Showing papers by "Korean Ocean Research and Development Institute published in 2023"

Radiocarbon Constraints on Carbon Release From the Antarctic Ice Sheet Into the Amundsen Sea Embayment

Abstract: The Amundsen Sea Embayment in West Antarctica is experiencing rapid ice mass loss, resulting in biogeochemical changes via altered nutrient and organic matter supply. However, organic carbon released from melting ice has not yet been accurately quantified. In this paper, we have integrated new dissolved organic carbon (DOC) data obtained close to the melting Dotson Ice Shelf (DIS) with published radiocarbon (Δ14C) data on sinking and suspended particulate organic carbon (POC), sedimentary OC, DOC and dissolved inorganic carbon to quantify the effect of ice melt to the carbon cycle. Elevated DOC concentrations in deep water near the DIS indicate the transport of carbon sources from the ice shelf to the water column at a rate of 4.6 ± 2.0 × 1010 g C yr−1. Furthermore, Δ14C-DOC measurements suggest there is a possible dark chemoautotrophic production under the influence of meltwater input. The vertical profile of Δ14C in the sedimentary OC from the Sea Ice Zone and the edge of the DIS demonstrates the presence of aged organic carbon sources during warm episodes at ∼11.5 and 15.9 ka BP. Our study indicates that deep water is not only affected by OC discharge from meltwater but also by biological processes due to altered nutrient inputs. Limited data hampers a precise assessment of the influence of meltwater on the carbon cycle. Further sampling in front of the DIS will be beneficial to enhance our understanding of the role of Antarctic Ice Sheet melting in the downstream ecosystem.

13-Year Observation of the CH4 across the sea surface in the Western Arctic Ocean

Abstract: Methane (CH4) is one of the most important greenhouse gases on Earth. Recent finding of the strong CH4 emissions in the Arctic Seas with shrinking the sea ice may amplify the Arctic warming leading to the positive feedback in the Arctic climate. Korea Polar Research Institute (KOPRI) has ongoing interest in Arctic environmental conditions including the potential release of the CH4 from the seabed to the water column and finally, further to the atmosphere. During the last 13 years throughout a series of campaigns on the Korean ice-breaker, R/V Araon, we measured CH4 concentrations at the surface ocean and overlying air in summer season to estimate the emissions from the western arctic seas including the Chukchi Sea, the Beaufort Sea, and the East Siberian Sea. We compare each of these seas and the Central Arctic Ocean covering the deep Arctic Ocean basin. The surface ocean showed super-saturation almost everywhere with respect to the CH4 in the overlying air. Nonetheless, we have insufficient regional coverage to assess any possible saturation anomaly trend in each sea. Flux densities of outgassing CH4 are modestly larger than the global mean value of the continental shelf except for the Central Arctic Ocean where the CH4 emission is slightly lower. Our estimate of CH4 emission in the East Siberian Sea is far larger than other Arctic Seas abiding by the previous observations, but its magnitude is far lower due likely to the distance from the hot spot area. Future methane flux studies should be extended to shallow, nearshore environments where rate of permafrost degradation should be greatest in response to ongoing marine transgression.

Revisiting the 1978 ML 5.2 Mt.Sokri earthquake, Korea

Abstract: The ML 5.2 earthquake occurred in Mt.Sokri (September 16, 1978), the center of South Korea. It was the fourth largest earthquake in South Korea since the modern seismic observation began. The Korea Meteorological Administration (KMA), the United States Geological Survey (USGS), and the International Seismological Centre (ISC) announced the location of the hypocenter respectively, but they were different. In this study, we analyzed the subsurface fault structure using current micro-earthquakes. We have used data collected by temporary seismic stations installed in the Mt.Sokri area by Pusan National University since May 2019 and the permanent seismic stations installed by KMA since 1978. KMA reported 188 earthquakes from 2007 to 2021 in the study area. We detected additional 280 micro-earthquakes using STA/LTA and template matching methods. The initial result of earthquake locations using HYPOELLIPSE was scattered across the study area. To obtain reliable locations, we relocated earthquakes using HypoDD. As a result, 468 earthquakes were relocated, about twice as many as those reported by KMA. We recognized earthquakes have occurred along WNW-ESE subsurface faults at the depth of 14 to 18km. We determined the focal mechanisms of 15 earthquakes with magnitudes greater than 2. The location of the Mt.Sokri earthquake was reviewed by comparing these results with the locations announced by the three institutions. Joint analysis of the focal mechanisms, distribution of earthquakes, and geological setting, the WNW-ESE plane was interpreted as the major fault plane. Apparently, the micro-seismicity locations in this study better correlated with the epicenter announced by USGS. However, it is difficult to confidently specify the location of the 1978 earthquake only to the current earthquakes.

Introduction to practical application and service systems of multi-satellite data including Geostationary Ocean Color Imager to maritime issues

Abstract: We are conducting a research project to develop algorithms to derive information on maritime issues based on images from Geostationary Ocean Color Imager (GOCI), GOCI-II and many others satellite sensors. We are aiming for several practical application areas which are to detect floating macroalgae, marine fog, harmful algal blooms, fine aerosol particles, low sea surface salinity water, to detect and forecast abnormal sea surface temperature, and to derive ocean water quality parameters and primary production. We are also focusing on candidates to discover new practical techniques using machine learning. These practical techniques are integrated into a maritime issue service system which consists of a data collection and processing system and a web-based data display and analysis system. A scheduler was configured for the automation of the data collection and processing system, and a detailed design was carried out. A system prototype based on open-source GIS service was developed. We will verify the performance of the techniques by comparing the results with high-resolution satellite data or reliable in-situ data.

Identification of bedrock depth and blind fault by HVSR analysis along two profiles in Pohang, South Korea considering optimal weather environment and seismometer burial depth

Abstract: Many deep faults do not reach the earth&#8217;s surface and thus are not recognized. Such faults are rarely mapped by standard surface geological mapping. This seriously hinders seismic risk mitigation efforts. In this study, we applied the horizontal-to-vertical spectral ratio (HVSR) method to identify blind faults invisible at the surface. Despite its simplicity and low-cost implementation, we noticed that HVSR results were unstable using data collected by exposed seismometers or under higher wind speeds. Therefore, three-component seismic sensors for ambient noise observations were buried at different depths to examine the effects of ground coupling, wind speeds, and precipitations. Results from a series of field tests under diverse conditions guided us to establish data selection criteria. The first required condition is that seismic sensors should be buried (>0.3 meters) to secure ground coupling and to avoid any direct exposure to wind or precipitations. The other is that data should be collected at low wind speeds (< 3 m/s). The requirements were applied to ambient noise data along two profiles traversing unnamed and inferred faults in Pohang, Korea. We initially estimated the resonance frequencies for each site, which varied from 0.41 to 2.52 Hz. They were then converted to bedrock depths using an empirical relationship between the resonance frequency and depth to bedrock observed at boreholes in the area. The estimated depths to bedrock along profiles ranged from 8.0 to -472.0 meters. The resulting depth profiles show significant lateral variations in the bedrock depth, including the one near the Gokgang fault at which the thickness to the major impedance contrasts decreased from 196 to 20 meters. Sudden variations were also observed at unexpected locations along the profile. We examined the details, especially for sites of apparent changes in bedrock depth, and compared their characteristics with other geophysical studies, including Vs30, MASW, Bouguer gravity anomaly, and adjacent stations correlation. Their results are all well correlated to each other and indicate rapid changes in bedrock depth. We attribute the rapid changes to vertical displacements by ancient faulting activity.

Tracking the pumice rafts from the recent eruption of the submarine volcano Fukutoku-Okanoba, Japan using Satellites and Lagrangian Particles tracking

Abstract: On 13 August 2021, the Fukutoku-Okanoba submarine volcano in the North Pacific Ocean was erupted. Satellites detected many pumice rafts that drifted westward to reach southern Japan in about two months. To cope with potential danger due to the pumice rafts, it is crucial to predict their trajectories. Using a Lagrangian particle tracking model, the trajectories of the rafts were investigated. The model results showed strong sensitivity to the windage coefficient of pumice rafts, which is uncertain and could cause large errors. By comparing the model results with satellite images using a skill score, the distance between a simulated particle and the nearest observed raft divided by the travel distance of the particle, an optimal windage coefficient was estimated. The optimal windage coefficients ranging between 2 to 3% produced pathways comparable to the obervation using satellites. The pumice rafts&#160; moved from Fukutoku-Okanoba, toward the Ryukyu Islands for approximately two months before being pushed toward Taiwan by the intensified wind. The techniques presented here may become helpful in managing coastal hazards due to diverse marine debris.

Assessment of Microplastic Abundance and Discharge from Greywater of Ships

Abstract: Greywater drained from showers, washbasins, laundry, and dishwashers can be discharged to the sea without further treatment unless in no discharge zone. In 2021, International Maritime Organization indicated greywater generated from ships as one of the possible sources of sea-based microplastics. However, there are only a few studies on microplastics in greywater, most of which have used the scientific literature for statistical estimation of the amount of microplastics in cruise ships. It is necessary to evaluate the amount of microplastics in real ships&#8217; greywater for accurate calculation of emission. This study aims to measure microplastics in a ship&#8217;s greywater by its usage and to estimate the preliminary global emission of microplastics from a ship&#8217;s greywater discharge into the ocean.Greywater was collected in three different holding tanks at 5-day intervals from a research vessel Onnuri of Korea Institute of Ocean Science and Technology (1,370 tons) before and during the cruise for 18 days (April 21&#8211;May 9, 2022) with 33 persons on board. A total of 83 m3 of greywater was generated during the cruise. The average microplastic abundance was 135,563&#177;87,141 n/m3 (range: 60,500&#8211;322,500 n/m3) in greywater. There were no significant differences in the abundance of microplastics in greywater usage (mainly galley, laundry and shower, and cabin washbasin). The level of microplastics in greywater in this study was several orders of magnitude higher than those in effluents from terrestrial wastewater treatment plants in the literature.The greywater generation rate during navigation was 0.15 m3/person/day, which was comparable to previous studies with various types of ships. The greywater sub-flows accounted for 51%, 17%, and 32% of tank A (drained from the galley and 5 cabins with showers), tank B (18 cabins, 2 laboratory rooms, and 4 washbasins), and tank C (laundry, shower, and washbasin), respectively. The number of microplastic from total greywater was highest in tank C (44%), followed by tank A (29%) and tank B (18%). However, there was no difference in the number and mass of microplastics. The annual microplastic load in greywater from R/V Onnuri was estimated to be 1.2&#8569;108 n/year or 91 g/year. Based on the greywater microplastic emission factor abundance in this study, it is estimated that about 28&#8569;1012 particles or 13&#8211;29 tons of microplastics could enter the global oceans from greywater of global fleets (>100 gross tonnages) in a year.

Seismic noise characteristics of PNU OBS network in 2021-2022

Abstract: Pusan National University deployed sixteen ocean bottom seismometers (OBSs) in the eastern offshore of the southern Korean peninsula. The primary purpose of the OBS network is monitoring earthquakes in the eastern offshore to investigate potential fault systems in the offshore region which was formidable using limited apertures by land-based observations. A seismic network's performance highly depends on each site's background noise level. We analyze the nature of the ambient noise and site response for ocean bottom seismometers (OBSs) deployed in the 2021-2022 period. The power spectral densities (PSDs) of the OBSs exhibited dis-similar features from those of land-based stations; most temporary broadband seismic stations on land showed relatively lower background noise levels. In the meanwhile, OBSs showed higher background noise levels. We report the nature of ambient noise at various channels, water depths, spatial locations, temporal variations, extreme weather conditions, and their potential causes. In general, horizontal components are noisier than vertical components. For longer periods, horizontal components are larger by ~45 dB. The probability density functions (PDFs) of OBSs show that the noise level is within the range of McNamara&#8217;s model (2004) for higher frequencies (3.5~50 Hz) although they are still high. When examining long periods (> 20 s), the noise level is higher than what would be given by McNamara&#8217;s model. Although we do not observe diurnal or weekly variations in OBS, as expected, we observe varying degrees of seasonal variations in OBSs. Apparently, water depth is the most important factor in deciding noise levels and their seasonal variations. At shallow-depth OBSs, we observe a strong correlation between noise levels and wave heights estimated by the Korea Meteorological Administration (KMA). The ambient noise is down to -130 dB for the band from 5 to 15 Hz, which provides the best signal-to-noise ratio for local microearthquakes. We also present the horizontal-to-vertical spectral ratio (HVSR) of the ambient noise recorded by OBSs. They present significant amplifications at lower frequencies, which indicates large amplification by combined effects due to lower density and lower wave velocity at shallow sediments, and greater depths to major impedance contrast. We confirm that modeling HVSR of noise data recorded by a three-component OBS offers a fast and inexpensive method for site investigation in deep water with the potential of in situ seafloor sediment characterization.

Assessment of 1-dimensional marine ecosystem model&amp;#160;in reproducing the seasonal patterns in the Yellow Sea Large Marine Ecosystem

Abstract: The large marine ecosystems (LMEs) are described as regional units for the marine research, monitoring, and management. The Yellow Sea (YS), located between Korean Peninsula and continental North China, is known as one of the most important LMEs in the world due to its high biodiversity and complex food web dynamics. Yellow Sea Cold Water Mass (also called YSCWM) formed by the remnant of winter cold water (<~11 &#176;C) in the central Yellow Sea remains throughout the summer, which is a striking hydrological phenomenon in the Yellow Sea and has important effects on the marine ecosystem. Against this background, we undertook a modelling study as a part of a research program of Korea Institute of Ocean Science and Technology (KIOST) to improve the understanding of the ecosystem structure and function and the physical-biological processes in the YS and to predict changes in the the fishery resources under future climate change scenarios. First of all, we applied the 1-dimensional marine ecosystem model (ERSEM-GOTM) to the station (35&#176;N, 124&#176;E) near the central YS affected by the YSCWM. Some inconsistencies between the model and the observations were founded: For examples, while primary production and bacteria carbon mass were overestimated in the model, the zooplankton carbon mass remaining high even after summer season were not represented, which shows clearly the need for model improvements to better capture the cycling of the YS biogeochemistry. Here we present the evaluation of the main aspects of the model behavior and discuss how we optimize the model performance for proper representation of the YS system.

Identification of ventilated and submarine glacial meltwaters in the Amundsen Sea, Antarctica, using noble gases

Abstract: To estimate the glacial meltwater distribution, we used five noble gases as tracers for optimum multiparameter analysis (OMPA) of the water masses in the Amundsen Sea, Antarctic. The increased number of tracers allowed us to define additional source waters at the surface, which have not been possible with a limited number of tracers. The highest fraction of submarine meltwater (SMW, ~0.6%) was present at the depth of 400 -- 500 m near the Dotson Ice Shelf. The SMW appeared to travel along an isopycnal layer to the continental shelf break >300 km away from the ice shelf. Ventilated SMW (VMW) and surface melts (up to 1.5%) were present in the surface layer <100 m. The distribution of SMW indicates that upwelled SMW, known as an important carrier of iron to the upper layer, amounts for 29% of the SMW in the Dotson Trough. The distinction between SMW and VMW made it possible to clearly distinguish the locally-produced SMW since the previous Winter Water formation from the fresh water (VMW) originated from the upstream; the production rate of the former was estimated as 53-94 G ton yr-1. The Meteoric Water fractions, consisted of SMW and VMW, comprised 24% of those derived from oxygen isotopes. This indicates that the annual input from basal melting is far less than the inventory of meteoric water derived from oxygen istopes.

A study on marine physical characteristics around an underwater reef using computational fluid dynamics

Abstract: The marine physical characteristics occurring around the underwater reef in waters more than 100 km away from the land were analyzed through computational fluid dynamics (CFD). A fixed jacket structure so-called Ieodo Ocean Research Station (I-ORS) for marine and atmospheric observations is installed on this underwater reef, and marine observation data have been continuously produced for 20 years. However, there is a concern that observation data may be affected by the underwater reef. We built a numerical modeling framework based on observational data and analyzed the results to find out how underwater reef affects I-ORS. As a result, it was confirmed that various marine physical characteristics (wake region, local upwelling region, suspended sediments, vortex shedding, etc.) appear around the underwater reef. Especially, particle analysis was performed considering the tidal cycle and density stratification to identify the mechanism of suspended sediments generation. Consequently, we were able to find a pattern for the diffusion of suspended sediments around the underwater reef and it is possible to understand various marine physical characteristics around the underwater reef.

Long-term changes in biogeochemical environments and their effects on dissolved oxygen concentrations in the East Sea

Abstract: The East Sea (ES, or East/Japan Sea) is a semi-enclosed marginal sea where deep convection occurs and is therefore appropriate to identify the signals of climate changes. The substantial decrease in dissolved oxygen (DO) concentration has been observed in the deep layers of the ES compared to the globally averaged condition. In addition, in-situ and satellite-based measurement datasets as well as model results showed the enhancement of biological production in the upper layers. As such, changes in biogeochemical environments have been recorded in the ES due to the climate change, which also has a clear impact on long-term changes in the DO concentration.This study investigates the alternations of biogeochemical environments, from the surface to the deep layer of the ES, using a coupled physical-biogeochemical model. This modelling study also allowed a quantitative estimation of the biological effect on the DO concentration.

Comparison Studies for Surface Water Visual Survey and Surface and Water-Column Trawl for Floating and Suspended Marine Plastic Debris

Abstract: A visual survey using a vessel is a representative method to assess the degree of pollution of floating plastic debris in marine environments. However, the visual survey may more easily miss plastic items on and just below water (e.g. plastic bags) than above water (e.g. PET bottles). In addition, there are very limited comparison studies for floating plastic debris on the water surface and suspended plastic debris in the water column. None of the studies quantitatively determined the difference in detection rate by visual and surface trawl surveys. The aim of this study is to evaluate what could be relatively missed and underestimated by surface water visual surveys.Floating plastic debris was monitored by visual and trawl surveys (depth of 0.5 m) in three coastal areas (rural area, GJ; aquafarm area, JH; urban and near river mouth area, SY) of Korea over the four seasons in 2022. In addition, during the visual survey of floating plastic debris in a fishing area (GH), near the river mouth of Han River, a shrimp beam trawl was used to collect plastic debris in the water column (water depth of 10 m) except for thin surface and bottom layer over three seasons in 2022. The seasonal patterns and composition of floating plastic debris in the surface water of JH, GJ, and SY were similar between the visual and trawl surveys. But, the mean densities of most plastics obtained from trawl surveys were 3 to 7 times higher than those from visual surveys. In particular, it was hard to detect small-sized, submerged, or dark-colored fishing gear with the visual survey. Patches with small items can increase the uncertainty of the visual survey. Therefore, visual surveys may underestimate the amount of marine plastic debris above and just below the water.Various types of floating plastic debris were observed by visual survey in the surface water of GH: plastic bags/sheets (54%), expanded polystyrene pieces (18%), plastic containers (4%), strapping (3%), plastic bottles/caps (3%), discarded fishing gear (1%), and other hard plastic pieces (14%). In the water column of GH, however, plastic bags/sheets (93%) predominated and followed by strapping (4%), discarded fishing gear (1%), and other plastics (1%). These results indicate that plastic bags/sheets and strapping would mainly submerge in the water column, but expanded polystyrene pieces, plastic containers, plastic bottles/caps, and other hard plastic pieces are more likely to float rather than sink. Thus, the application of only visual surveys for plastic pollution monitoring in water may largely miss and underestimate the plastic items transported on and below water such as plastic bags and sheets.

The occurrence and distribution of microplastics in epipelagic zone of the western Indian Ocean

Abstract: This study investigated the occurrence and distribution of microplastics utilizing zooplankton samples collected in the Western Indian Ocean because there is no information concerning epipelagic zone in the open ocean. We collected microplastics from three water layers [surface mixed layer(SML), middle layer(ML), lower layer(LL)] within 200 m using a Multiple Opening/Closing Net and Environmental Sensing (opening: 1 &#13217;) at 22 stations of 1 degree interval between 5&#176;N and 16&#176;S along the 67&#176;E of Western Indian Ocean in 2017. The microplastics were consistently found in almost all samples and the microplastic abundance ranged between 0.00-2.01 particles/&#13221; from the 3 layers. And the average microplastic abundance was highest in the lower layer (0.30&#177;0.09 particles/&#13221;) and lowest in middle layer (0.26&#177;0.08 particles/&#13221;). The percentage of fiber was highest in the SML (55.7%) and the LL (45.9%), and the percentage of film was highest in ML (46.8%). The microplastic abundance in the size of 1.0-5.0 &#13212; was highest in SML (42.0%), while the abundance in the size of 0.2-0.5 &#13212; was highest in ML(56.8%) and LL(54.5%). The stations can be divided into four sections including upwelling characterized by Seychelles-Chagos Thermal Ridge (SCTR) based on the 20&#8451;-isotherm depth (D20). The average microplastic abundance was the highest in SML (0.23&#177;0.06 particles/&#13221;) in 1&#176;S~5&#176;S, and in LL (0.50&#177;0.25 particles/&#13221;) at latitudes of 10&#176;S~16&#176;S and in LL (0.32&#177;0.16 particles/&#13221;) at latitudes between 5&#176;N~EQ. However, the average microplastic abundance at latitudes of 6&#176;S ~9&#176;S corresponding to the upwelling zone was highest in the ML (0.65&#177;0.38 particles/&#13221;) with the high percentage of film (68.7%). Cluster analysis by microplastics occurred in each water layers showed that the stations were divided into 3 groups in each layer. Groups in SML and LL were mainly clustered by fiber, whereas groups in ML was mainly clustered by film, which was associated with the upwelled region of Seychelles-Chagos Thermal Ridge (SCTR). Fourier transform infrared spectroscopy analysis showed that the main types of microplastics were dominated by fiber (40.6%) and film (73.2%) characterized by polycarbonate. Present results showed that meridional and vertical distribution of microplastics in the epipelagic zone varied with the physical characteristics of upwelling zone characterized by Seychelles-Chagos Thermal Ridge (SCTR) in the Western Indian Ocean.

Variation and possible causes of Marine Heatwaves under global warming condition

Abstract: Under a warming climate, extreme ocean warming events, namely Marine Heatwaves (MHW), have become more frequent and stronger in global ocean regions. This study examines how the long-term variability of global marine heatwave characteristics is affected by global warming. We quantify the long-term trends (1982-2022) of MHW and investigate the connection between mean climate change and MHW trends. Since 1982, MHW properties over most global regions have increased positive signals during winter and summer. We investigate the rapidly variation of marine heatwave duration and intensity over the global ocean regions compared to the global average change. In addition, this study reveals the possible atmospheric and oceanic processes driving these rapidly changes in ocean areas where MHW occurs dramatically increasing. For example, during winter, the MHW has increased rapidly over the northern East Sea region (over 600 %) compared to the past two decades and this region is influenced on the northward shift of warm ocean current. &#160;

Occurrence and Characteristics of Microplastics in in a Ship&amp;#8217;s Greywater According to Usage Patterns

Abstract: Marine microplastics are a global environmental issue. However, there are still large data and knowledge gaps in microplastics from sea-based sources. One of the concerned sea-based microplastic sources is ships' greywater discharge. Greywater generated from galley, laundries, showers, and washbasins in a ship can be discharged directly to the sea without treatment. In this study, we present the sampling approach of greywater and information about the abundance and characteristics of microplastics. To our knowledge, it is the first attempt to determine microplastic abundance and characteristics in ships' greywater according to its use categories (galley, laundry and shower, and cabin washbasin). Greywater samples were collected from three different holding tanks (tanks A, B, and C) at R/V Onnuri of Korea Institute of Ocean Science and Technology (KIOST). To enable the sample collection, the discharge system was converted to manual discharge and an additional pump and valve were installed on the pipeline connected to each tank. Greywater was sampled when the vessel was at anchor (1st sample) and during the research cruise (2nd sample). For the 1st sample, a grab sampling was conducted and for the 2nd sample, samples were collected at 5-day intervals. Semi-automated FTIR analysis was conducted for microplastic identification. During the analysis, fiber bundles composed of polyester (PES) and polypropylene (PP) were detected. Bundles were counted as one individual particle or composing particles were counted individually, if possible. The highest microplastic abundance was found in tank C from the laundry and shower room in which a large number of microfibers such as PES fibers were detected. The average microplastic abundances were 149,660&#177;77,574 n/m3 (62,000&#8211;209,600 n/m3) in 1st sample and 135,563&#177;87,141 n/m3 (75,000&#8211;177,667 n/m3) in 2nd sample. The microplastic abundances were similar and this can be attributed to the fact that people use the ship's facilities where greywater can be generated even while at anchor. In addition, not only the generation of microplastics but also greywater could be large during navigation. Though the microplastic abundances were similar in 1st and 2nd samples, a greater variety of polymers were detected in 2nd sample (25 types) than in 1st sample (15 types). Polymers used in paint were also highly detected in the 2nd sample (8%) than in the 1st sample (2%). This might be due to more diverse activities took place on the deck and inside the ship during the research activity than when at anchor. Fibers were more dominant in 2nd sample (66%) than in 1st sample (25%). This may be because more people use washing machines while sailing than at anchor. In addition, since many cabins are occupied during the research cruise than when at anchor, washing in cabins and fibers detached from fabrics from people&#8217;s activity during navigation might have contributed to relatively higher PES fiber composition in 2nd sample. The results of this study would be useful in understanding the sea-based microplastic pollution through ship&#8217;s greywater, and for estimation of the microplastic emission from ships to the marine environment.

The geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula

Abstract: The southeastern part of the Korean Peninsula is known to have high seismic activity and many Quaternary faults. Nonetheless, there have been uncertainties in estimating seismic hazards due to insufficient information on potential seismic sources. We investigated the geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula by detecting microearthquakes and determining their source parameters. We used the seismic data recorded at the Gyeongju hi-density broadband seismic network, the temporary seismic networks operated to monitor the aftershocks of two moderate earthquakes (the 2016 ML 5.8 Gyeongju and 2017 ML 5.4 Pohang earthquakes), and the national seismic network of South Korea. An earthquake catalog for the southeastern Korean Peninsula was built using automatic earthquake detection methods based on measurements of energy ratio. We identified the five clustered earthquake regions via the microearthquake distribution: the 2016 Gyeongju earthquake region (GJ), the 2017 Pohang earthquake region (PH), the eastern part of the Ulsan Fault (UF), eastern offshore Gyeongju (EG), and the western part along the Miryang Fault (MF). We determined the relative location and focal mechanisms of the earthquakes occurring in those regions using the double-difference location method and the P-wave first motion polarity method, respectively. Finally, the geometry of the earthquake causative faults was inferred using the spatial distribution of the relative locations and the focal mechanisms. It was found that there are at least two NNE-SSW trending fault segments and multiple NE-SW trending fault segments in the GJ and PH, respectively. In the case of MF, UF, and EG, it is difficult to relate directly to the surface faults, but the strikes of the causative faults, which are confirmed by the spatial distribution of earthquakes, are similar to those of the surface faults.

Rapidly Changing East Asian Marine Heatwaves Under a Warming Climate

Abstract: The East Asian marginal seas (EAMS) are one of the fastest-warming ocean regions globally. This study presents the long-term trends (1982–2020) of extreme ocean warming events called “marine heatwaves” over the EAMS and examines the relationships between marine heatwave trends and mean SST warming trends. We focus on five subregions with different influences from atmospheric perturbation and ocean currents: the northern East Sea (N-ES), southern East Sea, Yellow Sea, Korea Strait (KS), and East China Sea (ECS). During the past four decades, marine heatwave duration and intensity in the EAMS have increased to approximately +4 days and +0.3°C per decade on average, respectively. In summer, the positive trend of marine heatwaves is the highest in the ECS, primarily due to the rapidly increasing mean sea surface temperature (SST). In winter, the N-ES reveals remarkably rapid increases in marine heatwave properties in the last two decades, with increasing rates of approximately 6.2 (4.9) times longer total duration (stronger intensity) than the global average changes. Beyond the impact of the rapid increase in mean SST, the N-ES marine heatwaves can be further extended due to the northward shift of the East Korea Warm Current. In general, mean SST changes are critical to the increasing trend in marine heatwave duration and intensity. This study further emphasizes that the changes in ocean circulation may expedite more rapid changes in extreme ocean events, which can produce more vulnerability in some places, such as the N-ES, to marine heatwaves under continued global warming.

The record-breaking 2022 long-lasting marine heatwaves in East China Sea

Abstract: In 2022, there were record-breaking long-lasting marine heatwaves in the East China Sea, which persisted for 62 days during boreal summer. It was more than sixfold compared to the average duration of the marine heatwaves, which is 9.73 days. It would be recorded as a year when not only marine heatwaves but also various extreme events occurred throughout Asia, such as the summer flood in China and Pakistan. The question arises whether it is caused by La Ni&#241;a, the first &#8220;triple-dip&#8221; of the century. Here we will show key local and remote processes that caused the 2022 long-lasting marine heatwaves in the East China Sea. We have conducted a diagnostic analysis based on the mixed-layer heat budget equation to discover the characteristics of the marine heatwaves, i.e., frequency, duration, and intensity. Based on the equation, we found that weakening ocean vertical mixing and entrainment caused by a density stratification would drive the onset of the marine heatwave in the East China Sea. A large river discharge from the Yangtze River related to extreme rainfall in China would be responsible for the stratification by inducing a shallow mixed layer, and it could affect the weak ocean dynamics. Simultaneously, an anomalous anticyclonic circulation was settled in the corresponding region, and the combined effect of the ocean and atmosphere led to the onset of the marine heatwave. The anticyclonic circulation was sustained longer, resulting in the prolonged marine heatwaves in the East China Sea via enhanced shortwave radiation. In this study, we will discuss further where the stationary Rossby wave train originated and how it could lead to the persistent anticyclonic circulation in the East China Sea.

Dispersion of particle-reactive elements caused by the phase transitions in scavenging

Abstract: A generalized model of scavenging of the reactive radionuclide 239,240Pu was developed, in which the sorption-desorption processes of oxidized and reduced forms on multifraction suspended particulate matter are described by first-order kinetics. One-dimensional transport-diffusion-reaction equations were solved analytically and numerically. In the idealized case of instantaneous release of 239,240Pu on the ocean surface, the profile of concentrations asymptotically tends to the symmetric spreading bulge in the form of a Gaussian moving downward with constant velocity. The corresponding diffusion coefficient is the sum of the physical diffusivity and the apparent diffusivity caused by the reversible phase transitions between the dissolved and particulate states. Using the method of moments, we analytically obtained formulas for both the velocity of the center mass and apparent diffusivity. It was found that in ocean waters that have oxygen present at great depths, we can consider in the first approximation a simplified problem for a mixture of forms with a single effective distribution coefficient, as opposed to considering the complete problem. This conclusion was confirmed by the modeling results for the well-ventilated Eastern Mediterranean. In agreement with the measurements, the calculations demonstrate the presence of a maximum that is slowly descending for all forms of concentration. The ratio of the reduced form to the oxidized form was approximately 0.22-0.24. At the same time, 239,240Pu scavenging calculations for the anoxic Black Sea deep water reproduced the transition from the oxidized to reduced form of 239,240Pu with depth in accordance with the measurement data.

Cause of the cold condition over northeast Asia in April 202

Abstract: Although northern Asia's temperature was the fourth highest on record, Northeast Asia was severely damaged agricultural and marine products due to the cold condition in April 2020. Previous studies have shown that the dipole atmospheric circulation over Siberia and the East Sea (also referred to as the Japan Sea) rendered this cold environment. Here we show that the atmospheric structure affecting the cold condition over northeast Asia was a mixed result of the East Atlantic/Western Russia (EAWR) pattern and blocking. The wave train was originated from the vorticity forcing of northwest/central Russia and propagated toward the southeast via the climatologically westerly and northerly flows. Furthermore, the blocking days over Siberia increased approximately ten times in April 2020 than climatology along with the easterly anomaly over Mongolia&#8211;northeast China. The blocking occurrence might be connected to wavy westerly at the high latitudes. The strong blocking and EAWR pattern led to the robust dipole atmospheric structure with the prevailing northerly wind in April 2020, thereby causing the cold over northeast Asia. Our results help to understand the cause of the cold condition in April over northeast Asia and its impact on the land and ocean ecosystems.

Long-Term Change and Analysis of the Sedimentary Environment of Dadae Beach Using Unmanned Aerial Vehicles

Abstract: Dadae Beach, located at the Nakdong river estuary, has been continuously evolving over the years, and this is the result of complex interactions between natural and artificial factors. In particular, in the case of Dadae Beach, located at the estuary of the Nakdong river estuary, it is located at the boundary between the river and the ocean, and it is an environment in which various deposition mechanisms operate. It is a very difficult research task to analyze the beach evolution mechanism, and a long-term study using precise measurement methods is required. Therefore, in this study, precision unmanned aerial surveys were conducted three times (2015, 2019, and 2021) for 5 years to identify the sedimentary characteristics of Dadae Beach, and the sedimentary environment was analyzed through the analysis of surface sediment texture characteristics. Seasonal waves and winds caused by the East Asian monsoon climate are the main mechanisms for the sedimentation of Dadae Beach, and finegrained sediments are distributed throughout the beach. In addition, the formation of sandbar, which arose rapidly due to artificial influences such as the construction of estuary banks in the past, is a major factor in the evolution of large-scale beaches. This study is meaningful in identifying the mechanism of beach evolution and presenting quantitative analysis results through comparison of precision aerial survey data over a long period of time.

A data integration system for ocean climate change research in the Northwest Pacific

Abstract: A data integration and processing system was established to provide long-time data and real-time data to the researcher who are interested in long-term variation of ocean data in the Northwest Pacific area. All available ocean data of 6 variables (ocean temperature, salinity, dissolved oxygen, ocean CO2, nutrients) in the NWP area (0&#176;N - 65&#176;N, 95&#176;E - 175&#176;E) are collected from the Korean domestic organizations (KIOST, NFIS, KHOA, KOEM), the international data systems (WOD, GTSPP, SeaDataNet, etc.), and the international observation networks (Argo, GOSHIP, GLODAP, etc.). Total number of data collected is over 5 millions and observation dates are from 1938 to 2022. After referring to several QC manuals and related papers, QC procedures and test criteria for 6 data items were determined and documented. Several Matlab programs complying with QC procedures were developed and used to check quality of all collected data. We excluded duplicated data from the data set and saved them in 0.25&#176; grid data files. Long-term average over 40 years and standard deviation of data at each standard depths and grid point were calculated. All quality controlled data, qc flag, average, standard deviation of each ocean variables are saved in format of netCDF and provided to ocean climate researchers and numerical modelers. We also have 2 plans using the collected data from 2023 to 2025. The one is production of long-term grid data set focused on the NWP area, the other is developing a data service system providing observation data and reanalysis data together.Acknowledgement : This research was supported by Korea Institute of Marine Science & Technology Promotion(KIMST) funded by the Ministry of Oceans and Fisheries(KIMST-20220033)

Upper crustal anisotropy in the southeastern Korean Peninsula from shear wave splitting of local earthquakes

Abstract: Shear wave splitting (SWS) is a widely used technique to study the anisotropic properties of the Earth&#8217;s interior. The geological structure of the southeastern Korean Peninsula is represented as the Yangsan fault and Ulsan fault, which is controlled by the present-day compressional stress regime in the ENE-WSW direction. We analyzed shear wave splitting to understand the anisotropic features of the upper crust above the hypocentral depth in the southeastern Korean Peninsula using the local earthquake data from the Gyeongju Hi-density Broadband Seismic Network (GHBSN). The GHBSN is a dense array composed of 200 broadband stations, which covers an area of about 60&#215;60 km2 in the southeastern Korean Peninsula. We used the MFAST program (Savage et al., 2010) to measure the SWS parameters of fast polarization and delay time from shear waves of local earthquakes from January 2019 to December 2020. In addition, the TESSA program (Johnson et al., 2011) was employed to inspect the spatial variation in the anisotropy of the study region. To obtain reliable measurements of SWS parameters, rigorous constraints including quality control of the original waveforms were applied, and then, cycle-skipped measurements were manually removed. In final, we obtained the SWS measurements of 4260 records. Because the seismicity in the region is concentrated at the epicentral region of the 2016 Gyeongju earthquake sequence and the hanging wall of the Ulsan fault, raypaths are limited to a narrow azimuthal range. Both the raw and spatially averaged fast-polarization directions are dominant to be parallel either to major faults (structural anisotropy) or to the ENE-WSW (stress-induced anisotropy). Also, some stations and regions show bi- or multi-modal rose diagram of the SWS, representing that there is more than one factor of anisotropy to induce the SWS. The delay time of the SWS showed the right-skewed distribution. Tomographic result of the SWS delay time shows that, relatively high anisotropy is observed at the epicentral region of the 2016 Gyeongju earthquake sequence and the hanging wall of the Ulsan fault. It implies that microcracks at these regions are better developed compared to the remaining regions.

Observation of intensification of western boundary current in summer of 2021

Abstract: Due to climate change, the occurrence of extreme events such as typhoons, marine heat waves, storminess, and cold waves is increasing in many regions, and these events could dramatically change with significant impacts on the marine environment (e.g., ocean circulation). The East Korea Warm Current (EKWC) has been recognized to flow along the western boundary current of the East Sea (Japan Sea). To examine the variations of EKWC, six bottom-mounted current profiler moorings were operated off the east coast of Korea (the Hupo Bank and Wangdolcho) since June 2021. The observed mean current speed and their principal axis were 0.40 m/s and 58o (counterclockwise from the east) implying northeastward EKWC over the region. In August 2021, an unprecedentedly strong surface current was observed with a maximum of 1.89 m/s and observed currents showed similar variability at mooring sites and several depths. This strong current lasted for about a month, and then rapidly disappeared within a few days. At that time, the geostrophic currents based on satellite-altimetry has a strong current pattern with the Inertial Boundary Current pattern, which is one of the EKWC patterns that flows strongly northward currents closer coast. In addition, the highest mean speed of the EKWC near the mooring sites from 1993 was found in August 2021. The high-speed period was similar to the period of the North Pacific marine heat waves that were already reported, and the low-speed period was related to typhoon passage. This study reported the results of observed EKWC for two years from 2021 and the unprecedentedly enhanced EKWC in August 2021. In particular, it can be a case in which the rapid changes of western boundary currents interact with extreme events such as marine heatwaves and typhoons.