A three-dimensional non-hydrostatic model based on volumed-averaged, Reynolds-averaged Navier-Stokes (VARANS) equations in sigma coordinate, is applied to simulate the propagation process of irregular wave over a typical fringing coral reef profile, with emphasis on the changes of wave height and wave setup on the reef flat. Compared with the laboratory measured data of several groups of wave and water level parameters, the model is shown to be capable of simulating well the wave transformation over the reef profile with and without porous media. Across all cases, the porous cases decrease the wave height by 12% around the breaking point, and by 28% on the reef flat than the smooth cases. As for the mean water level, the results show that the maximum setdown decreases by 43% on average for the porous cases than the smooth cases, while the wave setup on the reef flat for corresponding porous and smooth simulations is found to agree with an average difference of only 6%. In addition, the variation of porosity in the range 0.47−0.87 auses little effect on the wave setup.

As an important part of monitoring oceanic phenomenon, it is essential to calibrate altimeter sea level height data. In 2020, the Haiyang-2C (HY-2C) satellite was sent to orbit as a follow-up mission of the HY-2B satellite. However, the quality of HY-2C sea level height is not fully known yet. In this paper, the quality and accuracy of HY-2C sensor geophysical data records (SGDR) of the latest version were assessed through the comparison with the HY-2B geophysical data records (GDR) and Jason-3 GDR measured at the same time. According to the results: self-crossover points analysis is carried out by star cross calibration of HY-2C satellite. The quality analysis results of sea level anomaly data of HY-2C SGDR are different. Through the comparison results, the optimal cubic spline interpolation method has the best quality analysis performance, with mean value is 0.03 cm and the standard deviation is 6.17 cm. The mean and standard deviation of sea level anomaly at the dual-crossing calibration of HY-2C and HY-2B satellites are −0.47 cm and 5.32 cm. The mean and standard deviation of sea level anomaly at the intersection of HY-2C and Jason-3 satellites are −0.3 cm and 5.32 cm. These results show that HY-2C has the same precision as HY-2B satellite and Jason-3 satellite. Data quality of HY-2C satellite is enough to meet the requirements of marine scientific research and application.

Characteristics of heavy metals in the Zhujiang River Estuary are mainly influenced by the interacting river-tide dynamics. Water and sediment samples were collected in the Zhujiang River Estuary and its adjacent zones in the summer of 2018. The present study aimed to investigate the estuarine behaviors (i.e., sedimentary, transportation, accumulation) of seven metals Hg, As, Zn, Cd, Pb, Cu, and Cr, which were co-influenced by the physicochemical properties in the estuary. The levels of heavy metals in sediments were higher than those dissolved in water. The heavy metals in sediments were more stable and the pollution was thus more serious. The results of Pearson correlation and principal component analysis showed that dissolved metals were more easily diluted and mixed, and the sediment metals were significantly influenced by the total organic carbon and redox. The metal partitioning between sediments and water was discussed as well in this study under the influence of estuarine dynamics, which indicated the phase exchange between multimedia in the estuary; Pb and Cr were more easily absorbed in the particulate particles, while Cd and Hg were intended to dissolve in water. The significant correlations between metals (e.g., Hg, Pb, and Zn) indicated the similar sources, and the principal component analysis was used to probe into the source contributions of heavy metals in sediments of the Zhujiang River Estuary, contributed mainly by industrial pollution, followed by agricultural pollution and atmospheric deposition. These findings will provide important information for the effective controls of heavy metal inputs and estuary management.

Fe is the most abundant variable-valence element in igneous rocks, and is also an important mineralizing element, mainly in the solid (mineral) and liquid (fluid) phases in Fe²⁺ or Fe³⁺ valence state, and participates in magmatic processes and various mineralization throughout. With the development of test analytical techniques (e.g. MC-ICPMS), the analysis of non-traditional stable isotope compositions such as Fe has become possible and has been successfully applied to the study of important geological processes such as magma source tracing, tracing of crystallization evolutionary processes and mineralization analysis in the last decade or so. Based on the analysis of the fractionation effect of Fe isotopes during magmatism, this paper summarized the latest results of Fe isotope composition studies in tracing the action of seafloor basaltic magmas (MORB, OIB, IAB and BABB, etc.) and discussed the main problems in the application of Fe isotope composition in tracing the action of seafloor magmas. The results of the comprehensive analysis show that the Fe isotope fractionation effect in igneous rocks is influenced not only by the processes of partial melting of magma source material, magma diffusion, fluid exsolution and crystallization differentiation, but also by the assimilation of surrounding rock material and seafloor alteration. Since Fe isotope analysis techniques (methods) have yet to be further refined, and the available data are limited and need to be screened for artifacts, caution is still needed when using Fe isotope compositions to analyze or recover magmatic sources and processes. It is urgent to establish a complete and reliable Fe isotope tracing system, which requires the recent work to select as many suitable samples as possible representing different tectonic environments and different rock types, to obtain (accumulate) more fine analytical data of original (unmodified or altered) samples, and to pay attention to the combination or mutual corroboration of multiple data in the process of using Fe isotope tracing for seafloor magmatism.

The Atlantic meridional overturning circulation (AMOC) is an important component of the climate system, of which change in the strength can affect meridional heat distribution between the northern and southern hemispheres. Proxy records show that changes in Atlantic Ocean circulation during the Late Pleistocene is associated with precessional cycle, but its physical mechanism remains unclear. Here we use a fully coupled climate model to investigate dynamics associated with AMOC changes in precessional band under glacial-interglacial climate conditions. Our results show that increase in boreal summer insolation can effectively weaken the AMOC during warm interglacial periods, while this weakening effect is reduced under glacial maximum. We further demonstrate that during the warm interglacial period increase in boreal summer insolation leads to sea surface warming and subpolar rainfall increase in North Atlantic, which jointly reduces sea surface density and hence the strength of deep water formation. During the glacial maximum period, climate responses to precessional change is of anti-phase impacts on the AMOC. At the low latitudes, a low pressure anomaly triggered by subtropical warming weakens atmospheric moisture export from the subtropical Atlantic to Pacific, increasing in net precipitation and hence freshening tropical sea surface in the North Atlantic. At the high latitudes, the warming-induced sea ice retreat promotes ocean heat loss via the enlarged ice-free area, and hence tends to strengthen the vertical mixing. The combined effects of low- and high-latitude responses finally leads to a trivial weakening of the AMOC. Overall, our results provide a systematic understanding of governing mechanism for precessionally-induced AMOC change under glacial-interglacial climatic backgrounds, shedding light on our interpretation of precessional periodicity in reconstructed ocean circulation changes during the Pleistocene.

This study utilizes a new functional analysis tool, multiscale window transform (MWT), to decompose the ocean circulation system in the Bay of Bengal (BOB) into three scale windows, namely, the background flow window (>96 days), the mesoscale window (24–96 days) and the high-frequency window (<24 days), and then uses the canonical energy transfer theory to investigate the intrinsic nonlinear multiscale interactions among these windows, on the basis of an eddy-resolving model simulation. It is found that multiscale interactions are strongest along the northwestern boundary and east of Sri Lanka. With intense barotropic and baroclinic instabilities, the canonical transfers of kinetic energy (KE) and available potential energy (APE) are mainly forward in these two regions. Mesoscale eddy kinetic energy (EKE) reservoir is mainly filled by the barotropic energy pathway with the kinetic energy of the background flow transferring to EKE, and secondarily from the baroclinic energy pathway with APE of the background flow transferring to the mesoscale APE and further converting to EKE. The gained EKE is found to further cascade to high-frequency motions, acting as an important dissipation mechanism of the mesoscale eddies in these regions. In contrast, the central BOB is mainly characterized by inverse KE cascades, where EKE and high-frequency kinetic energy (HKE) are gained via the baroclinic energy pathway, and then feed the background flow through inverse cascade processes. The northwest of Sumatra is also an area with strong mesoscale and high-frequency variability. Both barotropic and baroclinic energy pathways are the sources for EKE and HKE reservoirs in this region, with the baroclinic energy pathway playing the dominant role.

Previous studies have shown that the decadal modulation of the Kuroshio extension (KE) system is controlled by the Pacific decadal oscillation-associated forcing from downstream. However, recent observation reveals that this mechanism ceases to function after August 2017. Meanwhile, a large meander is under development in the KE’s upstream, i.e., south of Japan. Using the self-organizing map (SOM), we investigate the characteristic spatial and temporal patterns of the Kuroshio south of Japan and the KE and their causal relations, based on the 26-year (1993−2018) satellite altimetry data of sea level anomaly (SLA). The typical spatial patterns are well extracted, and their temporal trajectories indicate that the KE tends to be stable (unstable) when the upstream Kuroshio takes a large meander (an offshore nonlarge meander) path. To further unravel the underlying cause-and-effect relation between the two systems, we apply the information flow-based causality analysis to the typical regions of SLA and its associated temporal modes identified with the SOM. It is found that during the large meander event, the Kuroshio south of Japan and the KE are mutually causal, but have different hotspots. The information flows from the former to the latter mainly occur in the southeastern area off the Kii Peninsula and the time-mean ridge and trough of the KE jet, while those from the latter to the former are mainly concentrated in the time-mean ridge and trough of the KE jet, and the recirculation gyre of the Kuroshio. These results indicate that the Kuroshio large meander is an important factor influencing the KE’s stability, while the KE affects its upstream Kuroshio via modulating the associated recirculation gyres. In contrast, when the offshore nonlarge meander path is taken, a one-way causality is identified from the Kuroshio to the KE, mainly occurring over the Izu-Ogasawara Ridge and in the recirculation gyres. This may be attributed to the constantly downstream transport of negative SLAs into the KE’s recirculation gyre, which leads to an unstable KE.

During the past decades of years, the widespread restrictions and ban on the use of legacy persistent organic pollutants (POPs) such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) around the world have resulted in gradual decrease in their concentration in various environmental media. As an open sea area, the Northwest Pacific Ocean is far away from the continental area without obvious pollution point source, the ocean currents play an important role in the transportation and diffusion of POPs. In this study, the surface waters (2−5 m) and subsurface waters (150 m) in the Kuroshio area of the Northwest Pacific Ocean were collected and analyzed for dissolved OCPs and PCBs. The results showed that the concentrations of HCHs, DDTs, CHLs and PCBs in the surface waters ranged from 30.7 pg/L to 68.8 pg/L, 6.16 pg/L to 23.8 pg/L, 1.07 pg/L to 5.75 pg/L and 49.8 pg/L to 124 pg/L, respectively; the concentrations in the subsurface waters ranged from 27.3 pg/L to 68.4 pg/L, 7.06 pg/L to 14.1 pg/L, 0.518 pg/L to 10.1 pg/L and 34.1 pg/L to 68.4 pg/L, respectively. The concentration levels of OCPs in different water bodies were comparable, which may be related to the huge water body and internal homogeneity of the Kuroshio. The ratios of the various isomers of HCHs indicated that the sea area was dominated by lindane input, while the ratio of DDTs and CHLs showed that the DDTs and CHLs in the waters of the sea area were mainly derived from the residues of legacy. PCBs were dominated by tri-PCBs and tetra-PCBs, which consistented with the use of PCBs in East Asia. The large volume and uniform internal distribution of Kuroshio water mass have an important impact on the vertical distribution of pollutants, that is, the concentration and composition of OCPs in water at different depths are similar. At the same time, Kuroshio brings high temperature and high nutrient salt water masses, forming potential risks to the enrichment of pollutants in the marine organisms.

In order to understand the distribution characteristics, relationships and diffusion fluxes of nutrients and metal elements across the sediment-water interface, we investigated the vertical profiles of nutrients and metal elements through the diffusive gradient in thin-films (DGT) technology in Shenzhen Bay (SZB) and Maozhou River (MZR). The two-dimensional high-resolution available sulfur (DGT-labile S) distributions were also synchronously measured. The results showed that the mean concentrations of ${\rm{NH}}_4^+ $, P and S²⁻ and heavy metals of Cd, Co, Cu, Fe, Ni, Pb and Zn in porewater of MZR were significantly higher than those in the overlying water and the SZB, except for ${\rm{NO}}_3^- $ and Mo. The pollution degree of nutrients and metal elements in porewater of MZR was generally higher than that in SZB, but the pollutants of nutrients and metal elements in SZB were more than those in MZR. The spatial distribution of DGT-labile S in MZR indicated the distinguish bioturbation-induced tubes, which enhanced the spatial heterogeneity and led the increasing of solute concentrations with sediment depths. The diffusion fluxes of nutrients and metal elements ranged from −0.27 μg/(cm²·d) to 0.0065 μg/(cm²·d) in SZB, and from −0.061μg/(cm²·d) to 0.069 μg/(cm²·d) in MZR.

The outbreak of crown-of-thorns starfish has seriously threatened the ecological health of coral reefs, and the supplement of nutrients in seawater may be a key factor leading to the outbreak of starfish. Sandy sediments play a key role in regulating the nutrient concentration and structure in coral reefs. Therefore, crown-of-thorns starfish and sandy sediments were incubated using flow-through reactor, to analyze the effects of crown-of-thorns starfish excretion and dead body degradation on nutrient concentration and structure, and to explore the role of sandy sediments under activities of crown-of-thorns starfish. The results were as followed: (1) crown-of-thorns starfish excreted dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) at rates of (83.55±4.74) μmol/(ind.·h) and (2.53±0.03) μmol/(ind.·h), respectively, which maight provide nutritional conditions for the continuous outbreak of starfish; (2) sandy sediments could regulate the nutrient concentration changed by the excretion of starfish, about 70.7% of DIN and 91.4% of DIP were trapped in the sediments, but the increase of DIN/DIP caused by nutrient exchange at the sediment-seawater interface may be detrimental to coral growth; (3) the degradation of starfish organisms could promote the release of nutrients at the sediment-seawater interface. Based on the density of starfish, the released nutrients could cause the concentrations of DIN and DIP in the overlying water to increase by 0.32 μmol/L and 0.01 μmol/L, respectively, which maight promote the rapid growth of macroalgae and hinder the self-restoration of corals.