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Long-lasting Marine Heatwaves in the East Korea Bay in the East/Japan Sea: Characteristics and drivers
No full textThe East Korea Bay (EKB), located in the northwestern the East/Japan Sea (EJS), experiences the most intense and prolonged marine heatwaves within the EJS. In this study, we examine characteristics of the MHWs in the EKB from 1982 to 2018 and explore possible physical mechanisms for long-lasting MHWs using satellite data and reanalysis products. Over the 37 years, MHWs in the EKB lasted 32% longer (17±24 days) than the long-term average of the whole EJS.
Notably, two exceptionally prolonged MHWs were observed, primarily during cooling seasons (fall and winter): one lasting 161 days in 2008/9 and another for 126 days in 2017/8. During these two MHWs, ocean surface cooling, predominantly driven by latent cooling, was intensified while solar heating remained near normal, suggesting that ocean processes play a crucial role in maintaining these extended MHWs. Spatiotemporal distributions of sea surface height indicate that intensified, persistent anticyclonic eddies significantly contribute to maintaining the long-lasting MHWs. A heat budget analysis further supports that the anticyclonic eddies are the primary drivers of these extended MHWs. Our findings underscore the critical role of ocean processes, including eddies and currents, in driving extremely long-lasting MHWs in the EKB within the EJS, particularly during cooling seasons.1
Correlation between organic carbon regeneration and methane flux in mid-Yellow Sea sediments
No full textAfter collecting sediment using a box corer in the mid-Yellow Sea, sub-samples were collected from the sediment chamber and sediment incubation experiments were performed to calculate sediment oxygen consumption rate, nutrient flux, and methane flux. Sediment incubation experiments were conducted at a total 4 sites, and the experiments were conducted for approximately 120 hours (5 days). Organic carbon regeneration rate was calculated as the sediment oxygen consumption rate. The sediments at all sites were fine-grained, muddy sediments, and the organic carbon content ranged from 0.8% to 1.2%. The C/N ratio is in the range of 7 to 10, and most of the organic matter in the sediment is assumed to be of marine origin. The sediment oxygen consumption rate ranged from 0.9 mmol/m²/day¹ to 2.3 mmol/m²/day¹, a relatively low value compared to the sediment oxygen consumption rate in coastal waters. The organic carbon regeneration rate ranged from 3.03 g/m²/year¹ to 7.74 g/m²/year¹. The fluxes of nitrate showed conflicting results at each site. At the A08 site and P13 site, it was being consumed in the water column at –44 μmol/m²/day¹ and -51 μmol/m²/day¹, respectively. On the other hand, at the A05 site and G06 site, it was increasing at 38 μmol/m²/day¹, 8.6 μmol/m²/day¹, respectively. At the P13 site, phosphate was being consumed and flux was –11 μmol/m²/day¹, and at the A08 site, A05 site, and G06 site, phosphate fluxes were 25 μmol/m²/day¹, 27 μmol/m²/day¹, and 32 μmol/m²/day¹, respectively. At the A08 site, nitrate was leached out from the sediment at the beginning of the culture, but it is believed to be consumed in the water column due to a rapid decrease in nitrate over time. The P13 site shows a relatively low oxygen consumption rate compared to other sites, and it is believed that nitrate and phosphate were generated as organic matter decomposed continuously during the incubation time in the surface layer of the sediment. The fluxes of methane were 0.458 μmol/m²/day¹ and 0.056 μmol/m²/day¹ at the A08 site and P13 site, respectively, with a very small amount of methane seeped into the water column. A methane seeping was not detected at other sites. After 120 hours of sediment incubation, oxygen depletion not observed, very low concentrations of methane seeped out.1
Impact of sediment-derived organic matter on heterotrophic prokaryotes metabolism during hypoxia in Jinhae Bay
No full textHeterotrophic prokaryotes (HP) account for half of the community respiration rate in water columns due to their high biomass and active degradation of dissolved organic carbon (DOC). Heterotrophic organic carbon degradation serves as a primary biological oxygen sink in coastal ecosystems. The combination of stratification, reduced external oxygen inputs, and eutrophication from anthropogenic effects or river discharge results in dissolved oxygen (DO) depletion, leading to hypoxia (DO<2mg L-¹). Coastal hypoxia begins in the bottom layers and is driven by high transport of organic matter into the sediment, which enhances sediment respiration and rapid depletion of DO. By-products of sediment diagenesis, such as increased supply of nutrients, labile DOC, and reduced inorganic species, can further exacerbate or prolong hypoxia by affecting microbial activity in the overlying water. However, there is a significant knowledge gap on the regulation of HP by sediment-derived organic matter and its contribution to the development of coastal hypoxia. Therefore, elucidating the interaction between HP metabolism and sediment-derived organic matter as part of benthic-pelagic
coupling provides insight into the biogeochemical cycles of oxygen and carbon in coastal hypoxic basins. Jinhae Bay (JB) is a semi-enclosed bay located on the southeastern coast of Korea, and having shallow water depth(<30m) subject to seasonal hypoxia (May to November). In this study, we deployed an in situ benthic lander and conducted fine-scale water sampling at the oxycline in hypoxic bottom waters to understand the interaction between ediment-derived DOC and HP secondary production (HPP). We surveyed three sampling sites in June, August, and November 2024. Notably, HPP eaked for oxycline only at hypoxic bottom layer sites (33–102μg C L- ¹d- ¹,avg. 69±24μg C L- ¹ d- ¹). Excitation-emission matrix parallel factor (EEM-PARAFAC) analyses revealed that tyrosine-like fluorescent DOM (FDOMTy) significantly stimulated HPP in JB(p<0.05). Based on the benthic lander experiments, this FDOMTy was likely derived from sediment2
EMERGENCY ESCAPE SYSTEM OF A DETACHABLE TYPE FOR A SUBMARINE
No full text본 발명에 따른 유인 잠수정 비상탈출장치는 유인 잠수정의 비상 상황시 사람이 탑승한 내압동체가 사출되어 수면으로 부상하도록 된 것으로, 본체에 외형커버가 마련되고 외형커버가 내압동체를 감싸 구속하도록 구성됨으로써 비상 상황시 외형커버가 개방되면서 내압동체의 구속을 해제하고 사출장치(팽창부이)가 작동되어 되어 내압동체를 부상시킬 수 있는 것임
Characterization of Rogue Wave Occurrence During Typhoon Hinnamnor Using Directional Wave Spectra and High-Order Spectral Simulations
No full textRogue waves often occur unexpectedly during severe weather conditions, such as typhoons, where rapidly evolving sea states enhance nonlinear wave interactions. Typhoon Hinnamnor, one of the most intense storms in the Northwest Pacific during 2022, generated a sequence of extreme sea states that provide a valuable case for investigating rogue wave dynamics. Among them, two contrasting phases are analyzed: a wind-sea-dominated state before intensification and a swell-dominated state after re-intensification. Phase-resolving simulations are conducted using the Higher-Order Spectral (HOS) method, initialized with directional wave spectra from WAVEWATCH III (WW3) hindcast data. Key statistical parameters including wave skewness and excess kurtosis are examined to assess their roles in extreme crest formation. The HOS-simulated wave fields clearly capture the probability of highly nonlinear extreme crests, showing strong agreement with the Tayfun second- and third-order distribution models, while deviating significantly from the Rayleigh distribution base on linear theory. Results also reveal that rogue waves are more likely to occur in positively skewed sea states, emphasizing the importance of second order bound nonlinearities. In contrast, excess kurtosis remains near zero with a slight positive bias, indicating a limited role of third-order modulational processes. Probability density functions, cumulative distributions, and exceedance analyses further support the strong link between skewness and rogue wave probability. These findings underscore the critical role of evolving directional wave spectra in shaping nonlinear wave statistics and provide valuable insights for improving rogue wave prediction and maritime safety in storm-driven sea states.11Nsciescopuskc
Influence of station-to-station line orientation in estimating sea current speed using coastal acoustic tomography
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Investigation of antiviral activity of chlorophyll a derived from Tetraselmis sp. by RNA-Sequ analysis
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Vessel Detection Based on Ocean Satellite Data Using U-Net
No full textEffective maritime traffic management requires technologies capable of detecting and monitoring ships navigating vast ocean areas. Optical sensor images from ocean satellites allow intuitive interpretation with high resolution and, when combined with CNN, can achieve excellent object recognition performance. This study proposes a vessel detection method using optical sensor images based on the U-Net model. U-Net is a fully convolutional network-based model proposed for image segmentation. U-Net can apply various backbones to the encoder-decoder path to enhance detection performance, and the detection performance results were compared using VGG Net, ResNet, DenseNet, and EfficientNet. This study is expected to serve as a methodology for future ship detection using ocean satellite optical sensors.1
