North-western Sea Research Articles

Shear-driven vertical mixing and turbulent exchange over the continental slope in the northwestern Sea of Japan

Shear-driven vertical mixing and turbulent exchange over the continental slope in the northwestern Sea of Japan

First Investigations of Benthic Soft-walled Foraminifera and Gromiids (Protozoa) in the northwestern Sea of Japan

First Investigations of Benthic Soft-walled Foraminifera and Gromiids (Protozoa) in the northwestern Sea of Japan

Mercury and stable nitrogen isotope ratios in the hair of bearded seals (Erignathus barbatus nauticus) from the Sea of Okhotsk.

The mercury pollution status in the northwestern Sea of Okhotsk remains largely unexplored. In this study, hair samples were collected from 40 bearded seals harvested between August and October 2021 in the region. Total mercury (THg) concentrations in the samples exhibited a wide range from 137 to 1885ng/g (median: 407ng/g). While no significant differences in THg concentrations were found between male and female seals, distinctions were observed between young and potentially mature seals. Stable nitrogen isotope analysis indicated that juveniles and mature adults did not differ, although sample sizes were limiting. The higher THg concentrations in juveniles were attributed to variations in the seals' diets and/or variations in foraging locations during the juvenile stage which likely contribute to THg differences due to greater seasonal migration to offshore habitats. Notably, THg levels in bearded seals from the northwestern Sea of Okhotsk were lower in comparison to other pinniped species in the North Pacific. These findings, representing the first dataset for this pinniped species in the Russian segment of its habitat, contribute insights into mercury exposure in the Sea of Okhotsk mammalian population.

New records of Cuspidaria trosaetes Dall, 1925 (Bivalvia: Anomalodesmata: Cuspidariidae) in the Sea of Japan with notes on the genus Nordoneaera

For the first time carnivorous bivalve mollusc Cuspidaria trosaetes Dall, 1925 was recorded in the north-western Sea of Japan. There was only one species of Cuspidaria, C. ascoldica, previously known in this region. Alive specimens of C. trosaetes were collected in the Tatarsky Strait on the continental slope on muddy sediment at the depths of 531–589 m. Stomach contents of C. trosaetes consist of foraminifers, copepods and rissoid gastropods. Cuspidaria trosaetes was selected as a type species of a monotypic subgenus C. (Nordoneaera) Okutani, 1985, which is now considered a separate genus, based on the presence of a thick shell without sculpture and with thick periostracum, as well as a short rostrum. The first obtained data on anatomy of C. trosaetes suggest its close affinity with the type species of the genus Cuspidaria, C. cuspidata. Cuspidaria trosaetes and C. cuspidata share such features as the presence of 5 pairs of septal pores, thin elongated posterior labial palps and the presence of two rows of papillae on the rim of the common siphonal sheath. Taking into account new data we propose to synonymize the monotypic genus Nordoneaera with the genus Cuspidaria.

New morphological data for two rare species of sand-dwelling marine dinoflagellates, Amphidiniella sedentaria and Pachena cf. leibnizii

Abstract Benthic dinoflagellates have been the subject of extensive taxonomic research in recent decades. Studies of morphologies of already known species of benthic dinoflagellates from various geographical populations remain relevant, as these allow elucidation of some details that were overlooked in the original species descriptions or assessment of their morphological variability. In the present study, two rare species of dinoflagellates, Amphidiniella sedentaria and Pachena cf. leibnizii, have been studied, for the first time, from coastal sands of the northwestern Sea of Japan. In the cells of A. sedentaria from the Sea of Japan, we have found two anterior intercalar plates instead of one. Therefore, the original formula has been changed to APC 4′ 2a 7″ 5c 4s 6‴ 2⁗. As a result of the examination of P. cf. leibnizii from the Sea of Japan, we have counted seven precingular plates and six cingular plates, instead of six and five, respectively, indicated in the original description. The plate formula of the cells of P. cf. leibnizii from the Sea of Japan is APC 4′ 3a 7″ 6c 5s 5‴ 2⁗. It is currently difficult to judge whether these differences are morphological variations. Therefore, we have identified these cells as P. cf. leibnizii.

Population biology of crab Hapalogaster dentata parasitized by rhizocephalan Briarosaccus hoegi in the northwestern Sea of Japan.

We studied the population and reproductive characteristics of the stone crab Hapalogaster dentata (De Haan, 1849) (Anomura: Lithodidae) parasitized by Briarosaccus hoegi (Rhizocephala: Peltogastridae) from Peter the Great Bay (northwestern Sea of Japan) in 2023. The sex structure of the H. dentata population was female-biased and represented by 39.1% males and 60.9% females. The size-frequency distribution differed between males and females. The prevalence of parasitization of H. dentata by B. hoegi reached 6.7%. No relationship between crab sex and parasitization prevalence was found. Most of the parasitized specimens (94.8%) had only a single parasitic externa. The non-parasitized and parasitized crabs did not differ in main carapace length. The pleopods in most of the externa-bearing females were shortened or completely atrophied. H. dentata produced 1 clutch per year with ovigerous females occurring from October to May. An obvious delay in embryonic development was observed in winter. None of the parasitized H. dentata females were ovigerous. Externae with embryos of B. hoegi were found from May to July.

First Investigations of Benthic Soft-Walled Foraminifera and Gromiids (Protozoa) in the northwestern Sea of Japan

First Investigations of Benthic Soft-Walled Foraminifera and Gromiids (Protozoa) in the northwestern Sea of Japan

Older than you think: using U–Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, western North Sea

Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones, including the Helmsdale Fault and the Great Glen Fault (GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (Helmsdale Fault) and dextral (GGF) transtensional movements. This deformation has been widely attributed to Cenozoic post-rift fault reactivation. Onshore fieldwork and U–Pb calcite geochronology of five vein samples associated with transtensional movements along the Helmsdale Fault and a splay of the GGF show that faulting occurred during the Early Cretaceous ( c. 128–115 Ma, Barremian–Aptian), while the Helmsdale Fault preserves evidence for earlier Late Jurassic sinistral movements ( c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW–SE-directed Mesozoic rifting that formed the IMFB. Although there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings illustrate the importance of oblique-slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data. Supplementary Material: Appendix A – orthomosaic model obtained from unmanned aerial vehicle (UAV) photography of the Helmsdale locality (GeoTiff format); Appendix B – orthomosaic model obtained from UAV photography of the Shandwick locality (GeoTiff format); Appendix C – geochronology data; and Appendix D – additional thin section microphotographs of sample HD1 showing repeated cycles of syntaxial grain growth are available at https://doi.org/10.6084/m9.figshare.c.6708518

Interdecadal Enhancement in the Relationship between the Western North Pacific Summer Monsoon and Sea Surface Temperature in the Tropical Central-Western Pacific after the Early 1990s

Interdecadal Enhancement in the Relationship between the Western North Pacific Summer Monsoon and Sea Surface Temperature in the Tropical Central-Western Pacific after the Early 1990s

Changes in the Composition of Bloom-Forming Toxic Pseudo-nitzschia Diatoms in Surface Waters in Ussuri Bay, Northwestern Sea of Japan, during the Autumn Seasons of 2017–2022

Diatoms of the genus Pseudo-nitzschia are producers of the neurotoxin domoic acid that causes serious damage to marine fauna and aquaculture farms. These microalgae are known as the most abundant group of toxic phytoplankton in Peter the Great Bay, Northwestern Sea of Japan, during the bloom season, which, as was previously reported for members of this group in the study region, lasts in the autumn months. Autumnal blooms of toxic diatoms Pseudo-nitzschia spp. were studied in the period from 2017 to 2022 in Ussuri Bay, the largest body of water in Peter the Great Bay, which harbors numerous recreational area and aquaculture farms. As a result, the following changes in the composition of bloom-forming species were recorded: blooms were caused by the Pseudo-nitzschia delicatissima group in the period from 2017 to 2020 and by P. multistriata in 2021–2022. An assumption has been made that one of the factors responsible for blooms of P. multistriata, known as one of the most widespread species in Asian warm-water areas, is an abnormally high water temperature in the autumn of 2021 in the study area.

A Novel Mechanism for Extreme El Niño Events: Interactions between Tropical Cyclones in the Western North Pacific and Sea Surface Warming in the Eastern Tropical Pacific

Abstract This study presents a novel mechanism for the generation of extreme El Niño events by analyzing interactions between tropical cyclones (TCs) in the western North Pacific (WNP) in spring [March–May (MAM)] and summer [June–August (JJA)] and sea surface warming in the eastern tropical Pacific. It is suggested that anomalously strong TCs in the WNP in MAM and JJA are essential for the formation of extreme El Niño events. MAM TCs excite considerable westerly wind bursts (WWBs) and facilitate the generation of El Niño events in late spring. The sea surface temperature (SST) in the central-eastern tropical Pacific increases prominently during the following summer, which is due to the warm water carried by downwelling Kelvin waves induced by the anomalous westerlies in the western tropical Pacific associated with the WNP TCs, as well as the lessening cold water upwelling resulting from the deepening thermocline in the eastern tropical Pacific. The developing El Niño in turn contributes to the TC activities over the southeastern quadrant of the WNP in summer, characterized by a stronger intensity, higher frequency, and longer duration. The resulting JJA TC-induced westerlies could further enhance the eastern tropical Pacific warm SST anomalies, and thus an extreme El Niño event tends to appear in the following autumn and winter. These physical processes are verified by several sets of atmosphere–ocean coupled model experiments. Significance Statement Tropical cyclone activity is one of the most destructive phenomena in the world. Extreme El Niño events can also cause devastating climate disasters. Understanding the relationship between these two events can help with disaster forecasting and prevention. This study finds that TC activity in the western North Pacific contributes to the appearance of extreme El Niño events. Abnormally active TC activity in spring can cause strong near-equatorial westerly wind anomalies, eastward transport of warm water from the western tropical Pacific, and a deepening ocean thermocline in the east, resulting in the earlier onset of El Niño events. Influenced by the El Niño event, the TC activity in summer is strengthened, which in turn continues to promote the surface warming of the central-eastern tropical Pacific, eventually resulting in extreme event occurrence.

Using UAV-Based Photogrammetry Coupled with In Situ Fieldwork and U-Pb Geochronology to Decipher Multi-Phase Deformation Processes: A Case Study from Sarclet, Inner Moray Firth Basin, UK

Constraining the age of formation and repeated movements along fault arrays in superimposed rift basins helps us to better unravel the kinematic history as well as the role of inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) overlies rocks of the Caledonian basement, the pre-existing Devonian–Carboniferous Orcadian Basin, and a regionally developed Permo–Triassic North Sea basin system. IMFB rifting occurred mainly in the Upper Jurassic–Lower Cretaceous. The rift basin then experienced further regional tilting, uplift and fault reactivation during the Cenozoic. The Devonian successions exposed onshore along the northwestern coast of IMFB and the southeastern onshore exposures of the Orcadian Basin at Sarclet preserve a variety of fault orientations and structures. Their timing and relationship to the structural development of the wider Orcadian and IMFB are poorly understood. In this study, drone airborne optical images are used to create high-resolution 3D digital outcrops. Analyses of these images are then coupled with detailed field observations and U-Pb geochronology of syn-faulting mineralised veins in order to constrain the orientations and absolute timing of fault populations and decipher the kinematic history of the area. In addition, the findings help to better identify deformation structures associated with earlier basin-forming events. This holistic approach helped identify and characterise multiple deformation events, including the Late Carboniferous inversion of Devonian rifting structures, Permian minor fracturing, Late Jurassic–Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to these events

Effects of Two-Species Infestation by Rhizocephalan Barnacles on the Population of the Kelp Crab Pugettia aff. ferox (Decapoda: Brachyura: Epialtidae) in the Northwestern Sea of Japan

Effects of Two-Species Infestation by Rhizocephalan Barnacles on the Population of the Kelp Crab Pugettia aff. ferox (Decapoda: Brachyura: Epialtidae) in the Northwestern Sea of Japan

The genus Schizymenia (Nemastomatales, Rhodophyta) on the Russian coast of the northwest Pacific and description of S. tamarae sp. nov

ABSTRACT We analysed rbcL and COI sequence data of specimens of Schizymenia from the Sea of Okhotsk and Sea of Japan. Our results revealed a new species of Schizymenia, S. tamarae sp. nov., from the northwestern Sea of Japan. This species is distinct based on shape and the position of glandular cells. Morphological and genetic analyses confirmed that the previously described S. jonssonii is a synonym of S. dubyi var. palmata, which was originally described from the Kuril Islands. The latter taxon was synonymized with Neoabbottiella valentinae. We verified the synonymy of the three names and the affinity of the taxon with the genus Schizymenia. Since the name N. valentinae has priority at the rank of species we propose Schizymenia valentinae comb. nov. The only species of Schizymenia currently known to occur along the Russian coast are S. valentinae and S. tamarae. Schizymenia valentinae is distributed along southeastern Kamchatka, on the Commander Islands and Kurile Islands, and S. tamarae is known only from the Sea of Japan, where it occurs from Olga Bay to Peter the Great Bay on the Russian coast, and in Japan.

Eurasian Ice Sheet derived meltwater pulses and their role in driving atmospheric dust activity: Late Quaternary loess sources in SE England

The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25–23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments delivered by rivers draining Continental Europe possibly contributed additional source material to the first loess accumulation phase. We propose that sudden retreats of the North Sea Lobe released substantial amounts of sediment rich meltwater into the southern North Sea and Channel basins, driving accelerated dust emission, loess deposition and provenance variability in NW Europe during MIS 2. Moreover, we propose that this model of dust activity driven by proglacial sediment availability may be applicable for EIS marginal regions more widely, even where resultant loess cover is rarely preserved due to extensive erosion and reworking along the ice marginal spillway. This implies the role of ice sheets in controlling wider dust emission may be underestimated. In addition to driving changes in ocean circulation through meltwater pulses, ice sheet dynamics in the Quaternary may have also driven substantial and abrupt changes in atmospheric dust activity. This mechanism may in part explain the coupling between dust and climate events widely seen in Quaternary dust sediment records and suggests a possible major role of high latitude dust emission in MIS 2 dustiness across Europe and beyond.

Spatio-temporal variation in the zooplankton prey of lesser sandeels: species and community trait patterns from the Continuous Plankton Recorder

Abstract The phenology, distribution, and size composition of plankton communities are changing rapidly in response to warming. This may lead to shifts in the prey fields of planktivorous fish, which play a key role in transferring energy up marine food chains. Here, we use 60 + years of Continuous Plankton Recorder data to explore temporal trends in key taxa and community traits in the prey field of planktivorous lesser sandeels (Ammodytes marinus) in the North Sea, the Faroes and southern Iceland. We found marked spatial variation in the prey field, with Calanus copepods generally being much more common in the northern part of the study area. In the western North Sea, the estimated amount of available energy in the prey field has decreased by more than 50% since the 1960s. This decrease was accompanied by declining abundances of small copepods, and shifts in the timing of peak annual prey abundances. Further, the estimated average prey community body size has increased in several of the locations considered. Overall, our results point to the importance of regional studies of prey fields, and caution against inferring ecological consequences based only on large-scale trends in key taxa or mean community traits.

Skeletonema species (Bacillariophyta) from the northwestern Sea of Japan: morphology, ecology, seasonal and long-term dynamics

Abstract Skeletonema species are among the most important components of phytoplankton communities in the temperate and tropical Pacific Ocean. Data on Skeletonema species diversity and abundance in the northeastern Pacific are fragmentary. The long-term observations (1996–2019) of the phytoplankton from the coastal waters of the northwestern Sea of Japan resulted in five Skeletonema species being recorded: Skeletonema costatum, S. dohrnii, S. japonicum, S. marinoi and S. menzelii. For each of the species, a morphological description is provided based on electron microscopy. Ecological factors influencing the distribution of the species and their occurrence under certain environmental parameters are discussed. One of the species, S. menzelii, is a new record for Russia. Skeletonema costatum was confirmed to occur in the study area. Seasonal and interannual changes in the abundance of Skeletonema species were studied. The concentrations of the species varied from 20 cells l−1 to 12,700,000 cells l−1. From 1996 to 2018 there was a downward trend in the numbers of Skeletonema. Skeletonema japonicum was noted for the first time to bloom. Skeletonema dohrnii formed summer blooms; S. japonicum bloomed in the autumn. No Skeletonema blooms were detected in the winter months.

Modelling and mapping how common guillemots balance their energy budgets over a full annual cycle

Abstract The ability of individual animals to balance their energy budgets throughout the annual cycle is important for their survival, reproduction and population dynamics. However, the annual cycles of many wild, mobile animals are difficult to observe and our understanding of how individuals balance their energy budgets throughout the year therefore remains poor. We developed a hierarchical Bayesian state‐space model to investigate how key components of animal energy budgets (namely individual energy gain and storage) varied in space and time. Our model used biologger‐derived estimates of time‐activity budgets, locations and energy expenditure to infer year‐round time series of energy income and reserves. The model accounted for seasonality in environmental drivers such as sea surface temperature and daylength, allowing us to identify times and locations of high energy gain. Our study system was a population of common guillemots Uria aalge breeding at a western North Sea colony. These seabirds manage their energy budgets by adjusting their behaviour and accumulating fat reserves. However, typically during severe weather conditions, birds can experience an energy deficit over a sustained period, leading to starvation and large‐scale mortality events. We show that guillemot energy gain varied in both time and space. Estimates of guillemot body mass varied throughout the annual cycle and birds periodically experienced losses in mass. Mass losses were likely to have either been adaptive, or due to energetic bottlenecks, the latter leading to increased susceptibility to mortality. Guillemots tended to be lighter towards the edge of their spatial distribution. We describe a framework that combines biologging data, time‐activity budget analysis and Bayesian state‐space modelling to identify times and locations of high energetic reward or potential energetic bottlenecks in a wild animal population. Our approach can be extended to address ecological and conservation‐driven questions that were previously unanswerable due to logistical complexities in collecting data on wild, mobile animals across full annual cycles. Read the free Plain Language Summary for this article on the Journal blog.

Using a non‐invasive technique to identify suspected microplastics in grey seals (Halichoerus grypus) living in the western North Sea

Plastic pollution is of growing concern in marine ecosystems worldwide. Specifically, microplastics (<5mm) may interact with a variety of biota with the potential to cause harm to organism health. Studies investigating microplastics are increasing, yet their occurrence within free-ranging and living marine mammals remains largely unexplored. By using a protocol involving enzymatic digestion, filtration and microscopic identification, faecal samples collected from a grey seal (Halichoerus grypus) haul-out site in the North Sea were investigated for microplastic presence. Altogether, 71 suspected microplastic particles, consisting of both fibres and fragments in a variety of colours and sizes, were identified across 66 analysed faecal subsamples. The present study indicates that marine mammals are ingesting microplastics and that faecal material can be used to indirectly and non-invasively record microplastic uptake data in pinnipeds. Since the current paper is the first to document potential microplastic exposure among wild, living and free-ranging grey seals of the western North Sea, further research is needed to begin to understand the biological significance of these findings.

A pilot study one stimating the biomass of chub mackerel and jack mackerel in the northwestern sea of Jeju Island using trawl survey and frequency characteristics

A pilot study one stimating the biomass of chub mackerel and jack mackerel in the northwestern sea of Jeju Island using trawl survey and frequency characteristics