Copepod assemblages in a highly complex hydrographic region   总被引：2，自引：2，他引：2  

A.D. Berasategui  S. Menu Marque  M. Gmez-Erache  F.C. Ramírez  H.W. Mianzan  E.M. Acha 《Estuarine, Coastal and Shelf Science》2006,66(3-4):483-492

Community structure and diversity patterns of planktonic copepods were investigated for the Southwestern Atlantic Ocean between 34 and 41°S. Our objectives were (1) to define copepod assemblages, (2) to accurately identify their association to different water masses/hydrodynamic regimes, (3) to characterize the assemblages in terms of their community structure, and (4) to test if frontal boundaries between water masses separate copepod assemblages. Biogeographic patterns were investigated using multivariate analysis (cluster and ANOSIM analyses). Biodiversity patterns were examined using different univariate indexes (point species richness and taxonomic distinctness). Five regions of similar copepod assemblages were defined for our study area each one corresponding to different environments (freshwater, estuarine, continental shelf, Malvinas and Brazil current assemblages). These assemblages have major community structure differences. In spite of the complex oceanographic scenario of our study area, that can lead us to expect a pattern of copepod communities with diffuse boundaries, we found a strong spatial correspondence between these limits and the presence of permanent frontal structures.  相似文献   

Diel feeding patterns and the development of food webs in pelagic 0-group cod (Gadus morhua L.), haddock (Melanogrammus aeglefinus L.), whiting (Merlangiusmerlangus L.), saithe (Pollachius virens L.), and Norway pout (Trisopterus esmarkii Nilsson) in the northern North Sea     

Bromley  P. J.; Watson  T.; Hislop  J. R. G. 《ICES Journal of Marine Science》1997,54(5):846-853

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A new hypothesis about the surface circulation in the eastern basin of the mediterranean sea   总被引：3，自引：1，他引：3  

Najwa Hamad  Claude Millot  Isabelle Taupier-Letage 《Progress in Oceanography》2005,66(2-4):287

In time, the circulation of the Atlantic Water (AW) in the eastern basin of the Mediterranean Sea has been described differently, according to two major representations. The historical one, which began with the scheme from Nielsen in 1912 and has been refined up to the 1980s, favours a counterclockwise circulation in the whole basin, with AW flowing in its southern part as a broad flow off Libya and Egypt (from the Ionian to the Levantine subbasins), then continuing along Middle-East and Turkey before flowing back westwards. The more recent one, issued in the 1990s, favours a clockwise circulation in the northern part of the Ionian continuing offshore across the basin from the Cretan to the central part of the Levantine as the so-called “Mid-Mediterranean Jet”. This jet is depicted then as splitting both clockwise in the southeastern part of the basin and counterclockwise off Turkey (where this representation agrees with the former). Because the recent representation cannot be considered as a refinement of the historical ones, we have been interested in understanding why a given data set available to everybody is interpreted in such different ways.In the Algerian subbasin, the combined use of satellite infrared images and a significant amount of in situ data sets (hydrology and both Eulerian and Lagrangian current measurements) allowed us to solve a similar controversy. Therefore, we examined the circulation features in the eastern basin, undertaking the detailed analysis of 1000 daily and weekly composite images spanning the period 1996–2000, and of monthly composite images available since 1985. Whenever in situ observations were available, we have confronted them with the satellite thermal signatures and have shown that both are consistent. This paper focuses on the overall (basin scale) results while the detailed ones are published in an other paper. The new scheme we propose is basically a refined version of the historical ones: the circulation of AW is counterclockwise in the whole eastern basin but it is more constrained alongslope than previously thought, and the broadening historically schematised appears to be due to intense mesoscale eddies mainly generated by the instability of this circulation.  相似文献   

Capelin in Faroese waters-a messenger of harsh times?     

Jakupsstovu  Stein Hjalti i; Reinert  Jakup 《ICES Journal of Marine Science》2002,59(5):884-889

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High resolution velocity analysis of ocean bottom seismometer data by theτ-p method     

Masanao Shinohara  Naoshi Hirata  Narumi Takahashi 《Marine Geophysical Researches》1994,16(3):185-199

A method of high resolution seismic velocity analysis for ocean bottom seismometer (OBS) records is applied to the study of the shallow oceanic crust, especially sedimentary and basement layers. This method is based on the direct-p mapping and the-sum inversion. We use data obtained from a 1989 airgun-OBS experiment in the northern Yamato Basin, Japan Sea and derive P- and S-wave velocity functions that can be compared with the seismic reflection profiles. Using split-spread profile records, we obtain interface dips and true interval velocities from the OBS data. These results show good agreement with the reflection profile records, the acoustic velocities of core samples, and sonic log profiles. We also present a method for estimating errors in the derived velocity functions by calculating covariance of the derived layers' thicknesses. The estimated depth errors are about 150 m at shallow depths, which is close to the seismic wavelength used. The high resolution of this method relies on accurate determination of shot positions by GPS, spatially dense seismic observations, and the use of unsaturated reflected waves arriving after the direct water wave that are observed on low-gain component records.  相似文献   

Gravity anomalies and deep structure of the Ninetyeast Ridge north of the equator,eastern Indian Ocean — a hot spot trace model     

Manoj Mukhopadhyay  M. B. R. Krishna 《Marine Geophysical Researches》1995,17(2):201-216

The Ninetyeast Ridge north of the equator in the eastern Indian Ocean is actively deforming as evidenced by seismicity and its eastward subduction below the Andaman Trench. Basement of the ridge is elevated nearly 2 km with respect to the Bengal Fan; seismic surveys demonstrate continuity of the ridge beneath sediment for 700 km north of 10° N where the ridge plunges below the Fan sediment. The ridge is characterised by a free-air gravity high of 50 mgal amplitude and 350 km wavelength, and along-strike continuity of 1500 km in a north-south direction, closely fringing (locally, even abutting) the Andaman arc-trench bipolar gravity field. Regression analysis between gravity and bathymetry indicates that the ridge gravity field cannot be explained solely by its elevation. The ridge gravity field becomes gradually subdued northwards where overlying Bengal Fan sediments have a smaller density contrast with the ridge material. Our gravity interpretation, partly constrained by seismic data, infers that the ridge overlies significant crustal mass anomalies consistent with the hot spot model for the ridge. The anomalous mass is less dense by about 0.27 g cm^–3 than the surrounding oceanic upper mantle, and acts as a cushion for isostatic compensation of the ridge at the base of the crust. This cushion is up to 8 km thick and 400–600 km wide. Additional complexities are created by partial subduction of the ridge below the Andaman Trench that locally modifies the arc-trench gravity field.  相似文献   

Sea State and Rain: A Second Take on Dual-Frequency Altimetry     

Graham D. Quartly 《Marine Geodesy》2004,27(1):133-152

TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at K_u- and C-band. Thus, each gives two measurements of the normalized backscatter, σ⁰, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the K_u- and C-band σ⁰ values give an indication of rain. This study investigates differences between the two instruments using data from Jason's verification phase. Jason's K_u-band estimates of wave height are ∼1.8% less than TOPEX's, whereas its σ⁰ values are higher. When these effects have been removed the root mean square (rms) mismatch between TOPEX and Jason's K_u-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in σ⁰ with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the σ⁰ measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of-0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high σ⁰ regime, anomalous data can be caused by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data.  相似文献   

The physical structure of a cold filament in a Chilean upwelling zone (Península de Mejillones, Chile, 23°S)     

Marcus Sobarzo  Dante Figueroa 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12)

Cold filaments associated with Eastern Boundary Currents are typically narrower than 100 km but can be several hundred kilometers long, extending from the coast to the open ocean in upwelling areas. One such structure, observed off Península de Mejillones (23°S, Chile), was studied with both satellite images and two 5-days hydrographic cruises carried out during January 1997. The study used a coastal grid of 31 stations in an area of 165 ×155 km², approximately. The spatial distribution of the filament and its change between cruises are described from the horizontal distributions of dynamic height, temperature, salinity and dissolved oxygen. The filament was a shallow feature (thickness <100 m) and extended at least 165 km toward the open ocean. A meandering northward current flowed at the borders of the filament, separating oceanic and coastal waters of different physical properties. Comparisons of cross sections of the filament near the coast and in the oceanic zone show the ascent of the shallow salinity minimum (SSM), and its extension toward the ocean, bound to the filament. It is concluded that Subantarctic Water ((SAAW) distinguish by low salinity, high dissolved oxygen) and Equatorial Subsurface Water ((ESSW) high salinity, low dissolved oxygen, high nutrient content) form this filament, and that their relative proportions depend on the strength of the coastal upwelling. Thus, the knowledge of the dynamics of these structures is fundamental to better understanding of the spatial distribution of important biological variables, such as nutrients and chlorophyll, in the coastal ecosystem.  相似文献   

Stochastic modeling based on deterministic formulation: An example   总被引：1，自引：0，他引：1  

G. R. Dargahi-Noubary 《Mathematical Geology》1992,24(2):161-169

In the context of seismology, an example of stochastic modeling on the basis of an established deterministic formulation is presented. The advantages of this approach to modeling over those based solely on statistical fit are discussed. It is demonstrated that the result of applying this procedure is a model whose main parameter has a physical interpretation, and therefore a validation based on criteria other than statistical goodness of fit is also possible. Statistical inference together with some demonstrating examples are also included.  相似文献   

1979—2100年青藏高原夏季大气0 ℃层高度变化分析     

张怡  段克勤  石培宏 《冰川冻土》2022,44(1):34-45

大气0 ℃层高度是决定青藏高原冰冻圈消融状态的重要指标。基于ERA5再分析资料,分析了1979—2019年青藏高原夏季大气0 ℃层高度时空变化,发现青藏高原夏季大气0 ℃层高度介于4 423~5 972 m之间,以高原中南部（30°~32° N,83.5°~88.5° E）为高值中心,呈纬向分带状向四周逐渐降低。过去41 a青藏高原夏季大气0 ℃层高度总体呈持续上升趋势,高原北部上升趋势大于南部,祁连山地区上升趋势最为明显,为60 m?（10a）^-1,而在高原西南部略呈下降趋势。平均而言,青藏高原夏季地面温度每升高1 ℃,大气0 ℃层高度升高122 m。利用CMIP6模式数据,预估在SSP1-2.6、SSP2-4.5、SSP3-7.0和SSP5-8.5四种社会共享路径情景下,2020—2100年期间青藏高原夏季大气0 ℃层高度都呈现升高趋势,但不同情景下升高趋势在空间上差别较大。相对于1979—2014年参考时段,在四种情景下,到2081—2100年青藏高原夏季平均大气0 ℃层高度将分别升高265 m、394 m、576 m 和729 m;相对应的是到2081—2100年,在高原上处于夏季大气0 ℃层高度以下的冰川面积分别为第二次冰川编目数据的79%、86%、94%和98%。仅从夏季大气0 ℃层高度变化角度看,在SSP5-8.5情景下,到本世纪末期,预估除帕米尔高原和昆仑山西北部地区外,青藏高原其他地区的冰川在夏季将不存在积累区。  相似文献