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Microplastic–alga interactions: The role of Heterosigma akashiwo and Chattonella marina in aggregation, sinking, and resuspension dynamics
No full textMicroplastics (MPs) are ubiquitous contaminants in marine ecosystems, and their vertical distribution is critically governed by biological interactions, particularly aggregation with phytoplankton. Harmful algal blooms (HABs), through the production of organic exudates, have the potential to substantially modulate MP behavior by facilitating their aggregation, sedimentation, and long-term sequestration. In this study, we assessed the influence of two bloom-forming HAB species, Heterosigma akashiwo and Chattonella marina, on the fate of polyethylene (PE) and polypropylene (PP) MPs with varying densities and morphologies. Results indicate that MP aggregation was primarily driven by extracellular and intracellular polymeric substances released during algal growth and senescence, rather than by direct cell-to-particle adhesion. Both species enhanced the formation of MP–algae aggregates, thereby promoting the vertical transport of buoyant MPs. H. akashiwo induced rapid aggregation and sinking of low-density PE spheres, with sedimentation reaching 28% within 9 days, whereas C. marina exhibited a more gradual, yet persistent, sinking trend, attaining 9% over 13 days. Although high-density MPs generally exhibited higher sinking efficiencies, aggregate size and particle load per aggregate did not differ significantly between MP types. Sinking velocity increased in parallel with aggregate growth and algal decay, and a strong positive correlation was observed between chlorophyll a concentration and PE sinking rate across both species (R2 = 0.93). Notably, the settled aggregates remained structurally intact and resistant to microbial degradation for over three months under dark, low-temperature conditions, with no evidence of resuspension. These findings underscore the species-specific roles of HABs in regulating MP aggregation and vertical flux, offering critical insight into the biological mechanisms governing MP fate in the marine environment.1
Differentially Expressed Genes in Male Gamete of Ecklonia cava under Ocean Acidification
No full textOcean warming and acidification are major concerns in the context of global marine environmental change. These factors significantly influence the metabolism and physiology of marine organisms. Macroalgal beds, which play a crucial role in maintaining coastal biodiversity in temperate regions, have been declining due to these environmental stresses. In this study, we identified differentially expressed genes (DEGs) in the male gametes of Ecklonia cava, a dominant macroalgal species, to better understand the molecular impact of seawater acidification. RNA sequencing and Gene Ontology (GO) analyses were conducted after exposing male gametes to acidified conditions (pH 7.8) for 1 and 3 days. Genes associated with cellular metabolism activation, structural stability, energy production, and cellular stress response were commonly affected in both experimental groups. Specifically, the 1-day exposure group showed enrichment of GO terms such as glutathione metabolic process (GO:0006749), respiratory electron transport chain (GO:0022904), ammonium transmembrane transport (GO:0072488), signal transduction (GO:0007165), regulation of GTPase activity (GO:0043087), and regulation of small GTPase mediated signal transduction (GO:0051056). In contrast, the 3-day exposure group exhibited altered expression in GO terms related to respiratory electron transport chain (GO:0022904), heme binding (GO:0020037), NADP binding (GO:0050661), translational elongation (GO:0006414), small ribosomal subunit (GO:0015935), and the CCR4-NOT core complex (GO:0030015). These results reveal that ocean acidification induces dynamic transcriptional changes in E. cava male gametes, particularly in pathways related to energy metabolism, protein synthesis, and stress response, highlighting potential mechanisms underlying kelp adaptation to acidifying oceans.1
Comparative Analysis of Total Column Ozone from GK-2A/AMI and GK-2B/GEMS for Improving Atmospheric Correction of GOCI-II
No full textAccurate atmospheric correction is essential for producing reliable ocean color products from the Geostationary Ocean Color Imager-II (GOCI-II). A key step in this process is gaseous absorption correction, where total column ozone (TCO) serves as a critical input variable, particularly affecting transmittance in the UV and blue spectral bands. Since GOCI- II does not provide its own ozone retrievals, external datasets from co-orbiting geostationary satellites must be used. This study evaluates TCO products from the Advanced Meteorological Imager (AMI) onboard GK-2A and the Geostationary Environment Monitoring Spectrometer (GEMS) onboard GK-2B. Both datasets were spatially collocated to the GOCI-II Local Area (LA) grid using bilinear interpolation, and their accuracy was assessed against ECMWF ERA5 reanalysis data. Statistical metrics, including correlation, root mean square error, and bias, were calculated to quantify their performance. Results indicate that both AMI and GEMS TCO products show high correlations with ERA5. However, AMI exhibits lower errors and smaller bias, while GEMS shows larger errors and a tendency toward negative bias, especially during summer months. Spatial analysis further reveals that AMI provides more stable performance across the study region, whereas GEMS is more affected by seasonal variability. These findings suggest that AMI can be employed as the primary TCO source for GOCI-II atmospheric correction, with GEMS serving as a complementary dataset to mitigate gaps caused by cloud contamination. Future work will include applying these TCO datasets to GOCI-II gaseous absorption correction and comparing the resulting remote sensing reflectance (Rrs) to further assess their impact on ocean color retrievals.1
Upwelling shapes nitrate isotope distribution in the Seychelles–Chagos Thermocline Ridge in the Indian Ocean
No full textThe Seychelles–Chagos Thermocline Ridge (SCTR) is a persistent open-ocean upwelling region, yet its nitrate-isotope dynamics remain sparsely documented. To clarify how physical transport and biological uptake shape these signals, we measured nitrate concentrations and dual-isotope ratios (δ15N, δ18O) along a meridional section in the southwestern tropical Indian Ocean. Below the upper layer, isotopic compositions primarily reflect the origin and biogeochemical history of distinct water masses, including Circumpolar Deep Water from the south and denitrification-influenced Red Sea Overflow Water from the north. In the upper 100 m, however, patterns depart from simple Rayleigh or steady-state expectations and are best explained by two-end-member mixing between newly upwelled, low-isotope nitrate and surface waters containing isotopically enriched residual nitrate from prior assimilation. The mixing imprint becomes detectable only when nitrate drawdown exceeds ∼80%, indicating that physical mixing can overprint classical assimilation signals under moderate consumption. Together, these results clarify when curved trajectories in nitrate-isotope space should appear and provide a practical basis for interpreting nitrogen cycling in upwelling systems where nutrient supply, water-mass advection, and biological uptake jointly control the observed isotope distributions.11Ysciescopu
Zinc Isotope Fingerprints in Juvenile Fishes from Estuarine Nurseries with Different Pollution Histories: Perspectives for Environmental Monitoring and Fish Ecology
No full textZinc (Zn) isotopes are effective tracers of Zn cycling in marine environments and hold strong potential for ecological applications, yet they remain underexplored. This study analyzes Zn concentrations and isotope compositions (delta 66Zn) in 96 juvenile European seabass (Dicentrarchus labrax) and common sole (Solea solea) from three French estuarine nurseries-Seine, Loire, and Gironde-each with distinct Zn pollution histories. Seabass from the three estuaries exhibit similar trends in Zn bioaccumulation (body burden) and biodilution (concentration) with an increasing size and age. However, significant delta 66Zn differences among estuaries indicate that each system "stamps" a unique isotopic fingerprint on local fish populations. Intraestuarine variability among seabass age classes (1-4 years) is smaller than interestuarine differences. Juvenile soles consistently display higher delta 66Zn values than seabass of similar ages, suggesting that species-specific Zn homeostasis and ecological factors influence isotope compositions. Across estuaries, delta 66Zn patterns in fish mirror those in sediments, indicating that Zn sources drive the isotope compositions. These results confirm that anthropogenic Zn circulates through local food webs with both environmental and dietary sources influencing fish isotope compositions alongside homeostatic processes. Overall, Zn isotope analysis in juvenile seabass and common sole provides new insights for monitoring anthropogenic Zn bioaccumulation and elucidating dietary niches in fish ecology. Juvenile fish in estuaries show distinct Zn isotope signatures likely influenced by local environmental and dietary Zn sources and metabolism.11Nsciescopu
Developments and Evaluation of Prototype Acoustic System for the Reproduction of Marine Biological Sounds
No full textThe sounds of marine organisms serve as an important means for their survival and reproduction, with each sound serving purposes such as com- munication, mating, territoriality, echolocation, and foraging. This study presents the development and evaluation of a preliminary acoustic system designed to reproduce the underwater sounds of fish inhabiting the coastal waters of Korea. The underwater sounds of the three targets species (brown croaker, Pacific cod, and small yellow croaker) were recorded over an extended period using a hydrophone in a large sea cage. The acoustic char- acteristics of the recorded biological sounds were analyzed, and based on these characteristics, a sound reproduction algorithm was applied. To repro- duce biological sounds with a wide frequency bandwidth, a system was developed by coupling two transducers: one for low frequencies and one for mid frequencies. To evaluate the performance of the developed prototype system, both the actual recorded sounds and its reproduced sounds were transmitted from the system and recorded with hydrophone in a large sea cage environment. The two received signals were then compared and ana- lyzed in terms of similarity and correlation. The development of the systems is planned to be utilized in future research on biological sound management and ocean soundscapes. [Work supported by KRIT-CT-22-056.]1
Machine-Learning Prediction of Rare Earth Element (REE) in the Busan-Onsan Mud Belt: Geochemical Controls on Model Accuracy
No full textThe geochemical behavior of REEs in marine sediments reflects a complex interplay of mineral composition, grain size, and sedimentary provenance. Understanding how these geochemical and textural parameters govern REE distribution is essential for improving predictive models based on major element geochemistry. Machine learning techniques offer new opportunities for mineral resource prediction and evaluation. In this study, we applied a Random Forest model to predict REE concentrations in sediments from the Busan–Onsan mud belt using major element compositions, and examined the relationship between prediction accuracy and geochemical factors.
By comparing predicted and measured values, samples were classified into those within a ±5% confidence interval (True group) and those outside it (False group). Most elements (Al, Ca, Fe, Na, Mg, P, K, Ti) showed lower average concentrations in the True group, while only Si was higher. The True group was characterized by relatively coarse-grained size, poor sorting, and higher quartz content. It showed lower average REE values, which is likely consistent with the quartz dilution effect. In contrast, the False group was characterized by fine-grained size, and well sorting. It showed higher average REE values, which is likely to reflect increased prediction errors due to the heterogeneous contributions of terrigenous materials such as clay minerals, Fe-Mn oxides, and phosphates.
Principal component analysis (PCA) further supported this trend. The True group showed a pronounced association with Si and low correlation with REE. In contrast, the False group showed high correlations with Al, Fe, Ti, P, Na, and Mg, reflecting terrigenous input and a strong link with REE variability. This study suggests that the accuracy of REE prediction is likely influenced by the mineralogical composition of sediments, and further data and geochemical interpretation will be required to achieve more reliable results.2
Water and gas geochemistry of springs in Ulleungdo volcano, South Korea: Implications for degassing of upper mantle-derived volatiles in Northeast Asia
No full textUlleungdo, a volcanic island located in the back-arc basin (East Sea/Sea of Japan) of the Japanese arc, is one of the Cenozoic intraplate volcanoes in Northeast (NE) Asia. Due to the unique tectonic characteristics of the transition from the past back-arc opening phase to the current intraplate setting, elucidating the magma origin of this volcano allows us to evaluate the possible influence of diverse upper mantle components on intraplate magmatism. Here we report the results of water and dissolved gas geochemistry sampled from 13 springs in Ulleungdo. The springs can be categorized into high CO2 concentration (HC) and low CO2 concentration (LC) types, each exhibiting different evolutionary pathways. The HC springs show high 3 He/ 4 He ratios (1.04 to 5.87 Ra) and delta 13C-CO2 values (-7.3 to-5.1%o), indicating the release of mantle-derived helium and CO2. Although some of the LC springs also contain mantle-derived helium (0.98 to 4.51 Ra), their lower delta 13C-CO2 values (-22.3 to -17.3%o) and CO2/3He ratios (3.79 x 108 to 1.39 x 1010) reflect calcite precipitation during fluid ascent. The consistency of the 3 He/ 4 He ratios between the springs and the previously reported Ulleungdo volcanic rocks suggests the preservation of the helium isotope ratio in the Ulleungdo magma from at least 1.37 Ma to the present. Collectively, helium and carbon isotope compositions from Ulleungdo, Mt. Baekdu, and Wudalianchi in NE Asia could be determined by regional variations in continental lithospheric thickness. This may therefore be explained by a contribution from the subcontinental lithospheric mantle and/or interaction with the continental crust during fluid ascent, rather than an influx of subducted lithospheric material into magma sources. Our findings demonstrate that the interaction between magma derived from the upwelling asthenospheric mantle and the overlying continental lithosphere can be a key process in controlling the volatile geochemistry of the NE Asian Cenozoic intraplate magmatism.11Nsciescopu
Impact of water residence time and stratification on water quality improvement of an artificial brackish waterway
No full textStudy region
The Ara Waterway, an artificial inland brackish waterway in South Korea.
Study focus
This study investigates how water residence time and stratification affect water quality in an artificial brackish water system, which has different characteristics from natural environments and is under-researched, using numerical simulations. Various hydrodynamic conditions, including freshwater discharge and travel distances, were analyzed to understand their impact on residence times and stratification, offering insights for optimizing water quality management.
New hydrological insights for the region
This study demonstrates that stratification significantly impacts water quality more than residence time in artificial brackish waterways. In contrast to lakes or reservoirs, increasing freshwater discharge in artificial brackish waterways can enhance stratification, reducing vertical mixing and degrading water quality, especially in the bottom layers. In the F0 scenario, excluding freshwater inflow increased summer maximum dissolved oxygen by 1.37 times compared to the validation case. This suggests that breaking stratification, such as through underwater aeration systems, may be more effective than focusing on residence time. In the L15 scenario, with the longest travel distance, upstream total nitrogen and total phosphorus increased by 18.37 % and 26.12 %, while downstream levels decreased by 3.35 % and 10.52 %. Additionally, poorer quality freshwater can degrade overall water quality, even with shorter residence times. These findings emphasize the need for careful management of inflowing water to maintain water quality in artificial brackish waterways.11Ysciescopu
Lithospheric flexure and effective elastic thickness under the Ulleung Basin in the East Sea using gravitational coherence
No full textTo estimate a non-uniform effective elastic thickness (Te) of lithosphere across Korean Peninsula and the Sur- rounding Seas (KPSS), we employ gravitational coherence analysis between gravity anomalies and topography/ bathymetry data in the Fourier domain. Exploring crustal flexure and effective elastic thickness variations can offer insights into flexural strength, and evolutionary mechanics of the lithosphere under Ulleung Basin (UB). Our approach involves two scenarios: a large study area spanning the KPSS, and a more targeted investigation focused on UB. Dividing the study area into overlapping windows enables us to recover non-uniform Te values over the targeted regions. The UB study area is divide to 200 km by 200 km windows, and KPSS is divided to 400 km, 600 km, and 800 km windows to recover both short wavelengths and long wavelengths of Te. Our results reveal a Te range of 843 km for KPSS and recovered Te range from 1 to 10 km for UB. The estimated elastic thickness values in southern part of this basin are smaller compared to central and northern parts. These findings are consistent with prior estimations and comparative studies within the region, improving the understanding of UB’s lithospheric properties. The recovered Te values for UB (Te < 6 km) suggests a young and weak oceanic lithosphere under this region. The alignment between recovered Te configuration and tectonic features in KPSS displays a large-scale lithospheric structure.11Nsciescopu