Correlation of the distribution of normalized spectral radiances as an indicator of the features of water exchange in the Black Sea

A set of 128 images of the Black Sea obtained using the SeaWiFS color scanner data in 1998–2004 was processed to estimate the new capabilities of indication of the vertical inhomogeneity of the upgoing normalized radiance. The basin of the sea was divided into 430 frames with a size of 30 × 30 km. Correlation coefficients R between all the spectral radiances were calculated for all the frames of all the images. The correlation between the radiance distributions at 490 and 670 nm was most sensitive to the conditions of the radiance formation. This allowed us to find the situations in which the variations in the shortwave and long wave radiances in the frame appear opposite and are characterized by estimates R < ?0.7. It was shown that such distributions are indicators of the water exchange between the coastal and open sea areas. They are caused by a special optical stratification during the events of such exchange. A conclusion is made about the prospective of applying the estimates of the correlation of spectral radiances for diagnosis of the water exchange based on the current and archive materials of ocean color scanners.     

Penetration of coastal waters into the Eastern Mediterranean Sea using the SeaWiFS data

Offward transport of surface coastal waters was studied in the Eastern Mediterranean from 31° to 37° N between 31° to 36° E using cluster analysis of water-leaving radiance spectra from SeaWiFS color scanner imagery for spring-summer period of 1998. Some types of spectra were found to be characteristic of products of mixing of coastal and offshore waters and served as a quasiconservative tracer of water transport. Three sectors of the eastern coastal zone supplied colored and suspended matter into the open sea areas as occasional pulse discharges of 3-5 week periodicity. The Haifa sector was the most powerful source of such matter producing traceable separate radiance inhomogeneities as far as 200 km west of Haifa. It appears that the discharges were triggered when a set of specific conditions took place and that evolution and life time of discharged waters depended on currents and horizontal mixing. Advantages of cluster approach to imagery analysis are briefly discussed.     

On the long-term variability of normalized radiance of the Black Sea

Basin-wide distributions of normalized spectral radiances averaged over different time periods were plotted based on the estimates of the average radiance for 20 × 20 km squares in 482 digital images of the Black Sea obtained with a SeaWiFS color scanner in 1998–2004. Significant distinctions of the annual average distributions in the amplitude, localization, and configuration of basin-scale inhomogeneities allowed us to consider these distributions as yearly spectral-radiance portraits of the Black Sea that reflect specific features of the annual behavior of the hydrometeorological conditions over the Black Sea region. Seasonal features of the radiance distributions related to the wind field were discovered. Substantial interannual variability in the errors of the standard atmospheric correction algorithm resulting in an underestimation of the shortwave radiances were revealed. It is shown that the river discharge and the stratification of the layer sensed substantially influence the yearly spectral-radiance portraits of the Black Sea.     

Role of Kuroshio frontal eddy in exchange between shelf water and Kuroshio water in East China Sea

Basic patterns of the reversal of the Kuroshio water toward the shelf, intrusion of the shelf mixed waterinto the Kuroshio and uplifting of the near-bottom nutrient-rich water into the upper layer by the pumping of the frontal eddy are analyzed on the basis of satellite infrared images and hydrologic, chemical and biological observations. Results show that the Kuroshio frontal eddies play a very important role in the exchange between the shelf water and the Kuroshio water. The estimation of the average volume transports for three frontal eddy events indicates that the shelf mixed water entrained by an eddy into Kuroshio is 0.44×10~6 m3/s and the reversal Kuroshio water onto the shelf region only 0.04×10~6 m3/s. Along the whole shelf edge, the volume transport of the shelf mixed water entrained by the eddies into the Kuroshio is 1.8×10~6 m3/s. The nutrient (NO3-N) flux pumped to the euphotic zone and input to the continental shelf through a column with 1 m wide is 974 μmol/(s·m) when there is frontal eddy and only 79 μmol/(s·m) in the case of no frontal eddy. Yearly nutrient (NO3-N) flux input to the shelf area caused by the frontal eddy is 1.7×10~5 t/a.     

Mesoscale eddies in the area of peter the great bay according to satellite data

We have studied the characteristics of mesoscale eddies in the Peter the Great Bay and the adjacent area of the northwestern Sea of Japan. The characteristics were determined using infrared images (NOAA/AVHRR satellite data) for July–October periods of 2000–2004. It is established that anticyclonic eddies are always present in the indicated area, since they have been identified on 85% of the available cloudfree images. Characteristics of 43 anticyclonic eddies have been determined. Their diameters vary from 20 to 110 km, with the most probable sizes within 20–60 km. The typical eddy lifetime varies from 3 to 30 days. However, some medium-sized eddies (40–60 km) have been observed for a longer time (up to 40–60 days) and large eddies (60–110 km in diameter) remained for up to 1–2 months. Eddies drift southwestward and southward along the continental slope at a typical speed of 3–6 cm/s. There are interannual variations in the vortex structure of water flows in the area studied, which are manifested by the presence of a single large eddy occupying a large part of the bay in some years (2000, 2002, and 2003) or by the formation of several smaller eddies (2001 and 2004). The eddies contain warmer and less saline shelf waters (compared to the surrounding water) and transport it in their cores over quite a long distance. Thus, eddies are an essential element of the process of the intermediate low-salinity water-mass formation in the Sea of Japan. In addition, eddies play important role in the cross-shelf water exchange, providing rapid ventilation of the coastal zone and determining the variability of the biological processes.     

Numerical analysis of the mesoscale features of circulation in the Black Sea coastal zone

The results of simulating the hydrophysical fields of the Black Sea with a resolution of 1.64 × 1.64 km for January–September 2006 with the use of real atmospheric forcing are analyzed. Both vertical turbulent momentum exchange and vertical turbulent heat and salt diffusions are parameterized using the Mellor-Yamada level 2.5 scheme. The results of this numerical experiment are compared with similar data obtained with a horizontal resolution of 5 km. The features of the meso- and submesoscale dynamics of waters in individual sea regions are given. Possible physical mechanisms of forming meso- and submesoscale vortices are studied on the basis of energy analysis. It is shown that, in the absence of significant wind forcing, the main contribution to kinetic energy is made by the buoyancy force and wind-field inhomogeneities result in significant variations in both total vertical viscosity and total vertical diffusion.     

Discharge and surface plume measurements during manganese nodule mining tests in the north equatorial pacific

Rates, concentrations, and composition of mining discharge and the size and structure of the ensuing surface plumes were examined during North Pacific tests of scaled manganese nodule mining systems. Discharge was composed principally of bottom water and pelagic silts and clays, although nodule fragments with diameters less than 1 mm were also discharged at widely varying rates. Average flow rates of the discharge varied from 95 to 160 litres/s, with the solid fraction varying from 550 to approximately 2000g/s. The plume, as determined by particulate concentrations in excess of ambient oceanic conditions, extended approximately 5 km from the mining ship and had a width of about 1 km. Fe and Mn signatures allowed detection of the plume nearly 35 km from the source. The plume provided evidence of settling more rapidly than expected of silt and clay-size particles: a mean settling velocity of 6 × 10^?2 cm/s for the particulates in the plume and a mixed layer vertical turbulent eddy diffusivity of 1 × 10^?2m²/s have been inferred from the data. Field and laboratory data together suggest that the rapid settling was due to flocculation of the discharge particulates.     

南海中尺度涡温盐结构的季节特征及形成机制

本文利用最新的涡旋数据集和ARMOR3D数据,研究了南海中尺度涡温盐结构的季节特征及形成机制。合成分析的结果表明,在冬季,涡旋引起温度异常的水平分布在50米以浅表现为类似偶极型分布,而在50m以深则趋向于中心对称分布;在夏季,温度异常的水平分布均表现为中心对称的特征。涡旋引起盐度异常的水平分布也具有类似的季节特征,但是偶极型中的不对称性相对较弱。在垂向上,涡旋所致的温度异常表现为单层结构,而盐度异常则为三层结构。进一步的分析表明,涡旋所致温盐异常的垂向分布特征与背景温盐的垂向分层有关;而在50m以浅,温盐异常的水平分布的不对称特征主要由背景温盐场的水平平流所致。     

Identification of mantle and lithospheric components of the gravity field by isostatic gravity anomalies

All anomalous masses of the Earth are reflected in the free air gravity anomalies and the geoidal undulations. The low viscosity of the asthenosphere significantly reduces the possibility of existence of density inhomogeneities in the layer. This fact provides some physical basis for the separation of the gravity field anomalies. It has been shown by power spectrum analysis of the free air anomalies and gravity field of isostatically compensated model of the lithosphere for the North Atlantic and adjacent areas of America, Europe and Mediterranean, that the attraction of isostatically compensated model is significant for any wave length of the field. It causes significant error in the interpretation if long wavelength constituents of the free air gravity anomalies are considered as a field of deep anomalous masses. The isostatic anomalies und isostatic geoid are free from the influences of isostatically compensated lithosphere. The characteristic feature of the isostatic anomalies power spectrum is a pronounced minimum at the wavelength of about 1000 km. The relative homogeneity of the asthenosphere may explain this minimum. It means that principal density inhomogeneities of the Earth's interior are separated by the asthenospheric layer. Such a minimum has not been observed at the power spectrum of free air anomalies being masked by corresponding wavelength of the field of isostatically compensated lithosphere. Isostatic anomalies that reflect the differences between the real structure of the lithosphere and its isostatically compensated model have wavelengths less than 1000 km. Isostatic anomalies with the wavelength more than 1000 km reflect the attraction of density inhomogeneities situated under the level of isostatic compensation. The basic features of power spectrum of isostatic anomalies are the same for oceanic and continental areas. The method based on Kolmogorov-Wiener filtration which consideres statistical characteristics of the field has been developed to divide the isostatic gravity anomalies into lithosphere and mantle components. For the North Atlantic and adjacent areas the field of mantle inhomogeneities has been determined.     

Further study of synoptic variability in Wakasa Bay, Japan

Observations of synoptic variability from CTD and current meter measurements in Wakasa Bay, Japan in summer of 1980 and 1981 are compared with the results of 1979 reported by Yamagata, Umatani, Masunaga and Matsuura (1984). It is suggested that the speed and direction of propagation can basically be explained in terms of shelf wave dynamics.In the 1980 event, a dense (colder and more saline) water advanced eastward along the north coast at about 10 km day⁻¹. The lateral scale of the phenomenon was about 30 to 40 km, in agreement with the Rossby internal radius of deformation. The T-S and current data suggest that the 1980 cold event was dominated by phase propagation. In the 1981 event, a light (warmer and less saline) water area advanced eastward at the speed similar to the 1980 cold event, but the T-S and current data suggest that Lagrangian drift of water particles associated with strong eddy motions was not negligible.     

Salt Diapirs, Salt Brine Seeps, Pockmarks and Surficial Sediment Creep and Slides in the Canary Channel off NW Africa

Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, < 1km wide, with abrupt terminations and pockmarks associated with these mounds were probably eroded by dense brine and hydrocarbon seeps. The salt brines that eroded the gullies were formed where salt diapirs intersect the seafloor, or in the subsurface by circulating ground water heated by igneous activity along the Canary Ridge. If the brines originated in the subsurface they reached the seafloor along faults. Displacement of the surficial sediments by sliding and creep is probably the result of the expulsion of hydrocarbons and/or vertical motion of the Mesozoic evaporites. Microtopographic features along or near the east flank of the Canary Ridge are the creation of uplift of the ridge, hydrothermal activity, mass wasting processes and turbidity currents.     

Some characteristics of Yakutat Eddies propagating along the continental slope of the northern Gulf of Alaska

Data from array for real-time geostrophic oceanography (ARGO) profiling floats, oil tanker thermosalinographs, shipboard ADCP and towed-CTD surveys, and satellite altimetry are used to examine properties of two ∼200 km diameter, anticyclonic Yakutat Eddies that propagated westward at ∼1.5 km day⁻¹ along the continental slope of the northern Gulf of Alaska (GOA) in 2001 and 2003. The eddies had lifetimes of up to 5 years, remained close to the shelfbreak, and had relatively constant size and strength until they encountered the Alaskan Stream where they appeared to spawn smaller, shorter-lived anticyclones. The azimuthal velocity field was vigorous (25–40 cm s⁻¹) and in gradient wind balance with Rossby numbers of ∼0.05. Conservation of salt and azimuthal mass transports (between 20 m and the depth of the 32.2 isohaline) from shipboard surveys in May and August 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters. Chlorophyll concentrations were greater in the eddy than in ambient waters in both May and August. In May, the chlorophyll was patchily distributed, while in August dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center. The high August chlorophyll concentrations might have been fostered by a broad and shallow (<∼150 m) upwelling of the eddy center between May and August.It appears likely that as Yakutat Eddies approach the shelfbreak non-linear processes will modify the slope flow field (and the stability and structure of the shelfbreak front), leading to cross-slope flows and flow reversals. This interaction may induce ∼30 km-wide streamers of shelf water to flow around the trailing edge of the anticyclone. The role of streamers in the freshwater and nutrient budgets of the GOA shelf and basin is unknown, but their contribution to these budgets will depend on the trajectory of a Yakutat Eddy, especially its proximity to the shelfbreak as the eddy propagates along the GOA continental slope.     

Eddy diffusivity and coherent mesoscale eddy analysis in the Southern Ocean

The spatial distribution of eddy diffusivity, basic characteristics of coherent mesoscale eddies and their relationship are analyzed from numerical model outputs in the Southern Ocean. Mesoscale fluctuation information is obtained by a temporal-spatial filtering method, and the eddy diffusivity is calculated using a linear regression analysis between isoneutral thickness flux and large-scale isoneutral thickness gradient. The eddy diffusivity is on the order of O (103 m2/s) with a significant spatial variation, and it is larger in the area with strong coherent mesoscale eddy activity. The mesoscale eddies are mainly located in the upper ocean layer, with the average intensity no larger than 0.2. The mean radius of the coherent mesoscale cyclonic (anticyclonic) eddy gradually decays from (121.2±10.4) km ((117.8±9.6) km) at 30°S to (43.9±5.3) km ((44.7±4.9) km) at 65°S. Their vertical penetration depths (lifespans) are deeper (longer) between the northern side of the Subpolar Antarctic Front and 48°S. The normalized eddy diffusivity and coherent mesoscale eddy activity show a significant positive correlation, indicating that coherent mesoscale eddy plays an important role in eddy diffusivity.     

Influences of the Great Whirl on surface chlorophyll a concentra-tion off the Somali Coast in 2017

The general features of the Great Whirl (GW) off the Somali Coast in 2017 and its influences on chlorophyll a (Chl a) concentration were studied by using satellite data and model outputs. Results show that GW, which initiated at 7°N, 53°E on June 13, had a lifetime of 153 d with an average amplitude of 16 cm and an average radius of 205 km. After the formation of GW, the concentration of Chl a in the interior of GW showed a downward trend throughout its life cycle, except in early July and mid-October. In early July, the Chl a blooms in the interior of GW were attributed to the combined effect of three processes. They are eddy horizontal transportation, the deepening of the mixed layer caused by the monsoon and eddy pumping, and the upward transportation of nutrients caused by eddy-induced Ekman pumping. In October, the Chl a blooms were probably due to the weakening of GW. During the period, water exchange occurred more frequently across the eddy, thus phytoplanktons were imported into the interior of GW.     

An offshore eddy in the California current system Part IV: Plankton distributions

The distribution of plankton across a warm-core eddy system in the California Current 400 km off Point Conception, California was studied in January 1981. The eddy system, about 150 km in diameter at the 7°C isotherm, was made up of a 75 m thick surface layer, a cold-core region extending from 75 m to about 200 m, and a warm-core eddy below 200 m extending to at least 1450 m. Casts for the vertical distribution of chlorophyll/phaeophytin and integrating zooplankton net tows were taken at 37 stations located about 20 km apart on two orthogonal transects across the eddy system. Vertical distributions of microplankton were determined on one section from the eddy center to beyond the eastern edge. Integrated chlorophyll/phaeophytin values were highest to the north and east of the eddy system; across the system itself, there was only a small increase of values near the center. Asymmetrical distributions of maximum concen Current water was being entrained into the center of the eddy system from the northeast. Dinoflagellates were numerically the most important member of the microplankton, especially in the deep chlorophyll maximum. Zooplankton distributions indicated the intermingling of warm and cool water species throughout at least the upper 200 m of the eddy system. Some cold water species were as abundant inside the system as outside to the north and east; their numbers were much reduced in a band surrounding the system where warm water species were most abundant. The presence of species characteristic of different water types throughout the region of the eddy system provides an indication of the mixing that had occurred since the system originally formed. The biological data, together with the physical and chemical results, indicate the importance of frontal boundary processes and lateral entrainment of surrounding water into the eddy system in determining the character and productivity of such systems.     

水深可见光遥感方法研究进展

水深测量对于水利、航运、近海工程等具有重要作用。在总结国内外水体遥感测深主要方法和研究进展的基础上,对水深遥感反演中各类模型存在的问题进行了讨论。结果表明:理论解译模型模拟了光在水体内的辐射传输过程,水深反演精度较高,但模型计算需要大量的水体光学参数且计算过程烦琐;半理论半经验模型对理论解译模型进行了简化,所需水体光学参数少且具有较好的精度而被广为应用;统计相关模型通过直接建立遥感图像光谱值和实测水深之间的相关关系而获得水深数据,且计算相对简单,但由于实测水深值与遥感图像光谱值的事实相关性无法保证,使采用该类模型反演的水深结果有时并不理想。提高水深遥感反演精度,必须进一步加强遥感器研究,充分考虑水体中的溶解、悬浮物质等信息干扰,科学构建水深模型和大气校正模型。     

Indication of bottom transport in shallow marine regions based on the data of satellite ocean color scanners

By example of a testing area in the northern Caspian Sea, a case study has been conducted to examine the feasibility of indication of near-bottom water transport from the data of ocean color scanners (OCS) for the basins whose bottom is shallower than the lower limit of the water-leaving radiance origination layer. The testing area has provided the desirable diversity of radiance origination conditions owing to an isolated underwater ridge. Based on the archived materials of the OCS SeaWiFS for 2000–2004, statistics of spectral normalized water-leaving radiances of the testing area have been computed. Hypothetically, the displacements of a radiance maximum in reference to the ridge were due to different mechanisms of interaction of water motions with bottom relief and bottom sediments. The correspondence between the patterns of radiance maximum displacements and the current notions of general water transport in the vicinity of the testing area has been established. Hopefully, the archived data of OCSs can be useful for revealing the patterns of seasonal and interannual variability of the near-bottom water transport at shallows with favorable bottom properties.     

Satellite-measured temporal and spatial variability of the Tokachi River plume

River plumes have important effects on marine ecosystems. Variation in the extent and dispersal of river plumes is often associated with river discharge, wind characteristics and ocean circulation. The objectives of this study were to identify the Tokachi River plume by satellite, determine its relationship with river discharge and clarify its temporal and spatial dynamics. SeaWiFS multispectral satellite data (normalized water-leaving radiance: nL_w) with 1.1 km spatial resolution were used to determine the spatial and temporal variability of the plume during 1998–2002. Supervised maximum likelihood classification using six channels of nL_w at 412, 443, 490, 510, 555 and 670 nm with each band's spectral signature statistic was used to define classes of surface water and to estimate the plume area. Supervised maximum likelihood classification separated three to four classes of coastal water based on optical characteristics as a result of wind stress events. The satellite-observed plume area was correlated with the amount of river discharge from April to October. The plume distribution patterns were influenced by wind direction and magnitude, the occurrences of a near-shore eddy field and surface currents. Empirical orthogonal function (EOF) was used to express the spatial and temporal variability of the plume using anomalies of nL_w(555) monthly averaged images. The first mode (44% of variance) showed the turbid plume distribution resulting from re-suspension by strong wind mixing along the coast during winter. This mode also showed the plume was distributed along-shelf direction in spring to early autumn. The second mode (17% of variance) showed spring pattern across-shelf direction. EOF analysis also explained the interannual variability of the plume signature, which might have been affected by the flow of the Oyashio Current and the occurrence of a near-shore eddy field.     

Short-term instability of the coastal waters off Tuapse

We present the results of the investigation of the hydrodynamical regime of the coastal zone off Tuapse. We identified the spatial and temporal scales of the dynamic inhomogeneities. The intensity of the vertical component of the relative vorticity and its distribution in the waters of the coastal zone are estimated. We demonstrate that the effects found in the distributions of the relative vortex’s intensity and its orientation are able to lead to the formation of blocking water in marine coastal zones or, inversely, to prompt the ventilation of these waters. Based on the multidimensional statistical analysis, the relationship of the relative eddy distribution and the dynamical topography of the coastal waters was revealed which simplifies the problem of the blocking or ventilation of the coastal waters.     

The behavior and the role of the anti-cyclonic eddy in the Kuroshio large meander development

The processes underlying the development of the Kuroshio large meanders that occurred in 1986 and 1989 are investigated using a satellite SST data set and hydrographic data. In both processes visible on the satellite SST images, a round-shaped, lower SST region with a diameter of about 200 km is found to the east of the Kuroshio small “trigger” meander (Solomon, 1978) until the region became extinguished near theEnshu Nada. The lower SST region can be interpreted as an anti cyclonic eddy, mainly because of the existence of a warm water mass in the subsurface layer of this region. The warm water mass is characterized by a constant temperature of 18–19°C, the maximum thickness of which is about 400 m. The satellite images show that the eddy is closely related to the Kuroshio path transforming into a shape like the letter “S”. This means that the eddy plays an important role in the development of the Kuroshio large meander since this, too, tends to follow an “S”-shaped path. Added to this, the subsurface layer structure of the eddy is similar to that of the warm water mass offShikoku. This similarity, together with the eddy behavior visible on the satellite SST images, implies that the examined eddy corresponds to the warm water mass offShikoku. In other words, the warm water mass offShikoku can be advected near to theEnshu Nada when the Kuroshio large meander occurs.