Variability of Sea Surface Heights in the Baltic Sea: An Intercomparison of Observations and Model Simulations

Sea level changes in the Baltic Sea are dominated by internal, short-term variations that are mostly caused by the ephemeral nature of atmospheric conditions over the Baltic area. Tides are small and their influence decreases from western parts of the Baltic Sea to the Baltic Proper. Superimposed to the large short-term sea level changes (up to few decimeters from day to day) are seasonal and interannual variations (centimeters to decimeters). This study focuses on the comparison of sea surface heights obtained from observations and from a high resolution oceanographic model of the Baltic Sea. From this comparison, the accuracy of the modeled sea surface variations is evaluated, which is a necessary precondition for the further use of the oceanographic model in geodetic applications. The model reproduces all observed Baltic sea level variations very reliably with an accuracy of 5 to 9 cm (rms) for short-term variations (up to 2 months) and 8 cm (rms) for long-term variations (>2 months). An additional improvement of the model can be attained by including long-period sea level variations of the North Sea. The model performs well also in the case of extreme sea level events, as is shown for a major storm surge that occurred at the southern coast of the Baltic Sea in November 1995.     

Model of palaeoenvironmental evolution of the Black Sea region during the last glacial maximum—Holocene

A model for the palaeoenvironmental evolution of the Black Sea and its adjacent basins during the past 20.000 years, in which variations in sedimentation, erosion, and hydrologic processes as a result of climatic change are taken into consideration, is developed. The data used include those from five cruises in the Black Sea with the participation of the author, seismo-acoustic data in the possession of the Institute of Oceanology in Varna, and data from the published literature. The most important result is that the water level of the Black Sea is controlled largely by that of the Marmara Sea via the Bosporus sill. The water circulation in the south part of the Bosporus channel as natural regulative mechanism of the Black Sea level during 11800–9000 yr C¹⁴ BP is produced. A succession of climatic and water conditions for the Black Sea by pollen analysis is presented. The linear ridges on the Black Sea shelf as result of the lower Holocene regression are proved by means of a stratigraphic interpretation of the seismo-acoustic profiles. The levels of the Black Sea, Marmara Sea, and Mediterranean at regarded intervals of time are presented. An attempt at explanation of maximum number of facts from the study region with this model is made.     

A numerical study of transport dynamics and seasonal variability of the Yellow River sediment in the Bohai and Yellow seas

A sediment numerical model was embedded into a wave-tide-circulation coupled model to simulate the transport processes of the Yellow River-derived sediment considering the wave-induced vertical mixing (Bv) and the wave-current coupled bottom shear stress (BSS). Numerical results show that the main stream of the Yellow River-derived sediment moves first eastward off the northern Shandong Peninsula and then southward into the South Yellow Sea all year round. In spring, the sediment moves northeastward in the Bohai Sea. In summer, there is a northeastward branch of sediment in the Bohai Sea off the west coast of the Liaodong Peninsula, while the main part goes eastward to the Yellow Sea. The Yellow River-derived sediment transport from the Bohai Sea to the North Yellow Sea across the Bohai Strait is mainly limited to the top 10 m, and with a maximum centered at 37.9°N in summer. The transport from the North Yellow Sea to the South Yellow Sea across the transect of 37°N is mainly in the 0–30 m layer with a maximum around 123.7°E in autumn. The simulated Yellow River-discharged sediment deposits along the Shandong Peninsula and between 20 and 30 m isobaths in the Yellow Sea, which is consistent with observation. If surface waves are not considered in the model, the sediment deposits westward to the nearshore area in the South Yellow Sea. The sediment would deposit further southward in the numerical experiment results without wind influence. In the numerical experiment of no tide, there is hardly any sediment deposited on the Yellow Sea floor, while in the Bohai Sea most of the sediment is transported southward and northwestward around the river mouth instead of eastward as in the Control Run, indicating the tides play a key role in forming the deposition pattern.     

Modeling of Long-Term Evolution of Hydrophysical Fields of the Black Sea

The long-term evolution of the Black Sea dynamics (1980–2020) is reconstructed by numerical simulation. The model of the Black Sea circulation has 4.8 km horizontal spatial resolution and 40 levels in z-coordinates. The mixing processes in the upper layer are parameterized by Mellor-Yamada turbulent model. For the sea surface boundary conditions, atmospheric forcing functions were used, provided for the Black Sea region by the Euro mediterranean Center on Climate Change (CMCC) from the COSMO-CLM regional climate model. These data have a spatial resolution of 14 km and a daily temporal resolution. To evaluate the quality of the hydrodynamic fields derived from the simulation, they were compared with in-situ hydrological measurements and similar results from physical reanalysis of the Black Sea.     

Viscous model of plate tectonics for the Black Sea region (in relation to the problem of the late Cenozoic evolution of the Black Sea basins)

A numerical model of the Black Sea region (Northeastern Mediterranean) is presented in which it is regarded as a part of the mosaic plate ensemble consisting of the fixed East European platform; the active Arabian, Adriatic, and Pannonian plates; and passive East and West Black Sea and Mysian microplates, which are embedded in a plastically deformable regional orogenic matrix. The fields of displacements, stresses, and deformations in the region are calculated by means of the finite element method within the framework of a linear-viscous rheology approach to a system with nonhomogeneous viscosities. The velocity field obtained is in good agreement with published data of direct observations of plate displacements in the region. In the pressure field, areas of low pressure and decompression are established in the western part of Black Sea and in the south of the Mysian microplate. The poles of rotation of the East and West Black Sea microplates and of the Mysian microplate are computed. For the latter two microplates, significant rotational components are suggested. The East Black Sea microplate acts mostly as indenter, which transmits the collisional motion from the Arabian plate to the southern edge of the East European platform including the Crimea. According to the geodynamical model, the rates of the Cenozoic sedimentation in the Black Sea depression at the collision stage (Oligocene-Pliocene) result from the greater compression of the East Black Sea microplate as compared to the West Black Sea microplate, which, probably, experienced a kind of extension.     

渤海重现期波高的数值计算

利用RAMS大气模式给出的20年风场资料,利用SWAN近海波浪模式对渤海海域的波浪进行了20 a数值计算.通过与一般过程和大风过程的实测资料的对比后发现.波浪模拟值与实潮值符合地较好,SWAN模式适合渤海海域波浪的计算。通过分析发现.辽东湾常浪向为SSW。强浪向为SSW;渤海中部常浪向为S,强浪向为NE;渤海海峡常浪向为NNW,强浪向为NNW;莱州湾常浪向为S,强浪向为NNE;渤海湾常浪向为S.强浪向为NE。渤中偏东南海域(38°～39°N,119.5°～120.5°E)多年一遇有效波高最大.其中百年一遇有效波高最大值达到6.7m。     

东海陆架环流季节变化的模拟与分析

在改进POM模式基础上,建立1个中国东部海域斜压准预报模式,利用全球海洋模式结果并结合实测资料以及高精度卫星遥感SST资料,进行了东海陆架海域温盐及环流年循环的数值模拟,并系统分析了东海陆架环流系统及其季节变化、各暖流的路径等广为关注的问题。模式结果表明：黑潮主轴主体沿陆架坡折走向,中段黑潮流幅由南至北增宽,流速变大,流核所达深度变浅。浙闽沿岸流是一典型的季风环流,台湾暖流终年表现出东、北两分支结构,其分支表现出明显的季节性变化特征。在东海东北部陆架海域,冬季黑潮以其分支形式向北入侵,夏季则主要以大陆边缘流的形式向北进入陆架。论文对各暖流的水源也进行了相应的分析。     

Potential transport of plaice eggs and larvae between two apparently self-contained populations in the Irish Sea

A coupled physics particle-tracking model, driven by realistic meteorological forcing was used to examine the dispersal and transport of plaice eggs and larvae in the year 2000 from two spawning grounds in the Irish Sea. The model included passive transport of eggs and early stage larvae, diel vertical movements for larvae between 7 and 10.5 mm in body-length and tidally synchronised, vertical movements for larger larvae (>9 mm body-length). The year 2000 was chosen because of the availability of ichthyoplankton data with which to initialise the model. The majority of larvae originating from spawning in the eastern Irish Sea settled into nursery grounds along the Scottish, English and Welsh coasts, in agreement with previous findings. In contrast, a significant portion of larvae originating from spawning in the western Irish Sea was transported eastwards to these same nursery grounds. Transport across the Irish Sea resulted from the onset of tidally synchronised vertical behaviour encoded in the model for older larvae. Settlement of larvae into local nursery grounds along the Irish coast was limited. Because of the prevailing winds and currents in the region, plaice eggs and larvae are unlikely to be transported from east to west; in most years spawning in the western Irish Sea probably acts as an additional source of juveniles for nursery grounds along the Scottish, English and Welsh coasts.     

东海对马暖流水来源的数值模拟

本文通过二维数值模拟对1986年6月～1988年12月东海对马暖流水的来源问题进行了初步探讨,结果得出东海对马暖流水的来源基本上分为三种类型:(1)东海对马暖流水主要为东海黑潮水继续北上部分构成;(2)东海对马暖流水由东海黑潮水、东海陆架水以及东海北部黄海大陆沿岸水几部分混合而成;(3)东海对马暖流水几乎全部由东海北部的黄海大陆沿岸水构成。模拟与实测结果基本一致.     

南海海盆扩张成因质疑

从板块构造学、地球物理学和地球动力学等角度,结合南海中央海盆及其周边的地质、地球物理资料进行综合分析论证,对南海“扩张成因”模式提出质疑.认为南海“扩张成因说”不能成立,其中的几个核心问题是:(1)数学理论模型的边界参数选取存在多解性,其结果与地质地球物理资料不符或相去甚远;(2)无法解释海盆区地球物理探测和研究所表明的地壳结构及岩性特征,也无法解释海盆区的断裂分布和岩浆活动特征;(3)地球动力学诸方面难以支持南海“扩张成因说”成立;(4)南海海盆周边不存在与南海“扩张成因”相关的相互强烈作用的地球物理和地质构造特征;(5)南海海盆不具备大规模扩张的空间.南海“扩张成因说”已严重阻碍对南海和周边的地质与地球物理研究工作的深入和发展,应该放弃.     

海冰模式和数值预报

根据渤海冰情,在海冰动力学和热力学研究基础上,提出一种海冰动力一热力模式。该模式包括平整冰、堆积冰和开阔水三要素,采用粘一塑性本构关系计算冰内应力。利用参数化方法处理变形函数和热力增长率。该冰模式与潮流模式耦合研究渤海冰－潮相互作用,并与ＥＣＯＭ－Ｓｉ海洋模式耦合进行预报试验。该冰模式与大气模式联接,或应用气象部门数值天气预报产品进行海冰业务数值预报。本文还给出了预报结果。     

南海及邻近海域大气-海浪-海洋耦合精细化数值预报系统研制

本文主要介绍了南海及邻近海域大气-海浪-海洋耦合精细化数值预报系统的研制概况。预报区域为99°E~135°E,15°S~45°N,包括渤海、黄海、东海和南海及其周边海域。为了给耦合预报模式提供较准确的预报初始场,在预报开始之前,分别进行了海浪模式和海洋模式的前24小时同化后报模拟。海浪模式和海洋模式都采用了集合调整Kalman滤波同化方法,海浪模式同化了Jason-2有效波高数据;海洋模式同化了SST数据、MADT数据和ARGO剖面数据。为了改进海洋温度和盐度的模拟,我们在海洋模式的垂向混合方案中引入波致混合和内波致混合的作用。预报系统的运行主要包括两个阶段,首先海浪模式和海洋模式进行了2014年1月至2015年10月底的同化后报模拟,强迫场源自欧洲气象中心的六小时的再分析数据产品。然后耦合预报系统将同化后报模拟的结果作为初始场进行了14个月的耦合预报。预报产品包括大气产品（气温、风速风向、气压等）、海浪产品（有效波高和波向等）、海流产品（温度、盐度和海流等）。一系列观测资料的检验比较表明该大气-海浪-海洋耦合精细化数值预报系统的预报结果较为可靠,可以为南海及周边海洋资源开发和安全保障提供数据和信息产品服务。     

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Time series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW₉₄ class formed in the period 1989-1994 in the Labrador Sea.     

Hydraulic calculations of postglacial connections between the Mediterranean and the Black Sea

A series of simple hydraulic calculations has been performed to examine some of the questions associated with the reconnection of the Black Sea to the Mediterranean through the Turkish Strait System during the Holocene. Ryan et al.’s catastrophic flood scenario, whereby the erosive power of the marine in-fluxes, initiated after eustatic sea level reached the sill depth, opened up the Bosphorus, allowing saline water to pour into the Black Sea and filling it on a short time scale, is examined. The calculations show that although it might be possible to fill the palaeo-Black Sea within the order of a decade, a 1–2 year filling time scale is not physically possible. A hydraulic model is also used to examine the more traditional connection hypothesis of (near-)continuous freshwater outflow from the Black Sea, with a slowly increasing saline inflow from the Mediterranean beginning around 8–9 kyr BP. The model considers two forms for the structure of the Bosphorus: a shallow sill as seen today and a deep sill associated with no sediments filling the 100 m gorge above the bedrock in the strait. Sensitivity experiments with the hydraulic model show what possible strait geometric configurations may lead to the Black Sea reaching its present-day salinity of 18 psu. Salinity transients within the Black Sea are shown as a function of time, providing for values that can be validated against estimates from cores. To consider a deep, non-sediment-filled Bosphorus (100 m deep), the entry of Mediterranean water into the Sea of Marmara after 12.0 kyr BP is examined. A rapid entry of marine water into the Sea of Marmara is only consistent with small freshwater fluxes flowing through the Turkish Strait System, smaller than those of the present day by a factor of at least 4. Such a small freshwater flux would lead to the salinification of the Black Sea being complete by an early date of 10.2–9.6 kyr BP. Thus the possibility of a deep Bosphorus sill should be discounted.     

印度尼西亚海内潮生成及传播过程研究*

文章采用三维海洋模式MITgcm, 对印度尼西亚海(简称印尼海)内潮的生成和传播过程进行了研究。研究结果表明: 1)苏拉威西海和西北太平洋地区的内潮呈现明显的全日潮信号; 望加锡海峡、翁拜海峡、东北印度洋、帝汶海等站位的内潮呈现明显的半日潮信号; 2)印尼海区内潮的标准化振幅在苏拉威西海、望加锡海峡、翁拜海峡、马鲁古海、班达海、东北印度洋和西北太平洋地区均在温跃层附近达到最大, 约为20~40m; 在帝汶海地区在水深200m附近达到最大, 约为25~30m; 3)桑岭、斯兰海、翁拜海峡和帝汶海是主要的内潮生成区域, 内潮能通量达40kW·m^-1; 4)苏禄海的内潮能量主要来自于局地正压潮的转化, 苏拉威西海和班达海的内潮能量则主要来自外部的传入。     

渤海氮磷营养盐和叶绿素浓度时空分布数值模拟与富营养化评估

当前渤海富营养化风险仍居高不下,严重制约了环渤海社会经济可持续发展。开展近海富营养化评估与趋势分析是国家生态安全保障的需求, 其难点在于富营养化评价要素长期演变进程高质量数据的获取。基于HAMSOM海洋生态模型, 通过修正溶解有机氮(dissolved organic nitrogen, DON)的难/易降解组分降解动力学形式, 构建了适用于富营养化评估与趋势分析的渤海三维水动力/生物地球化学耦合模型。利用2019年渤海春、夏、秋、冬四个季节DON、溶解无机氮(dissolved inorganic nitrogen, DIN)、溶解无机磷(dissolved inorganicphosphorus, DIP)和叶绿素a(chlorophyll a, chl a)调查结果, 对模型进行了校正, 并利用1980年至2020年的长期调查结果进行了验证, 模拟结果与调查结果相比较, 在数值大小和变化趋势上均吻合较好, 相对标准偏差、相似性系数和Kappa系数分别为24%、0.77和0.60。利用模型模拟计算的DIN、DIP、DON和chl a长期演变进程数据, 计算了营养状态质量指数(nutritional quality index, NQI)。结果表明, 当前渤海富营养化状态整体上处于贫营养状态, 但在渤海湾、辽东湾和莱州湾湾底近岸海域处于富营养状态, 季节上5~10月份处于中等富营养化状态, 从长期变化趋势看, 渤海整体上富营养化状态趋于改善。与复合富营养化指数(compound eutrophication index, CEI)对比表明, 渤海富营养化评估按NQI计算结果与按CEI计算结果相当吻合, 相似性系数为0.83。文章建立的渤海富营养化评估方法具有较高可靠性, 可用于渤海富营养化评估。     

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

The Harvard Ocean Prediction System (HOPS) is configured to simulate the circulation of the Scotia Sea and environs. This is part of a study designed to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia in the eastern Scotia Sea are sustained by import of individuals from upstream regions, such as the western Antarctic Peninsula. Comparison of the simulated circulation fields obtained from HOPS with observations showed good agreement. The surface circulation, particularly through the Drake Passage and across the Scotia Sea, matches observations, with its northeastward flow characterized by three high-speed fronts. Also, the Weddell Sea and the Brazil Current, and their associated transports match observations. In addition, mesoscale variability, an important component of the flow in this region, is found in the simulated circulation and the model is overall well suited to model krill transport. Drifter simulations conducted with HOPS showed that krill spawned in areas coinciding with known krill spawning sites along the west Antarctic Peninsula continental shelf can be entrained into the Southern Antarctic Circumpolar Current Front (SACCF). They are transported across the Scotia Sea to South Georgia in 10 months or less. Drifters originating on the continental shelf of the Weddell Sea can reach South Georgia as well; however, transport from this region averages about 20 months. Additional simulations show that such transport is sensitive to changes in wind stress and the location of the SACCF. The results of this study show that krill populations along the Antarctic Peninsula and the Weddell Sea are possible source populations that can provide krill to the South Georgia population. However, successful transport of krill to South Georgia is shown to depend on a multitude of factors, such as the location of the spawning area and timing of spawning, and variations in the location of the SACCF. Therefore, this study provides insight into which environmental factors control the successful transport of krill across the Scotia Sea and with it a better understanding of krill distribution in the region.     

Response of the Baltic Sea to climate change—theory and observations

The dynamics controlling the response of the Baltic Sea to changed atmospheric and hydrologic forcing are reviewed and demonstrated using simple models. The response time for salt is 30 times longer than for heat in the Baltic Sea. In the course of a year, the Baltic Sea renews most of its heat but only about 3% of its salt. On the seasonal scale, surface temperature and ice-coverage are controlled by the atmospheric conditions over the Baltic Sea as demonstrated by e.g. the strong inter-annual variations in winter temperature and ice-coverage due to variations in dominating wind directions causing alternating mild and cold winters. The response of surface temperature and ice-coverage in the Baltic Sea to modest climate change may therefore be predicted using existing statistics. Due to the long response time in combination with complicated dynamics, the response of the salinity of the Baltic Sea cannot be predicted using existing statistics but has to be computed from mechanistic models. Salinity changes primarily through changes in the two major forcing factors: the supply of freshwater and the low-frequency sea level fluctuations in the Kattegat. The sensitivity of Baltic Sea salinity to changed freshwater supply is investigated using a simple mechanistic steady-state model that includes baroclinic geostrophic outflow from the Kattegat, the major dynamical factor controlling the freshwater content in the Kattegat and thereby the salinity of water flowing into the Baltic Sea. The computed sensitivity of Baltic Sea surface salinity to changes of freshwater supply is similar to earlier published estimates from time-dependent dynamical models with higher resolution. According to the model, the Baltic Sea would become fresh at a mean freshwater supply of about 60 000 m³ s⁻¹, i.e. a 300% increase of the contemporary supply. If the freshwater supply in the different basins increased in proportion to the present-day supply, the Bothnian Bay would become fresh already at a freshwater supply of about 37 000 m³ s⁻¹ and the Bothnian Sea at a supply of about 45 000 m³ s⁻¹. The assumption of baroclinic geostrophic outflow from the Kattegat, crucial for the salinity response of the Baltic Sea to changed freshwater supply, is validated using daily salinity profiles for the period 1931–1977 from lightship Läsö Nord.     

渤、黄、东海潮汐、潮流的数值模拟与研究

基于FVCOM海洋数值模式,采用高分辨率的三角形网格,对渤、黄、东海的潮汐、潮流进行数值模拟,并通过比较120个沿岸验潮站和14个潮流观测站的实测与模拟结果进行模型验证,两者符合较好。根据模拟结果,给出了四个主要分潮的潮汐同潮图和5m层潮流最大流速及最大潮流同潮时分布。渤、黄、东海共有5个半日分潮和3个全日分潮的独立旋转潮波系统,且都呈逆时针方向旋转;半日潮流和全日潮流各有12个圆流点;在冲绳岛和奄美岛两侧的4个半日潮流圆流点分别呈对称分布,其中有3个为本文首次给出;在日本九州岛西侧还新给出2个全日潮流圆流点。有关它们的存在性需要实测资料的进一步检验。     

东海与邻近海域水、热、盐通量的季节变化研究

本文基于高分辨率的区域海洋数值模式对东海及邻近海域进行温、盐、流的数值模拟,模拟结果与实测结果拟合较好。结果表明:东海与邻近海域的水交换过程具有显著的季节变化特征。从流量的角度看,台湾海峡、台湾-西表岛之间水道和西表岛-冲绳岛之间水道是外海水流入东海的3个主要水道,而冲绳岛-奄美大岛、吐噶喇海峡、大隅海峡、济州岛东部和黄东海断面是海水流出东海的水道;其年平均体积输运值分别为1.06×106 m3/s、20.49×106 m3/s、3.20×106 m3/s、-0.92×106 m3/s、-20.59×106 m3/s、-0.30×106 m3/s、-2.37×106 m3/s和-0.37×106 m3/s（向内为正）。对比发现,东海与邻近海域之间各水道的体积、热量和盐量输运均具有相似的季节变化趋势,其最大值往往出现在夏季（7月或8月）,最小值往往出现在冬季（1月或2月）。从7月到11月整个东海是流量净流出的过程,而从12月到翌年6月是流量净流入的过程,全年流量基本上保持平衡状态。东海终年存在向黄海的净输入,其体积、热量和盐量的年平均输运值分别为0.37×106 m3/s,0.027×1015 W和12.7×106 kg/s。