Responses of the Sea Surface Temperature and Suspended Matter Concentration to ENSO Events in the Bohai Sea

The sea surface temperature(SST)and sea surface suspended matter concentration data in the Bohai Sea were collected by multiple NOAA satellites from 1985 to 2018.The background calibration method was used to correct the systematic errors caused by the long-term observations through multiple NOAA satellites in this paper.Then,we studied the long-term variations of the sea surface temperature(SST)and sea surface suspended matter concentration(SSC)and their response to ENSO events in the Bohai Sea.Our results show that the SST and SSC of the Bohai Sea have been increasing since 1985,with an average rate of 0.04℃per year for SST,which is higher than the global average.The average increasing rate of SSC was 0.51 mg L^(-1)yr^(-1),which may be mainly due to the enhancement of winter monsoon in the Bohai.In winter,the SST and SSC of the Bohai Sea were higher in El Niño years than in La Niña years.In El Niño years,the ocean circulations were the main factor affecting the variation in SST.The robust circulation system caused by the strong winter monsoon enhances the water exchange between the cold water of the Bohai Sea and the warm water of the Yellow Sea,resulting in a higher SST in La Niña years.In summer,the SSTs of the Bohai Sea were lower in El Niño years than those in the La Niña years because of the decrease of the SST in the Western Pacific Ocean,the weakening of the subtropical high in the western Pacific,and its eastward shift caused by the El Niño events.

Oil Spill Risk Assessment of Offshore Pipeline in the Bohai Sea Under the Perspective of Ecological Protection

In recent decades,the exploration and development of marine oil and gas resources have increased significantly to meet the increasing energy demand of mankind.The Bohai Sea is a semi-closed continental sea that has a weak water exchange capacity and high ecological fragility.However,at present,more than 200 oil platforms have been built in the Bohai Sea,with more than 270 offshore oil pipelines having a length exceeding 1600 km.The oil spill pollution of offshore platforms has a great impact on the marine environment and ecosystems.Therefore,a comprehensive assessment of its risks is of great practical significance.This paper systematically constructs a comprehensive oil spill risk assessment model that combines the oil spill risk probability model and the ocean hydrodynamic model.This paper uses the Bohai Sea offshore pipeline as an example to assess its oil spill risk.The high-risk-value areas of the Bohai Sea offshore pipeline are mainly distributed at the bottom of Liaodong Bay,the bottom of Bohai Bay,near the Caofeidian area,and the northern part of the Yellow River Estuary.

Satellite-observed significant improvement in nearshore transparency of the Bohai Sea during pollution control

The Bohai Sea(BS)is the unique semi-closed inland sea of China,characterized by degraded water quality due to significant terrestrial pollution input.In order to improve its water quality,a dedicated action named“Uphill Battles for Integrated Bohai Sea Management”(UBIBSM,2018–2020)was implemented by the Chinese government.To evaluate the action effectiveness toward water quality improvement,variability of the satelliteobserved water transparency(Secchi disk depth,Z_(SD))was explored,with special emphasis on the nearshore waters(within 20 km from the coastline)prone to terrestrial influence.(1)Compared to the status before the action began(2011–2017),majority(87.3%)of the nearshore waters turned clear during the action implementation period(2018–2020),characterized by the elevated Z_(SD)by 11.6%±12.1%.(2)Nevertheless,the improvement was not spatially uniform,with higher Z_(SD)improvement in provinces of Hebei,Liaoning,and Shandong(13.2%±16.5%,13.2%±11.6%,10.8%±10.2%,respectively)followed by Tianjin(6.2%±4.7%).(3)Bayesian trend analysis found the abrupt Z_(SD)improvement in April 2018,which coincided with the initiation of UBIBSM,implying the water quality response to pollution control.More importantly,the independent statistics of land-based pollutant discharge also indicated that the significant reduction of terrestrial pollutant input during the UBIBSM action was the main driver of observed Z_(SD)improvement.(4)Compared with previous pollution control actions in the BS,UBIBSM was found to be the most successful one during the past 20 years,in terms of transparency improvement over nearshore waters.The presented results proved the UBIBSM-achieved remarkable water quality improvement,taking the advantage of long-term consistent and objective data record from satellite ocean color observation.

Recent tectonic stress field and major earthquakes of the Bohai Sea basin

渤海位于北华北新生代裂陷盆地的东部，是一个晚第四纪形成的内陆海盆．渤海盆地活动断裂发育，地震活动强烈，交会于渤海中部的NE向营口潍坊断裂带北段、庙西北一黄河口一临邑断裂带及NW向北京一蓬莱断裂带是主要的活动构造带，将海区分成4个次级新构造区，成为现代应力场作用的构造基础．综合研究38个震源机制解和75个井区应力场等资料，以及构造应力场二维数值模拟计算结果表明，渤海及其邻区现代构造应力场的压应力方向为NE60°～90°，张应力为SN—NW30°；以水平和近水平应力作用为主；不同构造区主应力方向存在一定的差异．现今渤海地区地壳发育以NNE-NE和NW-WNW走向的共轭剪切破裂为特征，是控制地震活动的主要构造．

Grain-Size Distribution of Surface Sediments in the Bohai Sea and the Northern Yellow Sea: Sediment Supply and Hydrodynamics

The grain-size distribution of surface sediments in the Bohai Sea(BS) and the northern Yellow Sea(NYS), and its relationship with sediment supply and hydrodynamic environment were investigated based on grain-size compositions of surface sediments and modern sedimentation rates. The results showed that the surface sediments in the BS and the NYS were primarily composed of silty sand and clayey silt with a dominant size of silt. In addition, the Yellow River delivered high amount of water and sediments to the BS, and they are dominated in surface sediments(mainly silt) in the Bohai Bay, the Yellow River mouth, the center of the BS, and the north coast of Shandong Peninsula. The coarse-grained sediments were mainly deposited at the river mouth due to the estuarine filtration and physical sorting. Meanwhile, there was a significant relationship among the modern sedimentation rate, the surface sediment grain size distribution and sediment transport pattern. The areas with coarser surface sediments generally corresponded low sedimentation rates because of strong erosion;whereas the sedimentation rate was relatively high at the place that the surface sediments were fine-grained. Furthermore, the grain-size trend analysis showed that the areas with fine-grained surface sediments such as the mud area in the central BS and the upper Liaodong Bay were the convergent centers of surface sediments, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident.

Dynamic shear modulus and damping ratio characteristics of undisturbed marine soils in the Bohai Sea,China

This paper presents results from a series of stress-controlled undrained cyclic triaxial tests on the undisturbed marine silty clay,silt,and fine sand soils obtained from the Bohai Sea,China.Emphasis is placed on the major factors for predominating the dynamic shear modulus(G)and damping ratio(λ)in the shear strain amplitude(γ_(a))from 10^(-5) to 10^(-2),involving depth,sedimentary facies types,and water content of marine soils.The empirical equations of the small-strain shear modulus(G_(max))and damping ratio(λ_(min))using a single-variable of depth H are established for the three marine soils.A remarkable finding is that the curves of shear modulus reduction(G/G_(max))and the damping ratio(λ)with increasing γ_(a) of the three marine soils can be simply determined through a set of explicit expressions with the two variables of depth H and water content W.This finding is validated by independent experimental data from the literature.At the similar depths,the G value of the marine soils of terrestrial facies is the largest,followed b_(y) the neritic facies,and the G value of the marine soils of abyssal facies is the smallest.The sedimentary facies types of the marine soils have slight effect on theλvalue.Another significant finding is that the shear modulus reduction curves plotted against the γ_(a) of the three marine soils at the similar depths are significantly below those of the corresponding terrigenous soils,while the damping curves plotted against γ_(a) are just the opposite.The results presented in this paper serve as a worthful reference for the evaluation of seabed seismic site effects in the Bohai Sea due to lack of experimental data.

Reassessment of the Distribution of Mantle CO_(2) in the Bohai Sea,China:The Perspective from the Source and Pathway System

Research on the distribution of mantle CO_(2)should involve comprehensive analysis from CO_(2)source to accumulation.The crust-mantle pathway system is the key controlling factor of the distribution of mantle CO_(2),but has received little attention.The pathway system and controlling factors of CO_(2)distribution in the Bohai Sea are analyzed using data on fault styles and information on the mantle and lithosphere.The relation between volcanic rocks and the distribution of mantle CO_(2)is reassessed using age data for CO_(2)accumulations.The distribution of mantle CO_(2)is controlled by uplift of the asthenosphere and upper mantle,magma conduits in the mantle and fault systems in the crust.Uplifted regions of the asthenosphere are accumulation areas for CO_(2).The area with uplift of the Moho exhibits accumulation of mantle CO_(2)at depth.CO_(2)was mainly derived from vertical migration through the upper mantle and lower crust.The fault style in the upper crust controls the distance of horizontal migration and the locations of CO_(2)concentrations.The distribution of mantle CO_(2)and volcanic rocks are not the same,but both probably followed the same pathways sometimes.Mantle CO_(2)in the Bohai Sea is concentrated in the Bozhong sag and the surrounding area,particularly in a trap that formed before 5.1 Ma and is connected to crustal faults(the Bozhang faults)and lithospheric faults(the Tanlu faults).

Interannual Variability and Scenarios Projection of Sea Ice in Bohai Sea Part Ⅰ: Variation Characteristics and Interannual Hindcast

The Bohai Sea is one of the southernmost areas for sea ice formation in the northern hemisphere.Sea ice disasters in this body of water severely affect marine activities and the safety of coastal residents.In this study,we analyze the variation characteristics of the sea ice in the Bohai Sea and establish an annual regression model based on predictable mode analysis method.The results show the following:1)From 1970 to 2018,the average ice grade is(2.6±0.8),with a maximum of 4.5 and a minimum of 1.0.Liaodong Bay(LDB)has the heaviest ice conditions in the Bohai Sea,followed by Bohai Bay(BHB)and Laizhou Bay(LZB).Interannual variation is obvious in all three bays,but the linear decreasing trend is significant only in BHB.2)Three modes are obtained from empirical orthogonal function analysis,namely,single polarity mode with the same sign of anomaly in all of the three bays and strong interannual variability(82.0%),the north–south dipole mode with BHB and LZB showing an opposite sign of anomalies to that in LDB and strong decadal variations(14.5%),and a linear trend mode(3.5%).Critical factors are analyzed and regression equations are established for all the principal components,and then an annual hindcast model is established by synthesizing the results of the three modes.This model provides an annual spatial prediction of the sea ice in the Bohai Sea for the first time,and meets the demand of operational sea ice forecasting.

Comprehensive Investigation and Assessment of Nutrient and Heavy Metal Contamination in the Surface Water of Coastal Bohai Sea in China

With the rapid development of industrialization and urbanization of coastal regions,eutrophication and metal pollution have caused serious environmental problems in China.To better understand the potential environmental risks associated with nutrients and heavy metals,the surface water was comprehensively investigated in the coastal Bohai Sea.A total of 150 sites were sampled from seven coastal regions,and the concentrations of nutrients(DIN and DIP)and metals(Cd,Pb,Zn,Cu,Cr,As and Hg)in the surface seawater were measured.The results showed that the DIN concentration of about 50%sites exceeded the Grade-I of Seawater Quality Standard of China.Due to high concentrations of DIN,the status of eutrophication was serious in the Bohai Bay and Shuangtaizi Estuary.According to Seawater Quality Standard of China,Pb,Zn,Hg and Cu were the main metal pollutants in the coastal Bohai Sea.There was generally low ecological risk caused by heavy metals,but certain hotspots existed near Shuangtaizi Estuary and Changxingdao Island.

Seasonal variability in dissolved oxygen in the Bohai Sea,China

Deoxygenation has frequently appeared in coastal ecosystems over the past century due to the joint infl uence of increasing anthropogenically induced nutrient inputs and global warming.The semi-enclosed Bohai Sea is a typical system that is prone to deoxygenation,with regular hypoxia events consistently recorded in recent decades.Based on in-situ observation data collected in large-scale voyage surveys in the Bohai Sea during 2008-2017,the seasonal variability in dissolved oxygen(DO)and its controlling mechanisms were studied.The results indicated that in spring and autumn,the DO distributions exhibited similar spatial patterns in the surface and bottom layers,while in summer,its spatial distribution was characterized by large-scale oxygen-poor zones distributed off the Qinhuangdao Coast and the central southern Bohai Sea in the bottom layer.The controlling mechanisms of the DO distribution varied from season to season.Spring and autumn DO distributions were dominated by the seawater temperature.Under the combined eff ects of stratifi cation and decomposition,the summer bottom DO exhibited dual-core distribution.On the one hand,stratifi cation could greatly impede vertical mixing,resulting in reduced bottom DO replenishment.On the other hand,the increased bottom organic matter intensifi ed the decomposition processes,inducing massive DO consumption and elevated dissolved inorganic nitrogen concentrations.In addition,the stronger stratifi cation might be the reason for the more severe deoxygenation in the southern oxygen-poor zones in summer.Our study provides guidance for an in-depth understanding of the DO seasonality in the Bohai Sea and the mechanisms that modulate it and for the improvement of hypoxia forecasts in ocean models.

Application of an ice-ocean coupled model to Bohai Sea ice simulation

The HAMSOM(Hamburg Shelf Ocean Model),a high-resolution regional ice-ocean coupled model,was applied to investigate the seasonal evolution of Bohai Sea ice for winter 2015/2016.HAMSOM was initialized with monthly climatological temperature and salinity data from WOA13 and driven by hourly meteorological data obtained from the NCEP above the sea surface and tides at the open boundary.The ice model used here is a modifi ed Hibler-type dynamic-thermodynamic sea ice model based upon viscous-plastic rheology.The ice extent,concentration,area,thickness,length of ice season as well as the distance between the top of Liaodong Bay(North China)and the outer ice edge line were simulated and compared with the observed data.Three types of modeling experiments were carried out to investigate the eff ects of wind,tide,and both wind and tide on Bohai Sea ice.The results show that wind,as both a dynamic and a thermodynamic factor,has a signifi cant impact on the ice thickness,ice area,and ice-freezing and ice breakup dates as well as the ice velocity,while tides are a dynamic factor that infl uences only the ice velocity.During the severe ice period,the wind speed intensity increased by 25%,the average ice thickness thickened by approximately 4.0 cm in Liaodong Bay,approximately 2.1 cm in Bohai Bay and approximately 2.5 cm in Laizhou Bay,and the total ice coverage area and total ice actual area increased by about 2×104 km 2 and 1.4×104 km 2,respectively.While the tidal amplitude intensity increased by 25%,the average ice velocity increased by approximately 0.1 m/s.

Meiofaunal Community Spatial Distribution and Diversity as Indicators of Ecological Quality in the Bohai Sea, China

The Bohai Sea is a semi-enclosed marginal sea in the North West Pacific. Meiofauna samples were collected from 22 stations in the Bohai Sea to document the spatial distribution, structure, and diversity of the meiofaunal community and investigate the major factors influencing the community features. A total of 20 higher taxa of meiofauna were identified. The dominant group was Nematoda, accounting for 90.8% of the total meiofaunal abundance on average, followed by Copepoda, Bivalvia, Polychaeta, Kinorhyncha, and Ostracoda. Meiofaunal abundance ranged from 121 ± 89 ind(10 cm2)-1 to 3042 ± 1054 ind(10 cm2)-1. Diversity indices also varied among different stations, with a Margalef's richness index(d) of 1.1–3.1, Shannon-Wiener diversity index(H′) of 0.7–1.8, and Pielou's evenness index(J′) of 0.4– 0.8. Meiofaunal abundance and diversity indices were significantly lower in the areas of Bohai Bay and adjacent to Laizhou Bay. The correlation analysis showed that meiofaunal abundance and diversity indices are closely linked to variations in sediment silt-clay content, medium grain size(MDΦ), and chlorophyll-a concentrations. The ecological quality status of most stations can be ranked from poor to moderate based on meiofaunal richness. According to the value of nematode to copepod ratio(Ne:Co ratio), most stations are uncontaminated, except seven stations are slightly or moderately contaminated. Both meiofaunal richness and Ne:Co ratio indicate the poor ecological quality of three stations adjacent to Laizhou Bay. The efficiency of the meiofauna communities as environmental indicators will be tested in a greater area in the future studies.

Spatio-temporal variation of subtidal macrobenthic fauna and the ecological assessment of Longkou Artificial Island construction in Bohai Sea, China

To evaluate the status and changes of macrobenthic communities related to the construction of the Longkou Artificial Island(LAI)in the Bohai Sea,China,four annual surveys were conducted from 2010 to 2013.Significant changes on environmental variations and macrobenthic communities were observed in 2013 after the LAI construction a couple of years later.The changing environment was primarily presented by lower values of pH,dissolved oxygen(DO),organic material(OM)percentage,and higher salinity,suspended particulate matter(SPM)concentration and oil concentration.The main dominant species shifted from Polychaeta taxa in 2010 to Mollusca taxa in 2013 due to the changes of environmental variables.An apparent miniaturization tendency in body size of macrobenthic species was presented from 2010 to 2013.The biodiversity indices increased yearly from 2010 to 2013.However,inter-site homogenization was observed in both the community structure and health status.Multivariate AZTI Marine Biotic Index(M-AMBI)analysis showed that the health status of stations changed depending on its original status and distance to the LAI.However,no significant differences were found in the spatial distribution of either environmental variables or abundance,biomass and biodiversity of macrobenthic communities.All the results will provide a basis for the long-term ecological assessment of reclamation.

Quantitative Evaluation of Sea-ice Disaster in Bohai Sea Based on GOCI and Sentinel-1

The Circum-Bohai-Sea Region is an important economic zone of China.The sea ice,which occurs at each winter,is the major marine hazard of the Bohai Sea.As a result,it is very important to evaluate the damage effects quantitatively in this region,which is seldom studied and analyzed systematically using long-time-series data.In this paper,the sea-ice disaster in the Bohai Sea is evaluated quantitatively based on the Sentinel-1 and GOCI.For different hazard-bearing bodies of the marine transportation and the offshore constructions,different sea-ice-hazard indexes are defined,which can be applied to analyze the sea-ice disaster quantitatively in the Bohai Sea,including the annual and inter-annual variations in the period from 2011 to 2017.The analysis results can provide the reference of the sea-ice monitoring in the Bohai Sea.

Coupling virio-and bacterioplankton populations with environmental variable changes in the Bohai Sea

Uncovering the role of environmental factors and finding critical factors which harbor significant fractions in governing microbial communities remain key questions in coastal marine systems.To detect the interactions between environmental factors and distributions of virio-and bacterioplankton in trophic coastal areas,we used flow cytometry to investigate the abundance of virio-and bacterioplankton covering 31 stations in the Bohai Sea of China.Our results suggested that the average abundance of total virus(TV)in winter(~2.29×108 particles/mL)was slightly lower than in summer(~3.83×108 particles/mL).The mean total bacterial abundance(TB)was much lower in winter(~2.54×107 particles/mL)than in summer(~5.43×107 particles/mL).Correlation analysis via redundancy analysis(RDA)and network analysis among virioplankton,bacterioplankton and environmental factors revealed that the abundances of viral and bacterial subpopulations depend on environmental factors.In winter,only temperature significantly influenced the abundances of virio-and bacterioplankton.In summer,in addition to temperature,both salinity and nutrient(SiO2)had a remarkable impact on the distribution of virioand bacterioplankton.Our results showed a clear seasonal and trophic pattern throughout the whole water system,which revealed that temperature and eutrophication may play crucial roles in microbial distribution pattern.

Distribution and phenogenetic diversity of Synechococcus in the Bohai Sea, China

Synechococcus is one of the most abundant picocyanobacteria in marine ecosystem,and the absence of Prochlorococcus would make it indispensable as a primary producer in the Bohai Sea,North China.However,the abundance distribution and genetic diversity of Synechococcus in this region have rarely been reported.In this study,the distribution pattern of Synechococcus abundance was investigated during four cruises in April,June,August,and November from 2018 to 2019,moreover,its phenogenetic diversity was studied based on high-throughput sequencing of the cpe BA operon.The results demonstrate that phycoerythrin-containing Synechococcus was most abundant in August when temperature was high and oxygen saturation was low.During this period,Synechococcus pigment type(PT)2 was abundant in the Bohai Bay and Laizhou Bay under conditions of high nutrient concentration,temperature,and turbidity.In comparison,PT3,especially those clusters characterized with high or variable ratio of phycourobilin and phycoerythrobilin,was predominant in the Bohai Strait and Liaodong Bay under conditions of high salinity,pH,and oxygen saturation.Furthermore,co-occurrence correlations using network analysis revealed that Synechococcus PTs were related to 15.37%-43.48%of the prokaryotic genera.Synechococcus PT3c/PT3d and PT2 were the most important PTs in the network.The hierarchical clustering revealed that taxa co-occurred with Synechococcus PTs diff ered among samples.It could be attributed to the substance exchange and the environmental impact,which calls for more studies in the future.

Diversity and community structure of eukaryotic microalgae in surface sediments in the central Bohai Sea,China,based on a metabarcoding approach

Sediment samples were collected at 17 stations in the central Bohai Sea,China,and the diversity and community structure of eukaryotic microalgae were assessed by metabarcoding the V4 region of 18S r DNA.A total of 930 operational taxonomic units(OTUs)were detected for microeukaryotes,including 98algal OTUs.The algal communities comprised 42 genera belonging to 19 classes of six phyla,and they were dominated by chrysophytes and dinoflagellates.Dinoflagellates were also the most diverse microalgal group.The nano-sized dinoflagellates Biecheleria halophila and Azadinium trinitatum occurred abundantly in the study area;however,they have not been reported previously,as they may be overlooked or misidentified in light microscopy.Many pico-sized chlorophytes were detected in the sediment samples.Sixteen of the detected OTUs were assigned to potentially harmful and/or bloom-forming microalgae,suggesting some potential risks of harmful algal blooms in the central Bohai Sea.The capacity of metabarcoding to detect morphologically cryptic and small species makes this method a sufficiently sensitive means of detection for assessing eukaryotic microalgae in sediments.

Tintinnid community throughout the Bohai Sea during the spring

As one of the important microzooplankton in marine pelagic habitats,tintinnids are classified as neritic genera,oceanic genera and cosmopolitan genera.Until now,we know little about the interaction between neritic and oceanic genera in continental shelves.Low species richness area was found in the mixing area between neritic and oceanic genera in the East China Sea.In this study,we investigated the spatial distribution of tintinnid community throughout the entire Bohai Sea in May(spring)of 2014 to find out:(1)whether the tintinnid assembalges differed in the three major bays bordering this shallow inland sea;(2)whether there was low species richness area in the Bohai Sea.Three genera and 11 species attributed to neritic and cosmopolitan taxa were reported from this region.Tintinnid abundance averaged(81±216)ind./L(0–1234 ind./L).Tintinnid community differed within the three major bays,with each characterized by different tintinnid taxa.Referring to the average abundance of three bays,tintinnids were most abundant in the Laizhou Bay((328±445)ind./L),and least abundant in the Liaodong Bay((34±57)ind./L).A low species richness area occurred in the central Bohai Sea(20–40 m isobaths),in some stations of which no tintinnid was recorded.Our study demonstrates that tintinnid community varied greatly over small spatial scales,and low species richness area was found in the mixing area between neritic and oceanic genera within this inland sea.

Spatiotemporal Variations and Driving Factors of Coastline in the Bohai Sea

The utilization and protection of coastlines play a crucial role in the sustainable development of coastal cities.The coastline designations in recent years have witnessed more coastal areas worldwide undergoing significant land reclamation for agriculture,industry,and urbanization purposes.This study used remote sensing images from 1986 to 2016 to analyze spatiotemporal changes in the coastlines of 13 cities around the Bohai Sea,which cover one city(Tianjin City)and three provinces(Liaoning,Hebei,and Shandong).Using coastline and socioeconomic data from 1986 to 2016,a partial least-squares regression(PLSR)model was established to analyze factors affecting the utilization of coastlines in each city.The results showed that from 1986 to 2016,the retention rates of natural coastlines in the cities around the Bohai Sea decreased,and the overall coastline expanded toward the sea.Furthermore,the impacts of human activities were prominent on the silty mud and sandy coastlines.Economic development,population growth,and urbanization were the main drivers of the development and construction of coastal cities,which changed the coastlines around the Bohai Sea to a state of high-intensity use.In addition,national macro policies and the external market environment indirectly drove the intensity of coastline use through regulations and interventions in cities.However,there were significant differences in the levels of development of the cities surrounding the Bohai Sea.In the future,the differences in the original coastal resources and urban development planning must be considered,the traditional parameters of economic development must be changed,the efficiency of coastline utilization must be improved,and urban clusters must be integrated.

Long-term trend analysis of wave characteristics in the Bohai Sea based on interpolated ERA5 wave reanalysis from 1950 to 2020

Reasonably understanding of the long-term wave characteristics is very crucial for the ocean engineering.A feedforward neural network is operated for interpolating ERA5 wave reanalysis in this study,which embodies a detailed record from 1950 onwards.The spatiotemporal variability of wave parameters in the Bohai Sea,especially the significant wave height(SWH),is presented in terms of combined wave,wind wave and swell by employing the 71 years(1950–2020)of interpolated ERA5 reanalysis.Annual mean SWH decreases at−0.12 cm/a estimated by Theil-Sen estimator and 95th percentile SWH reflecting serve sea states decreases at−0.20 cm/a.Inter-seasonal analysis shows SWH of wind wave has steeper decreasing trend with higher slopes than that of swell,especially in summer and winter,showing the major decrease may attribute to the weakening of monsoon.The inner Bohai Sea reveals a general decreasing trend while the intersection connecting with the Yellow Sea has the lower significance derived by Mann-Kendall test.Meanwhile,95th percentile SWH decreases at a higher rate while with a lower significance in comparison with the mean state.The frequencies of mean wave directions in sub-sector are statistically calculated to find the seasonal prevailing directions.Generally,the dominant directions in summer and winter are south and north.A similar variation concerning to SWH,the trend of the mean wave period is provided,which also shows a decrease for decades.