The response of the mixed layer depth (MLD) and subduction rate in the subtropical Northeast Pacific to global warming is investigated based on 9 CMIP5 models. Compared with the present climate in the 9 models, the response of the MLD in the subtropical Northeast Pacific to the increased radiation forcing is spatially non-uniform, with the maximum shoaling about 50 m in the ensemble mean result. The inter-model differences of MLD change are non-negligible, which depend on the various dominated mechanisms. On the north of the MLD front, MLD shallows largely and is influenced by Ekman pumping, heat flux, and upper-ocean cold advection changes. On the south of the MLD front, MLD changes a little in the warmer climate, which is mainly due to the upper-ocean warm advection change. As a result, the MLD front intensity weakens obviously from 0.24 m/km to 0.15 m/km (about 33.9%) in the ensemble mean, not only due to the maximum of MLD shoaling but also dependent on the MLD non-uniform spatial variability. The spatially non-uniform decrease of the subduction rate is primarily dominated by the lateral induction reduction (about 85% in ensemble mean) due to the significant weakening of the MLD front. This research indicates that the ocean advection change impacts the MLD spatially non-uniform change greatly, and then plays an important role in the response of the MLD front and the subduction process to global warming.

The Changjiang River Estuary (CRE) in the East China Sea suffers from seasonal hypoxia in summer. The vertical distributions and seasonal changes of microbial communities in the CRE were well documented. However, little is known about the diurnal changes of bacterial communities in the hypoxic zone of the CRE. Here, 16S rRNA gene analysis was used to explore the changes of bacterial communities in the oxic surface and hypoxic middle seawater layers during 24 h in the CRE. Significant differences between the hypoxic and oxic layers were observed: the phyla Cyanobacteria, Bacteroidetes and Acidimicrobiia were enriched in the oxic layer, whereas the phylum SAR406 and the class Deltaproteobacteria were more abundant in the hypoxic layer. In addition, some subtle diurnal variations of the bacterial relative abundance were found in both two layers. The relative abundance of Synechococcus increased at night, and this change was more obvious in the hypoxic layer. The similar trend was also found in some phototrophic and several heterotrophic bacteria, such as Rhodobacteraceae, OM60 and Flavobacteriaceae. Their relative abundances peaked at 16:00 in the oxic layer, while the relative abundances peaked at around 7:00 and decreased until 13:00 in the hypoxic layer. Together, the results of the present study suggest that some photosynthetic bacteria and several heterotrophic bacteria have similar diurnal variations implying the light and physicochemical heterogeneity in the course of a day are important for bacterial diurnal changes in the CRE.

Extracellular polymeric substances (EPS) are present externally to the microorganisms and play an important role in attachment and biofilm formation. These polymers possess antibacterial and antifouling activities. In this study, the antifouling activity of EPS produced by an epibiotic bacterium associated with macroalga Ulva lactuca was assessed against fouling bacteria and barnacle larvae. Results indicate that the EPS isolated from the epibiotic bacterium inhibits the biofilm formation of the bacteria without much antibacterial activity. Also, the EPS reduced the settlement of barnacle larvae on the hard substrate under laboratory conditions. The epibiotic bacterium was identified as Kocuria flava based on 16S rRNA gene sequencing. The EPS was further analysed using Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) to understand the biochemical composition. NMR analysis revealed the presence of polysaccharides, proteins, acetyl amine and succinyl groups. Scanning electron microscope analysis indicated that the EPS consisted of aggregated and irregular sphere-shaped particles.

The statistical characteristics and vertical thermohaline properties of mesoscale eddies in the Bay of Bengal are studied from the view of satellite altimetry data and Argo profiles. Eddy propagation preferences in different lifetimes, eddy evolution process, and geographical distribution of eddy kinetic properties are analyzed in this area. Eddies exist principally in the western Bay of Bengal, and most of them propagate westward. There is a clear southward (equatorward) preference for eddies with long lifetimes, especially for cyclones. Moreover, the eddies in different areas of the bay show different north-southward preferences. Evolution of eddy kinetic properties with lifetime shows that eddies have the significant three-stage feature: the growth period in the former one-fifth lifetime, the stable period in the middle two-fifth to four-fifth lifetime, and the dying period in the last one-fifth lifetime. Large-amplitude and high-intensity eddies occur only in the relatively confined regions of highly unstable currents, such as the East Indian Coastal Current and eastern Sri Lanka. Based on Argo profile data and climatology data, the eddy synthesis method was used to construct three-dimensional temperature and salt structures of eddies in this area. The mean temperature anomaly is negative/positive to the cyclonic/anticyclonic eddies in the upper 300×10⁴ Pa, and below this depth, the anomaly becomes weak. The salinity structures of positive anomalies inside cyclonic eddies and negative anomalies inside anticyclonic eddies in the Bay of Bengal are not consistent with other regions. Due to the special characteristics of the water mass in the bay, especially under the control of the low-salinity Bay of Bengal water at the surface and the Indian equatorial water in the deep ocean, the salinity of seawater shows a monotonic increase with depth. For regional varieties of temperature and salinity structures, as the eddies move westward, the temperature anomaly induced by the eddies increases, the effecting depth of the eddies deepens, and the salinity structures are more affected by inflows. In the north-south direction, the salinity structures of the eddies are associated with the local water masses, which comprise low-salinity water in the northern bay due to the inflow of freshwater from rivers and salty water in the southern bay due to the invasion of Arabian Sea high-salinity water from the north Indian Ocean.

The analysis of growth bands in the eyestalk has been increasingly used for estimating crustacean ageing and molting. In this study, we developed an effective method to process and observe the eyestalk microstructure of the swimming crab (Portunus trituberculatus). We found that dark pigmentation as a result of boiling has an influence on the observation of the eyestalk microstructure. Choosing an unboiled eyestalk, this study compared the cross section and longitudinal section, and concluded that the cross section is suitable for the observation of growth increments with 6.1% CV (coefficient of variation), and growth bands are suitable for the observation of the longitudinal section with 5.4% CV. The width of growth increments near the edge of the endocuticle is small, and the width of growth increments of the middle part of the endocuticle is large. Relationship of number of growth bands to molting time was fitted to a linear function with the slope not significantly different from 1, indicating that growth bands are formed associated with molting. Periodicity of growth increment formation was calculated as 3.7 d, however was not verified. Our results provide a new improved technique for identification of crustacean molting and growth.

Atmospheric CO₂ is one of key parameters to estimate air-sea CO₂ flux. The Orbiting Carbon Observatory-2 (OCO-2) satellite has observed the column-averaged dry-air mole fractions of global atmospheric carbon dioxide (XCO₂) since 2014. In this study, the OCO-2 XCO₂ products were compared between in-situ data from the Total Carbon Column Network (TCCON) and Global Monitoring Division (GMD), and modeling data from CarbonTracker2019 over global ocean and land. Results showed that the OCO-2 XCO₂ data are consistent with the TCCON and GMD in situ XCO₂ data, with mean absolute biases of 0.25×10⁻⁶ and 0.67×10⁻⁶, respectively. Moreover, the OCO-2 XCO₂ data are also consistent with the CarbonTracker2019 modeling XCO₂ data, with mean absolute biases of 0.78×10⁻⁶ over ocean and 1.02×10⁻⁶ over land. The results indicated the high accuracy of the OCO-2 XCO₂ product over global ocean which could be applied to estimate the air-sea CO₂ flux.

The power performances of a point absorber wave energy converter (WEC) operating in a nonlinear multi-directional random sea are rigorously investigated. The absorbed power of the WEC Power-Take-Off system has been predicted by incorporating a second order random wave model into a nonlinear dynamic filter. This is a new approach, and, as the second order random wave model can be utilized to accurately simulate the nonlinear waves in an irregular sea, avoids the inaccuracies resulting from using a first order linear wave model in the simulation process. The predicted results have been systematically analyzed and compared, and the advantages of using this new approach have been convincingly substantiated.

Arsenic (As) and mercury (Hg) are pollutants presented in marine environment. A process of atomic fluorescence spectrometry was proposed for the simultaneous determination of As and Hg in marine sediment samples (n = 38) collected from the Changjiang River Estuary and adjacent East China Sea. The proposed method used an optimized pretreatment procedure in an aqua regia–H₂O digestion system. Recoveries of As and Hg increased to 97% and 98%, respectively, with suitable precisions (2.7%–4.1%) under optimized process conditions. As and Hg were widely presented in these samples, with the ranges of content values were 2.39–8.77 μg/g for As and 48.03–410.8 ng/g for Hg. Results indicate that anthropogenic factors strongly influence the abundances of As and Hg in investigated samples. The preliminary environmental risk assessment was investigated using the geoaccumulation index (I_geo) and anthropogenic contribution rate (M). Findings reveal that Hg demonstrates a strong ecological risk (with average values of 1.3 and 72% for I_geo and M, respectively) in the sediments from the Changjiang River Estuary and adjacent East China Sea. Therefore, Hg should be considered in future investigations.

Pampus minor is an important commercial fish. Due to the similarity of external morphological characteristics among the genus Pampus species, P. minor has often been identified as the juvenile group of both P. cinereus and P. argenteus. While little genetic background on this species is known, this study was based on control region sequences and provided the first evaluation of the genetic signature of 264 individuals of P. minor from 11 populations along the coasts of China and Malaysia. The results indicate high genetic haplotype diversity and low nucleotide diversity in this species. Additionally, two differentiated haplotype lineages were identified in the P. minor populations. However, phylogenetic structures corresponding to the geographical locations were unable to be established. Analysis of molecular variance identified a vast majority of the genetic variation occurring within populations. F-statistic test value (F_ST) of pairwise indicated that great differences existed between the Chinese and Malaysian P. minor populations. For the Chinese populations, the genetic differences were insignificant with the exception of the Xiamen population, which is a marginal population. During the late Pleistocene, a population expansion of P. minor occurred. These expanded populations originated from the glacial refugium in the South China Sea and then rapidly occupied and adapted to their new habitat. The results of this study provide genetic information for ensuring the protection and management of P. minor resources.

Harboring polyextremotolerant microbial topsoil communities, biological soil crusts (biocrusts) occur across various climatic zones, and have been well studied in the terrestrial drylands. However, little is known about the functional metabolic potential of microbial communities involved in the biogeochemical processes during the early succession of biocrusts on the tropical reef islands. We collected 26 biocrusts and bare soil samples from the Xisha Islands and Nansha Islands, and applied a functional gene array (GeoChip 5.0) to reveal nitrogen (N) cycling processes involved in these samples. Both physicochemical measurement and enzyme activity assay were utilized to characterize the soil properties. Results revealed the composition of N-cycling functional genes in biocrusts was distinct from that in bare soil. Additionally, microorganisms in biocrusts showed lower functional potential related to ammonification, denitrification, N assimilation, nitrification, N fixation, and dissimilatory nitrate reduction to ammonium compared to bare soils. Although the abundance of nifH gene was lower in biocrusts, nitrogenase activity was significantly higher compared to that in bare soils. Precipitation, soil physicochemical properties (i.e., soil available copper, soil ammonia N and pH) and soil biological properties (i.e., β-glucosidase, fluorescein diacetate hydrolase, alkaline protease, urease, alkaline phosphatase, catalase and chlorophyll a) correlated to the N-cycling functional genes structure. Nitrate N and ammonia N were more abundant in biocrusts than bare soil, while pH value was higher in bare soil. Our results suggested biocrusts play an important role in N-cycling in coral sand soil, and will be helpful in understanding the development and ecological functions of biocrusts on tropical reef islands.