Sea ice is a special element of marine environment in high-latitude seas. The freezing process of sea ice is also a process of continuous salt removal from sea water, in which the salinity below sea surface increases. In the rapid melting process of sea ice, melted water with a low salinity is mixed with surface seawater, thus reducing the salinity. However, due to the differences in seawater quality and dynamic conditions in different frozen sea areas, the influences of seawater freezing-melting process on the salinity of surface water varies greatly. In this paper, in the Bohai Sea which is the icy sea in the lowest latitude in the northern hemisphere, estuaries, artificial islands, flat coastal regions, sea regions with ice floes and other sea regions with different hydrodynamic conditions, were selected as the monitoring regions to monitor water quality in three freezing stages: pre-freezing, post-freezing, and post-melting stages through field sampling. According to the water quality data in the northeastern part of Liaodong Bay with the most severe pollution in the freezing-melting process, the content of inorganic nitrogen increased firstly and then decreased, whereas the content of petroleum hydrocarbons decreased firstly and then increased. The study provides the basic data and theoretical support for the water quality assessment of Bohai Sea ice area. INTRODUCTION The Bohai Sea is the icy sea with the lowest latitude in the northern hemisphere and the only icy sea in China. The Bohai Sea has a freeze-up period of 3 to 4 months every winter and sea ice usually covers 1/3 of the total area of the Bohai Sea including the entire coast in the Bohai Sea. In recent years, the pollution in the Bohai Sea is increasingly serious. Especially, the sea regions with severe ice conditions mostly coincide with the sea regions with poor water quality and heavy pollution and are widely concerned in the studies on water quality assessment and crossing transportation of pollutants. In addition, the migration of pollutants in the ice-water media during the freezing and melting process of seawater has an important impact on marine ecosystems. The precipitation of ice crystals during the freezing process in winter and the release of pollutants in ice during the melting phase in spring increase the concentrations of seawater pollutants. Therefore, it is necessary to evaluate the influences of sea ice on seawater pollutants for the pollution control in Liaodong Bay. However, related influencing mechanisms and observation techniques should be further improved.

With the development of technology and the influence of global warming, the marine resources development is possible in extremely cold regions, such as polar and subpolar regions. The jacket platform which is widely used in oil and gas exploitation all over the world, has expansive application prospects in the future, as it is technology matures. In order to verify the applicability of the jacket structure in extreme cold such as in polar and subpolar regions, the structural responses of the jacket structure under the action of severe sea ice are analyzed using a finite element method. The results show that traditional jacket structure doesn't meet the requirements of the specification. The wall thicknesses of pile legs need to be increased to improve the ice-resist performance of the jacket structure. The results show that the ice-resist performance can be improved effectively by this method. However, the effects of improving the ice-resist performance are gradually weakened with the increase of wall thickness, and the cost is also increasing dramatically. Therefore the structural cost and the ice-resist performance should be considered comprehensively in the practical application. INTRODUCTION The extremely cold locations such as Polar and subpolar regions, contain abundant mineral, oil, gas, and wind energy resources. It is a fatal attraction to all countries in the world because of the short supply of global resource (Gautier et al., 2009). It is hard to develop marine resources in these regions, as they are usually underpopulated, tarvel is difficult and ice conditions are severe. But, it is possible to develop it in the future, as the freezing time becomes shorter and the temperature becomes higher with the global warming. More and more countries are working on developing the polar resources, such as, the opening of the Arctic Route (Ellis et al., 2009; Wang et al., 2015),and the exploration of polar oil and gas resources (Wassink et al., 2013). Beside the Polar Regions, some marine resources development projects have also been carried out in the subpolar region (Denney, 2009). For example, Russia has exploited oil and gas resources on the continental shelf near Sakhalin island in the subpolar region. Offshore oil and gas resources are exploited using the bottom-supported platforms, gravity concrete platforms and subsea equipment in the sea (Wang, 2016). But these development patterns are costly. The reason for choose those methods is that the sea ice is severe in the winter in Sakhalin Sea. In addition, there are considerable marginal oil fields in the Sakhalin sea area. The existing oil and gas resources exploitation methods are too expensive for marginal oil fields exploitation. Meanwhile, these sea areas are rich of wind energy resources. The existing structural forms are obviously unable to meet the economic requirements of wind energy development. Hence, a structure with good economy and mature technology is needed for the marine resources development in these regions. As the most common structure, the jacket structure has a good application prospect in marginal offshore oilfield exploitation, as it is technology mature and economical (Wei, 2010). It had been widely used in oil and gas production in Bohai Bay of China. The ice forces and ice-resist design problems of the jacket structure were solved by researchers through field monitoring, numerical simulation and model test methods (Wang et al, 2015; Wang and Ji, 2017; Zhang et al, 2017). The jacket structure was also widely used in the marginal oil fields production in Cook Inlet (Liu et al, 2015). Jacket structures will be used in more and more marine resources development in cold region with the technology developing and global warming. However, at present, it is not suitable for marine resources development in some extremely cold regions.

ABSTRACT Sea ice is the main risk source for cold water acquisition of coastal nuclear power plants at high latitudes. In the waters with better hydrodynamic conditions, crushed ice accumulation is the main cause for blocking cooling water intakes of nuclear power plants. Therefore, the risk of sea ice accumulation should be assessed for nuclear power plants. In the study, the risk assessment and case analysis of sea ice dynamic accumulation in front of nuclear power intakes were performed. Firstly, theoretical analysis and historical case analysis indicated that the main risk indicators of sea ice dynamic accumulation are ice thickness, concentration, velocity, size and duration. Secondly, the technical process of dynamic sea ice accumulation risk assessment of intake port based on simulation was established. The sea ice accumulation risk should be considered or not depending on sea ice environmental conditions. Finally, a coastal nuclear power plant in the Bohai Sea was selected as an example to verify the assessment model. With the dilated disk discrete element model, sea ice dynamic accumulation was simulated. The ice blockage degree in the water intake channel was selected as the indicator for risk grading. The thresholds of sea ice risk levels corresponding to different blocking levels of intake channel as well as corresponding design recurrence periods were calculated. The overall ice force caused by ice accumulation was also evaluated. The assessment method of dynamic sea ice accumulation risk proposed in this paper can be applied in the risk management of equipment involving the cold water intake function in ice-covered sea areas. INTRODUCTION China's first ice area nuclear power project, Liaoning Hongyanhe Nuclear Power Plant, has entered the commercial operation stage. A nuclear power plant consumes a large quantity of circulating cooling water during operation. The nuclear power project in the cold area of China is facing the safety risk of cold water intake, especially the risk that the sea ice may pose to water intakes. The experiences in the operation of nuclear power projects in ice regions in China are not enough and especially the anti-icing design standard of the cold water intake projects is not available. In addition, the mechanism of the impact of ice floes on the water intake of cold sources is not clear. Therefore, the economic industry and ecological environment in the northern seas of China are exposed to unknown risks caused by potential ice disasters of nuclear power projects. The operation state of the water intake directly affects the operation safety and reliability of the power plant and the problem of water intake blockage is one of its important safety problems. Ice floes in front of the water intake of a nuclear power plant is prone to be sucked into the water intake, thus blocking the water intake (Ding, 2000; Xu and Yue, 2009). Therefore, it is necessary to analyze the mechanism of floating ice accumulation in front of the water intake of a nuclear power plant and analyze the water intake safety for early warning.

ABSTRACT Based on the evolution law of ice conditions under climate change scenarios, this paper explored ice-induced vibration of the structures of offshore wind turbine in a certain area of Liaodong Bay. Firstly, the probability fitting analysis was performed with the data of sea ice extents (5 levels) from 1950 to 2018 under different scenarios. Secondly, the ice thickness probability density function of the sea area was corrected based on the analysis result. Thirdly, the numerical simulation of wind turbine structure was carried out and the dynamic ice forces of the wind power infrastructure was determined according to the ice force function for the transient dynamic analysis. The simulation results indicated found that climate change had a direct impact on the attenuation of ice conditions. Due to the decreased sea ice extent, the fatigue life of engineering structures in the study sea area was increased by 1.86%. INTRODUCTION Accurate reliability assessment is important in the planning, design and safe operation of ocean engineering structure in ice covered areas. In recent years, with the development of the marginal oilfields in the Liaodong Bay, economic indicators are the main indicators to be considered in the structural strength design of platforms. If the designed values of sea ice parameters are too low, the structure in ice area will be frequently exposed to great risks; if the designed values of sea ice parameters are too high, the production cost will be significantly increased. Therefore, it is necessary to reduce the engineering cost in the design of marine projects under the premise of meeting the structural strength. In general, the control load of offshore engineering structures in the ice-covered area is ice load, so the alternating stress caused by ice sheet in front of marine structures is an important factor of structural fatigue failures. The indicators influencing the structural stress are ice thickness and ice velocity. Ice condition data used in previous assessments of marine structures were basically collected in the 20th century. However, compared with the 20th century, climate change in the 21st century has attenuated the overall ice situation in China's seas in the past 20 years (LIU Yongqing, 2017). Therefore, it is necessary to evaluate the reliability of offshore engineering structures based on the ice data in recent years.

ABSTRACT In the paper, economic impacts on China's various maritime industries within two years were simulated based on the input-output model (IO model) in economics and input-output tables. As analysis, the sea ice disaster in the winter from 2009 to 2010 caused a total direct economic loss of 6.318 billion yuan in China, out of which 3,487 billion yuan was in Liaoning Province. According to the calculation results, indirect economic losses in Liaoning Province reached 885 million yuan, accounting for 25.3% of direct economic losses. INTRODUCTION Bohai Sea and northern Yellow Sea of China are on the edge of the Northwest Pacific Ocean and the seasonal icing sea regions with the lowest altitude in the world. China's sea ice is mainly frozen from sea water and the ice period is about 3 to 4 months. The area of the coastal icing regions in China accounts for about 6.0% of China's total land area and involves nearly 20% of China's total population and 30% of China's GDP. This area is an important economic zone in northern China and the center of northeast Asian economic circle. Due to the rapid development of marine economy, a large number of population and industries have gathered in the coastal regions. Oil-related industries such as oil exploitation, aquaculture, port shipment, petrochemical refining and metallurgy, and steel metallurgy are densely distributed in the ice-covered sea regions and corresponding coastal regions (Gu, 2014; Liu, 2017). Sea ice can damage marine structures and various offshore facilities, squeeze ships, block ports and waterways, and destroy aquaculture facilities. According to statistics of sea ice disasters, the severe sea ice disaster roughly occurs once every 5 to 6 years and sea ice disasters even occur every year in some areas. Many serious sea ice disasters have caused heavy losses (Yang, 1994; Liu 2016). For example, in the winter from 2009 to 2010, the direct economic losses caused by sea ice in China amounted to 6.318 billion yuan (Sun, 2011). Sea ice disasters are the main marine disasters in winter in the Bohai Sea and the northern Yellow Sea.

ABSTRACT The vertical stratification of water temperature in seawater can be used to predict the generation of sea ice and ensure the safety of marine production activities. In the study, a seawater temperature profile measurement system was constructed. Seawater temperature profile data were measured by the profile measurement system in a sea pond in Liaodong Bay and collected by a LabVIEW-based program. Measured data is sent to a remote server and posted on the Internet through DTU module to realize real-time monitoring of the temperature profile in the field. Through analyzing these data, a solid foundation for the study on seawater temperature profile can be laid. INTRODUCTION An evident water temperature stratification phenomenon exists in seawater due to its high specific heat capacity and other factors. The phenomenon is particularly evident in winter(Zhang et al., 2016)] and directly affects the formation of sea ice in winter. In Yellow Sea and Bohai Sea, the sea water temperature profile before sea ice freezing shows a typical three-layer structure (Xiu et al., 2009): the upper layer, the thermocline, and the lower layer, as shown in Fig. 1. The three- layer structure of water temperature profile in Bohai Sea is described as follows. Firstly, water temperature profile in the layer from near surface to the depth of h is a linear profile with a gradient of zero. Secondly, water temperature profile in the layer from the depth of h to the depth of H is the thermocline displaying the sharply decrease temperature with the increasing depth. In the thermocline, the profile is a linear profile with a basically constant gradient and the temperature gradient can be expressed with the average gradient. Thirdly, water temperature profile in the layer from the depth of H to the sea bottom is also a linear profile, but the temperature is basically a constant and the gradient is approximately zero.

Abstract The sleet and snow disaster in southern China in 2008, Hurricane Katrina (2005) and Hurricane Sandy (2012) in the United States are all natural catastrophes with serious casualties, huge property losses, and large affected area. In the paper, from the perspective of comprehensive risk prevention, we re-examined the three typical catastrophes. We compared the risk of hazards, vulnerability of sensitive infrastructure, disaster prevention, emergency response, recovery, and other aspects in the three catastrophes. Moreover, we analyzed the similarities and differences in catastrophe coping modes between the two countries and proposed advices for disaster response and risk prevention in China. Introduction In recent years, disasters frequently occurred worldwide and caused heavy casualties and huge economic losses. Recent disasters include Wenchuan Earthquake and the sleet and snow disaster in southern China in 2008, Haiti Earthquake in 2009, Fukushima nuclear leakage of 2011 in Japan, Hurricane Sandy in 2012, and Nepal Earthquake in 2015. These disasters frequently remind people that in spite of the development in global economy, science, technology, and early warning measures, all risks cannot be avoided completely. With the economic and social development, the accelerated urbanization progress, population and wealth accumulation in large cities, human vulnerability in major natural disasters is also more significant. According to the statistics from the World Bank (2006a, 2006b), from 1984 to 2003, more than four billion people in developing countries have been affected by various natural disasters and the economic losses caused by natural disasters from 1990 to 1999 have exceeded 15 times of the loss from 1950 to 1959. According to global disaster database (EM-DAT) in Centre for Research on the Epidemiology of Disasters (CRED) and historical disaster data of Swiss Reinsurance Company and Munich Reinsurance Company, in the past 20 years, the frequency of disasters is rising and corresponding casualties and economic losses also increase (Scheuren et al., 2008).

Abstract Sea ice is the dominant envirornnental factor to nuclear power plants in ice-covered region, especially for the cold source water intake. In order to monitor the sea ice risk of water intake to the only nuclear power plants in ice-covered region of China, Fiber Bragg Grating (FBG) strain sensors were used to directly measure the water intake coarse grids strain during May 2014 and Feb. 2015. Effective coarse grid strain data was obtained in and out of ice period. Analysis results show that the impact by submerged floe ice was not measured. This method could be used to monitor the sea ice risk condition of water intake by submerged floe ice, and then contribute to ensure the cold resource safety of nuclear power plant of cold regions during ice period. INTRODUCTION Sea ice is the dominant envirornnental condition in the Bohai Sea of China (Yue and Bi, 1998). For the traditional business, such as oil exploration, harbor and navigation, sea ice action will induce the physical damage on ocean engineering structural (Zhang, et al., 2015), which is the main sea ice risk mode. For the purpose of the safety production during winters, research on sea ice risk mechanics and reduction method, management during ice period had been conducted since 1990's (Qu, Y., et al, 2006; Yue, Q.J., et al, 2009; Huang, Y, 2010, Zhang, D.Y., et al., 2006; Xu, N. and Yue, QJ, 2011). Nuclear power plant is one of the new kinds of industry in Bohai Rim Economic Circle; therefore the sea ice risk is a new challenge issue. Based on the accident of nuclear power plant (WIKIPEDIA, 2015), the possible influence to cold resource should be the primary issue effect when considering the sea ice risk. Hong Yan He Nuclear Power Plant (LHNP) is the first nuclear power plant in ice covered region of china, which was llllder operation on Jlllle 2013. "While the mechanics for sea ice risk to cold source water intake is not clear. Either there is no recommendation on design or production to prevent sea ice. Water intake is the first position for water supply of cold resource in nuclear power plant. Since water intake is exposed to the natural sea water with low temperature, the sea ice floe or ice accumulation will reduce the effective area of water intake channels. Under distinct low tide level and serious wave, the appearance of submerge floe ice would act on the coarse grid. In one case, the coarse grid will be destroyed by significant ice impact, or the llllderwater ice block could be formed in the front of coarse impact, and then risk the safety of water intake.

Abstract In this paper, we analyzed the data of marine disasters in Chinese coastal areas in 24 years from 1989 to 2012. According to the analysis results, the uncertainty degree of marine disaster hazards increased and the exposure and vulnerability of coastal hazard bearing bodies also gradually increased. After 2000, the proportions of economic loss in marine GDP and national GDP were significantly reduced. Furthermore, we proposed the improvement advices for the establishment of the integrated risk management system in China in the following three aspects: marine disaster risk awareness, quantitative analysis supporting technology and decision optimization.

Abstract The ice-induced structural vibration is basically controlled by the value and period of dynamic ice force. For the conical structure, the value of ice force on the upward cone is larger than downward cone and the ice force period is much more complex. Field measurements in the Bohai Sea indicate that the ice force period and broken length of sea ice are mainly determined by the cone shape (upward or downward, width). When the cone is narrow, the dynamic ice force period is significantly different between the upward and downward cones. When the cone is wide, the difference is not significant.

ABSTRACT Full scale tests were conducted on a monopod structure before and after an icebreaking cone was added. The effectiveness of mitigating ice induced vibration through adding ice-breaking cone was evaluated based on test data. It was found that significant ice induced vibration can occur on both of vertical and conical structures, but that vertical structures suffer from more intense and harmful steady state vibration. The dynamic ice force and structure response of vertical and conical structure were discussed based on test data. INTRODUCTION The concept of reducing ice force by adding ice-breaking cone to vertical structure has been proved by the theoretical and experimental work (Wessels.E and Kato.K.,1988; Koh Izumiyama, 1991). Though the details of the effects on ice induced vibration are not yet completely understood. Persistent steady vibration will occur on vertical structures under certain ice condition, and could induce serious accident. Icebreaking cones have been added, while strong vibrations are still persisting on some structures, such as the jacket oil platform in the Bohai Bay. Meanwhile conical and inclined structures have some other problems, such as increase the structure width at the waterline complicated fabrication and the danger to vessels. After the ice-breaking cones were first installed on the vertical legs of jacket structures in the Bohai Bay since 1988, the cones have been widely used. Field measurement systems for studying the ice force and structural response to ice motion have been installed on seven jacket structures, some with cones and some without. Jacket structure JZ9- 3WHPE is a monopod structure, and full scale tests were conducted on the structure before and after ice-breaking cone added. This paper first demonstrates the theoretical explanation for ice induced structure vibration, and relates it to the form of dynamic ice force history.

ABSTRACT In order to study the ice force on jack-up structure which has cylindrical leg with gear teeth, a series of model tests are conducted to compare the ice forces on two cylindrical indentors of the same diameter, one of which has gear teeth on both sides scaled from the prototype jack-up platform and the other has no gear teeth. Results of the model tests indicated that ice forces on the jack-up indentor vary slightly when the angle between ice moving direction and gear teeth direction changes, which accords with prediction before test. However, the gear teeth did not increase magnitude of ice force significantly, which means that ice load formulation of jacket platform could be applied to jack-up structure. On the other hand, ice induced steady state vibration and lock-in between structural response and dynamic ice force still exist on jack-up structure, which attributes to the nearly same crushing failure on jacket platforms here. INTRODUCTION Fixed foundation offshore platforms such as jack-up, jacket structures, concrete structures are used to drill or produce hydrocarbon beneath the seabed. In high latitude waters which are infested by ice, structures have to undergo remarkable ice forces acting at water level. According to decades of study on ice actions, ice forces acting on structures mostly depend on structure's shape at ice level, because different structure shapes result in significantly different failure modes of ice sheet and lead to distinct ice force magnitudes. (figure 1 shown in paper) The most commonly used offshore platforms have cylindrical legs at water level, and when level ice sheet acts on this type of structures, ice crushes on cylindrical leg and leads to the biggest ice force (Fig.1). In some cases crushing ice force might induce strong vibration of structure (Sodhi, 1988, Engelbrektson, 1989, 1997, Yue et al. 2001, 2002).