated it was the bottleneck to limit the energy transfer in the benthic food chain. The analysis of the overall characteristics of the ecosystem shows that the total system throughput of the Chongming Island adjacent waters ecosystem was 2 909.42 t/(km²·a), which was lower than that of the nearby marine ecosystem. Phytoplankton contributes 60% of the energy to the total primary productivity of the ecosystem and was the main nutrient source of this ecosystem. The total primary production/total respiration is 1.99 and the system omnivorous index is 0.18. This indicate that the Chongming Island adjacent waters ecosystem has low maturity, simple trophic interaction, and low recovery ability after disturbance. Sensitivity analysis showed that functional group biomass was the main index that affected the accuracy of ecosystem model output. The results of this study can provide a reference for the evaluation of the effect of the Changjiang River fishing ban.

Based on the high-resolution oceanic numerical model product of MITgcm with a resolution of (1/48)°, the geostrophic balanced motion and unbalanced wave motion are decomposed via the frequency-wavenumber spectrum analysis method to analyze the distribution of submesoscale characteristics and diagnose the main factors affecting their seasonal variations in the Agulhas current system. The results show that the submesoscale processes in the Agulhas current system have a significant seasonal distribution with strong features in winter but weak features in summer. The mixed layer baroclinic instability is the main reason affecting the submesoscale seasonal differences in the area. In addition, the geostrophic balanced motions are predominant in the submesoscale process in the regions with stronger eddy kinetic energy (EKE) and have no obvious seasonality. For the regions with weaker EKE, the balanced and unbalanced geostrophic motions show significant seasonality, where the local mixing layer shallowness is responsible for the increase of the unbalanced kinetic energy in summer. Our analysis helps to further clarify the characteristics of submesoscale seasonal variation and its primary factors in the Agulhas current system. The effective separation of geostrophic balanced and unbalanced motion enhances our understanding of energy transformation between multiscale processes in the ocean.

Based on the data from 56 acoustic survey sections in the southwestern Indian Ocean from 2011 to 2020, a total of 201 diel vertical migration were observed. The characteristics of diel vertical migration of the deep scattering layer and its spatiotemporal differences were analyzed. The research results show that the deep scattering layer in the southwestern India Ocean exhibits a stratification phenomenon, with the first scattering layer located in the shallow water layer below 200 m. The average depth of its nautical area scattering coefficient (NASC) peak is (58.66 ± 24.63) m, and there is a significant difference between summer and winter (p < 0.001); the second scattering layer is located in the water layer between 400 m and 700 m, with an average depth of (589.02 ± 66.33) m for its NASC peak. There is no significant difference between summer and winter (p = 0.51). The average time for the scattering layer to migrate upwards is 16:20, the average time for the end of migration is 18:31, and the average migration rate is (5.28 ± 1.53) cm/s; the average time for the scattering layer to start migrating downwards is 4:38, and the average time for the end of migration is 6:52. The average migration rate is (5.56 ± 2.13) cm/s. As latitude increases, the start time of downward migration become later and the migration rate slows down; as the longitude increases, the migration rate of the scattering layer also slows down, and there is a significant difference between different longitude sea areas (p < 0.001). Analysis suggests that studying the seasonal changes in the physical and chemical environment of the sea area, as well as the different life cycle stages of organisms in the scattering layer, are the main reasons for the spatiotemporal differences in the vertical structure and diurnal vertical migration characteristics of the scattering layer. They are of great significance in explaining the diurnal vertical migration behavior of tuna and indicating the distribution of tuna fishing grounds.

The Sardinops melanostictus and the Scomber japonicus are important economic species in the northwestn Pacific Ocean, and exploring the correlation between their habitat changes is conducive to the rational development and management of fishery resources. This study utilizes fishery data of Sardinops melanostictus and Scomber japonicus in the northwestern Pacific Ocean from June to November between 2017 and 2021. By incorporating three key environmental variables, namely sea surface temperature, sea surface height, and chlorophyll a mass concentration, habitat models with different weights are constructed. The models are then validated using fishery data from 2021. The optimal models are selected to predict the most suitable habitat distribution of Sardinops melanostictus and Scomber japonicus under different El Niño-Southern Oscillation (ENSO) events. The study analyzes the differences and synchronicity in the spatial and temporal distribution of the most suitable habitat between the two species under different ENSO events. The results indicate that the suitable habitat area of Sardinops melanostictus (above 15%) was higher than that of Scomber japonicus (less than 6%) under different ENSO events; however, the growth rate of the most suitable habitat area for Sardinops melanostictus under La Niña events is higher than that of El Niño events. The former has a growth rate of 0.197 and the latter has a growth rate of 0.123, on the contrary, the growth rate of Scomber japonicus under the La Niña event is lower than that of El Niño event, the former has a growth rate of 1.114 and the latter has a growth rate of 2.082; additionally, when the distribution locations of Sardinops melanostictus and Scomber japonicus are close to each other, it promotes favorable conditions for their habitats. On the other hand, when the distribution locations are far apart, it somewhat inhibits the increase in the suitable habitat area for Scomber japonicus. The co-variation of suitable habitat areas for Sardinops melanostictus and Scomber japonicus under different ENSO events may be related to their interspecies relationship (competition/predation-prey) and the distribution of ocean currents in the northwestern Pacific Ocean.