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A key regulator of cell wall glycoprotein degradation in unicellular green microalga Chlamydomonas
No full text1
Discovery of Laophontidae (Copepoda, Harpacticoida) from marine plastic debris: Pseudonychocamptus setadefectus sp. nov. and Heterolaophonte discophora (Willey, 1929)
No full textTwo species belonging to the family Laophontidae Scott T., 1905 were identified among harpacticoid copepods collected from marine plastic debris (MPD) stranded along the Korean coastline. These species were assigned to the genera Pseudonychocamptus Lang, 1944 and Heterolaophonte Lang, 1948. Pseudonychocamptus setadefectus sp. nov. conforms to the generic diagnosis, displaying sexual dimorphism in the armature of the swimming legs. It is distinguished from its six congeners by possessing only two endites on the maxillary syncoxa, notably lacking the proximal endite bearing the seta that is present in all other known species within the genus. Although most morphologically similar to P. colomboi Ceccherelli, 1988, the new species differs in several key characteristics, including the number of setae on the maxillary endopod, the relative length ratios of setae on the female P5 exopod, the presence of an inner seta on the male P5 exopod, and the asymmetry of the male P6. The second species, Heterolaophonte discophora (Willey, 1929), was previously reported from the Atlantic coast of Canada and the Pacific coasts of the USA and Japan. The Korean specimens closely correspond to these previous records, yet exhibit intraspecific variation, particularly in the setal count on the female P3 enp-2. Additional morphological differences were also observed, including variations in the segmentation of the male P3 endopod and in the number of setae on the maxillary endopod. Based on the sexually dimorphic traits observed in males, we propose the subdivision of the genus Heterolaophonte into four distinct species groups. The discovery of P. setadefectus sp. nov. and H. discophora on anthropogenic MPD underscores the potential role of such substrates as microhabitats for benthic harpacticoid copepods.11Ysciescopu
Distribution and behaviors of dissolved trace elements in the northwestern Pacific marginal seas
No full textTrace element behaviors in ocean waters are crucial in regulating phytoplankton growth, influencing oceanic primary production (Lohan & Tagliabue, 2018). This study investigates the biogeochemical cycling of trace elements in the marginal seas of the northwestern Pacific, East/Japan Sea (EJS) and Yellow Sea (YS), with different environmental settings. The distribution patterns of trace elements in the EJS were categorized into three groups. Mn, Fe, and Co showed a considerable influence from atmospheric input in the surface layer and significant benthic input in the bottom water. However, Ni and Cu were removed from the surface water and had a limited influence from the benthic input. The distributions of Zn and Cd were more strongly regulated by biological activity. On top of that, we discovered an unusual decoupling between the concentrations of Zn and SiO42-, with a negative relation between these two components being observed in the deeper layers (> 500 m) of the EJS. This decoupling could largely be attributed to the intensive regeneration processes or additional shelf input. In the shallow waters of the YS, all trace elements exhibited a vertically conserved distribution owing to rapid water mixing. In this study, the fractionations of rare earth elements ((Nd/Er)PAAS and Ce/Ce* ratios) were also used to trace the scavenging processes and the input of water mass. Moreover, the benthic flux of Mn was found to be considerably higher than the atmospheric deposition flux previously reported near the study area in EJS (Seo et al., 2022). The cycling of trace elements in the marginal seas around Korea has been rarely reported; thus, our data could have a critical impact on elucidating the marine biogeochemical cycling in the North Pacific.1
Monitoring of macroalgae distribution around Dokdo in the East Sea (2022-2024) by underwater photogrammetric method
No full textThe waters surrounding Ulleungdo and Dokdo, located in the southwestern part of the East Sea, are characterized by the confluence of cold and warm currents, making them one of the regions with the highest sea surface temperature increase rates around the Korean Peninsula. Geographically, Dokdo, situated 216.8km from the mainland, is the outermost island of the peninsula. Along with Ulleungdo, it is an ideal location for monitoring the impacts of transparency among Korean coastal areas, providing an excellent environment for underwater imaging studies.
From 2022 to 2024, 13 surveys were conducted in the southern ‘Hokdomgul’ underwater cave of Dokdo to facilitate long-term monitoring of macroalgae habitats. Using underwater image-based seafloor mapping techniques, the surveys assessed water temperature, macroalgae coverage, distribution patterns, and dominant species across an average of 151.62m^2 per survey. Dominant species observed included Ecklonia cava, Eisenia bicyclis, Sargassum spp., Padina arborescens, Codium fragile, and Cladophoraceae sp.. The macroalgae coverage rates relative to the surveyed area were 18.1% in 2022, 18.4% in 2023, and significantly increased to 53.7% in 2024.
The annual coverage for Ecklonia cava and Eisenia bicyclis showed consistency across the entire survey area, varying with seasonal and water temperature changes. In the case of Padina arborescens, it flourished from May to August before disappearing. Sargassum spp. was observed starting in August in 2022 and 2023. However, in 2024, it exhibited a relatively high coverage rate from May to November, significantly contributing to the increased distribution rate of macroalgae in the surveyed area that year. The underwater image-based seafloor mapping technique effectively captured these trends, underscoring its utility as a valuable tool for monitoring short- and long-term changes in marine ecosystems.1
Holocene variations in Chinese clay deposition in coastal deposits of the South Sea of Korea: Implications for Kuroshio variability
No full textWe quantified the temporal variation in the contribution of Chinese riverine sediments to the South Sea of Korea over the last 6 kyrs using elemental composition and clay mineral proxy models. This revealed significant variations throughout the Holocene, with major changes around ~5.2, ~4.2–3, and ~1.5 ka, likely driven by changes in the Kuroshio Current dynamics in the northwestern Pacific marginal sea. Notably, Chinese clays from the Huanghe (Yellow) and Changjiang (Yangtze) Rivers contributed up to ~70% of the total sediment deposition throughout most of the Holocene period until ~1 ka, challenging the idea that Korean rivers alone would have regulated sediment deposition in the coastal region of the South Sea. Around ~7 ka, the abrupt increase in Chinese clay deposition in the Korean shelf and coastal regions, followed by its sudden decrease by ~1.5 ka, reflects the onset of the Kuroshio inflow (i.e., the Tsushima Warm Current) and the establishment of the modern circulation system in these marginal seas, respectively. Additionally, a notable shift from Changjiang to Huanghe clay dominance after ~5.2 ka suggests the strengthening of the Cheju Warm Current (a branch of the Kuroshio), which transported smectite-rich sediments from the southeastern Yellow Sea to the South Sea shelf. A temporary reduction in Chinese clay contributions between ~4.2 and 3 ka provides clear evidence of a suppressed Kuroshio inflow associated with global climate change (e.g., the late Holocene neoglacial event). Our study provides a comprehensive understanding of the sedimentary response of Chinese clays to Kuroshio variability in the northwestern Pacific marginal seas.1
Paleoceanographic evolution of surface and bottom waters at the Conrad Rise in the Indian sector of the Southern Ocean since the Last Glacial Maximum
No full textMulti-proxy paleoceanographic data were acquired using the high-resolution analyses on a 10.47 m long piston core (COR-1bPC) at the Conrad Rise located south of the Antarctic Polar Front (Antarctic Zone) in the Indian sector of the Southern Ocean. The 22 AMS 14C datings of planktonic foraminifera and the calibration between d18O values of planktonic foraminifera and well-dated EPICA-Dome C ice core profile established the robust chronology that records about 43,000 cal yr BP. In terms of biogenic opal and CaCO3 contents, an increase of surface water productivity from the last glacial period to the Holocene is attributed to the reduced sea ice coverage and more supply of nutrients by the resumed upwelling of Circumpolar Deep Water, which is typical of the Antarctic Zone in the Southern Ocean. The extremely low and consistent CaCO3 content during the last glacail period indicates that bottom waters were more corrosive and such severe carbonate dissolution is related to the slow ventilation of global circulation (North Atlantic Deep Water and Antarctic Bottom Water). The other productivity proxies (TOC and TN contents) show the opposite variation to the biogenic opal and CaCO3 contents, suggesting that another factor, except for the production, controls more seriously the preservation of organic matters. In addition, based on C/N ratios and d13C values of sediment organic matters, differential degradation of organic matters highlights the oxygenation change of bottom waters since the last glacial period. The global circulation ventilation and respired CO2 accumulation are key to the preservation of organic matter in the Antarctic Zone of the Southern Ocean, in addition to the strength and efficiency of biological carbon pump.1
Simple Eulerian-Lagrangian approach to solve equations for sinking particulate organic matter in the ocean
No full textA gravitational sinking of the particulate organic matter (POM) is a key mechanism of the vertical transport of carbon in the deep ocean and its subsequent sequestration. The size spectrum of these particles is formed in the euphotic layer by the primary production and various mechanisms including food web consumption. The mass of particles, as they descend, decreases under bacterial decomposition and the influence of grazing by filter feeders which depends on the water temperature and oxygen concentration, particle sinking velocity, age of the organic particles, ballasting and other factors. In this study, we consider the influence of the size and age of particles, temperature and oxygen concentration on their dynamics and degradation processes. The model takes into account feedback between the degradation rate and sinking velocity of particles. We rely on the known parameterisations, but our Eulerian-Lagrangian approach to analytically and numerically solving the problem differs, allowing the model to be incorporated into biogeochemical global ocean models with relative ease. Two novel analytical solutions of the system of the one-dimensional Eulerian equation for POM concentration and Lagrangian equations for particle mass and position were obtained for constant and age-dependent degradation rates. At a constant rate of particle sinking, they correspond to exponential and power-law profiles of the POM concentration. It was found that feedback between degradation rate and sinking velocity significantly changes POM concentration and POM flux vertical profiles. The calculations are compared with the available POM concentration and flux measurement data for the latitude band of 20-30oN in the Atlantic and Pacific Oceans and 50-60o in the Southern Ocean. The dependence of the degradation rate on temperature significantly affected the profiles of POM concentration enhancing the degradation of sinking particles in the upper layers of the oceans and suppressing it in the deep layers of the oceans. The influence of oxygen concentration in all cases considered was insignificant compared to the temperature distribution with depth.1
Molecular and Physiological Responses of Tigriopus koreanus to 6PPD-Quinone Exposure
No full textThe increasing demand for tires, driven by the growth of the automobile industry, has led to the annual production of approximately 1.5 billion tires worldwide. Tire wear particles (TWP), generated through friction between tires and road surfaces, have recently gained attention due to their environmental impact. Among these particles, 6PPD is widely used as an antioxidant and antiozonant to enhance tire durability, while its oxidation product, 6PPD-quinone (6PPD-Q), has raised significant concerns due to its toxicity.
In this study, we investigated the acute and chronic toxicity of 6PPD-Q at four concentrations (25, 50, 100, and 200 μg/L) on the benthic copepod Tigriopus koreanus. To assess the molecular and metabolic effects of 6PPD-Q, we conducted transcriptomic and metabolomic analyses. While 6PPD-Q did not induce significant chronic toxicity within 96 hours, it exhibited dose-dependent negative effects on development and fecundity. Antioxidant indicators showed that the total glutathione-to-oxidized glutathione ratio increased in a dose-dependent manner, and both reactive oxygen species (ROS) and superoxide dismutase (SOD) levels were elevated at low concentrations but decreased at high concentrations. Transcriptomic analysis revealed significant alterations in gene expression related to metabolism, defense mechanisms, development, and oxidative stress responses. Metabolomic analysis further confirmed disruptions in lipid metabolism, which correlated with the transcriptomic findings.
These results provide valuable insights into the molecular and physiological effects of 6PPD-Q on benthic organisms, contributing to a better understanding of the broader environmental risks associated with tire-derived pollutants.2