A case study of continental shelf waves in the northwestern South China Sea induced by winter storms in 2021

This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.

Securing offshore resources development:A mathematical investigation into gas leakage in long-distance flexible pipes

Gas flexible pipes are critical multi-layered equipment for offshore oil and gas development.Under high pressure conditions,small molecular components of natural gas dissolve into the polymer inner liner of the flexible pipes and further diffuse into the annular space,incurring annular pressure build-up and/or production of acidic environment,which poses serious challenges to the structure and integrity of the flexible pipes.Gas permeation in pipes is a complex phenomenon governed by various factors such as internal pressure and temperature,annular structure,external temperature.In a long-distance gas flexible pipe,moreover,gas permeation exhibits non-uniform features,and the gas permeated into the annular space flows along the metal gap.To assess the complex gas transport behavior in long-distance gas flexible pipes,a mathematical model is established in this paper considering the multiphase flow phenomena inside the flexible pipes,the diffusion of gas in the inner liner,and the gas seepage in the annular space under varying permeable properties of the annulus.In addition,the effect of a variable temperature is accounted.A numerical calculation method is accordingly constructed to solve the coupling mathematical equations.The annular permeability was shown to significantly influence the distribution of annular pressure.As permeability increases,the annular pressure tends to become more uniform,and the annular pressure at the wellhead rises more rapidly.After annular pressure relief followed by shut-in,the pressure increase follows a convex function.By simulating the pressure recovery pattern after pressure relief and comparing it with test results,we deduce that the annular permeability lies between 123 and 512 m D.The results help shed light upon assessing the annular pressure in long distance gas flexible pipes and thus ensure the security of gas transport in the emerging development of offshore resources.

Freshening of the Intermediate Waters in the Northern South China Sea over the Past Six Decades

The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the long-term changes in the intermediate water in the SCS have not been thoroughly studied due to limited data,particularly in relation to its thermodynamic variations.This study utilized reanalysis data products to identify a 60-year trend of freshening in the intermediate waters of the northern South China Sea(NSCS),accompanied by an expansion of low-salinity water.The study also constructed salinity budget terms,including advection and entrainment processes,and conducted an analysis of the salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of the intermediate water in the NSCS.The analysis revealed that the freshening in the northwest Pacific Ocean and the intensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes in the NSCS.Additionally,a weakened trend in the intensity of vertical entrainment also contributes to the freshening in the NSCS.This study offers new insights into the understanding of regional deep sea changes in response to variations in both thermodynamics and oceanic dynamic processes.

Simulations and Projections of Winter Sea Ice in the Barents Sea by CMIP6 Climate Models

Dramatic changes in the sea ice characteristics in the Barents Sea have potential consequences for the weather and climate systems of mid-latitude continents,Arctic ecosystems,and fisheries,as well as Arctic maritime navigation.Simulations and projections of winter sea ice in the Barents Sea based on the latest 41 climate models from the Coupled Model Intercomparison Project Phase 6(CMIP6)are investigated in this study.Results show that most CMIP6 models overestimate winter sea ice in the Barents Sea and underestimate its decreasing trend.The discrepancy is mainly attributed to the simulation bias towards an overly weak ocean heat transport through the Barents Sea Opening and the underestimation of its increasing trend.The methods of observation-based model selection and emergent constraint were used to project future winter sea ice changes in the Barents Sea.Projections indicate that sea ice in the Barents Sea will continue to decline in a warming climate and that a winter ice-free Barents Sea will occur for the first time during 2042-2089 under the Shared Socioeconomic Pathway 585(SSP5-8.5).Even in the observation-based selected models,the sensitivity of winter sea ice in the Barents Sea to global warming is weaker than observed,indicating that a winter ice-free Barents Sea might occur earlier than projected by the CMIP6 simulations.

Tracing the sources of nutrients through the Tsushima/Korea Strait

The nutrients from the East China Sea(ECS) through the Tsushima/Korea Strait(TS) strongly impact the eco system of the Japan Sea(JS).The complex origins of the Tsushima Warm Current and the various nutrient sources in the ECS result in complex spatial-temporal variations in nutrients in the TS.Using a physical-biological model with a tracking technique,we studied the effects of nutrient sources from the ECS on the TS.Among all the nutrient sources,the Kuroshio has the highest nutrient concentrations in the TS.Its maximum concentration occurs at the bottom,while those of rivers and atmospheric depo sition occur at the surface,and that of the Taiwan Strait occurs in the middle layer.The nutrient transport through the TS exhibits similar seasonal variations,as does the volume transport.The transport of nutrients from the Kuroshio accounts for more than 85% of the total.The transport of nutrients from the Taiwan Strait is greater during autumn and winter.The transport of dissolved inorganic nitrogen(DIN) from both rivers and atmospheric deposition through the TS peak in August.Nutrient transport cannot be equated with volume transport.The DIN in the less saline zone originates not only from rivers but also from atmospheric deposition and the Kuroshio.The transport of nutrients from the Taiwan Strait is not as significant as its volume transport in the TS.

STUDY ON DEVELOPMENT STRATEGY OF SHIPPING CENTERS AND TRANSPORTATION NETWORKS IN THE YELLOW SEA RIM

It is very important to establish cooperative mechanism to guarantee allmembers to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategiesof shipping centers and transportation network are discussed based on economic globalizationtendency. The results argue that a united transportation network should be built in order to promotethe economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai,Pusan, Kobe, and Tokyo as cores. The authorities of China, Japan, R. 0. Korea and D. P. R. Koreashould make more efforts to build a set of cooperation institutions based on raising thetransportation efficiency.

NATO and EU Strategies for the Black Sea Region： The Challenge of Power Balance in New Security Environment

The article gives an overview on the dynamic political processes in the Black Sea region after some major geostrategic changes posing instability concerns in the region. The aim is to summarise the policy tendencies of the international organisations （NATO and EU） towards Russia and to present some analytical thoughts on current Euro-Atlantic strategies. Proposed is a different way of thinking based on the ＂congagement＂ approach.

The Romania-US Strategic Partnership and the Security of the Wider Black Sea Region: Historical Landmarks

The Strategic Partnership,launched in 1997 with the purpose of becoming an advanced mechanism of bilateral cooperation between Romania and the United States regarding fields of strategic interest for both countries,is an important element of maintaining peace and stability in South-Eastern Europe and in the Black Sea area.The Partnership determined a substantial evolution of the bilateral relations based on an intense political speech,as an important aspect for the regional security,and promoted democracy near the Euro-Atlantic community.Romania’s relation with the United States,being focused on security aspects,proves its utility,considering that to this day the North Atlantic Alliance and the European Union do not have a common strategic vision regarding the Wider Black Sea Region.This is due to conceptual differences and to the fact that,unlike Central and Eastern Europe—where the integrations of NATO and EU were linked,in the Black Sea area,the situation is different,having in mind that only Romania and Bulgaria have been part of these structures.This study’s purpose is to present both the evolution of this cooperation format between Romania and the United States in the last two decades and its relevance for the new regional security system.In the circumstances in which the events in Ukraine in 2014 lead to unprecedented tension(Post-Cold War)between the Russian Federation and the Occident,the USA’s involvement in ensuring the security of the extended Black Sea Region gains even more relevance.

Hydrocarbon reserves of the South China Sea:Implications for regional energy security

The countries such as China,Vietnam,Philippines,Malaysia,Indonesia and Brunei that border South China Sea region have immense stakes in exploring and exploiting the natural resources of the region including hydrocarbon.More than the hydrocarbon reserves,the South China Sea is home to World’s high-networth trade route that brings the interests of non-geographic entities to this region.Further,the purported reserves of hydrocarbon in the region are in the orders of Persian Gulf but are not yet properly explored and the reserves recovered owing to territorial and non-claimant stakeholder’s influences/interventions.This paper is a synopsis of information on the hydrocarbon reserves of the South China Sea region,and evaluates the territorial and extra-territorial interests in the light of energy security and equitable development and utilization of natural resources from a geological perspective.We also suggest several measures for future consideration and implementation.

Arctic sea ice volume export through the Fram Strait: variation and its effect factors

Arctic sea ice export is important for the redistribution of freshwater and sea ice mass.Here,we use the sea ice thickness,sea ice velocity,and sea ice concentration(SIC)to estimate the exported sea ice volume through the Fram Strait from 2011 to 2018.We further analyse the contributions of the sea ice thickness,velocity and concentration to sea ice volume export.Then,the relationships between atmospheric circulation indices(Arctic Oscillation(AO),North Atlantic Oscillation(NAO),and Arctic Dipole(AD))and the sea ice volume export are discussed.Finally,we analyse the impact of wind-driven oceanic circulation indices(Ekman transport(ET))on the sea ice volume export.The sea ice volume export rapidly increases in winter and decreases in spring.The exported sea ice volume in winter is likely to exceed that in spring in the future.Among sea ice thickness,velocity and SIC,the greatest contribution to sea ice export comes from the ice velocity.The exported sea ice volume through the zonal gate of the Fram Strait(which contributes 97%to the total sea ice volume export of the Fram Strait)is much higher than that through the meridional gate(3%)because the sea ice flowing out of the zonal gate has the characteristics of a high thickness(mainly thicker than 1 m),a high velocity(mainly faster than 0.06 m/s)and a high concentration(mainly higher than 80%).The AD and ET explain 53.86%and 38.37%of the variation in sea ice volume export,respectively.

Analyzing the Impact of Blockchain Models for Securing Intelligent Logistics through Unified Computational Techniques

Blockchain technology has revolutionized conventional trade.The success of blockchain can be attributed to its distributed ledger characteristic,which secures every record inside the ledger using cryptography rules,making it more reliable,secure,and tamper-proof.This is evident by the significant impact that the use of this technology has had on people connected to digital spaces in the present-day context.Furthermore,it has been proven that blockchain technology is evolving from new perspectives and that it provides an effective mechanism for the intelligent transportation system infrastructure.To realize the full potential of the accurate and efficacious use of blockchain in the transportation sector,it is essential to understand the most effective mechanisms of this technology and identify the most useful one.As a result,the present work offers a priority-based methodology that would be a useful reference for security experts in managing blockchain technology and its models.The study uses the hesitant fuzzy analytical hierarchy process for prioritizing the different blockchain models.Based on the findings of actual performance,alternative solution A1 which is Private Blockchain model has an extremely high level of security satisfaction.The accuracy of the results has been tested using the hesitant fuzzy technique for order of preference by similarity to the ideal solution procedure.The study also uses guidelines from security researchers working in this domain.

A review of science–policy interface for water governance in the Caspian Sea

Science and policy have been interlinked for decades and perform essential nexus conditions in the governing aspects of environmental scenarios.This review paper examines the present challenges in the science–policy interface in terms of water governance in the Caspian Sea and identifies effective conditions that may be used in the current context to enhance the mechanism.The evaluation of the science–policy link in the water policy of the Caspian Sea reveals a gap between knowledge producer and governance system,impeding the translation of scientific information into action.Complicated and context-dependent solutions make it challenging to establish effective science–policy processes in the Caspian Sea water governance settings.Establishing a common governing authority,implementing water and resource management regulations,and protecting the natural environment through legal frameworks are crucial steps to address these concerns and ensure sustainable development.Collaboration among coastal states is essential in environmental,economic,and social aspects of regional development.However,the lack of a comprehensive approach,coherent activities,and effective utilization of national and regional power has hindered efforts to halt the environmental degradation of the Caspian Sea.Local governments need to recognize their responsibility to protect and utilize the Caspian Sea for present and future generations,considering both environmental and human security.The interlinkage of the Caspian Sea water governance with the Organization for Economic Co-operation and Development(OECD)water governance principles offers a framework for policymakers to assess gaps and make necessary amendments to existing mechanisms.Effective science–policy interaction,engagement of diverse stakeholders,institutionalizing agreements,and addressing collective action issues are critical for successful water governance.

Application of LICOM to the numerical study of the water exchange between the South China Sea and its adjacent oceans

On the basis of 900-year integration of a global ocean circulation model-LICOM driven by ECMWF reanalysis wind data with uniform 0.5°-grids, a quantitative estimate of the annual and monthly mean water exchange of the South China Sea （SCS） with its adjacent oceans through 5 straits is obtained. Among them, the annual transport is the largest in the Luzon Strait, then in the Taiwan Strait, and then in the Sunda Shelf, in the Balabac Strait and in the Mindoro Strait in turn, the largest monthly transport variation appears in the Luzon Strait and Sunda shelf. It is shown that the mass transport through the Taiwan Strait is affected by monsoon, while the transport through the Luzon Strait may be associated with the bifurcation position of the North Equatorial Current off the east Philippines shore; the transports in the Luzon Strait and Sunda Shelf are out of phase in direction but well correlated in magnitude. The annual and monthly mean heat and salinity exchange of the SCS through the straits are also calculated and shown to be in phase with the mass transport. The Kuroshio water carries about 0.43 PW heat transport and 151.33 kt/s salinity transport into the SCS, while most of them is carried out of the SCS through the Taiwan Strait and Sunda Shelf annually. The further model integration based on the 900-year integration for another 44 a from 1958 to 2001 driven by real wind data （ERA40 data） shows that the monthly mean mass transport via these straits varies annually with a large variation range, which may be associated with the seasonal and interannual variations in the current field and sea surface height in the SCS. The mean mass transport through the Taiwan Strait, Luzon Strait, Mindoro Strait, Balabac Strait and Sunda Shelf is 2.012×10^6, -4.063×10^6, -0.124×10^6, -0.083×10^6 and 2.258×10^6 m^3/s, respectively.

DYNAMIC CHARACTERISTICS OF SEASONAL THERMOCLINE IN THE DEEP SEA REGION OF THE SOUTH CHINA SEA

The dynamic characteristics of the seasonal thermocline in the deep sea region of the South China Sea were analyzed by using seasonal mean temperature climatology. The thermocline undergoes remarkably seasonal variation throughout a year, is thinnest and weakest in winter, and thickest in spring, strongest in summer and fall. Due to the upper Ekman transport caused by monsoon over the SCS, the thermocline slopes upward(downward) in winter(summer) from northwest to southeast, but there is no pileup of upper warm water along the monsoon direction. In addition, the intrusion of the Kuroshio loop through the Luzon Strait, and some local eddies in the SCS, can notably affect the depth, thickness and strength of the thermocline in the deep sea region of the SCS.

The cooling and moistening effect on the formation of sea fog in the Huanghai Sea

With the sea surface observations from ICOADS for the years 1960-2002, the conditions of coohng, evaporauon anu water vapol transportation are analyzed and compared for the formation of seasonal sea fog in April-July in the Huanghai Sea. It is found that sea surface cooling is always existent during the fog seasons while sea surface evaporation only appears in April-June in the Huanghai Sea. Local evaporation alone is not sufficient to form fogs though it may lead to light ones. Water vapor transported from the low-latitudes accomplished by specific synoptic systems is the most important condition for sea fog formation. In general, the moistening effect is more important than the cooling one.

Seasonal variation of water transport through the Karimata Strait

Four trawl-resistant bottom mounts, with acoustic Doppler current profilers(ADCPs) embedded, were deployed in the Karimata Strait from November 2008 to June 2015 as part of the South China Sea-Indonesian Seas Transport/Exchange and Impact on Seasonal Fish Migration(SITE) Program, to estimate the volume and property transport between the South China Sea and Indonesian seas via the strait. The observed current data reveal that the volume transport through the Karimata Strait exhibits significant seasonal variation. The winteraveraged(from December to February) transport is –1.99 Sv(1 Sv=1×10~6 m^3/s), while in the boreal summer(from June to August), the average transport is 0.69 Sv. Moreover, the average transport from January 2009 to December2014 is –0.74 Sv(the positive/negative value indicates northward/southward transport). May and September are the transition period. In May, the currents in the Karimata Strait turn northward, consistent with the local monsoon. In September, the southeasterly trade wind is still present over the strait, driving surface water northward, whereas the bottom flow reverses direction, possibly because of the pressure gradient across the strait from north to south.

A numerical study of the South China Sea deep circulation and its relation to the Luzon Strait transport

A fine-resolution MOM code is used to study the South China Sea basin-scale circulationand its relation to the mass transport through the Luzon Strait. The model domain includes the South China Sea, part of the East China Sea, and part of the Philippine Sea so that the currents in the vicinity of the Luzon Strait are free to evolve. In addition, all channels between the South China Sea and the Indonesian seas are closed so that the focus is on the Luzon Strait transport. The model is driven by specified Philippine Sea currents and by surface heat and salt flux conditions. For simplicity, no wind-stress is applied at the surface.The simulated Luzon Strait transport and the South China Sea circulation feature a sandwich vertical structure from the surface to the bottom. The Philippine Sea water is simulated to enter the South China Sea at the surface and in the deep ocean and is carried to the southern basin by western boundary currents. At the intermediate depth, the net Luzon Strait transport is out of the South China Sea and is fed by a western boundary current flowing to the north at the base of the thermocline. Corresponding to the western boundary currents, the basin circulation of the South China Sea is cyclonic gyres at the surface and in the abyss but an anti-cyclonic gyre at the intermediate depth. The vorticity balance of the gyre circulation is between the vortex stretching and the meridional change of the planetary vorticity. Based on these facts, it is hypothesized that the Luzon Strait transports are determined by the diapycnal mixing inside the entire South China Sea. The South China Sea plays the role of a 'mixing mill' that mixes the surface and deep waters to return them to the Luzon Strait at the intermediate depth. The gyre structures are consistent with the Stommel and Arons theory (1960), which suggests that the mixing-induced circulation inside the South China Sea should be cyclonic gyres at the surface and at the bottom but an anti-cyclonic gyre at the intermediate depth. The simulated gyre circulation at the intermediate depth has been confirmed by the dynamic height calculation based on the Levitus hydrography data. The sandwich transports in the Luzon Strait are consistent with recent hydrographical observations.Model results suggest that the Kuroshio tends to form a loop current in the northeastern South China Sea. The simulated Kuroshio Loop Current is generated by the pressure head at the Pacific side of the Luzon Strait and is enhanced by the β-plane effects. The β - plane appears to be of paramount importance to the South China Sea circulation and to the Luzon Strait transports. Without the β-plane, theLuzon Strait transports would be greatly reduced and the South China Sea circulation would be complete-ly different.

Simulation of Suspended Sediment in the Yellow and East China Seas

Described is an initial attempt to simulate the suspended sediment dynamics relating to tidal and wave forcing during summertime in June 1980 and August 1981 for the Yellow and East China Seas continental shelf. The cohesive/non-cohesive sediment resuspension and movement generated by the interaction between current and wave are modeled by use of ECOMSED and WAM Cycle 4. Model results are compared with observations in US-China Marine Sedimentation Dynamics Program performed for 1980-81 at off the Changjiang estuary. The main features of simulations show that suspended sediment concentrations during the summer decreased markedly offshore as observed during the simulation periods. As for some discrepancies for the mouth of the estuary with high river discharges, i.e., the Changjiang River, the model did not properly reproduce the over-mixing situation in the summer; thus distinct vertical concentration variation in this local region is not agreeable with observation. However, general dispersal patterns of suspended sediment movement seem to be agreeably reproduced for the nearshore shallow region. Some of the procedures of simulation and results are presented and discussed.

Clay mineral distribution in surface sediments of the South China Sea and its significance for in sediment sources and transport

Clay minerals of surface sediments in the South China Sea （SCS） are analyzed with X-ray diffraction, and their transport is explored with a grain size trend analysis （GSTA） model. Results show that clay mineral types in various sedimentary environments have different sediment sources and transport routes. Sediments in the northern SCS （north of 20°N） between the southwest of Taiwan Island and the outer mouth of the Pearl River have high contents of illite and chlorite, which are derived mainly from sediments on Taiwan Island and/or the Yangtze River. Sediments from the Pearl River are characterized by high kaolinite and low smectite content, and most are distributed in the area between the mouth of the Pearl River and northeast of Hainan Island and transported vertically from the continental shelf to the slope. Characterized by high illite content, sediments from Kalimantan Island are transported toward the Nansha Trough. Sediments from Luzon Island are related with volcanic materials, and are transported westwards according to smectite distribution. On the Sunda Shelf, sediments from the Mekong River are transported southeast in the north while sediments from the Indonesian islands are transported northward in the south. Ascertaining surface sediment sources and their transport routes will not only improve understanding of modem transportation and depositional processes, but also aid paleoenvironmental and paleoclimatic analysis of the SCS.

Numerical simulation of the Kuroshio intrusion into the South China Sea by a passive tracer

Owing to lack of observational data and accurate definition,it is difficult to distinguish the Kuroshio intrusion water from the Pacific Ocean into the South China Sea（SCS）.By using a passive tracer to identify the Kuroshio water based on an observation-validated three-dimensional numerical model MITgcm,the spatio-temporal variation of the Kuroshio intrusion water into the SCS has been investigated.Our result shows the Kuroshio intrusion is of distinct seasonal variation in both horizontal and vertical directions.In winter,the intruding Kuroshio water reaches the farthest,almost occupying the area from 18°N to 23°N and 114°E to 121°E,with a small branch flowing towards the Taiwan Strait.The intrusion region of the Kuroshio water decreases with depth gradually.However,in summer,the Kuroshio water is confined to the east of 118°E without any branch reaching the Taiwan Strait; meanwhile the intrusion region of the Kuroshio water increases from the surface to the depth about 205 m,then it decreases with depth.The estimated annual mean of Kuroshio Intrusion Transport（KIT） via the Luzon Strait is westward to the SCS in an amount of –3.86×106 m3/s,which is larger than the annual mean of Luzon Strait Transport（LST） of –3.15×106 m3/s.The KIT above 250 m accounts for 60%–80% of the LST throughout the entire water column.By analyzing interannual variation of the Kuroshio intrusion from the year 2003 to 2012,we find that the Kuroshio branch flowing into the Taiwan Strait is the weaker in winter of La Ni？a years than those in El Ni？o and normal years,which may be attributed to the wind stress curl off the southeast China then.Furthermore,the KIT correlates the Ni？o 3.4 index from 2003 to 2012 with a correlation coefficient of 0.41,which is lower than that of the LST with the Ni？o 3.4 index,i.e.,0.78.