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1.
As described by [Csanady, G.T., Hamilton, P., 1988. Circulation of slope water. Continental Shelf Research 8, 565–624], the flow regime over the slope of the southern Middle Atlantic Bight (MAB) includes a current reversal in which southwestward flow over the upper and middle slope becomes entrained in the northeastward current adjacent to the Gulf Stream. In this paper we use satellite-derived data to quantify how lateral motions of the Gulf Stream impact this current system. In our analysis, the Gulf Stream’s thermal front is delineated using a two-year time series of sea surface temperature derived from NOAA/AVHRR satellite data. Lateral motions of the Gulf Stream are represented in terms of temporal variations of the area, east of 73°W, between the Gulf Stream thermal front and the shelf edge. Variations of slope water flow within this area are represented by anomalies of geostrophic velocity as derived from the time series of the sea level anomaly determined from TOPEX/POSEIDON satellite altimeter data. A strong statistical relationship is found between Gulf Stream displacements and parabathic flow over the continental slope. It is such that the southwestward flow over the slope is accelerated when the Gulf Stream is relatively far from the shelf edge, and is decelerated (and perhaps even reversed) when the Gulf Stream is close to the shelf edge. This relationship between Gulf Stream displacements and parabathic flow is also observed in numerical simulations produced by the Miami Isopycnic Coordinate Model. In qualitative terms, it is consistent with the notion that when the Gulf Stream is closer to the 200-m isobath, it is capable of entraining a larger fraction of shelf water masses. Alternatively, when the Gulf Stream is far from the shelf-break, more water is advected into the MAB slope region from the northeast. Analysis of the diabathic flow indicates that much of the cross-slope transport by which the southwestward flow entering the study region is transferred to the northeastward flow exiting the region occurs in a narrow band roughly centered at 36.75°N, order 150 km north of Cape Hatteras. This transport, and thus the cyclonic circulation of the southern MAB, strengthens when the Gulf Stream is relatively close to the shelf edge, and weakens when the Gulf Stream is far from the shelf edge. 相似文献
2.
The eddy formation determined as an anticyclonic spin-off eddy of the Gulf Stream is analysed from the CTD data of surveys made in the Gulf Stream region. The differences in its structure and conditions of formation from cyclonic eddies of this type observed previously are examined. Barotropic instability of the Gulf Stream's main jet is considered as a possible reason for such unstable disturbances existing at the south boundary of the Gulf Stream.Translated by M. M. Trufanov. 相似文献
3.
Herbert L. Windom Suchada Silpipat Aurapin Chanpongsang Ralph G. Smith Manuwadi Hungspreugs 《Estuarine, Coastal and Shelf Science》1984,19(2):133-142
Sediment cores and grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs.Accumulation rates of sediments in the Upper Gulf measured using the 210Pb method, appear to vary from ca. 4 to 11 mm yr?1. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately transported to the Lower Gulf. Metal concentrations in Upper Gulf sediments appear to be dominantly controlled by natural inputs. 相似文献
4.
The homogeneous residual circulation in Hauraki Gulf arising from the tides, steady winds, and oceanic inflows is considered by use of a depth‐averaged 2‐dimensional numerical model. Vertical current structure of the wind‐driven circulation is derived by using the computed wind‐induced sea surface slopes, the wind stress, and a prescribed vertical eddy viscosity. Tidal residual circulation is weak, less than 0.01 ms‐1 over most of the Gulf. The response of the Gulf to wind‐forcing indicates a preference for north‐west/south‐east directed winds, the flow through the Gulf being more than 3 times as strong as for winds from other directions. Surface currents are mainly in the wind direction, but subsurface currents reveal closed circulation cells in near‐coastal areas. Simple oceanic inflows give rise to water movements which penetrate to the inner part of the Gulf. 相似文献
5.
Abstract. The soft substratum macrobenthic assemblages of the midlittoral zone, along the atidal shores of the upper Thermaikos (polluted) and Strymonikos (unpolluted) Gulfs in the North Aegean Sea, arc qualitatively and quantitatively described. The composition of each of the seven assemblages found (four in Thermaikos and three in Strymonikos Gulf) is statistically tested and discussed in relation to abiotic factors. One of the four Thermaikos Gulf assemblages is located on a silt to fine sand substrate in brackish waters and is characterized by the dominance of the polychactc Hedisie diversicolor and the amphipod Corophium orientate. The other three assemblages arc located on coarse substrates and characterized by the very high dominance of the bivalve Donacillu corneu and the polychactc Ophelia bicornis (both of which are exclusive inhabitants of the midlittoral zone); the First is additionally characterized by the very high dominance of the polychactc Nerine cirratulus , both the second and the third by the dominance of turbellarians due to the pollution of the Gulf (stations located near sewage discharge, high organic carbon, low oxygen). In Strymonikos Gulf, one of the three assemblages is dominated by H. diversicolor and C. orientate; it is similar to the corresponding assemblage found in Thermaikos Gulf, although located on a relatively coarSér sediment. The second is dominated by D. cornea and O. bicornis and is also similar to that of Thermaikos Gulf. The third assemblage does not have a corresponding one in Thermaikos Gulf, is located on a substrate consisting of granules to pebbles, arid is characterized by the high dominance of the amphipods Allorchestes aquilinus and Echinogammarus olivii and the isopod Sphaeroma Sérratum. The corresponding assemblages of the two gulfs are compared. The results of the data analysis are discussed and compared with the literature. 相似文献
6.
The seismic stratigraphy and sedimentary architecture of the Amundsen Gulf Trough and adjacent slope, Canadian Beaufort Sea margin, are investigated using a grid of 2-D seismic reflection data. The inner-shelf of the Amundsen Gulf Trough is interpreted to be composed predominantly of exposed or near-surface bedrock, overlain by a spatially-discontinuous veneer of glacimarine to open-marine sediment. There is a seaward transition from exposed bedrock on the inner-shelf to a thick (up to 500 m) outer-shelf prograding wedge of acoustically semi-transparent sediment. Eight seismic sequences, divided into four megasequences, are described from the outer-shelf stratigraphy. Eight till sheets are identified from Megasequences A to C, providing evidence for at least eight Quaternary ice-stream advances through the Amundsen Gulf Trough to the shelf break. A trough-mouth fan with a minimum volume of about 10,000 km3 is present on the adjacent slope. The Amundsen Gulf ice stream probably represented the most northwesterly marine-terminating ice stream of the Laurentide Ice Sheet through much of the Quaternary, providing a major route for ice and sediment transfer to the Arctic Ocean. The youngest till sheet within the Amundsen Gulf Trough, Megasequence D, was probably deposited by a subsidiary ice stream, the Anderson ice stream, subsequent to retreat of the last, Late Wisconsinan Amundsen Gulf ice stream. This provides evidence of dynamic ice-sheet behaviour and the reorganisation of the northwest Laurentide Ice Sheet margin during the last deglaciation. A number of buried glacigenic landforms, including palaeo-shelf break gullies and a grounding-zone wedge with a volume of 90 km3, are described from the Amundsen Gulf Trough stratigraphy. Lateral grounding-zone wedges are identified at the northern and southern lateral margins of the Amundsen Gulf and M'Clure Strait troughs, respectively, and are interpreted to have been formed roughly contemporaneously by ice streams in Amundsen Gulf and M'Clure Strait. 相似文献
7.
Oil spill in the Gulf of Mexico and spiral vortex 总被引：2，自引：2，他引：0
<正>Drilling rig Deepwater Horizon in the Gulf of Mexico,leased by BP PLC from Transocean Ltd.,exploded and caught on fire on April 20,2010.The drilling location is at some 50 miles(80 kilometers)off the coast of Louisiana 相似文献
8.
Gulf of Mexico sediment sources and sediment transport trends from magnetic susceptibility measurements of surface samples 总被引：1，自引：0，他引：1
The magnetic properties from 200 trigger core-top and Van Veen grab sediment samples recovered from throughout the Gulf of Mexico have been analyzed and used to characterize sediment source and flow pattern distributions. Magnetic parameters included are anhysteretic remanent magnetism (ARM) and magnetic susceptibility (MS) measurements. Results from these measurements are compared to previously determined calcium carbonate percentages, and clay and hematite influx trajectories into the Gulf of Mexico for the same samples reported by Balsam and Beeson [Balsam, W.L. and Beeson, J.P., 2003. Sea-floor sediment distribution in the Gulf of Mexico, Deep-Sea Res. I, 50, 1421–1444.]. The ARM results give an estimate of magnetic grain size distributions, and by analogy, grain size distributions in general, whereas MS patterns show high detrital sediment accumulation zones within the Gulf. The dominant influx of modern high susceptibility sediment into the Gulf of Mexico appears to originate from the Red River, flow into Atchafalaya River Basin and out into the Gulf from Atchafalaya Bay, with significant additional contributions from the Mississippi River through the Southwest Pass of the Mississippi River Delta. This material then moves across the continental shelf and down through the Mississippi Canyon into the deep Gulf where it is redistributed at depths > 3600 m. The eastern shelf margins in the Gulf, offshore from Alabama and Florida, are accumulating calcite- or quartz-rich medium to fine-grained sediment that has a very low or diamagnetic MS signature. From the Louisiana to Texas Gulf coast margins, MS is moderate to high, suggesting a river influx of magnetic constituents from the volcanic fields in New Mexico, and from igneous and metamorphic sources in the Mississippi Basin. Offshore from western Mexico, the MS is high to moderate, but the Yucatan Shelf margin is characterized by low to diamagnetic MS values due to sediment dominated by calcite sands and oozes, a trend that continues to the east onto the West Florida Shelf. Additional measurements of samples collected in association with sites characterized by hydrocarbon seepage exhibit anomalously low MS values. The samples from the lower shelf and slope areas are typified by iron reduction by bacterial organisms in these samples. These results produce anomalous localized lows in the MS trends observed. 相似文献
9.
Research of chromium speciation in the Bohai Gulf showed that content of particulate chromium in estuarine area rea ched more than 90%, so it is an existing dominant speciation in the Bohai Gulf. Ratio between trivalent chromium to total dissolved chromium is over 80%, whereas contents of hexavalent chromium is very low. The mean content of Cr (Ⅲ) is 5.6 times higher than that of Cr (Ⅵ). Thus trivalent chromium is the prinicipal speciation of valency state of chromium in the Bohai Gulf.Under the physical and chemical condition at the eatuary transferring mechanism of chromium in seawater of Bohai Gulf is done by absorption, complexion and subsequent settlement in the sediments of trivalent chromium by suspended matter. Therefore suspended matter plays a part on the purification of sewater for this gulf. 相似文献
10.
During two “Valdivia” cruises, 1971 and 1972, bathymetric and geologic studies have been made at the junction between the Gulf of Aden and the Afar rift systems, namely in the Gulf of Tadjura and the nearly closed basin of the Ghubbet el Kharab (western end of the Gulf of Aden). A predominantly east-northeast striking fracture zone determines the morphologic structure of the central part of the gulf. The western end of the Gulf of Tadjura, including the Ghubbet el Kharab, is characterized by northwest striking normal faults.Up to 40 m thick subrecent sediments of the Ghubbet, mainly composed of diatoms, clay minerals, and volcanic glass, are already affected by a system of normal faults. 相似文献
11.
《Oceanologica Acta》1998,21(1):59-68
Sound-speed computations from CTD casts in the Arabian Gulf during 1992, reveal spatial and temporal variations in acoustic properties. Hydrographic conditions affecting sound speed propagation were seasonally investigated. A monotonic decrease in sound speed profiles with depth was commonly observed at almost all the stations in the Gulf. However, an exception occurred at Hormuz strait during winter. The water exchange pattern between the Gulf of Oman and the Arabian Gulf seems to influence the sound-speed structure, especially in the southern part of the latter. Winter profiles along the Gulf axis showed almost vertically homogenous sound speed. Maximum speeds are observed in summer, with a strong gradient associated with the development of the summer thermocline layer. Horizontal distributions in both winter and summer show a decreasing trend in sound speed from the Strait of Hormuz to the head of the Gulf. The resultant profiles provide a more comprehensive and reliable data set than any that have been reported in the literature. Shallowness and multiple refraction and reflection in the Arabian Gulf may cause sound speed energy to be trapped. No sound channel was detected inside the Gulf. A correlation analysis shows that sound speed is closely correlated with temperature throughout the Gulf, except in winter in the southern half where salinity effects, as a result of inversion and water exchange at the entrance, are found to be dominant. 相似文献
12.
Lyne Morissette Martin Castonguay Claude Savenkoff Douglas P. Swain Denis Chabot Hugo Bourdages Mike O. Hammill J. Mark Hanson 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):2117
In order to have a global view of ecosystem changes associated with the collapse of groundfish species in the Gulf of St. Lawrence during the early 1990s, Ecopath mass-balance models were constructed incorporating uncertainty in the input data. These models covered two ecosystems (northern and southern Gulf of St. Lawrence; NAFO divisions 4RS and 4T), and two time periods (before the collapse, in the mid-1980s, and after it, in the mid-1990s). Our analyses revealed that the ecosystem structure shifted dramatically from one previously dominated by piscivorous groundfish and small-bodied forage species during the mid-1980s to one now dominated only by small-bodied pelagic species during the mid-1990s in both southern and northern Gulf. The species structure in the northern Gulf versus southern Gulf was different, which may explain why these two ecosystems did not recover the same way from the collapse in the early 1990s. Productivity declined in the northern Gulf after the collapse but increased in the southern Gulf. The collapse of groundfish stocks resulted in declines in the mean trophic level of the landings in both the northern and the southern Gulf. Even though fishing mortality was then intentionally reduced, this part of the total mortality was taken up by predation. The temporal changes in the internal structure of both ecosystems are reflected in their overall emergent properties. 相似文献
13.
北部湾沉积物中重金属元素的地球化学特征及物源初探 总被引：5，自引：1，他引：5
本文根据北部湾沉积物岩心样调查结果计算了铜、铅、锌、镉、汞、砷等重金属元素的背景值,并分析了其与南海陆架区和南海全海域沉积物背景值、广西土壤背景值之间的差异.对北部湾表层沉积物中重金属含量及近10 a的变化趋势以及岩心样中重金属元素含量近百年以来的变化趋势综合分析结果表明:北部湾近岸海域沉积物中铜、砷、汞、镉重金属元素含量总体呈增长趋势,北部湾中部海域沉积物中重金属元素含量的年际变化有升有降,至湾口处沉积物中重金属元素的含量基本不变.综合评价结果表明,北部湾近岸沉积物中砷、汞、镉等重金属元素的地球化学特征明显受到广西人类活动的影响.北部湾沉积物中的重金属元素主要来源于人类活动影响下的广西沿岸陆源输入,经由琼州海峡的外部海域物质输入也有贡献. 相似文献
14.
The Gulf Stream system has been numerically simulated with relatively high resolution and realistic forcing. The surface fluxes
of the simulation were obtained from archives of calculations from the Eta-29 km model which is an National Center for Environment
Prediction (NCEP) operational atmospheric prediction model; synoptic fields are available every 3 hour. A comparison between
experiments with and without surface fluxes shows that the effect of the surface wind stress and heat fluxes on the Gulf Stream
path and separation is closely related to the intensification of deep circulations in the northern region. Additionally, the
separation of the Gulf Stream and the downslope movement of the Deep Western Boundary Current (DWBC) are reproduced in the
model results. The model DWBC crosses under the Gulf Stream southeast of Cape Hatteras and then feeds the deep cyclonic recirculation
east of the Bahamas. The model successfully reproduces the cross-sectional vertical structures of the Gulf Stream, such as
the asymmetry of the velocity profile, and this structure is sustained along the downstream axis. The distribution of Root
Mean Square (RMS) elevation anomaly of the model shows that the eddy activity of the Gulf Stream is realistically reproduced
by the model physics. The entrainment of the upper layer slope current into the Gulf Stream occurs near cross-over; the converging
cross-stream flow is nearly barotropic.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
16.
L. J. Paul 《新西兰海洋与淡水研究杂志》2013,47(3):535-558
The changing pattern of water temperature in the Hauraki Gulf at approximately two‐monthly intervals during one and one‐half seasonal cycles in 1965–66 was determined from sea surface temperatures and bathythermograph profiles. Surface and bottom temperatures ranged from 22.0°c and 20.5°c respectively in March to 12.5°c and 13.0°c in July‐September. Seasonal temperature ranges and short‐term variations were greatest in the shallow south‐west Gulf. In winter the Gulf water was coolest close to shore. It was typically isothermal in depth but a temperature inversion of approximately l°c frequently formed, probably because of the combination of strong winds and an increased outflow of cool, low salinity water from harbours and bays. A similar inversion in Colville Channel may have been caused by more complex tidal and/or ocean current conditions. In spring and summer the Gulf became thermally stratified, with warmest temperatures in the shallow areas. Thermoclines were generally irregular in position and size, and probably represented solar heating and minor current boundaries rather than a distinct separation of major water masses. In late summer and autumn bottom temperatures increased and almost equalled the maximum surface temperature. During autumn surface water temperatures close to land decreased rapidly to return the Gulf to its winter isothermal condition. Local factors (wind, rainfall, tides, depth of water, and proximity to land) probably influence sea temperatures in the Gulf. Seawards of a line from Cape Rodney to Cape Colville oceanic conditions prevail; water temperatures are more constant and increase to seaward in both winter and summer. Oceanic and Gulf waters meet and mix in the Rodney‐Colville area, and Gulf water is transported east through Colville Channel. The extent of oceanic water penetration into the Gulf at depth is unknown. 相似文献
17.
P.A. Yeats 《Marine Chemistry》1993,43(1-4)
The freshwater discharge from the Gulf of St. Lawrence and Hudson Bay accounts for more than 80% of the total freshwater discharge from eastern Canada and approximately 70% of the total discharge from the eastern seaboard of North America, from Baffin Island to Florida. If the Gulf of Mexico is included, the Gulf of St. Lawrence/Hudson Bay discharge is still more than half of the total.Both the Gulf of St. Lawrence and Hudson Bay have some distinctly estuarine characteristics and discharges of metals can be estimated using estuarine models. For Al, Mn, Fe, Co, Ni, Cu and Zn, the distributions can be described by simple, highly significant relationships with salinity. These regressions can be used in conjunction with knowledge of water discharges to estimate net metal inputs to the North Atlantic from these two systems.Most of the discharge from the Gulf of St. Lawrence flows along the Scotian Shelf to the Gulf of Maine. Metal-salinity relationships can also be used to estimate metal transports through this region for some metals. The applicability of this estuarine model, however, tends to break down as the oceanography becomes more complex and metal distributions are determined more by oceanic rather than estuarine processes. 相似文献
18.
A multidisciplinary study in the Gulf of Cadiz is revisited, using additional diagnostic modelling tools. The dissolved trace metal (Cu, Ni, Zn, Co) distributions in the Gulf of Cadiz are analysed using modelled tracer evolutions, field observations and the concept of tracer ages. This study shows that a significant part of the observed metal distributions can be explained by the metal inputs of three river systems (Guadiana, Rio Tinto and Odiel, Guadalquivir) discharging into the Gulf of Cadiz, while the remainder of the signal is most likely associated with the benthic metal remobilisation along the shelf of this coastal region. 相似文献
19.
Temporal variability of Centropages typicus in the Mediterranean Sea over seasonal-to-decadal scales
《Progress in Oceanography》2007,72(2-3):214-232
Centropages typicus is one of the most common, abundant and best studied calanoid copepods in neritic waters of the Mediterranean Sea, which means it can provide useful information about the long-term dynamics of the Mediterranean epipelagic ecosystem. This paper presents the first comparative overview of the seasonal and long-term variability of C. typicus in different Mediterranean regions. This review is based on quantitative information from the published literature and novel data from five ongoing zooplankton time-series carried out in the Mallorca Island (Balearic Sea), the Bay of Villefranche (Ligurian Sea), the Gulf of Naples (Tyrrhenian Sea), the Gulf of Trieste (North Adriatic Sea), and the Saronikos Gulf (Aegean Sea). In most Mediterranean regions, C. typicus has a perennial occurrence, with peaks of abundance that reflect the succession of different generations. Throughout the Mediterranean, the annual cycle of C. typicus is characterized by minima in winter and major peaks in April–June, which is earlier than those observed in European Atlantic waters, where the peaks are more frequently recorded in summer and fall. In the regions investigated, the annual cycle shows remarkable similarities in terms of timing, but notable differences in the peak height; populations are far more abundant in coastal north-western regions and less abundant in the eastern basin. In the long-term, changes in C. typicus phenology observed in the Bay of Villefranche and in the Gulf of Naples are related to the North Atlantic Oscillation (NAO) index. In these two regions, the species responds to climate forcing similarly in terms of average seasonal patterns (bi-modal patterns in years of positive NAO, unimodal patterns in years of negative NAO) but oppositely in terms of quantity, indicating different influence of the NAO on the two regions. At decadal scales, C. typicus populations show high interannual variability with marked geographical differences. In some areas, the patterns are clearly characterized by alternate phases of higher and lower annual abundances, at higher frequency (mainly 1–2 years) in the Gulf of Naples, and lower frequency in the Saronikos Gulf (mainly 4–5 years) and in the Gulf of Trieste (mainly 5–6 years). Synchronous phases of increasing or decreasing abundance are discernable only for a few sites and short periods, for example from 1998 to 2000 in the Gulf of Naples, Gulf of Trieste and Saronikos Gulf. The regional differences observed in the long-term patterns of C. typicus populations suggest that the temporal dynamics of this species are significantly more affected by local conditions than by any possible common driving force acting at basin scale through teleconnections. 相似文献
20.
Reza Sadeghi Hamid Reza Esmaeili Fatah Zarei Bettina Reichenbacher 《Marine Ecology》2021,42(1):e12629
The Persian Gulf and Oman Sea are characterized by an interesting paleoclimatic history and different ecological settings, and offer a unique study area to investigate the genetic structure of marine organisms including fishes. The Ornate goby Istigobius ornatus is widely distributed throughout the tropical Indo‐West Pacific including the Persian Gulf and Oman Sea. Here, we present the population structure, genetic diversity, and demographic history of four populations of I. ornatus from the latter two regions using the D‐loop marker of mitochondrial DNA. The results reveal a shallow genealogy, a star‐like haplotype network, significance of neutrality tests, and unimodal mismatch distribution. This is concordant with a recent demographic expansion of I. ornatus in the Persian Gulf and Oman Sea at about 63,000–14,000 years ago, which appears to be related to Late Pleistocene sea level fall and rise. The results of the pairwise Fst estimates imply high gene flow along the coast of the Persian Gulf, which is probably due to larval dispersion, whereas the Oman Sea population clearly differs from all Persian Gulf populations. The AMOVA result indicates that 7.74% of the variation is related to differences among ecoregions, while inter‐ and intra‐population differences explained ?3.20% and 95.47% of the variation, respectively. The haplotype network depicts two groups of haplotypes, most of them were specific to the Persian Gulf. No further evidence for geographic lineage substructuring was evident. The Mantel test result indicates that isolation by distance is not the main mechanism that promoted the genetic differentiation among the studied populations of I. ornatus. We suggest that cumulative effects of ecological and geographic barriers such as salinity, oceanographic conditions, and the presence of the Strait of Hormuz have shaped the genetic structure of I. ornatus in the Persian Gulf and Oman Sea. 相似文献