Model study of the upper circulation in the Sulu Sea and its relation to the South China Sea circulation

According to the satellite remote sensing monthly mean sea surface temperature data from 1998 to 2002, it is shown that, the Sulu Sea is dominated by a cold eddy both in summer and winter. A coupled single-layer/two-layer model is employed here to study the summery and wintry characteristics and dynamic mechanism of the upper circulation in the Sulu Sea. According to the numerical experiments, it is found that, due to the local monsoon stress cud, the upper circulation in the Sulu Sea is dominated by a weak anticyclonic eddy in summer and a strong cyclonic eddy in winter. Once there is a large outflow via the Sibutu Passage flowing out of the Sulu Sea in summer, the upper circulation in the Sulu Sea may be dominated by a cyclonic eddy instead of the normal anti- cyclonic one. Moreover, in summer, the water exchange between the Sulu Sea and South China Sea via the Mindoro and Balabac Straits might have some effect on the separation position and strength of the northward western boundary current next to the Indo - China Peninsula in the southern South China Sea.     

Simulated Pathways of the Northwestern Pacific Water in the Okhotsk Sea

Izvestiya, Atmospheric and Oceanic Physics - Water exchange between the Pacific Ocean and the Okhotsk Sea through the Kuril Straits and transport of Pacific waters into and from the Okhotsk Sea are...     

Seasonal Variations of Water Masses and Sea Level in the Southwestern Part of the Okhotsk Sea

A new grid data set for the southwestern part of the Okhotsk Sea was compiled by using all the available hydrographic data from the Japan Oceanographic Data Center, World Ocean Atlas 1994 and the other additional data sources with the resolution of about 10 km. We examine the seasonal variations of areas and volumes of Soya Warm Current Water (SWCW) and East Sakhalin Current Water (ESCW) and show that the exchanges of these water masses drastically occur in April and November. The peculiar variation of sea level in this region is also related with the water mass exchange. Sea level at the Hokkaido coast of the Okhotsk Sea reaches its minimum in April about two months later than in the case of ordinary mid-latitude ocean, and its maximum in December besides the summer peak. The winter peak of sea level in December is caused by the advent of fresh and cold ESCW which is accumulated at the subsurface layers (20–150 m) through the Ekman convergence by the prevailing northerly wind. Sea level minimum in April is caused by the release of the convergence and the recovery of dense SWCW that is saline and much colder than that in summer.     

Dense water formation and circulation in the Barents Sea

Dense water masses from Arctic shelf seas are an important part of the Arctic thermohaline system. We present previously unpublished observations from shallow banks in the Barents Sea, which reveal large interannual variability in dense water temperature and salinity. To examine the formation and circulation of dense water, and the processes governing interannual variability, a regional coupled ice-ocean model is applied to the Barents Sea for the period 1948-2007. Volume and characteristics of dense water are investigated with respect to the initial autumn surface salinity, atmospheric cooling, and sea-ice growth (salt flux). In the southern Barents Sea (Spitsbergen Bank and Central Bank) dense water formation is associated with advection of Atlantic Water into the Barents Sea and corresponding variations in initial salinities and heat loss at the air-sea interface. The characteristics of the dense water on the Spitsbergen Bank and Central Bank are thus determined by the regional climate of the Barents Sea. Preconditioning is also important to dense water variability on the northern banks, and can be related to local ice melt (Great Bank) and properties of the Novaya Zemlya Coastal Current (Novaya Zemlya Bank). The dense water mainly exits the Barents Sea between Frans Josef Land and Novaya Zemlya, where it constitutes 63% (1.2 Sv) of the net outflow and has an average density of 1028.07 kg m⁻³. An amount of 0.4 Sv enters the Arctic Ocean between Svalbard and Frans Josef Land. Covering 9% of the ocean area, the banks contribute with approximately 1/3 of the exported dense water. Formation on the banks is more important when the Barents Sea is in a cold state (less Atlantic Water inflow, more sea-ice). During warm periods with high throughflow more dense water is produced broadly over the shelf by general cooling of the northward flowing Atlantic Water. However, our results indicate that during extremely warm periods (1950s and late 2000s) the total export of dense water to the Arctic Ocean becomes strongly reduced.     

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

A fine-resolution MOM code is used to study the South China Sea basin-scale circulationand its relation to the mass transport through the Luzon Strait. The model domain includes the South China Sea, part of the East China Sea, and part of the Philippine Sea so that the currents in the vicinity of the Luzon Strait are free to evolve. In addition, all channels between the South China Sea and the Indonesian seas are closed so that the focus is on the Luzon Strait transport. The model is driven by specified Philippine Sea currents and by surface heat and salt flux conditions. For simplicity, no wind-stress is applied at the surface.The simulated Luzon Strait transport and the South China Sea circulation feature a sandwich vertical structure from the surface to the bottom. The Philippine Sea water is simulated to enter the South China Sea at the surface and in the deep ocean and is carried to the southern basin by western boundary currents. At the intermediate depth, the net Luzon Strait transport is out of t     

南海中尺度涡的形转、内转及平移运动研究

中尺度涡旋的运动整体可分为两部分：平移及转动。平移指涡旋在整个生命周期内的水平移动,而转动除了包括内转 （海表地转流引起的涡旋自身水体转动） 外,还包括形转 （涡旋实际边界最佳拟合椭圆的转动）。本文基于 1993—2018 年共计 26 年间的卫星高度计涡旋识别与追踪数据,首次对南海中尺度涡旋的完整运动形式,即形转、内转、平移展开了系统的研究。其中,对内转及平移的分析,可通过涡旋的识别追踪数据集直接进行;为研究涡旋形转,提出了一种基于涡旋识别追踪数据自动提取涡旋形转信息的算法,以此得到涡旋形转方向、每天形转的角度以及形转圈数等信息,获得涡旋形转数据集。通过对涡旋识别追踪数据以及形转数据集的统计分析发现：南海涡旋的平移方向多为西向,且其速率呈偏态分布,主要以南海南部偏高。同样,涡旋的内转速率也呈偏态分布,高速率内转的涡旋主要分布在吕宋海峡附近。涡旋的形转主要以南海南部速率偏高,且与涡旋的寿命及长轴有一定的关系,倾向于随着涡旋寿命的增长、涡旋长轴的增大而变慢。同时南海涡旋的这三种不同运动形式之间也存在一定的相关性。     

Manganese carbonates in the upper quaternary sediments of the Deryugin basin (Sea of Okhotsk)

The mineral and chemical compositions of authigenic carbonates are studied by several methods in a sediment core obtained from the axial zone of the Deryugin riftogenic basin. Manganese carbonates (kutnahorite, rhodochrosite) associated with manganiferous calcite, manganiferous pyrite, and nontronite are first identified in the Sea of Okhotsk. Manganese carbonates in the Holocene diatomaceous ooze were presumably formed due to diagenetic transformation of sedimentary manganese hydroxides, organic matter, and biogenic silica, while those found in the underlying turbidites precipitated owing to the intermittent influx of endogenic fluids migrating along sand interbeds.     

Features of eddy kinetic energy and variations of upper circulation in the South China Sea

The features of eddy kinetic energy (EKE) and the variations of upper circulation in theSouth China Sea (SCS) are discussed in this paper using geostrophic currents estimated from Maps of Sea Level Anomalies of the TOPEX/Poseidon altimetry data. A high EKE center is identified in the southeast of Vietnam coast with the highest energy level 1 400 cm2 ·s~(-2) in both summer and autumn. This high EKE center is caused by the instability of the current axis leaving the coast of Vietnam in summer and the transition of seasonal circulation patterns in autumn. There exists another high EKE region in the northeastern SCS, southwest to Taiwan Island in winter. This high EKE region is generated from the eddy activities caused by the Kuroshio intrusion and accumulates more than one third of the annual EKE, which confirms that the eddies are most active in winter. The transition of upper circulation patterns is also evidenced by the directions of the major axises of velocity variance ellipses between 10°and 14.5°N     

南海海盆中尺度涡移动速度统计分析

基于1993-2017年卫星高度计数据得到的中尺度涡追踪产品,分析了1000 m以深南海海盆中尺度涡移动速度C的时空分布特征。结果表明,南海海盆气候态平均的中尺度涡纬向移动速度c_x均为西向,经向移动速度c_y在海盆西北侧为南向,东南侧为北向。c_y随经度的变化与背景经向流的变化一致,相关系数达0.96,而c_x的变化与背景纬向流和β效应有关。c_x和C存在明显季节变化,夏季最慢,冬季最快。年际变化上,c_x和c_y的大值多发生在太平洋年代际涛动（PDO）负位相期的La Nina年。中尺度涡在其生命周期的开始和结束阶段（即生成和耗散阶段）移速较快,而在稳定的“中期”阶段移动缓慢。该趋势与涡旋转速呈反相关,相关系数为-0.93。以移速小于1.5 cm/s和大于15.4 cm/s定义的极慢和极快涡旋,分别占总涡旋数量的1.5%和1.9%。移速极慢的涡多出现在海盆的中部,且主要发生在夏季;移速极快的涡多出现在海盆的边缘,且主要发生在冬季。机制分析显示,南海海盆中尺度涡移动速度的时空分布受到大尺度背景流场调制。     

Observation of the anticyclonic eddy formation off the Black Sea coast

An anticyclonic eddy with a horizontal dimension of 20 km travelling north-westwards at a speed of 10 cm/s has been found during an experiment carried out off the Black Sea coast. Dynamic instability owing to horizontal velocity shear could be the reason for its origin. The eddy's passage favours the development of shear instability and the generation of short-period internal waves.Translated by Mikhail M. Trufanov.     

The tectonics of the Okhotsk Sea

The northern and central parts of the Okhotsk Sea form an epiMesozoic platform. The hetero-aged acoustic basement is represented by deformed geosynclinal rocks from Cretaceous to Precambrian in age. The slightly deformed sedimentary cover levelled the uneven surface of the acoustic basement, and this Upper Paleogene—Neogene cover filled up the system of the structural basins. The general NW—SE and W—E extensions of the taphrogenic horsts and grabens of the acoustic basement were formed due to extension and subsidence of the earth's crust during the late Paleogene—Neogene.     

Matter composition and formation conditions of the Pliocene-Pleistocene sediments in the Kuril basin (sea of Okhotsk)

An integrated (petrographical and micropaleontological) study of the sedimentary cover samples dredged from the lower slopes of the Kuril deep-sea basin was carried out. The Pliocene-Pleistocene sediments are mainly represented by tuffaceous sedimentary rocks (tuffites, tuffaceous muds, tuffaceous diatomites, tuffaceous silts, tuffaceous sandstones, etc.). Significant admixtures of pyroclastic matter, especially of volcanic glasses, indicates that the sedimentation process was accompanied by explosive volcanism. The data obtained give evidence about the intensification of the tectonomagmatic regime within the region under study during the Pliocene-Pleistocene time. By the beginning of the Pliocene, a deep-sea basin with a well-manifested continental and/or island slope and a narrow shelf already existed. The Pliocene-Pleistocene deposits accumulated in a cold well-aerated deep-sea basin under oxic conditions and downslope sediment transport.     

Barotropic Response of the Sea of Okhotsk to Wind Forcing

We have examined wind-induced circulation in the Sea of Okhotsk using a barotropic model that contains realistic topography with a resolution of 9.25 km. The monthly wind stress field calculated from daily European Centre for Medium-Range Weather Forecasting (ECMWF) Re-Analysis data is used as the forcing, and the integration is carried out for 20 days until the circulation attains an almost steady state. In the case of November (a representative for the winter season from October to March), southward currents of velocity 0.1–0.3 m s⁻¹ occur along the bottom contours off the east of Sakhalin Island. The currents are mostly confined to the shelf (shallower than 200 m) and extend as far south as the Hokkaido coast. In the July case (a representative for the summer season from April to September), significant currents do not occur, even in the shallow shelves. The simulated southward current over the east Sakhalin shelf appears to correspond to the near-shore branch of the East Sakhalin Current (ESC), which was observed with the surface drifters. These seasonal variations simulated in our experiments are consistent with the observations of the ESC. Dynamically, the simulated ESC is interpreted as the arrested topographic wave (ATW), which is the coastally trapped flow driven by steady alongshore wind stress. The volume transport of the simulated ESC over the shelf reaches about 1.0 Sv (1 Sv = 10⁶ m³s⁻¹) in the winter season, which is determined by the integrated onshore Ekman transport in the direction from which shelf waves propagate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Winter Oceanographic Conditions in the Southwestern Part of the Okhotsk Sea and Their Relation to Sea Ice

In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick first-year ice (average thickness 0.6 m). This vertically uniform winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100–300 m depth zone less saline, colder, and richer in oxygen (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and a heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting. This revised version was published online in August 2006 with corrections to the Cover Date.     

An eddy-driven abyssal circulation in a bowl-shaped basin due to deep water formation

Numerical experiments were performed to investigate the effects of eddies generated in deep water formation processes on an abyssal circulation in a closed bowl-shaped basin. Two sets of experiments were performed. One set was eddy-restricted experiments in which only a volume-driven (upwelling-driven) circulation was simulated and the other set was eddy-permitted experiments in which both a volume-driven circulation and an eddy-driven circulation were simulated. In the two layer experiment where the lower layer water is formed, a mean along-slope current is formed in the lower layer for both the eddy-restricted and eddy-permitted experiments. The direction of the current was not unique in the eddy-restricted experiment, but it was cyclonic in the eddy-permitted experiment. In the three layer experiments where water of the intermediate layer is formed, the mean along-slope current in the lowest layer is negligibly small in the eddy-restricted experiment, while it is large and cyclonic in the eddy-permitted experiment. The driving forcings of the eddy-driven circulation are quantified in terms of eddy fluxes of relative vorticity (Reynolds stress) and layer thickness (bolus velocity). These terms increase as the volume of the newly formed water increases, but they do not change greatly with the slope height. The magnitude of these terms changes with the slope width, but the sum of these terms does not vary greatly. As a result, the intensity of the eddy-driven circulation depends primarily on the volume of newly formed water. These dependences of eddy fluxes were interpreted using downgradient diffusion of potential vorticity.     

日本海、鄂霍次克海和白令海的古海洋学研究进展

边缘海的存在使大陆和大洋之间的物质和能量交换变得相当复杂。在构造运动和海平面升降的控制下,边缘海和大洋之间时而连通时而隔绝,各种古气候变化信号都在一定程度上被放大。基于近期有关西北太平洋边缘海的古海洋学研究成果,简要概述了日本海、鄂霍次克海、白令海以及北太平洋地区自中新世以来的古气候和古海洋环境演化特征,并认为它们与全球其它地区一样也受控于因地球轨道参数变化引起的太阳辐射率的变化,大尺度的气候变化具有与地球轨道偏心率周期相对应的100ka周期,而41ka的小尺度周期则受地球自转轴斜率变化的控制。一些突发性的气候变化则是由气候不稳定性、海峡的关闭与开启和其它一些地球气候系统的非线性活动所驱动。但同时作为中高纬度边缘海,它们的古海平面、古海水温度、古洋流等古海洋环境因子的变化特征还受到冰盖扩张和退缩、构造运动、冰川性地壳均衡补偿、东亚季风等因素的影响,具有一定的区域特点。     

Ferromanganese crusts from the Sea of Okhotsk

New data on the microstructures and the mineral and chemical compositions of ferromanganese crusts obtained from the western slope of the Kuril Island Arc in the Sea of Okhotsk during cruises of the R/V Vulkanolog are discussed. The study of the crusts using analytical electron microscopy methods revealed that their manganese phase is represented by vernadite, Fe-vernadite, todorokite, asbolane, and asbolane-buserite, while the iron phase consists of hematite, hydrohematite, ferroxyhite, and magnetite. The assemblage of lithic minerals includes apatite, quartz, epidote, and montmorillonite. According to the chemical analysis, most of the crusts contain a significant share of volcanogenic and hydrothermal material, which is evident from the elevated values of the Mn and Ti modules, the low concentrations of some trace elements, and the positive Eu anomaly in the rare earth elements composition.