Acoustic characteristics of the north-eastern Atlantic Ocean

The vertical structure of the climatic and seasonal fields of the estimated speed of sound in the north-east Atlantic Ocean is considered. Zonation according to typicalc(z) profiles allowing for seasonal variations was carried out. It is shown that the water areas with a dual-channel vertical hydroacoustic structure vary essentially throughout the year. The features of the structure of the sound speed field in the lenses of the Mediterranean Sea waters are investigated. The effect produced by a lens on the characteristics of the sound propagation is studied.Translated by Mikhail M. Trufanov.     

海洋岛附近海域春季海洋水文测量结果分析

利用2006年4月在海洋岛附近海域的CTD测量资料,系统分析了该海域温度、盐度、密度和声速的平面分布和垂直分布特征,并探讨了其形成机理。分析指出:4月份是海洋岛附近海域季节性跃层的生成期,海区会产生正跃层、逆跃层、冷中间层、暖中间层等复杂的垂直结构;中间层和底层水文要素受海流的影响较大,而表层水文要素主要受海面风场和气温的影响。     

Vertical distribution of the sound speed in the Gulf Stream system

Using archived historical data on the temperature/salinity distribution, this paper describes the structure of the mean seasonal and the actual field of the computed speed of sound in the Gulf Stream region. The formation of acoustic channels of large, medium, and small size is considered, depending on the vertical thermohaline structure of waters. The paper provides statistical characteristics of the sound speed field and acoustic channels of waters interacting in the Gulf Stream system. Translated by Vladimir A. Puchkin.     

菲律宾海的声速剖面结构特征及季节性变化

应用Argo资料研究了菲律宾海的声速剖面结构特征。通过统计分析选取了合理的跃层标准,分析了主跃层、季节性跃层和表面正梯度层的区域性分布及季节性变化。结果表明,菲律宾海主要受赤道流系和北太平洋西边界流系的支配,其环流结构和水团配置对声场结构影响很大;主跃层的经向差异显著,但季节性变化较小,其平均位置由南向北逐渐加深,强度逐渐减弱;季节性跃层的分布及变化主要受混合层的季节性变化以及北部海区冬季温跃层通风过程的影响,夏季较强较厚,冬季较弱较薄;深海声道轴季节性变化较小,南极中层水和北太平洋中层水的温盐差异是其经向分布差异的主要原因。综合考虑海区声速结构区域性和季节性特征,将其归纳为6种典型结构,得出了各类声速剖面的模态特征及垂直结构参数的统计特征值。     

Seasonal variability of acoustic characteristics in the northern Black Sea continental slope area

The peculiarities of seasonal variability of the calculated sound speed and elements of its vertical stratification in the northern Black Sea continental slope are considered. Typical acoustic structures have been identified. The impact of seasonal variability of the sound speed upon the ray characteristics of acoustic fields is studied. Translated by Vladimir A. Puchkin.     

Development of fouling communities on vertical structures in the Baltic Sea

The pillars of the bridge connecting the Island of Öland with the Swedish mainland were rebuilt between 1990 and 2000. The renovation produced pristine vertical concrete substrates, which became submerged in known years and seasons. The fouling communities on the pillars were examined in 2001 to determine whether the community structure could be explained in terms of either orderly successional development or of seasonal variation in the settlement of benthic organisms. As well, the communities on the pillars were compared to communities on the vertical surfaces of boulders in the area. The results indicated that an annual species composition is the final stage in the succession on the observed, vertical constructions. The few perennial species add to the variation between pillars as they increase in biomass (Polysiphonia fucoides) or become out-competed (Balanus improvisus). Also, observed seasonal differences in the biomass of these perennial species indicated that the time of year free space becomes available might be an important determinant of the future structure of the community. Comparison between the pillar and boulder communities showed that the artificial structures were not surrogates for the natural hard substrate: pillar communities differed in that they lacked most perennial algal species and had a high biomass of B. improvisus.     

Climatological Estimation of Environmental Uncertainty Over the Middle Atlantic Bight Shelf and Slope

Historical hydrographic data are used to determine the spatial and seasonal patterns of uncertainty in thermohaline and sound-speed fields in a well-sampled region, the continental shelf and slope in the Middle Atlantic Bight (MAB). Several different historical databases are combined to produce two-dimensional (2-D) plan view and cross-shelf fields of temperature, salinity, and sound speed in two separate regions, the New England shelf and the shelf off Delaware and Maryland. In addition, spatial maps of the sound-speed fields reveal that the maximum variance of the sound speed occurs at the edge of the continental shelf, in the vicinity of the shelfbreak front. The standard deviation of the sound speed was largest during the spring and summer, with magnitudes as large as 14 m/s in a narrow band coinciding with the mean position of the shelfbreak front. During spring the peak in variance was located near the surface outcrop of the front, but during summer the maximum variance was centered at a depth of 30 m, immediately beneath the seasonal thermocline. Comparisons with both synoptic measurements from the Shelfbreak PRIMER experiment as well as moored time series from the Nantucket Shoals Flux Experiment confirm that the shelfbreak front is a "hotspot" of uncertainty (maximum variance), and that the vertical structure of the peak variance is dependent on the presence or absence of the seasonal thermocline     

Acoustic characteristics of seawater in the area of the coastal discharge front off the Guinean shore

Regularities in the structure and variability of the acoustic characteristics of Guinean shelf waters during the rainy season have been identified as a result of the generalization of the sound speed fields derived from temperature and salinity observations. Three areas with qualitatively different hydroacoustic properties have been revealed, namely, (i) near-shore shallow waters, where a near-surface haline acoustic channel occurs by virtue of intensive seawater freshening; (ii) a discharge front accommodating an intermediate acoustic waveguide in the temperature jump layer; and (iii) off-shore shelf areas displaying a characteristic alteration of the sound speed vertical gradient sign at thec(z) profile.Translated by Vladimir A. Puchkin.     

Large-scale vertical hydroacoustic structure of the North Atlantic and its seasonal variability

A classification based on the number and types of large-scale acoustic waveguides is proposed for the mean seasonal profiles of sound speed propagation. A scheme for North Atlantic zoning, using typical curves of the sound speed vertical distribution, is given. The channel axis's position is shown not to depend on the water mass haline properties, being controlled by the temperature field vertical stratification.Translated by Vladimir A. Puchkin.     

Spatial and Temporal Variations of Sound Speed at the PN Section

Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spreading of warm water from the Kuroshio Extension into the Perturbed Area

The path of the Kuroshio Extension describes two stationary meanders with crests at approximately 144°E and 150°E. The short-term meridional fluctuations of the warm water spreading northward from the first crest at the surface and its vertical structure were analyzed by using 5-day-mean surface temperature maps published by JAFIC, montly 100-m-depth temperature maps edited by the JMA, and CTD data obtained by the R.Vs.Kofu-Maru, Hakuho-Maru andTansei-Maru cruises from 1990 to 1994. A Northern Boundary of the Spreak Kuroshio Water (NBSKW) and a Southern Boundary of the Spread Kuroshio Water (SBSKW) at the surface were defined as the northern and southern boundary of the pronounced meriodional temperature gradients, respectively. The vertical structure of the Spread Kuroshio Water was analyzed in terms of its T-S properties. The location of the NBSKW at the surface corresponds well with the northern boundary of the subsurface high salinity water that represents the Spread Kuroshio Water. The short-term meridional fluctuations of the northern and southern boundary of the Spread Kuroshio Water at the surface were studied through the spectral analysis of the maximum latitude of the two lines defined. We obtained the following results: (1) the meridional fluctuations of the NBSKW and SBSKW at the first creast have major periods between 16 and 38 days; (2) the 50 day running mean of the SBSKW at the first crest, for the purpòse of this study, can be generally used as indicative of the location of the Kuroshio axis; and (3) the northward extent of the Spread Kuroshio Water and the velocity of the meridional shift suggest seasonal variability that could be related with their vertical structure.     

Spatial/temporal variations in zooplankton biomass and ecological characteristics of major species in the southern part of the Japan Sea: a review

During the 1990s many studies on zooplankton in the Japan Sea have been carried out. In this review, I have synthesized the study of horizontal distribution, seasonal and annual variations of zooplankton biomass, and ecological characteristics of major component species in the southern Japan Sea, which area is influenced by the warm Tsushima Current. The zooplankton biomass (annual mean) in the southern Japan Sea was lower than in the subarctic Pacific, including the northern Japan Sea, and similar to biomass levels in Kuroshio waters. Temporal variations in zooplankton biomass showed both seasonal and year-to-year components. Seasonal biomass increases to a maximum in spring with a weak secondary peak in autumn. As for long-term changes, 3–6 year cycles were identified, with the dynamics of the surface warm Tsushima Current and the subsurface cold water playing important roles in determining the yearly zooplankton community structure and biomass. Cold water species in the southern Japan Sea had extensive diel vertical migrations whose range is restricted in summer by the development of a thermocline. Among these species, the herbivores Euphausia pacifica and Metridia pacifica encounter a lower food supply, resulting in lower growth rates. The vertical dispersal of epipelagic carnivorous zooplankton such as Sagitta elegans and Themisto japonica to the deep-sea is probably facilitated by reduced interspecific competition. Their interaction with Japan Sea Proper Water, characterized by near-zero temperatures in the meso- and bathypelagic zones suppresses growth rates of the mesopelagic zooplankton. The lack of micronektonic predators in the mesopelagic zone may allow the persistence of slow growing populations.     

Vertical structure of larval fish assemblages during diel cycles in summer and winter in the southern part of Bahía de La Paz, México

The effect of environmental variables on the vertical structure of larval fish assemblages in a tropical coastal lagoon was analyzed. Ichthyoplankton samples were collected from the near-bottom and surface strata near the mouth of a subtropical lagoon during contrasting seasonal conditions of temperature, photoperiod, light intensity, and tidal heights. During summer, larval fish assemblages had high species richness (R) and were dominated by tropical species. During winter, assemblages had lower R values and were dominated by subtropical and temperate species. Vertical distribution patterns of the taxa were determined by the interaction of environmental variables and behavior of each species to maintain their position in a stratum in the water column, or to achieve vertical migrations induced by environmental stimuli that, in this case, were thermal gradient, column water stratification, and intensity of light. Depth position and vertical migration of fish larvae, coupled with the flood and ebb tide conditions, played an important role in their retention and displacement toward the lagoon. Fish larvae with distribution restricted to the inner part of the inlet, such as Achirus mazatlanus, Etropus sp., and several gobies, were more abundant in the near-bottom stratum during the ebb tide, allowing them to avoid exportation, whereas those that could spawn outside, but depended on the inlet as a nursery area, were more abundant near the surface during flood tide, such as Abudefduf troschelii and Stegastes rectifraenum.     

第二岛链以东附近海域冬季水文要素特征分析

利用西太平洋冬季海洋综合调查获取的数据资料,分析了第二岛链以东附近海域冬季温度、盐度、声速和密度的分布特征和变化规律。使用Ocean Data View海洋数据软件对资料进行网格化处理,同时采用Wilson方法和垂直梯度法计算声速和声速梯度。分析数据结果表明:第二岛链以东附近海域冬季温度随深度增加而减小,且750 m以浅变化幅度较大;而盐度和声速的垂直结构特征均表现为从表层向下先减小后增大,但各自存在不同的临界深度。海区存在温度和声速双跃层结构,上跃层强度大,厚度小;下跃层强度较小,厚度较大。     

Distribution and number change of the Littorinid(Gastropoda) on intertidal hard bed in the Jiulong Estuary, Fujian Province

-Among four species of Littorinid, Littorina scabra, L. brevicula, Nodiliitorina millegrana and N. pyramidalis pyramidalis, on the hard intertidal zone in the Jiulong Estuary, Fujian, L. scabra has the most extensive distribution both vertically and horizontally, and the highest anual average density. The uppermost limit of vertical distribution of N. pyramidalis pyramidalis is higher than the other three Littorinid. Desiccation is a main factor affecting the uppermost limit of vertical distribution of the Littorinid. The increasing wave action will raise the uppermost limit vertical distribution of Littorinid. With seasonal changes, the densities of the Littorinid also change in different tidal zonations. Difference in salinity is the main factor affecting the horizontal distribution of the Littorinid in the estuary.     

Synoptic variability of the acoustic characteristics in tropical Atlantic waters

Synoptic variability of the sound speed and parameters of the SOFAR channel in the tropical Atlantic are considered. The synoptic component of the temporal and spatial dispersions of sound speed is singled out. The synoptic processes are shown to essentially affect the vertical hydroacoustic structure on a 1-month scale. It has been found that synoptic variations in the sound speed field penetrate as far as the SOFAR channel axis and deform it considerably.Translated by V. Puchkin.     

Horizontal structure of the temperature field of the upper layer in the northwest part of the Tropical Atlantic

By using the data of observations over the spatial variability of the temperature field in the northwest part of the Tropical Atlantic carried out in a test range 400 × 400 miles in size with a horizontal resolution Δx ≈ 2 km and a vertical resolution Δ_z ≈ 0.5 m, we recorded quasiperiodic fluctuations of temperature with semidiurnal period in the subsurface layer. The internal baroclinic waves with the same period generated, most likely, on the northeast shelf of South America and propagating to the northeast are detected in the seasonal thermocline. The vertical fine structure of the temperature field has different intensities in the test range. The maximum levels of dispersions of temperature fluctuations are recorded on the boundary of the North Equatorial Countercurrent and the North Equatorial Current. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 44–52, November–December, 2006.     

Effects of disturbance of seawater excited by internal wave on GNSS-acoustic positioning

Traditional Global Navigation Satellite System-Acoustic (GNSS-A) positioning assumes the Layered Model in the sound speed structure, and any of horizontal perturbation of seawater degrades its accuracy. However, the use of the Gradient Model analytically demonstrated that the horizontal gradient of the sound speed structure and displacement can simultaneously be solved using multiple transponders for each of ping. We applied this technique to our observed data and found it unsuitable for real data. We confirmed that a horizontal perturbation with wavelength shorter than the horizontal extent of the transponder array significantly violates the linear approximation in the Gradient Model. Our vertical 2D numerical simulation of internal waves (IWs) forced by tidal oscillation showed that such small-scale IWs could effectively be generated by nonlinear cascade from large-scale IWs of the major tidal constituents. In addition, a small-scale IW in deep water typically has a period of 3–4 h, which degrades positioning accuracy significantly, whereas an IW of much shorter period in shallow water has less effect after removal of the fluctuation by time averaging within a typical observation period. Apparent array position obtained in the synthetic test based on the simulated IW-derived sound speed structure showed features quite similar to that observed in real surveys. To incorporate such deeper perturbation, we proposed a Disturbance Model using dual sea surface platforms, that can solve time-varying perturbation in the vicinity of each transponder.

     

Quantification of vertical density variations of salt-marsh vegetation

Density and structure of salt-marsh canopies control the reduction of water flow by the vegetation, which may cause inter alia increased accretion. This paper presents and evaluates two methods that quantify the vertical density variations of salt-marsh canopies: the vertical biomass distribution and the lateral obstruction ratio obtained from a binarised picture. The former provides accurate results and is well adapted to define canopy heights; the second reflects the flow hindrance better, but is unsuitable for dense canopies. Both methods are used to illustrate density variation over short distances in Spartina marshes and to monitor two English salt-marshes over one year. The results demonstrate the great seasonal variability in the vegetation, which must be taken into account when long-term predictions are extrapolated from short-term measurements.     

南海北部陆架陆坡区海流观测研究

针对2006-2009年期间,南海北部陆架陆坡区3个站ADCP海流连续观测资料,采用功率谱分析、潮流调和分析方法,重点分析了陆架陆坡区100 m,200 m和1 200 m水深海域海流的垂向结构,探讨了环流的季节变化和空间分布特征,特别讨论了南海暖流和北陆坡流的时空变化特征。结果表明,陆架陆坡区潮流类型属于不规则日潮,深水站点中层表现为正规全日潮类型,垂向为"三层结构",甚至更加复杂。O₁,K₁,M₂,S₂等分潮总体上为顺时针旋转,在深水站点,基本表现为西北－东南走向的往复流形态。从能量角度看,表层和底层海流中,潮流所占份额较大,分别占30%~40%和40%~50%,中层较小,约为20%。对东沙群岛西南陆架陆坡区环流,观测计算结果证实了西向强流的存在,且垂向结构具有显著的季节变化,在200 m水深处没有明显的南海暖流,只是10~30 m以上层次存在逆风海流。海南岛以东海域连续15个月表层环流的结果表明,冬季明显受到南海暖流的影响,存在东北向的逆风海流,夏秋季的环流表现为西南向,流速较强,夏季也存在逆风情况,造成上述情形的原因可能是该地南海暖流的流轴具有季节性变化——冬季偏南,夏季偏北。