Stratification in central Bohai Sea and how it has shaped hypoxic events in summer

In the last 10 years(2012-2021),five hypoxic events have been observed in summer in the central Bohai Sea(CBS).Frequent and persistent hypoxia will have an impact on the ecosystem of the CBS.In this paper,historical sea temperature(ST),salinity(SAL),density(Den),and dissolved oxygen(DO)concentration data from three stations in the CBS are analyzed via the linear regression method,and the correlations between the stratification factors(ST,SAL,and Den)and DO concentration are determined.The thresholds of the stratification factors at the three stations in June in the year in which hypoxia occurred were determined and applied to survey data from 29 stations in late May to early June in 2022 in the CBS;this assessment found that the data from 19 stations indicated that hypoxia was about to occur.In August,the survey data showed that 14 out of the 29 stations indicated hypoxic conditions,of which 12 were from the predicted 19 stations,meaning that the estimation accuracy reached 63%.The same approach was applied to data from June 2023.The data for August from a bottom-type online monitoring system in the CBS verified the occurrence of hypoxic events around Sta.M2.The results show that the strength of the seawater stratification plays a leading role in hypoxic events in the summer in the CBS,and the thresholds of the stratification factors can be used to predict the occurrence of hypoxic events.

Spatial correlations in time and frequency domains between chlorophyll-a concentration and environmental factors in the Bohai Sea

Based on the reconstructed MODIS data and ECMWF reanalysis data from 2003 to 2021,spatial correlations between chlorophyll a(Chl a)and sea surface temperature(SST),photosynthetically available radiation(PAR),aerosol optical thickness(AOT),and wind speed(WS)in the Bohai Sea were analyzed from the perspective of time domain and frequency domain.Results indicate that the frequency domain analysis was more conducive to revealing the correlations between Chl a and environmental factors.The spatial pattern of time-domain correlations was similar to the isobaths of the Bohai Sea,which was positive in shallow waters and negative in deep waters for SST,PAR,and AOT,and was reversed for WS.Frequency-domain correlations were obtained by performing Fourier Transform and were higher than correlations in time domain.The spatial distributions indicated that the effects of SST and PAR on Chl a were greater than AOT and WS in the Bohai Sea.Additionally,cross-spectrum analysis was applied to explore the response relationships.A depth-dependent pattern was shown in correlations and time lags,indicating that the influential mechanism of environmental factors on Chl-a concentration is related to seawater depth.

Response of phytoplankton communities to environmental changes in the Bohai Sea in late summer (2011−2020)

Understanding the dynamics of phytoplankton communities in coastal zones is crucial for the management and conservation of coastal ecosystems.Previous research indicated that the phytoplankton community structure and dominant taxa in the Bohai Sea(BHS)have exhibited significant shifts from the 1990s to the early 2010s in response to environmental changes,especially the change in nutrient structure.This study comprehensively investigated the variations in net-collected phytoplankton(>76μm)community structure,diversity,and environmental factors in the BHS during the late summers of 2011-2020,aiming to understand the recent trend in phytoplankton community structure and to explore the interactions between the communities and the environment.During the study period,the nutrient status in the BHS was characterized by a decrease in dissolved inorganic nitrogen(DIN)concentration,an increase in dissolved inorganic phosphorus(DIP)concentration,and a return of the nitrogen-to-phosphorus(N/P)molar ratio(hereinafter referred to as N/P ratio)to the Redfield ratio since 2016.The eutrophication index(EI)in the BHS remained stable and was generally at a low level(<1).The Dia/Dino index fluctuated but did not show an obvious trend.Overall,the eutrophication,the imbalance in nutrient ratio,and the shift in phytoplankton community structure did not continue during the study period.The increased abundance of phytoplankton was strongly associated with elevated concentrations of DIN,as well as higher N/P and nitrogen-to-silicon(N/Si)ratios,whereas the greater diversity was strongly linked to higher concentrations of DIP.Diatoms and dinoflagellates showed significant differences in their interactions with the environment,and their relative dominance was related to water column depth and stratification intensity;their impacts on the phytoplankton community diversity were also significantly different.The variations of certain dominant species,i.e.,Skeletonema costatum,Paralia sulcata,and Tripos longipes,exhibited strong links to the changes in nutrient structure in the BHS.The findings of this study contribute to understanding the regional environmental changes and provide insights into the adaptive strategies of coastal ecosystems in response to environmental shifts and fluctuations.

Temporal and Spatial Distribution of DIN and DIP Concentrations and Source Apportionment Along the Bohai Sea of China During 2015-2022

The Bohai Sea is one of the most polluted sea areas in China.In this study,we used 2184 integrated concentrations of dissolved inorganic nitrogen(DIN)and dissolved inorganic phosphorus(DIP)in the Bohai Sea of China during spring(March,April,and May),summer(June,July,and August),and autumn(October and November)from 2015 to 2022 to explore the trends and sources of nutrients variations.From 2015 to 2022,DIN showed a downward trend until 2020 and then an upward trend,whereas DIP exhibited a stable trend with a slight decrease.The concentrations of DIN and DIP had similar seasonal pattern which was the highest in autumn(0.292±0.247 mg/L for DIN and 0.013±0.016 mg/L for DIP)but lower in spring(0.267±0.238 mg/L for DIN and 0.006±0.010 mg/L for DIP)and summer(0.263±0.324 mg/L for DIN and 0.008±0.010 mg/L for DIP).Sources of DIN and DIP apportioned by the positive matrix factorization(PMF)model were riverine input,sediment resuspension,sewage discharge,atmospheric deposition,and underground input.During 2015-2022,the largest contributor to DIN was sewage discharge(28.7%)and the largest contributor to DIP was sediment resuspension(44.6%).Seasonally,DIN in spring and autumn was dominated by sewage discharge(45.4%and 27.8%,re-spectively).Whereas in summer,it was dominated by riverine input(32.4%)and atmospheric deposition(29.7%).DIP was dominated by sediment resuspension during all three seasons(35.8%-52.5%).In addition,the increase in DIN concentrations in 2021 and 2022 were mainly due to the incremental input of river discharge and atmospheric deposition caused by increased precipitation during sum-mer and autumn.

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．

Numerical modeling of tidal current of LNG terminal in Caofeidian,Bohai Sea

In order to reasonably simulate tidal currents around small structures such as piles in a large-scale model domain, a 2-D hydrodynamic integrated model for Bohai Sea is established with the finite element method. The grid can be discretionarily refined as a non-structure triangle or quadrilateral so that piers can be treated as one or several impermeable elements with an area of 20 to 30 km^2 in a model domain over 85 700 km^2. The computational results of tidal levels and horizontal velocities are in good agreement with the field data. Based on the computed results by the model, the layout of an open 105 DWT liquefied natural gas （LNG）terminal in Caofeidian, Bohal Sea is effectively and reasonably optimized. It can be concluded that the model is suitable and reasonable for direct simulation of tidal currents around small structures in projects.

Fecundity of Hemirhamphus sajori (T. et S.)in the Yellow and Bohai Seas

１９９３年５月在荣成和龙口，１９９４年５月在青岛和庄河收集了小鳞鱼箴（Ｈｅｍｉｒｈａｍｐｈｕｓｓａｊｏｒｉ，Ｔ．ｅｔＳ．）标本。分析结果表示１９９４年繁殖力（平均２２９７４）大于１９９３年繁殖力（平均１６０４０）。卵径分布和平均体长指示洄游距离较长的个体的卵径和体长较大。

Applications of Bias-removed Ensemble Mean in the Gale Forecasts over the Yellow Sea and the Bohai Sea

Based on the daily sea surface wind field prediction data of Japan Meteorological Agency(JMA) forecast model,National Centers for Environmental Prediction(NCEP GFS) model and U.S.Navy Operational Global Atmospheric Prediction System(NOGAPS) model at 12:00 UTC from June 28 to August 10 in 2009,the bias-removed ensemble mean(BRE) was used to do the forecast test on the sea surface wind fields,and the root-mean-square error(RMSE) was used to test and evaluate the forecast results.The results showed that the BRE considerably reduced the RMSEs of 24 and 48 h sea surface wind field forecasts,and the forecast skill was superior to that of the single model forecast.The RMSE decreases in the south of central Bohai Sea and the middle of the Yellow Sea were the most obvious.In addition,the BRE forecast improved evidently the forecast skill of the gale process which occurred during July 13-14 and August 7 in 2009.The forecast accuracy of the wind speed and the gale location was also improved.

Study on the wave extreme parameters of the Bohai Sea with the numerical simulation using SWAN

Wave fields in Bohai Sea from 1985 to 2004 were simulated using SWAN wave model by inputting high-resolution hindcast wind fields dataset. Comparisons of wave heights between simulation and observation show good agreement in general. According to the annual extreme values of simulation, this paper gives wave extreme parameters with different return-period for all computation grids in Bohai sea.

Spatial distribution of dissolved Pb,Hg,Cd,Cu and As in the Bohai Sea

Characteristics of the spatial distribution of selected dissolved heavy metals were analyzed during large scale surveys from August t2 to 25, 2003 in the Bohai Sea. Dissolved Pb was the only element with average concentrations higher than the grade-one sea water quality standard of China. The spatial distribution of dissolved Pb in surface water was similar to those of Cd, Cu and As, where the isopleths generally indicated decreasing values from the bays to the central areas. Only for Hg did the high concentrations not only appear in Liaodong Bay, Bohai Bay and Laizhou Bay, but also in the Central Area, viz. not only in inshore but also in offshore areas. Vertical distributions of dissolved Pb, Cd, Cu and As were largely uniform, while that of dissolved Hg increased with depth. We infer that the input of pollutants from land was the main influencing factor for the detected distribution patterns of dissolved heavy metals, followed by the dynamics of sea water, release from bottom sediments and biochemical processes. Comparing with historical data, average concentrations of dissolved heavy metals appear to decline in recent years.

NUMERICAL SIMULATION AND DYNAMIC STUDY OF THE WINTERTIME CIRCULATION OF THE BOHAI SEA

This numerical study of the Bohai Sea wintertime circulation by means of a two dimensional barotropic model with resolution of 1/24° in longitude and latitude showed that the Bohai Sea wintertime circulation is dominated by local monsoon winds. The major current components include the Bohai Warm Current, the North Shandong Coastal Current, and the Liaodong Gyre. The Bohai Warm Current originates from the Yellow Sea Warm Current at the northern part of Bohai Strait, meanders westwards and finally enters the northern part of Bohai Bay. The North Shandong Coastal Current flows along the southwest shore of Bohai Bay and Laizhou Bay and exits from the Bohai Sea through the south Bohai Strait. The anticyclonic Liaodong Gyre is located in the north of Liaodong Bay. A pair of eddies and the small scale Jinzhou Gyre are found between the Bohai Warm Current and the Liaodong Gyre. The computed volume transport for both the Bohai Warm Current and North Shandong Coastal Current is about 0.03 Sv (1 Sv=1×10 6 m 3/s). The numerical experiments showed that the combined effect of local monsoon winds and bottom topography dominate the formation of the circulation pattern. The Coriolis force and the wind stress curl are of certain importance. The beta effect, the momentum advection and the open boundary condition have little influence on the circulation pattern.

Preliminary study on seasonal succession and development pathway of phytoplankton community in the Bohai Sea

Phytoplankton species composition and species succession were determined in 1998-1999 based on 2 nestle investigation cruises in the Bohai Sea and two monthly monitoring stations at Penglai and Changdao for 15 months. The seasonal succession and pathway of phytoplankton community in the Bohai Sea were discussed complementarily with history data. The main process of Phytoplankton community development in the Bohai Sea was controlled by temperature and nutrient replenishes. There were two cell abundance peaks in an annual variation, the main peak in April and the secondary peak in September. In winter, the cell abundance was low due to the low temperature, the phytoplankton community was mainly made up of small-celled diataoms. In spring, the phytoplankton community was developed very quickly by small-celled diatom in suitable conditions of temperature and nutrients. In summer, the cell abundance decreased and big-celled diatoms became predominated. In autumn, because of the replenish of nutrient, big-celled diatoms and dinoflagellates formed another cell abundance peak. during the annual variation of phytoplankton community in the Bohai Sea, species succession was the main process of community development, the species sequence just occur at special areas and special periods. The evolution of phytoplankton community in the Bohai Sea accords with the hypothesis of Margalef's phytoplankton community of four stages. But the size feature is contrary to the hypothesis, which may be caused by nutrient replenish in autumn in Bohai Sea and the top to down control.

Nutrients concentration and changes in decade-scale in the central Bohai Sea

The nutrients contents and distributions are discussed briefly, based on the data obtained in 1998～1999. Besides explanation of the results,a 20 a time series data of nutrients and biological parameters for central Bohai Sea are reviewed. It is found that both concentration and relative content of nutrients have been changed dramatically. The increase of nitrogen and decrease of phosphate and silicate led to the dramatically increase of N/P ratio and the decrease of Si/N ratio. The situation of nitrogen limiting in central Bohai Sea is gradually changing to that of relative lack of phosphate and silicate. The decrease of the Huanghe River input to the Bohai Sea may be responsible for this change. These in turn may limit the growth of diatom and thus promote the development of pyrrophyta if other conditions (e.g. temperature and hydrodynamics) are suitable. We conclude that this may be the major inducement factor of pyrrophyta red tide in the Bohai Sea.

The estimate of sea ice resources quantity in the Bohai Sea based on NOAA/AVHRR data

The research on sea ice resources is the academic base of sea ice exploitation in the Bohai Sea. According to the ice-water spectrum differences and the correlation between ice thickness and albedo, this paper comes up with a sea ice thickness inversion model based on the NOAA/AVHRR data. And then a sea ice resources quantity （SIQ） time series of Bohai Sea is established from 1987 to 2009. The results indicate that the average error of inversion sea ice thickness is below 30%. The maximum sea ice resources quantity is about 6×109 m3 and the minimum is 1.3×109 m3. And a preliminary analysis has been made on the errors of the estimate of sea ice resources quantity （SIQ）.

Bohai sea-9145重组脂肪酶基因工程菌的发酵表达条件优化

为提高大肠杆菌(E.coli)基因工程菌产Bohai sea-9145重组脂肪酶(Lipase,EC3.1.1.3)的能力,有效制备Bohai sea-9145脂肪酶。采用单因素实验、Plackett-Burman实验和Box-Behnken响应面设计实验,对该重组酶基因工程菌的发酵表达条件进行了优化。最终确定的最佳条件是:接种量为1.5%,培养基的初始p H为8.0,诱导剂IPTG的添加时间为3.5 h,终浓度为0.5 mmol/L,诱导时间为15 h,诱导温度为16℃,摇床转速为200 r/min,经优化后该菌的产酶量是优化前的9.72倍。

Joint land-sea seismic survey and research on the deep structures of the Bohai Sea areas

This paper presents the survey and research work of two land-sea profiles in the Bohai Sea, China, carried out in 2010-2011, including the seismic sources on land and in the sea, the ocean bottom seismographs （OBS） and their recovery, the coupling of OBS and the environment noise in sea area, the data quality of OBSs, and the result of data analysis. We focused on the investigation of crustal structures revealed by the two NE／EW-trending joint land-sea profiles. In combination with the Pn-velocity distribution and gravity- magnetic inversion results in the North China Craton, we propose that the undulation of the Moho interface in the Bohai and surrounding areas is not strong, and the lithospheric thinning is mainly caused by the thinning of its mantle part. The research result indicates that obvious lateral variations of Moho depth and seismic velocity appear nearby all the large-scale faults in Bohai Sea, and there is evidence of underplating and reforming of the lower crust by mantle material in the Bohai area. However, geophysical evidence does not appear to support the ＂mantle plume＂ or ＂delamination＂ model for the North China Craton destruction. The crustal structure of the Bohai Sea revealed ＂a relatively normal crust and obviously thinned mantle lid＂, local velocity anomalies and instability phenomena in the crust. These features may represent a combined effect of North China-Yangtze collision at an early stage and the remote action of Pacific plate subduction at a late stage.

RAPD analysis of wild stock of penaeid shrimp (Penaeus chinensis )in Chinese coastal waters of the Huanghai Sea and coastal waters of the Bohai Sea

Genetic diversity of 32 individuals of P. chinensis in the Chinese coastal waters of the Huanghai and Bobal Seas was detected by RAPD technique. Twenty decamer primers of OPI were used for DNA amplification for each individual. The results showed that: Seventeen primers obtained reproducible fingerprints, and the bands were clear. Thirty--nine of 106 loci detected were polymorphic, amounting to 36. 8 %. Mean genetic distance was 0. 094 1 0. 020 6; 68 markers (63. 2 % of the total) showed stable homogeneity in all of the 32 individuals.

Distribution of green algae micro-propagules and their function in the formation of the green tides in the coast of Qinhuangdao,the Bohai Sea, China

Since 2015, a novel green tide has been recurring in the coastal areas of Qinhuangdao at the western coast of the Bohai Sea in China, threatening the environment and ecosystem of the Beidaihe seaside holiday resort along the coast. Micro-propagules of the green algae including gametes, spores, micro-germlings and micro-vegetative fragments play an important role in the formation of green tides. They serve as a "seed source" of green macroalgae, and their distributions could reflect and influence the "algae source" of green tides. In this study,monthly surveys in the inshore and offshore areas of the Qinhuangdao coast were conducted from April to September 2016 and in January 2017 to investigate the tempo-spatial distribution patterns and the biomass variations of the green algae micro-propagules. The obtained results show that micro-propagules were mainly distributed in the inshore areas with a significantly decreasing abundance towards offshore areas. Their biomass was highest in July and August, and lowest in winter. The areas that were affected by the green tides showed a remarkably higher abundance of micro-propagules compared to other areas. These micro-propagules could serve as the "seed" source of green tides. Their distribution patterns indicate that the green tide in the coastal areas of Qinhuangdao originated locally.

Numerical simulations and comparative analysis for two types of storm surges in the Bohai Sea using a coupled atmosphere-ocean model

The Bohai Sea is extremely susceptible to storm surges induced by extratropical storms and tropical cyclones in nearly every season. In order to relieve the impacts of storm surge disasters on structures and human lives in coastal regions, it is very important to understand the occurring of the severe storm surges. The previous research is mostly restricted to a single type of storm surge caused by extratropical storm or tropical cyclone. In present paper, a coupled atmosphere-ocean model is developed to study the storm surges induced by two types of extreme weather conditions. Two special cases happened in the Bohai Sea are simulated successively. The wind intensity and minimum sea-level pressure derived from the Weather Research and Forecasting (WRF) model agree well with the observed data. The computed time series of water level obtained from the Regional Ocean Modeling System (ROMS) also are in good agreement with the tide gauge observations. The structures of the wind fields and average currents for two types of storm surges are analyzed and compared. The results of coupled model are compared with those from the uncoupled model. The case studies indicate that the wind field and structure of the ocean surface current have great differences between extratropical storm surge and typhoon storm surge. The magnitude of storm surge in the Bohai Sea is shown mainly determined by the ocean surface driving force, but greatly affected by the coastal geometry and bathymetry.

Estimating biological reference points for Largehead hairtail(Trichiurus lepturus) fishery in the Yellow Sea and Bohai Sea

It is important to find a reliable method to estimate maximum sustainable yield(MSY)or total allowable catch(TAC)for fishery management,especially when the data availability is limited which is a case in China.A recently developed method(CMSY)is a data-poor method,which requires only catch data,resilience and exploitation history at the first and final years of the catch data.CMSY was used in this study to estimate the biological reference points for Largehead hairtail(Trichiurus lepturus,Temminck and Schlegel)in the Yellow Sea and Bohai Sea,based on the fishery data from China Fishery Statistical Year Books during 1986 to 2012.Additionally,Bayesian state-space Schaefer surplus production model(BSM)and the classical surplus production models(Schaefer and Fox)performed by software CEDA and ASPIC,were also projected in this study to compare with the performance of CMSY.The estimated MSYs from all models are about 19.7×104–27.0×104 t,while CMSY and BSM yielded more reasonable population parameter estimates(the intrinsic population growth rate and the carrying capacity).The biological reference points of B/BMSY smaller than 1.0,while F/FMSY higher than 1.0 revealed an over-exploitation of the fishery,indicating that more conservative management strategies are required for Largehead hairtail fishery.