In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo (2004 to 2020) and RAMA (2007 to 2020) profiles data in the Bay of Bengal and eastern equatorial Indian Ocean (EEIO). Temperature inversion exists (17.5% of the total 39 293 Argo and 51.6% of the 28 894 RAMA profiles) throughout the year in the entire study area. It shows strong seasonal variation, with the highest occurrences in winter and the lowest in spring. Besides winter inversion in the northern Bay of Bengal, two other regions with frequent temperature inversion are identified in this study for the first time: the northeastern part of the Bay of Bengal and the eastern part of the EEIO during summer and autumn. Driving processes of temperature inversion for different subregions are revealed in the current study. Penetration of heat (mean ~25 W/m²) below the haline-stratified shallow mixed layer leads to a relatively warmer subsurface layer along with the simultaneous cooling tendency in mixed layer, which controls more occurrence of temperature inversion in the northern Bay of Bengal throughout the year. Comparatively lower cooling tendency due to net surface heat loss and higher mixed layer salinity leaves the southern part of the bay less supportive to the formation of temperature inversion than the northern bay. In the EEIO, slightly cooling tendency in the mixed layer along with the subduction of warm-salty Arabian Sea water beneath the cold-fresher Bay of Bengal water, and downwelling of thermocline creates a favorable environment for forming temperature inversion mainly during summer and autumn. Deeper isothermal layer depth, and thicker barrier layer thickness intensify the temperature inversion both in the Bay of Bengal and EEIO.

The melt onset dates (MOD) over Arctic sea ice plays an important role in the seasonal cycle of sea ice surface properties, which impacts Arctic surface solar radiation absorbed by the ice-ocean system. Monitoring interannual variations in MOD is valuable for understanding climate change. In this study, we investigated the spatio-temporal variability of MOD over Arctic sea ice and 14 Arctic sub-regions in the period of 1979 to 2017 from passive microwave satellite data. A set of mathematical and statistical methods, including the Sen’s slope and Mann-Kendall mutation tests, were used to comprehensively assess the variation trend and abrupt points of MOD during the past 39 years for different Arctic sub-regions. Additionally, the correlation between Arctic Oscillation (AO) and MOD was analyzed. The results indicate that: (1) all Arctic sub-regions show a trend toward earlier MOD except the Bering Sea and St. Lawrence Gulf. The East Siberian Sea exhibits a significantly earlier trend, with the highest rate of −9.45 d/decade; (2) the temporal variability and statistical significance of MOD trend exhibit large interannual differences with different time windows for most regions in the Arctic; (3) during the past 39 years, the MOD changed abruptly in different years for different sub-regions; (4) the seasonal AO has more influence on MOD than monthly AO. The findings in this study can improve our knowledge of MOD changes and are beneficial for further Arctic climate change study.

The concentrations of five forms of phosphorus (P) including exchangeable or loosely adsorbed P (Ex-P), Fe-bound P (Fe-P), authigenic P (Auth-P), detrital P (Det-P), and organic P (Org-P) from the basin among the Marcus-Wake seamounts (19.4°–24°N, 156.5°–161.5°E) in the western Pacific Ocean were quantified using a sequential extraction method (SEDEX) to investigate the distribution and sources of different P species. Concentrations of total P (TP) varied from 14.0 μmol/g to 44.1 μmol/g, with an average of (32.4±7.7) μmol/g. Inorganic phosphorus, which was the major chemical form of sedimentary P, ranged from 12.6 μmol/g to 40.6 μmol/g, while the concentration of Org-P varied between 1.38 μmol/g and 5.18 μmol/g, accounting for 83.4%–93.4% and 6.6%–16.6% of the TP, respectively. The relative proportions of the five P species followed the order of Det-P>Auth-P>Org-P>Fe-P>Ex-P. On average, Det-P was the major P sink resulted from the atmospheric input and accounted for approximately 58.9%±12.4% of the TP. Auth-P and Org-P comprised 22.8%±11.4% and 11.5%±3.0% of the TP, respectively, while Fe-P accounted for 5.1%±2.6%. Lastly, Ex-P comprised 1.6%±0.3% of the TP. Org-P exhibited a negative correlation with Fe-P and Auth-P, while Fe-P showed a positive correlation with Auth-P. This indicated that the formation of Fe-P and Auth-P was at the expense of the regeneration or remineralization of Org-P during early diagenesis. High concentrations of Det-P and Auth-P as well as a low ratio of total organic C to reactive P (TOC/Rea-P) suggested that the aeolian input may play a significant role in sedimentary P budget in the study area. Additionally, well-oxygenated bottom water and low sedimentation rate could be responsible for the low TOC/Org-P ratio in the sediment.

Deep-seated gas in seabed sediments migrates upwards from effect of external factors, which easily accumulates to form gasbags at interface of shallow coarse-fine sediments. Real-time monitoring of this process is important to predict disaster. However, there is still a lack of effective monitoring methods, so we attempt to apply multi-points pore water pressure monitoring technology when simulating forming and dissipation of gasbags in sediments through laboratory experiment. This study focuses on discussion of sensitivity of pore water pressure monitoring data, as well as typical changing characteristics and mechanisms of excess pore water pressure corresponding to crack generation, gasbag formation and gas release. It was found that the value of excess pore water pressure in sediments is negatively correlated with vertical distance between sensors and gas source, and the evolution of gasbag forming and dissipation has a good corresponding relationship with the change of excess pore water pressure. Gasbag formation process is divided into three stages: transverse crack development, longitudinal cavity expansion, and oblique crack development. Formation of gasbag begins with the transverse crack at the interface of coarse-fine sediments while excess pore water pressure attenuates rapidly and then drops, pressure remains almost unchanged when cavity expanses longitudinally, oblique crack appeared in final stage of gasbag evolution while excess pore water pressure accumulated and dissipated again. The variation curve of excess pore water pressure in gas release stage has saw-tooth fluctuation characteristics, and the value and time of pressure accumulation are also fluctuating, indicating the uncertainty and non-uniqueness of gas migration channels in sediments.

In the western and central Pacific Ocean, upper strata waters exhibit highly dynamic oceanographic features under ENSO variability. This has been proved to be responsible for the dynamic change of both abundance and zonal distribution of skipjack tuna (Katsuwonus pelamis). Although causality has been suggested by researchers using physical–biological interaction models, cumulative evidence needs to be obtained and the tenability of assertion needs to be tested from an ecological habitat perspective, based on fisheries data. For purse seine fishery, the use of catch per unit effort (CPUE) as an indication of the abundance is confusing because of technical improvements over the whole exploitation history and unbalanced individual fishing characteristic of vessels. It is particularly interesting to discriminate between habitat characteristics in comparative scenarios of CPUE application. This study identified habitat traits based on a series of oceanographic factors from a global ocean reanalysis model. A comparison was conducted between two habitat models based on unprocessed purse seine CPUE and standardized CPUE considering fishing characteristics. The results suggest that standardized CPUE could model the regular zonal shift of habitat compatible with the observed fishing efforts transfer, and achieved better prediction capacity than unprocessed CPUE. Furthermore, the habitat of skipjack tuna was also characterized and linked with surface and subsurface thermal environment, ocean current, dissolved oxygen, biotic environment, and ENSO variability. The monthly-averaged habitat suitable index, derived from the optimal habitat model prediction, showed a significant linear relationship with the southern oscillation index, which suggested that El Niño episodes eventually provide more preferable habitat for skipjack tuna under ENSO variability.

The size-spectrum model has been considered a useful tool for understanding the structures of marine ecosystems and examining management implications for fisheries. Based on Chinese tuna longline observer data from the central and eastern tropical Pacific Ocean and published data, we developed and calibrated a multispecies size-spectrum model of twenty common and commercially important species in this area. We then use the model to project the status of the species from 2016 to 2050 under five constant-fishing-mortality management scenarios: (1) F=0; (2) F=F _recent, the average fishing mortality from 2013 to 2015; (3) F=0.5F _recent; (4) F=2F _recent and (5) F=3F _recent. Several ecological indicators were used to track the dynamics of the community structure under different levels of fishing, including the mean body weight, slope of community size spectra (Slope), and total biomass. The validation demonstrated that size-at-age data of nine main catch species between our model predictions and those empirical data from assessments by the Western and Central Pacific Fisheries Commission matched well, with the R ²>0.9. The direct effect of fishing was the decreasing abundance of large-sized individuals. The mean body weight in the community decreased by ~1 500 g (21%) by 2050 when F doubled from F _recent to 2F _recent. The higher the fishing mortality, the steeper the Slope was. The projection also indicated that fishing impacts reflected by the total biomass did not increase proportionally with the increasing fishing mortality. The biomass of the main target tuna species was still abundant over the projection period under the recent fishing mortality, except Albacore tuna (Thunnus alalunga). For sharks and billfishes, their biomass remained at relatively higher levels only under the F=0 scenario. The results can serve as a scientific reference for alternative management strategies in the tropical Pacific Ocean.

It has been widely recognized that biological invasion has become one of the greatest threats to the ecosystem. Codium fragile is an invasive species which exhibits a variety of attributes like parthenogenesis, winter fragment, and vegetative reproduction; and therefore, it has become a successful invader, colonizing most subtropical regions. In China’s southeast coastal aquaculture waters, the green algal bloom caused by C. fragile will probably become a serious problem. In order to understand more details about the species, an experiment focused on its reproductive characteristics was conducted using culture established from a sample collected in the aquaculture raft of the Nan’ao Island in the South China Sea. The results showed that there were two types of gametes resembling aplanospores and zoospores respectively, both of which were able to germinate. During the gametes liberation, a long mucilage tube was formed out of the mouth of the gametangium assisting dispersal of gametes away from the parent plant. This tube was adapted not only to its surrounding flowing water environment but also to its parent plant’s outer gelatinous structure. In general, the optimum temperature for gametes release and germination was 15−20°C and 15°C, respectively, which corresponded to the local offshore marine water. The plant was observed to produce vegetative buds under favourable reproductive conditions which were called propagules. They were capable of developing into filamentous thalli. The results will provide some scientific evidences for revealing the biological mechanism of bloom and control strategies of invasive green algae.

Long-term variations in population structure, growth, mortality, length at median sexual maturity, and exploitation rate of threadfin bream (Nemipterus virgatus) are reported based on bottom trawl survey data collected during 1960–2012 in the Beibu Gulf, South China Sea. Laboratory-based analyses were conducted on 16791 individuals collected quarterly in eight different sampling years. Average body length, estimated asymptotic length, and percentage of large individuals have decreased significantly with the growth of marine catch and fishing power, indicating individual miniaturization of this fish species. Estimated exploitation rates indicate that the N. virgatus stock in the Beibu Gulf was moderately exploited in 1960 and 1962 and overexploited after 1992. This stock was taking a good turn in status in 2012, with the lowest exploitation rate since 1992 and ceased downward trend in length indexes. These results suggest that management measures to reduce fishing pressure may have a positive influence on the biological characteristics of this commercial fish species. Biological characteristics of most commercial fish species have phenotypic plasticity and might change over years in response to fisheries management. Therefore, attentions should be paid on variations in fish biological characteristics, when evaluating the effectiveness of current measures to control the total catch for all fisheries.

The identity of Rostraria bierii, originally described as a larval amphinomid from Cape Setozaki, Pacific coast of Japan, is investigated. Based on the original description and illustrations, reinterpretations conclude the “larva” to represent a partial juvenile or adult magelonid specimen, broken after the first chaetiger. The original figures are compared with several known magelonid species to justify the new placement. The authors suggest the supposed amphinomid larva is a Magelonidae taxon inquirendum. The identity of the species is discussed in line with the current knowledge of the Magelonidae in the western Pacific and a key to all known species within the region is provided to aid identifications. Current gaps in our taxonomic knowledge of the Magelonidae of the western Pacific are highlighted and discussed.

Antitumor activity is one characteristic function of some certain antimicrobial peptides (AMPs) found in recent years. In the present study, we attempted to detect potential anticancer activity of a recombinant piscidin 5-like from Larimichthys crocea (rLc-P5L) which owned widely antibacterial and strong antiparasitic activity in vitro. The light microscope observation indicated rLc-P5L was of antitumor activity to HeLa cells, 293T cells and L929 cells. MTT assay showed the toxic sensitivity of rLc-P5L to three tumor cell strains was 293T>L929>HeLa. Scanning electron microscope (SEM) results showed rLc-P5L behaved like a lytic peptide to cause damage on cells membrane of L929 cells by forming globular clusters, even pores at 60 μmol/L, or degrading membrane to make it completely lose cytoskeleton structure at 80 μmol/L; rLc-P5L treatment also resulted in DNA degradation. Fluorescence observation results indicated rLc-P5L could cause L929 cells at least two obvious changes: one is nucleus, nuclear chromatin condensed in the margin, nuclear volume became smaller and shrank to be out of shape, or lysed to be debris; the other is cytoskeleton, they became disordered and polarized to make cells atrophic shapes, or even lysed to be debris. In summary, rLc-P5L owned potential anticancer activity causing membrane structure damage and genome DNA degradation. Interestingly, treatment with different concentration of rLc-P5L seemingly caused the similar but different changes, whether it indeed gave rise to cancer cells diverse death way, the further studies should be performed, and the detailed mechanisms were still need further explored.