Western Sea Research Articles

SDUST2020MGCR: a global marine gravity change rate model determined from multi-satellite altimeter data

Abstract. Investigating the global time-varying gravity field mainly depends on GRACE/GRACE-FO gravity data. However, satellite gravity data exhibit low spatial resolution and signal distortion. Satellite altimetry is an important technique for observing the global ocean and provides many consecutive years of data, which enables the study of high-resolution marine gravity variations. This study aims to construct a high-resolution marine gravity change rate (MGCR) model using multi-satellite altimetry data. Initially, multi-satellite altimetry data and ocean temperature–salinity data from 1993 to 2019 are utilized to estimate the altimetry sea level change rate (SLCR) and steric SLCR, respectively. Subsequently, the mass-term SLCR is calculated. Finally, based on the mass-term SLCR, the global MGCR model on 5′ × 5′ grids (SDUST2020MGCR) is constructed by applying the spherical harmonic function method and mass load theory. Comparisons and analyses are conducted between SDUST2020MGCR and GRACE2020MGCR resolved from GRACE/GRACE-FO gravity data. The spatial distribution characteristics of SDUST2020MGCR and GRACE2020MGCR are similar in the sea areas where gravity changes significantly, such as the eastern seas of Japan, the western seas of the Nicobar Islands, and the southern seas of Greenland. The statistical mean values of SDUST2020MGCR and GRACE2020MGCR in global and local oceans are all positive, indicating that MGCR is rising. Nonetheless, differences in spatial distribution and statistical results exist between SDUST2020MGCR and GRACE2020MGCR, primarily attributable to spatial resolution disparities among altimetry data, ocean temperature–salinity data, and GRACE/GRACE-FO data. Compared with GRACE2020MGCR, SDUST2020MGCR has higher spatial resolution and excludes stripe noise and leakage errors. The high-resolution MGCR model constructed using altimetry data can reflect the long-term marine gravity change in more detail, which is helpful in studying seawater mass migration and its associated geophysical processes. The SDUST2020MGCR model data are available at https://doi.org/10.5281/zenodo.10701641 (Zhu et al., 2024).

Occurrence and distribution of phycotoxins in the Antarctic Ocean

Lipophilic phycotoxins (LPTs) and domoic acid (DA) in Antarctic seawater, as well as parts of the South Pacific and the Southern Indian Oceans were systematically investigated. DA and six LPTs, namely pectenotoxin-2 (PTX2), okadaic acid (OA), yessotoxin (YTX), homo-yessotoxin (h-YTX), 13-desmethyl spirolide C (SPX1), and gymnodimine (GYM), were detected. PTX2, as the dominant LPTs, was widely distributed in seawater surrounding Antarctica, whereas OA, YTX, and h-YTX were irregularly distributed across the region. The total concentration of LPTs in surface seawater ranged from 0.10 to 13.57 ng/L (mean = 2.20 ng/L). ∑LPT levels were relatively higher in the eastern sea areas of Antarctica than in the western sea areas. PTX2 was the main LPT in the vertical profiles, and the PTX2 concentration was significantly higher in the epipelagic zone than water depths below 200 m. The predominant sources of PTX2 and OA in Antarctic sea areas are likely to be Dinophysis.

Assessment of Offshore Wind Power Potential and Wind Energy Prediction Using Recurrent Neural Networks

In recent years, Taiwan has actively pursued the development of renewable energy, with offshore wind power assessments indicating that 80% of the world’s best wind fields are located in the western seas of Taiwan. The aim of this study is to maximize offshore wind power generation and develop a method for predicting offshore wind power, thereby exploring the potential of offshore wind power in Taiwan. The research employs machine learning techniques to establish a wind speed prediction model and formulates a real-time wind power potential assessment method. The study utilizes long short-term memory networks (LSTM), gated recurrent units, and stacked recurrent neural networks with LSTM units as the architecture for the wind speed prediction model. Furthermore, the prediction models are categorized into annual and seasonal patterns based on the seasonal characteristics of the wind. The research evaluates the optimal model by analyzing the results of the two patterns to predict the power generation conditions for 1 to 12 h. The study region includes offshore areas near Hsinchu and Kaohsiung in Taiwan. The novelty of the study lies in the systematic analysis using multiple sets of wind turbines, covering aspects such as wind power potential assessment, wind speed prediction, and fixed and floating wind turbine considerations. The research comprehensively considers the impact of different offshore locations, turbine hub heights, rotor-swept areas, and wind field energy on power generation. Ultimately, based on the research findings, it is recommended to choose the SG 8.0-167 DD wind turbine system for the Hsinchu offshore area and the SG 6.0-154 wind turbine system for the Kaohsiung offshore area, serving as reference cases for wind turbine selection.

Characteristics of Black Sea dispersion of freshened and polluted transitional waters from the Dnipro-Bug estuary after destruction of the Kakhovka Reservoir dam

This study examines the characteristics of distribution of large volumes of freshened and polluted transitional waters from the Dnipro-Bug estuary across the northwestern part of the Black Sea (NWBS) that was caused by destruction of the Kakhovka HPP dam in June 2023. From June 6, 2023 to June 12, 2023 14.4 km³ of water were discharged from the Kakhovka Reservoir into the Dnipro-Bug estuary and subsequently into the sea. This volume constitutes 27% of the total annual average natural runoff of the Dnipro River (53.5 km³). During the initial days following the dam destruction water flow through the breach amounted to 40-50 thousand m³/s. The water carried a variety of pollutants into the sea that were present in the water of the Kakhovka Reservoir, in its bottom sediments, and also washed off from the flooded territories of the lower Dnipro area (more than 2000 hectares).
 The analysis of the distribution characteristics was conducted using satellite images of the sea surface color and chlorophyll a concentrations, as well as the results of hydrodynamic modeling with application of the 3-D variant of a numerical hydrodynamic model Delft3D-Flow Flexible Mesh. It was established that the plume of freshened and polluted water initially spread across the Dnipro-Bug estuarine region of the NWBS and then moved towards the sea coast of Odesa reaching it on June 9-10, 2023. Subsequently, the plume began to spread along the western sea coast and reached the Tuzlivski Limans area on June 14, 2023. After this the narrow plume of dispersed water along the sea coast began to dilute when moving towards the open sea in the form of "tongues" that had formed over the sea bottom elevations. The modeling of dispersion of a conservative neutral buoyancy admixture serving as a marker of pollution spread with the transitional waters from the Dnipro-Bug estuary showed that reduction in pollution levels took place solely due to hydrodynamic dilution (up to 60% in Odesa District of the NWBS and up to 30% in the Danube-Dniester interfluve area of the river water pollution level observed in Kherson).
 The identified characteristics were determined based on the water circulation process that formed in the Dnipro-Bug estuarine area under the influence of significant sea level gradients resulting from the inflow of large volumes of freshened transitional waters through the estuary and the Kinburn Strait during the first days, and then followed by the density currents formed at the hydrofront between the transformed river water and surrounding sea. The influence of wind conditions manifested itself in the form of spread across the NWBS of the plume of dispersed transitional water from the Dnipro-Bug estuary and the hydrofront's position and configuration. Though wind-induced currents were not dominant, they still influenced the water dynamics and distribution of concentrations of admixtures, for instance, chlorophyll a, within the freshened plume that was outlined by the hydrofront. They also promoted penetration along the coastal shallow area of transformed river water towards Odesa.

Drifter-Observed Reversal of the South China Sea Western Boundary Current From Summer to Autumn

Abstract This study analyzes the formation, reversal, and variation of the South China Sea Western Boundary Current (SCSWBC) by nine trajectories of Beidousatellite-tracked drifters, combined with reanalysis current data and satellite remote sensing wind data. It is indicated that: (1) the maximum current speeds of Drifters 1490016, 1490026, 1488526, 862259, and 927745 exceed 1.5 m/s, with the speed of Drifter 862259 even reaching 2.3 m/s in the strong current region of the SCSWBC; (2) the SCSWBC in autumn can be sourced from either the northeastward current in the central South China Sea in summer or the westward current in the northeastern South China Sea in September; (3) the monsoon wind transition is attributed for the formation, disappearance, and reversal of the SCSWBC from summer to autumn; and (4) the interannual variation of the SCSWBC mainly depends on the transition time of the monsoon wind.

Southern South China Sea boundary current transition from summer to winter

The characteristics and mechanism of the southern South China Sea (SCS) Western Boundary Current (WBC) summer-winter transition have been investigated. The transition typically starts in early October and lasts for about two weeks. Above the thermoclines (~100 m), the transition is simultaneous with depth, while below the thermoclines the transition in deeper layer significant lags that in the shallow layers. The geostrophic balance dominates the transition of WBC. Above the thermocline, the transition is determined by the barotropic pressure gradient component. Below the thermocline, the transition is determined by the competition between the barotropic and baroclinic pressures components. When the southern SCS WBC transition above the thermocline starts, the barotropic and baroclinic pressures components offset each other below the thermocline, resulting in the lag of the geostrophic balance. With the depth increases, more time is needed for the barotropic pressures component to enhance enough to dominate a geostrophic balance, which induces the transition lag with depth. Changes in the barotropic pressure gradient component are mainly due to the variations in SCS basin scale wind stress curl, while changes in the baroclinic pressure gradient component below the thermocline are associated with the warming of the deeper water column caused by the downwelling near the continental slope and the disappearing of upwelling off Vietnam.

Eastward across the Western Sea: The Indian Oceanic Trafficking of Africans into China

AbstractDespite its greater extensiveness in comparison to the ferrying of their West African counterparts across the Atlantic Ocean into bondage in the New World, the history of the extraction of East Africans to serve as slaves in the various lands that ring the Indian Ocean is barely known to most of us. Particularly as Westerners, our knowledge of even the sketchiest outlines of the latter phenomenon pales before what we know intimately about the intricacies of the former. Furthermore, unknown altogether to too many is the fact that—from at least as early as the eighth century of the Common Era—these East African slaves were exported as distantly as China. Based principally on the pertinent Chinese sources, this study raises and investigates three fundamental questions concerning this conveyance of East Africans into China. First, who were the original enslavers of these East Africans and thus the prime purveyors of their entrance over the centuries into bondage in China? Second, how—that is, by land or by sea—and under what auspices were these East Africans typically transported from their homelands mainly along the eastern African coastline to a locale as far away as China? Third and finally, what was the probable fate of these East Africans once they had arrived in China? The essay concludes with a consideration of the consequentiality of this largely overlooked and therefore unheralded saga amidst the history of Chinese institutionalised servitude overall.

Bycatch reduction plan of offshore dredge in the western sea, Korea

Bycatch reduction plan of offshore dredge in the western sea, Korea

Contrasting the Impacts of Intraseasonal Oscillations on Yangtze Precipitation during the Summer of 1998 and 2016

In 1998 and 2016, boreal summer intraseasonal oscillation (BSISO) could reach the middle-lower reaches of the Yangtze River basin (YRB), leading to extreme precipitation. Based on multiple daily data, this study reveals the differences in BSISO events and mechanisms between 1998 and 2016. In June–July of 1998 (2016), YRB precipitation was impacted by 30–60-day oscillation, i.e., BSISO1 (10–30-day oscillation, i.e., BSISO2), with two strong (three) precipitation events occurring. In 1998, when BSISO1 was in phases 1–4 (phases 5–8), the YRB experienced a wet (dry) episode. In 2016, when BSISO2 was in phases 1–2 and 7–8 (phases 3–6), the YRB experienced a wet (dry) episode. In 1998, in event 1, the active convection of the YRB first originated in the South China Sea–western Pacific (SCS–WP) and then in the tropical Indian Ocean (IO). In 1998, in event 2, the active convection of the YRB originated in the SCS–WP. In 2016, in events 1 and 3, the active convection of the YRB originated from the SCS–WP. In 2016, in event 2, the active convection of the YRB originated from the tropical IO and the extratropical WP. Different SST and atmospheric circulations explain different BSISO modes that dominate in the YRB. In 1998 (2016), in summer, (no) strong easterly wind anomalies occurred in the SCS–WP, which are favorable (unfavorable) for the enhancement of BSISO1. Accompanying the suppressed BSISO1, BSISO2 was enhanced in 2016.

고구려 부흥운동기 사야도의 위치에 대하여

The three representative figures of the revival movement are Go Yeon-mu(高延武), Gum Mo-zam(劍牟岑) and An Seung(安勝). Gum Mo-zam met An Seung on the Saya island(史也島) and moved to the Jaeryeong(載寧) in 670. The Saya island is estimated to be the Soya island(蘇爺島) in Incheon. But this is only the reason why the pronunciation is similar. The place where Gum Mo-zam and An Seung met is around the Jaeryeong Plain(載寧平野) in Hwanghae-do. If you look at the map of the Joseon Dynasty, there was a sea in Jaeryeong Plain. The name of the sea is Jeryang(濟粱), and there is the Chol island(鐵島) in the center of the Jeryang Sea. The Chol island is located where Daedong River and Jaeryeong River meet. The Chol island was the center of transportation by the waterways of the Daedong River and Jaeryeong River. The western part of the Chol island was recognized as the sea until the Joseon Dynasty. In ancient times, the western sea(西海) can be said to be from the west of the Chol island. The position of the Chol island should be determined in consideration of the ancient terrain. Looking at the ancient terrain and the process of Gum Mo-zam descending southward, the position of the Saya island is estimated to be the Chol island.

중국의 회색지대(Gray Zone) 전략과 우리 군의 대응 방안

In this article, I discuss China’s Gray Zone strategy, which involves increasing their naval power and using asymmetric tactics to become a rising maritime power. After examining this strategy, I then discuss the sources of conflict between South Korea and China, as well as our military’s response plan. The article also mentions that although South Korea and China established diplomatic relations in 1992, there are still many unresolved issues between two countries. Especially, issues such as the demarcation of the western sea border, development of the continental shelf, marine scientific research activities, and marine environmental conservation are still unresolved. Meanwhile, China is increasing its naval power and pursuing a Gray Zone strategy at sea using its Coast Guard(CCG) and Maritime Militia(PAFMM). Gray zone refers to the ambiguous middle ground between war and peace, and it refers to an indeterminate intermediate zone that does not belong to a specific area. China is pursuing a strategy that undermines the existing order by using gray zone operations in the maritime gray zones of countries with maritime territorial disputes and un-demarcated maritime boundaries in the East China Sea and South China Sea. By using non-military means, China is pursuing a “fait accompli” strategy through numerical superiority, gradualism, and repetitive activities while preventing the situation from escalating into armed conflict. China uses its Coast Guard and Maritime Militia as the main means of its gray zone strategy, which are essentially China’s second naval force and perform various missions on behalf of the People’s Liberation Army Navy. In Korea, there are many factors that cause conflicts with China in the ocean, such as the undefined Exclusive Economic Zone(EEZ) boundary and illegal fishing by Chinese vessels. China pursues a gray zone strategy to gain an advantageous position in future negotiations with Korea. Therefore, the Korean military must establish the following measures to protect its maritime interests. The response strategy below is based on a correct understanding of the gray zone strategy, which is part of China’s asymmetric strategy. First, in the event of a maritime dispute with China, governance should be established to integrate and operate available assets. Second, a cooperative system should be established to prevent accidental conflicts between Korea and China. Third, a naval forward base in the West Sea should be built to curb China’s eastward movement. Fourth, strategies should be sought to respond in conjunction with allies. Fifth, the military’s countermeasures and tactics for responding to the gray zone strategy should be developed.

Phase Shift of the Winter South China Sea Western Boundary Current Over the Past Two Decades and Its Drivers

AbstractThe winter South China Sea (SCS) western boundary current (WBC) has presented a significant weak–strong–weak phase shift in the last two decades, as revealed by observations and model products. Its phase shift has mainly been attributed to the joint effect of wind stress curl over the SCS and Luzon Strait transport (LST). Changes in the wind stress curl and planetary vorticity input through the Luzon Strait are the two major sources maintaining the winter SCS WBC state in different phases. The LST is closely related to the Kuroshio strength and thus the Pacific North Equatorial Current (NEC) bifurcation. Therefore, the winter SCS WBC phase shift is attributed to phase shifts of the winter monsoon and the NEC bifurcation, which are mostly related to those of the Indian Ocean Dipole Mode and Atlantic Multidecadal Oscillation, respectively. Understanding the SCS circulation low‐frequency variability is essential to forecast its thermodynamic state and regional climate effect.

Rifting/spreading propagation interacts with preexisting transform faults: 3D geodynamic modeling

The divergent rifting/spreading centers and the strike-slip transform faults are the essential tectonic units on Earth, the dynamic evolution of which regulates the development of rifting/spreading basins. The propagation of rifting/spreading centers may interact with pre-existing transform faults, but how they interact with each other remains enigmatic. Here we use three-dimensional geodynamical numeric models to systematically simulate the interaction between rifting/spreading propagation and the pre-existing transform faults. Our model results provide the following findings. 1) The pre-existing transform faults affect rifting/spreading propagation promoting the formation of ridge segments with an offset distance, facilitating the process of spreading of the western sea basin and restraining the propagation of the east sea basin. Yet, the evolution of the transform faults is regulated by rifting/spreading propagation, featured by the increase of its length, the change in its width along strike and the presence of lineated magmatism. 2) The initial length and orientation of the pre-existing transform faults largely affect rifting/spreading propagation, i.e., large transform fault length favors the formation of large offset between ridge segments, and oblique transform faults facilitate the formation of overlapped spreading centers. 3) Model results shed new light on the evolution of the South China Sea basin, implying that the observed ridge segments in the east and southwest sub-basins, the difference of the Zhongnan Fault Zone width along strike and the lineated volcanos along the Zhongnan Fault Zone are the results of the interaction between the rifting/spreading propagation and the pre-existing transform fault.

Sr, Nd, and Pb isotope provenance of surface sediments on the East Siberian Arctic Shelf and implications for transport pathways

The East Siberian Arctic Shelf (ESAS) is a crucial area for sea ice formation and exportation in the Arctic Ocean. Precise sedimentary identification in the ESAS is vital to trace sea ice transport. However, tracking sea ice transport is challenging due to the complexity of the sediment sources and transport processes in the ESAS. In this study, we investigated Sr, Nd, and Pb isotopes in residual fractions of recent surface sediments in the ESAS to explore the distribution, sources, and transport pathways of terrigenous materials and track regional sea ice transport. Our results show that approximately 20–30% of the Western Laptev Sea (WLS) sediments were derived from Siberian flood basalt, characterized by a high εNd (ca. -9.0) and a high 87Sr/86Sr ratio (ca. 0.715). Furthermore, most sediments of the Eastern Laptev Sea–Western East Siberian Sea (ELS–WESS) were derived from ancient clastic and metamorphic rocks, with the lowest εNd values (ca. -12.3), highest 87Sr/86Sr ratios (ca. 0.717), and highest 207Pb/206Pb ratios (ca. 0.836). Additionally, sediments in the Eastern East Siberian Sea–Western Chukchi Sea (EESS–WCS) had the highest εNd values (ca. -7.6), lowest 87Sr/86Sr ratios (ca. 0.712), and relatively high 207Pb/206Pb ratios (ca. 0.830) due to the influence of Okhotsk–Chukotka volcanic belt (OCVB) weathering products, which contributed approximately 10–20% of the local sediments. Eastern Chukchi Sea (ECS) sediments showed relatively low εNd values (ca. -9.2), low 87Sr/86Sr ratios (ca. 0.712), and the lowest 207Pb/206Pb ratios (ca. 0.810), which probably influenced by coast erosion inputs from Alaska and Yukon River material transported via Pacific Sea Water. Based on the sediment provenance with Nd isotope, sea ice formed in the WLS and ELS–WESS is predominantly transported by the Trans-Polar Drift (TPD) to the Eurasian Basin and Fram Strait. This study provides insights for further understanding and tracking sea ice transport processes from the ESAS to the Arctic Ocean.

Winter–Summer Transition in the Southern South China Sea Western Boundary Current

Abstract The winter–summer transition in the southern South China Sea (SCS) western boundary current (WBC) is studied. Two categories have been identified. In case 1, the southern SCS WBC transition in the lower layer (below the thermocline) lags that in the upper layer (above the thermocline). In case 2, there is no transition lag at full depth. In both categories, the geostrophic balance dominates the transition. In case 1, the upper layer geostrophic balance is dominated by the sea surface height pressure gradient (SSHPG) and Coriolis forcing during southern SCS WBC transition. Therefore, there is no transition lag with depth in the upper layer. Below the thermocline layer, the competition between the SSHPG and the density pressure gradient (DPG) determines the transition. During the transition, the amplitudes of the SSHPG and DPG are basically equivalent. The SSHPG needs time to develop sufficiently larger than the DPG. Therefore, the transition in the deeper layer significantly lags that in the shallower layer. The reversal of the SSHPG is mainly attributed to the change in the basin-scale wind stress curl over the southern SCS. The change in the DPG is mainly associated with the cooling of the water along the western continental slope, which is induced by upwelling. In case 2, there is no cooling along the western continental slope, and then the amplitude of the DPG is always far smaller than that of the SSHPG. Responding to the change in the SSHPG, the southern SCS WBC transition behaves consistently at full depth. Significance Statement We have a comprehensive understanding of the South China Sea (SCS) circulation patterns in winter and summer. However, their seasonal transitions remain unclear, and a better understanding of them is potentially helpful for improving ocean circulation modeling and prediction. This paper focuses on the winter–summer transition in the SCS western boundary current (WBC). Above the thermocline (∼100 m), the transition behaves consistently in the vertical direction and is controlled by the conversion of the sea surface height–induced pressure gradient. Below the thermocline, the transition in the deeper layer of the WBC significantly lags that in the shallower layer of the WBC, which is associated with the competition between the SSH-induced pressure gradient and the density-induced pressure gradient at the sea surface.

Genetic variation in the spotted seal (Phoca largha Pallas, 1811) from the Rimsky-Korsakov Archipelago (Peter the Great Bay, western sea of Japan) as inferred from mitochondrial DNA control region sequences

The genetic variation in the breeding concentrations of spotted seals (Phoca largha) inhabiting the Rimsky-Korsakov Archipelago (Peter the Great Bay, Sea of Japan) was studied using the control region of the mitochondrial genome. A total of 17 haplotypes in the control region and adjacent threonine and proline tRNA genes of 535 bp were identified in 32 largha underyearlings. The haplotype network revealed two mitochondrial lineages of spotted seals separated by fixed mutation steps. An analysis of molecular variation (AMOVA) and phylogenetic reconstruction showed significant genetic differentiation between two groups of individuals from the same pupping sites. The obtained results are compared with available data for other parts of the spotted seal range. Possible events in the last glacial that have led to the sympatry of distinct spotted seal lineages in Peter the Great Bay are discussed.

Slantwise Convection in the Irminger Sea

AbstractThe subpolar North Atlantic is a site of significant carbon dioxide, oxygen, and heat exchange with the atmosphere. This exchange, which regulates transient climate change and prevents large‐scale hypoxia throughout the North Atlantic, is thought to be mediated by vertical mixing in the ocean's surface mixed layer. Here we present observational evidence that waters deeper than the conventionally defined mixed layer are affected directly by atmospheric forcing in this region. When northerly winds blow along the Irminger Sea's western boundary current, the Ekman response pushes denser water over lighter water, potentially triggering slantwise convection. We estimate that this down‐front wind forcing is four times stronger than air–sea heat flux buoyancy forcing and can mix waters to several times the conventionally defined mixed layer depth. Slantwise convection is not included in most large‐scale ocean models, which likely limits their ability to accurately represent subpolar water mass transformations and deep ocean ventilation.

Analysis of the relationship between the ENSO phenomenon, Net Primary Productivity and catches of yellowfin tuna in Sibolga Waters, Indonesia

Abstract. Fadhilah A, Leidonald R, Susetya IE, Dewinta AF. 2022. Analysis of the relationship between the ENSO phenomenon, Net Primary Productivity and catches of yellowfin tuna in Sibolga Waters, Indonesia. Biodiversitas 23: 4440-4447. The eastern Indian Ocean includes the western seas off of North Sumatra. They have a high potential for catching fish, which is a measure of their degree of primary production. Numerous factors, including oceanic conditions and the El Niño Southern Oscillation (ENSO) phenomena, frequently have an impact on its potential. Additionally, ENSO has an influence on the availability of nutrients that generate chlorophyll, a component of primary production, as well as water mass. It is also responsible for anomalies of sea surface temperature (SST) that occur in the Pacific Ocean. Therefore, this study aims to determine the effect of the ENSO phenomenon on primary productivity as well as the abundance of yellowfin tuna (Thunnus albacares) in the western waters of North Sumatra. Data were obtained from the Aqua MODIS level 3 satellite for analysis of net primary productivity (NPP) using various parameters, namely Vertically Generalized Production Model (VGPM), Ocean Niño Index (ONI), yellowfin tuna catch, winds from ERDDAP, and currents from AVISO. Its relationship with the abundance of yellowfin tuna, and ENSO was then determined using the Pearson correlation. The VGPM calculation showed that NPP for 2016-2020 ranged from 275.169 mgC/m2 to 994.898 mgC/m2. The study also revealed that the ENSO phenomenon has a weak relationship with primary productivity and the abundance of yellowfin tuna with correlation values of 0.262 and -0.191, respectively.

Provenance Discrimination of Siliciclastic Sediments in the Western Sea of Japan over the Past 30 kyr: Evidence from Major, Trace Elements, and Pb Isotopes

Abstract The Sea of Japan (JS), a unique marginal sea without any large river influxes in the western Pacific, provides ample information about the evolution of sea level, East Asian monsoons (EAM), sea ice activity, and ocean currents in geological time. However, insufficient investigation in the western JS limits our knowledge of East Asian climate change. This study utilizes major and trace elements and Pb isotopes of fine siliciclastic components (<63 μm) of core LV53-18-2 and determines the provenances using statistical methods and discrimination diagrams. The results show that the terrigenous debris of LV53-18-2 was mainly composed of aeolian dust from northeast China, ice-rafted debris (IRD), and volcanic materials from the Far East coast over the last 30 kyr. During the late last glacial period, sea ice activity carried weakly weathered IRD to the study area. Meanwhile, the strengthened East Asian winter monsoon (EAWM) brought dust from northeast China to the study site owing to the cold climate and enlarged sandy land. During the late last deglacial period to early Holocene (15-8 kyr), ascending boreal summer insolation drove the intense melting of sea ice. This led to the deposition of large amounts of weakly weathered IRD and remarkably influenced the chemical composition of the core. After 8 kyr, the global sea level rose to -15 m below the modern sea level and opened the Tatar Strait. Consequently, freshwater supplied by the Amur River entered the JS and gave birth to the Liman Cold Current (LCC), which transported more mafic materials from the Kema terrane upstream.

Circadian and Tidal Changes in Snapping Shrimp (Alpheus brevicristatus) Sound Observed by a Moored Hydrophone in the Coastal Sea of Western Jeju

Numerous studies have evaluated the acoustic characteristics of soniferous snapping shrimp, but a few are based on long-term mooring measurements. In this study, underwater ambient noise signals were collected from a hydrophone moored 10 m from the sea bed in the coastal sea of western Jeju, South Korea, from mid-September 2019 for 90 days to analyze the variation in the sound of snapping shrimp. The kernel signal and a threshold value were utilized to identify the snapping shrimp, and the snap rate per minute was computed for quantitative analysis. The results show that the mean and standard deviation of the snap rate in the western sea of Jeju was 2132 ± 432 per minute during the whole measurement period. The surface water temperature and tidal level decreased by 7 °C from 25 °C and 50 cm from 190 cm, respectively, over 90 days. The snap rate decreased from September mainly due to the decrease in water temperature by 71 times per minute for every 1 °C decrease. It showed a circadian cycle, increasing by 17~24% at sunrise and sunset compared to the daytime minimum. The snap rate at night was the highest in late summer but the rate dropped like the one during the day in late fall. The snap rate at high tide was 13% higher on average than at low tide. The circadian and tidal changes of the snapping shrimp sound from long-term mooring measurements may be used as primary data for underwater ambient noise and the ecological behavior of snapping shrimp.