Sea In August Research Articles

Location and elimination of Anisakis simplex third stage larvae in Atlantic herring Clupea harengus L

We here describe the location of anisakid third stage larvae in Atlantic herring Clupea harengus L. caught in the North Sea in August 2023. We further demonstrate how industrial processing (mechanical gutting, removal of entrails, head, tail, hypaxial anterior musculature and vertebral column) reduces the overall infection and worm load in the musculature. The isolated anisakid larvae were identified as Anisakis simplex sensu stricto by a combination of morphometrics and molecular methods (PCR of rDNA and mtDNA, sequencing, BLAST analysis). As a baseline we examined a total of 75 specimens of freshly caught and ungutted herring and showed a positive correlation between host size (fish length and weight) and infection level. The overall prevalence of infection was 84 %, the mean intensity 11.3 (range 1–38 parasites per fish) and the abundance 9.52. The main part of the overall worm population was associated with stomach and pyloric caeca in the body cavity (77 %) and only 5 % was found in the musculature. Larvae occurred in the hypaxial part of the musculature (21), the epaxial part (7 worms) and the caudal part (5 worms). The prevalence of muscle infection was 28 % and the mean intensity 1.6 (range 1–5) parasites per fish and abundance 0.44 parasites per fish. In order to assess the effect of industrial processing on worm occurrence in the fish we examined a total of 67 specimens of herring, from exactly the same batch, but following processing. This included removal of organs in the body cavity, cutting the lower part of the hypaxial segment but leaving the right and left musculature connected by dorsal connective tissue. Five out of these fish carried one larva (prevalence 7.5%, mean intensity 1, abundance 0.07 larvae per fish), and these worms were located in the ventral part of the anterior musculature (2), in the central part of the anterior musculature (2) and one larva in the central part of the caudal musculature. The industrial processing reduced the overall occurrence (abundance) of worms in the fish from 9.52 to 0.07 (136 times reduction) and the occurrence in the musculature from 0.44 to 0.07 (6.28 times reduction). The overall prevalence was reduced from 84 % to 7.5 % (11.2 times reduction). Muscle infection prevalence fell from 28 % to 7.5 % (3.7 times reduction). We then followed another batch of herring following a marinating process (11% NaCl for 24 h and subsequent incubation in acetic acid and vinegar) by artificially digesting the flaps during week 1–8. Although a total of 31 larvae were recovered from 144 fish examined no live nematode larvae were isolated. The importance of fish handling, processing and marination for consumer safety is discussed.

A Three-Dimensional Spatial Interpolation Method and Its Application to the Analysis of Oxygen Deficit in the Bohai Sea in Summer

Dissolved oxygen (DO) plays a pivotal role in sustaining marine ecosystems. The Bohai Sea in China is a semi-enclosed sea, and oxygen-deficit events occur from time to time due to human activities. At present, there is a notable absence of any convenient and precise method for obtaining three-dimensional spatial data on DO, and the exploration of the physical mechanisms influencing oxygen deficit remains incomplete. This investigation uses the linear radial basis function (RBF-Linear) fitting method to conduct three-dimensional spatial interpolation for DO, which demonstrates minimal inaccuracy. Then, the RBF-Linear fitting method is utilized to collect a comprehensive three-dimensional spatial dataset encompassing temperature, salinity, and DO in the Bohai Sea in August from 2016 to 2018. The results indicate discernible interannual variations in the extent, area, and distribution of oxygen deficiency during summer in the Bohai Sea. Mechanism analysis reveals that intense precipitation episodes and an increase in wind stress curl exacerbate oxygen depletion. Additionally, the degree, location, and area of the two oxygen-deficit cores (off the Yellow River Estuary and off the Qinhuangdao) in the Bohai Sea are influenced by several factors, including current velocity, direction, local circulation position, and net horizontal transport rate. Furthermore, the study suggests that oxygen deficiency in the Bohai Sea region is currently in its early stages, with a limited degree of injury and a restricted range of influence. The use of a three-dimensional spatial interpolation method to create a complete DO field in three-dimensional space simplifies the research challenges associated with marine oxygen deficit. Moreover, this study holds particular significance for guiding the development of marine fisheries.

Size at Sexual Maturity of Deep-Sea Unexploited Caribbean Metanephrops binghami (Boone, 1927) and Overexploited Mediterranean Nephrops norvegicus (Linnaeus, 1758) Using Morphometric and Gonadal Staging Approaches

The deep-sea Caribbean lobster (Metanephrops binghami) and the Norway lobster (Nephrops norvegicus) are Nephropidae species of high commercial interest. Although the first one still remains unexploited, the second is overexploited in the Mediterranean Sea. For effective fisheries management, size at sexual maturity is an essential indicator to protect immature individuals from exploitation. The estimation of this indicator can, however, be biased due to the difficulty of differentiating juveniles from adults by their size structure due to the natural process of molting. This study aims to estimate the size at sexual maturity of M. binghami and N. norvegicus females by comparing the effectiveness of the morphometric method versus the macroscopic evaluation of gonad maturity. Samples of M. binghami were collected from the Colombian Caribbean Sea in August and December 2009, March and May 2010, and August 2020 to May 2021. Samples of N. norvegicus were collected from the northwestern Mediterranean Sea from 2019 to 2022. Similar sizes at sexual maturity were found for M. binghami between the morphometric approach (ranging from 28.6 to 33.9 mm cephalothorax length, CL) and the gonadal staging approach (31.4 mm CL). Conversely, for N. norvegicus, the morphometric approach yielded higher measurements (between 27.2 and 30.4 mm CL) than the gonadal approach (26.0 mm CL). This discrepancy might stem from the intense fishing overexploitation conditions of N. norvergicus, leading to a physiological adaptation that enables earlier gonadal maturation at faster rates than morphometric adaptation. Further research is required to elucidate these discrepancies and the effect of overexploitation on physiological (i.e., mature gonads) and functional maturity (i.e., capacity to brood eggs at a larger size).

Mapping harmful microalgal species by eDNA monitoring: A large-scale survey across the southwestern South China Sea

A large-scale sampling was undertaken during a research cruise across the South China Sea in August 2016, covering an area of about 100,000 km2 to investigate the molecular diversity and distributions of micro-eukaryotic protists, with a focus on the potentially harmful microalgal (HAB) species along the east coast of Peninsular Malaysia. Environmental DNAs from 30 stations were extracted and DNA metabarcoding targeting the V4 and V9 markers in the 18S rDNA was performed. Many protistan molecular units, including previously unreported HAB taxa, were discovered for the first time in the water. Our findings also revealed interesting spatial distribution patterns, with a marked signal of compositional turnover between latitudinal regimes of water masses, where dinophytes and diatom compositions were among the most strongly enhanced at the fronts, leading to distinct niches. Our results further confirmed the widespread distribution of HAB species, such as the toxigenic Alexandrium tamiyavaichii and Pseudo-nitzschia species, and the fish-killing Margalefidinium polykrikoides and Karlodinium veneficum. The molecular information obtained from this study provides an updated HAB species inventory and a toolset that could facilitate existing HAB monitoring schemes in the region to better inform management decisions.

Dependency of Arctic zooplankton on pelagic food sources: New insights from fatty acid and stable isotope analyses

AbstractGlobal warming causes dramatic environmental change to Arctic ecosystems. While pelagic primary production is initiated earlier and its intensity can be increased due to earlier ice melt and extended open‐water periods, sea‐ice primary production is progressively confined on a spatio‐temporal scale, leading to unknown consequences for the ice‐associated (sympagic) food web. Understanding ecological responses to changes in the availability and composition of pelagic and sympagic food sources is crucial to determine potential changes of food‐web structure and functioning in Arctic marine communities under increasingly ice‐free conditions. Focus was placed on the importance of suspended particulate organic matter vs. sympagic organic matter for 12 zooplankton species with different feeding modes covering five taxonomic groups (copepods, krill, amphipods, chaetognaths, and appendicularians) at two ice‐covered, but environmentally different, stations in the north‐western Barents Sea in August 2019. Contributions of diatom‐ and flagellate‐associated fatty acids (FAs) to total lipid content and carbon stable isotopic compositions of these FAs were used to discriminate food sources and trace flows of organic matter in marine food webs. Combination of proportional contributions of FA markers with FA isotopic composition indicated that consumers mostly relied, directly (herbivorous species), or indirectly (omnivorous and carnivorous species), on pelagic diatoms and flagellates, independently of environmental conditions at the sampling locations, trophic position, and feeding mode. Differences were nevertheless observed between species. Contrary to other studies demonstrating a high importance of sympagic organic matter for food‐web processes, our results highlight the complexity and variability of trophic structures and dependencies in different Arctic food webs.

Water Masses in the Western Part of the Chukchi Sea in August 2019 and Their Hydrochemical Features

The distribution of water masses in August 2019 in the Chukchi Sea, and their hydrochemical features are i-nvestigated using shipboard data from the transarctic expedition onboard the R/V Professor Levanidov. The work was carried out in the southern shallow part of the sea and in the northern part of the sea outside the 70-meter isobath. Six main water masses were identified: Alaskan and Anadyr Coastal Water (ACW), Siberian Coastal Water (SCW), Melt Water (MW), Summer Bering Sea Water (BSW), Remnant Pacific Winter Water (RWW) and Atlantic Water (AW). Their features are described and analyzed. It was revealed that the water masses of the Chukchi Sea are characterized by a high spatial variability of hydrochemical parameters, especially the BSW, RWW and AW. In the southern part of the Chukchi Sea the presence of very high values of ammonium nitrogen in the bottom layer was noted (up to 12.6 µM). In august 2019, transformed AW, typically residing below 150 m, were observed at a depth of 117–137 meters, characterized by salinity values from 34.2 to 35.7, high content of mineral silicon (93–97 µM), low elevated values of apparent oxygen utilization (240–270 µM), and unusually low N* (a measure of the fixed nitrogen excess relative to phosphorus) values (down to −24.0 µM). At the same time, the AW observed at depths below 140 m did not have such hydrochemical features.

Elemental Composition of Particulate Matter in the Euphotic and Benthic Boundary Layers of the Barents and Norwegian Seas

The increasing influence of Atlantic inflows in the Arctic Ocean in recent decades has had a potential impact on regional biogeochemical cycles of major and trace elements. The warm and salty Atlantic water, entering the Eurasian Basin through the Norwegian Sea margin and the Barents Sea, affects particle transport, sink, phyto-, and zooplankton community structure and could have far-reaching consequences for the marine ecosystems. This study discusses the elemental composition of suspended particulate matter and fluffy-layer suspended matter derived from samples collected in the Barents Sea and northern Norwegian Sea in August 2017. The mosaic distribution of SPM elemental composition is mainly determined by two factors: (i) The essential spatial variability of biological processes (primary production, abundance, and phytoplankton composition) and (ii) differences in the input of terrigenous sedimentary matter to the sea area from drainage sources (weak river runoff, melting of archipelago glaciers, etc.). The distribution of lithogenic, bioessential, and redox-sensitive groups of elements in the particulate matter was studied at full-depth profiles. Marine cycling of strontium in the Barents Sea is shown to be significantly affected by increasing coccolithophorid bloom, which is associated with Atlantic water. Mn, Cu, Cd, and Ba significantly enrich the suspended particulate matter of the benthic nepheloid layer relative to the fluffy layer particulate matter within the benthic boundary layer.

Assessment of Four White Sea Brown Seaweed Extracts as Biostimulants of Plant Growth

The study was aimed on the assessment of extracts from four arctic brown seaweeds (Ascophyllum nodosum, Fucus vesiculosus, Laminaria digitata and Saccharina latissimi) as stimulators of plant growth. Seaweeds were collected from the Rebalda Bay of the White Sea in August 2021. Extracts were obtained by isopropanol maceration method, then vacuum-dried at 40°C and stored at -4°C. Protein, polyphenols, chlorophyll, carotenoids, alginates, mannitol and polysaccharides contents of extracts were determined. Wheat and cucumber seedlings were used as test plants. Extracts from all four brown seaweeds enhanced growth, accelerated development of plants and increased chlorophyll content in leaves. Plant responses to seaweed extracts were concentration-dependent. Higher concentration of A. nodosum and F. vesiculosus extracts inhibited plant growth possibly due to higher phenolic content. The results show that investigated seaweed extracts obtained by isopropanol maceration method with subsequent drying and freezing have proven to be effective in plant growth stimulation.

The Composition, Structure, and Biomass of Zooplankton in the Chukchi Sea in August and September 2019

The Composition, Structure, and Biomass of Zooplankton in the Chukchi Sea in August and September 2019

Dolioletta advena sp. nov., a New Species of Doliolid (Tunicata, Thaliacea) from the Adriatic Sea

The Adriatic Sea, as a part of Mediterranean, is one of the best investigated areas in the world regarding zooplankton. Nevertheless, in the last decade four new species of gelatinous zooplankton were described from the Adriatic Sea. Whether these species are newcomers or they were simply overlooked is still under investigations. Here we provide a description of a new species of Doliolida from the genus Dolioletta, Dolioletta advena sp. nov., found in the Adriatic Sea in August 2021, in a period of high sea temperatures and salinities, suggesting its thermal predilection. Its blastozooids dominated the studied doliolid blastozooid communities in the South Adriatic, except in the 50–100 m depth layer at a coastal Lokrum station. Blastozooids of D. advena sp. nov. possess unique morphological features which easily distinguish it from other doliolid species: the most prominent feature being the curved digestive tract where the intestine does not form a tight coil as in other Dolioletta species. The placement of this species in the genus Dolioletta is corroborated by COI phylogenetic analysis which showed that D. advena sp. nov. forms a well-supported monophyletic clade with Dolioletta gegenbauri (81% bootstrap support). In addition to D. advena sp. nov. COI sequence, we provide COI sequences of five doliolid and one pyrosomatid species, which will greatly improve the availability of thaliacean sequences for metabarcoding studies. The origin of D. advena sp. nov. is unknown, but given the fact that doliolids are well investigated in the Mediterranean Sea, it is likely that it arrived with sea currents either through the Suez Canal or the Strait of Gibraltar. Future investigations will confirm or reject this hypothesis.

Diversity and antimicrobial activity of marine nudibranch associated bacteria against tropical human skin pathogens

Background: Skin disease is the fourth most common disease among all diseases. The number of cases of skin diseases continues to increase, and people commonly use antibiotics to treat these diseases. Nevertheless, overuse of antibiotics can increase the resistance of these pathogens. Hence, the study of novel antibiotic compounds against multi-drug resistant (MDR) skin pathogens is urgently needed. Methods: This study describes the antimicrobial diversity of bacteria associated with three species of marine nudibranchs (Jorunna funebris, Gymnodoris rubropapulosa, and Glossodoris atromarginata) sampled from Jepara coastal waters, the North Java Sea in August 2020. A total of 115 bacterial strains were selected for their prospective antipathogenic compounds against the pathogens Cutibacterium acnes, Staphylococcus aureus, Candida albicans, and Malassezia furfur. Results: A total of 24 bacterial isolates (20.87%) exhibited antimicrobial activity against the pathogens that were selected and molecularly identified. Analyses of the gene of 16S rRNA discovered that these 24 isolates were associated with 11 genera of the phyla Firmicutes, Proteobacteria, and Actinobacteria, including Bacillus as the dominant genus, followed by Streptomyces, Gordonia, Salinicola, Thalassospira, Halomonas, Dietzia, Brevibacterium, Paracoccus, Pseudovibrio, Pseudoalteromonas, and Pseudomonas. None of the 24 antimicrobial bacterial strains possessed type-1 polyketide synthases (PKS-I). One strain possessed type II polyketide synthases (PKS-II), and five strains possessed non-ribosomal peptide synthetase (NRPS) genes. The amounts of bacterial genus and strains in the three nudibranchs differed significantly, as did the proportions of antimicrobial strains in each nudibranch species. The antibacterial strains isolated from G. atromarginata were the highest number (62.5%), followed by J. funebris (20.8%) and G. rubropapulosa (16.7%). Conclusions: These results demonstrate that nudibranch species harbor prominent and varied communities of bacteria and reveal that many nudibranch-associated bacteria have the potential for the advancement of broad-spectrum antibiotics.

Diversity and antimicrobial activity of marine nudibranch associated bacteria against tropical human skin pathogens

Background: Skin disease is the fourth most common disease among all diseases. The number of cases of skin diseases continues to increase, and people commonly use antibiotics to treat these diseases. Nevertheless, overuse of antibiotics can increase the resistance of these pathogens. Hence, the study of novel antibiotic compounds against multi-drug resistant (MDR) skin pathogens is urgently needed. Methods: This study describes the antimicrobial diversity of bacteria associated with three species of marine nudibranchs (Jorunna funebris, Gymnodoris rubropapulosa, and Glossodoris atromarginata) sampled from Jepara coastal waters, the North Java Sea in August 2020. A total of 115 bacterial strains were selected for their prospective antipathogenic compounds against the pathogens Cutibacterium acnes, Staphylococcus aureus, Candida albicans, and Malassezia furfur. Results: A total of 24 bacterial isolates (20.87%) exhibited antimicrobial activity against the pathogens that were selected and molecularly identified. Analyses of the gene of 16S rRNA discovered that these 24 isolates were associated with 11 genera of the phyla Firmicutes, Proteobacteria, and Actinobacteria, including Bacillus as the dominant genus, followed by Streptomyces, Gordonia, Salinicola, Thalassospira, Halomonas, Dietzia, Brevibacterium, Paracoccus, Pseudovibrio, Pseudoalteromonas, and Pseudomonas. None of the 24 antimicrobial bacterial strains possessed type-1 polyketide synthases (PKS-I). One strain possessed type II polyketide synthases (PKS-II), and five strains possessed non-ribosomal peptide synthetase (NRPS) genes. The amounts of bacterial genus and strains in the three nudibranchs differed significantly, as did the proportions of antimicrobial strains in each nudibranch species. The antibacterial strains isolated from G. atromarginata were the highest number (62.5%), followed by J. funebris (20.8%) and G. rubropapulosa (16.7%). Conclusions: These results demonstrate that nudibranch species harbor prominent and varied communities of bacteria and reveal that many nudibranch-associated bacteria have the potential for the advancement of broad-spectrum antibiotics.

Under-Ice Light Field in the Western Arctic Ocean During Late Summer

The Arctic is no longer a region dominated by thick multi-year ice (MYI), but by thinner, more dynamic, first-year-ice (FYI). This shift towards a seasonal ice cover has consequences for the under-ice light field, as sea-ice and its snow cover are a major factor influencing radiative transfer and thus, biological activity within- and under the ice. This work describes in situ measurements of light transmission through different types of sea-ice (MYI and FYI) performed during two expeditions to the Chukchi sea in August 2018 and 2019, as well as a simple characterisation of the biological state of the ice microbial system. Our analysis shows that, in late summer, two different states of FYI exist in this region: 1) FYI in an enhanced state of decay, and 2) robust FYI, more likely to survive the melt season. The two FYI types have different average ice thicknesses: 0.74 ± 0.07 m (N = 9) and 0.93 ± 0.11 m (N = 9), different average values of transmittance: 0.15 ± 0.04 compared to 0.09 ± 0.02, and different ice extinction coefficients: 1.49 ± 0.28 and 1.12 ± 0.19 m−1. The measurements performed over MYI present different characteristics with a higher average ice thickness of 1.56 ± 0.12 m, lower transmittance (0.05 ± 0.01) with ice extinction coefficients of 1.24 ± 0.26 m−1 (N = 12). All ice types show consistently low salinity, chlorophyll a concentrations and nutrients, which may be linked to the timing of the measurements and the flushing of melt-water through the ice. With continued Arctic warming, the summer ice will continue to retreat, and the decayed variant of FYI, with a higher scattering of light, but a reduced thickness, leading to an overall higher light transmittance, may become a more relevant ice type. Our results suggest that in this scenario, more light would reach the ice interior and the upper-ocean.

Роман Доріт Лінке „По той бік блакитної межі”: екскурс в минуле „оссі” для сучасних підлітків

The article analyses the debut historical juvenile novel by the German writer Dorit Linke (b. 1971) “Beyond the Blue Border” (“Jenseits der blauen Grenze”, 2014) in the aspect of the literary, historical and pedagogical potential of the text. The main events take place in the Baltic Sea in August 1989 when youths tried to escape from Rostock to West Germany with flashbacks into their life in the GDR. The connection between the periods of the late 1960s and 1980s is emphasized. It was a time of formation or changing the worldview of the main novel’s characters, which belong to three different generations: 1933 (grandfather), 1968 (parents) and 1989 (teenagers). The title of the book points to a kind of marine locus, representing the key stereotypes about the element of water and the inner state of the heroes. The sea is regarded as a constitutive topos, which not only performs the traditional background function of nature but also turns into an artistic image of a literary text. The narrative from the perspective of a teenage girl makes it possible to explain better to the reader of the appropriate age the motives of the incredible act of their peers and helps to get insight into the everyday life of the “Ossi” (residents of East Germany) in contrast to the “Wessi” (West Germans). In this way, the modern German historical juvenile literature demonstrates the relevance for its recipients, performing the cognitive and didactic functions without aggressive interference in the minds of adolescents.

Intermediate plumes of low oxygen in the southeastern Baltic Sea

Closely spaced CTDO profiling on the pathway of saltwater flow in the southeastern Baltic Sea in August and December 2019 revealed low oxygen intermediate layers-plumes with dissolved oxygen concentration (DOC) less than 2 mg/l under the upper boundary of permanent halocline. At the same time, DOC in the underlying layers was higher and reached 5.0–5.3 mg/l. In order to test the hypotheses about the origin of the intermediate hypoxic plumes, numerical hydrodynamic modelling was performed for time intervals including the measurement periods. The model was validated against bottom current velocity instrumental measurements by a TCM (Tilt Current Meter) moored on the track of the CTDO profiling. Numerical experiments with Lagrangian particles of neutral buoyancy coupled with the operational circulation model showed that sub-halocline hypoxic intermediate layers in the southern part of the Eastern Gotland Basin and in the Gdańsk Basin could be formed as a result of intrusion into the underlying bottom layer of denser, moderately oxygenated water from the Słupsk Furrow, which replaced the old anoxic and hypoxic water of Gotland and Gdańsk origin. It is assumed that cyclonic eddy activity above the saltwater flow along sloping bottom caused fragmentation of the hypoxic intermediate layer into separate plumes. The hypoxic intermediate layers in the Słupsk Furrow, in accordance with the results of monitoring measurements and modelling the motion of particles of neutral buoyancy, could be formed in the Bornholm Basin and moved eastward over the Słupsk Sill.

Influence of Riverine Discharge and Timing of Ice Retreat on Particle Sedimentation Patterns on the Laptev Sea Shelf

AbstractWe studied the influence of river discharge and timing of ice retreat on sinking fluxes of total particulate matter and its components in the Laptev Sea in August–September 2017 and 2018. Vertical fluxes were measured with short‐term sediment traps located on the shelf adjusted to the Lena and Khatanga Rivers inflows (four shallow stations in 2017) and in Vilkitski Strait/Trough area (two deeper stations) in 2018. One station outside the Khatanga plume was repeated in both years. The effect of river discharge manifested by high total particle flux (1–1.6 g m−2 d−1), high Si (0.3 g m−2 d−1) and Al (0.1 g m−2 d−1) fluxes, a high proportion of terrigenous organic carbon (10.7%–27.5% total organic carbon) was clearly recognizable only in the shelf area closest to the Lena inflow. Large contribution of the lithogenic matter to the flux on the Laptev shelf is suggested to result also from sediment resuspension (caused by the tidal mixing and upwelling events), lateral offshore transport of sediment just above the seabed, and coastal abrasion. The magnitude of vertical fluxes of total particulate matter and organic carbon was two to three times higher in 2017 (late ice retreat) than in 2018 (early ice retreat). Centric diatoms dominated protist flux in 2017 while in 2018, dinoflagellates and tintinnids dominated. The contribution of protists to the biogenic organic carbon flux reached 62% in 2018 versus <1% in 2017. Zooplankton fecal pellet flux was not influenced by river discharge but was higher soon after ice melt.

Differential horizontal migration patterns of two male salmon sharks (Lamna ditropis) tagged in the Bering Sea

BackgroundThe salmon shark (Lamna ditropis) is a widely distributed apex predator in the North Pacific Ocean. Many salmon sharks from the eastern North Pacific, specifically Prince William Sound, Alaska, have been satellite tagged and tracked, but due to the sexual segregation present in salmon sharks, most of these tagged sharks were female. Consequently, little information exists regarding the migration patterns of male salmon sharks. To better understand the migration and distribution of this species, information on the male component of the population as well as from sharks outside of Prince William Sound, Alaska, is needed. In this study, we deployed satellite transmitters on two mature male salmon sharks caught in the Bering Sea.ResultsThe two mature male salmon sharks tagged in the Bering Sea exhibited distinct migration patterns. The first male, tagged in August 2017, traveled to southern California where it remained from January to April after which it traveled north along the United States’ coast and returned to the Bering Sea in August 2018. The second male, tagged in September 2019, remained in the North Pacific between 38° N and 50° N before returning to the Bering Sea in July of year one and as of its last known location in year two. The straight-line distance traveled by the 2017 and 2019 sharks during their 12 and 22 months at liberty was 18,775 km and 27,100 km, respectively.ConclusionsBefore this study, our understanding of salmon shark migration was limited to female salmon sharks satellite tagged in the eastern North Pacific. The 2017 male salmon shark undertook a similar, but longer, north–south migration as tagged female sharks whereas the 2019 shark showed little overlap with previously tagged females. The different migration patterns between the two male sharks suggest distinct areas exist for foraging across the North Pacific. The return of both sharks to the Bering Sea suggests some fidelity to the region. Continued tagging efforts are necessary to understand the population structure of salmon sharks in the North Pacific. This tagging study highlights the importance of opportunistic efforts for obtaining information on species and sex with limited distribution data.

Contribution of Changjiang River discharge to CO2 uptake capacity of the northern East China Sea in August 2016

Despite the known significant effect of the Changjiang River on the surface fugacity of CO2 (fCO2) in the northern East China Sea (ECS) during summer, the influence of the river on CO2 uptake capacity has yet to be quantified. In this study, spatial variation in surface fCO2 was studied in the northern ECS in August 2016. The controlling factors on surface fCO2 were identified and quantified. Surface fCO2, as influenced by the Changjiang River, was up to 250 μatm lower than that of oceanic surface water. Biological activity in the river-influenced region lowered surface fCO2 150 μatm–300 μatm below the physical mixing line of oceanic water with low-salinity and high-CO2 Changjiang River water and contributed to CO2 drawdown. The northern ECS was a CO2 sink for the atmosphere, with an average CO2 flux of −6.74 ± 2.89 mmol C m−2 d−1. The CO2 uptake capacity was correlated with salinity, implying an importance of northeastward extension of Changjiang River plume, not the amount of the discharge.

Observations of different effects of an anti-cyclonic eddy on internal solitary waves in the South China Sea

Internal solitary waves (ISWs) were observed by mooring data in the South China Sea in August and September 2014. Normally the arrival pattern of ISWs is relatively regular and the ISW amplitudes have a positive correlation with the magnitude of semidiurnal tidal currents near the Luzon Strait. However, the ISW amplitudes observed in the second spring tide of September are significantly large when an anti-cyclonic eddy is passing the mooring. When an ISW passes the eddy center, its amplitude reduces to nearly zero, but when an ISW passes the eddy edge, its amplitude increases by 50%. A deepened thermocline always damps the ISW amplitudes, whilst the eddy-induced background currents at different locations may have varied effects on the ISW amplitudes, e.g., the background current at the eddy center tends to damp the ISW amplitude but that at the eddy edge amplifies the ISW amplitude. The different effects of a deepened thermocline and eddy-induced background currents near the eddy edge may damp or amplify the ISW amplitude.

Distributions of radiocesium and radium isotopes in the western Bering Sea in 2018

We examined the spatial variations in radiocesium (134Cs and 137Cs) and radium (226Ra and 228Ra) concentrations (activities) in and around the western Bering Sea in August 2018. 134Cs concentrations in the surface seawater samples were 1.1–2.0 mBq/L, decay-corrected to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident date. The northward slope current-dominated water of the Bering Sea exhibited higher 134Cs concentrations (345 Bq/m2 of the column inventory at a site near the slope), along with higher 228Ra concentrations and lower salinities relative to the Aleutian Basin area in the western Bering Sea. The observed features were considered to be a consequence of the arrival of FDNPP-derived radiocesium-rich and lower salinity Alaskan Stream water from the Pacific Ocean side, and subsequent mixing of the 228Ra-rich shelf water in the eastern slope area of the Bering Sea.