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1.
This study set out to test the hypothesis that hurricanes and tropical storms limit the recruitment and subsequent survival of massive non-branching corals on the barrier reef off the coast of Belize in the Gulf of Honduras. Overall, the surface areas of 523 individual coral specimens were measured, and recruitment dates were then modelled. There was no significant difference in coral cover or coral biodiversity between any of the sites studied (p > 0.1). There were significant differences in non-branching coral recruitment in years when hurricanes impacted the area (p < 0.05) compared with years when no hurricanes impacted the area. There were significantly more non-branching massive corals recruited in non-hurricane years (mean 7.7) than in hurricane years (mean 3.8; p = 0.011). When years with tropical storms are added to the years with hurricanes, there was significantly lower coral recruitment (mean 4.7) relative to non-storm or hurricane years (mean 7.4; p = 0.019). These results show that hurricanes and severe storms limited the recruitment and survival of massive non-branching corals of the Mesoamerican barrier reef and on patch reefs near the Belize coast in the Caribbean, and suggests that marine park managers may need to assist coral recruitment in years where there are hurricanes or severe storms.  相似文献   

2.
利用50a(1950—2007年)的SODA(Simple Ocean Data Assimilation)数据分析了南海上层温度锋分布特征以及季节变化规律。结果表明:受季风、太阳辐照以及诸多因素影响,温度锋季节变化明显,锋面结构复杂。冬季,温度锋基本沿陆架分布,存在于南海北部海区,从台湾海峡一直延伸到北部湾,发育比较显著;春季,主要出现在南海北部海区、北部湾、越南东部海岸,分布比较广泛;夏季温度锋出现概率增加,出现区域扩大,越南东部出现大面积温度锋;秋季南海中西部海域存在大面积的温度锋。  相似文献   

3.
Ron Boyd  Shea Penland 《Marine Geology》1984,60(1-4):391-412
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4.
The northern Gulf of Mexico and its diverse natural resources are threatened by population and development pressure, and by the impacts of rising sea level and severe storms. In the wake of the devastating 2005 hurricane season, and in response to the complex management issues facing the region, the U.S. Geological Survey organized the multidisciplinary “Northern Gulf of Mexico Ecosystem Change and Hazards Susceptibility” project. This special issue of Geo-Marine Letters hosts a few of the early results in the form of 11 papers covering three themes: (1) the control exerted by the underlying geologic framework on geomorphology and nearshore processes and features; (2) impact of human activities on nearshore water quality; and (3) hurricanes and associated effects.  相似文献   

5.
Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments.  相似文献   

6.
The climatological characteristics of landfalling Gulf of Mexico hurricanes are presented, focusing on the basic parameters needed for accurately determining the structure and intensity of hurricanes for ocean response models. These include the maximum sustained wind, radius of maximum winds, the Holland-B parameter, the peripheral or far-field pressure, the surface roughness and coefficient of drag, and the central pressure for historical hurricanes in the Gulf.Despite evidence of a slight increase in the annual number of named storms over the past 50 years, presently there is no statistically significant trend in tropical storms, hurricanes, or major hurricanes in the Gulf of Mexico. In addition, the long-term variability of tropical cyclones in the Gulf reflects the observed variability in the Atlantic basin as a whole. Analyses of hurricane winds from multiple sources suggest the presence of a bias toward overestimating the strength of winds in the HURDAT dataset from 7% to 15%. Results presented comparing HURDAT with other sources also show an overestimation of intensity at landfall, with an estimated bias of ~10%.Finally, a review of recent studies has shown that hurricane frequencies and intensities appear to vary on a much more localized scale than previously believed. This exacerbates the sampling problem for accurate characterization of hurricane parameters for design and operational applications.  相似文献   

7.
Storms are one of the most important controls on the cycle of erosion and accretion on beaches. Current meters placed in shoreface locations of Saco Bay and Wells Embayment, ME, recorded bottom currents during the winter months of 2000 and 2001, while teams of volunteers profiled the topography of nearby beaches. Coupling offshore meteorological and beach profile data made it possible to determine the response of nine beaches in southern Maine to various oceanographic and meteorological conditions. The beaches selected for profiling ranged from pristine to completely developed and permitted further examination of the role of seawalls on the response of beaches to storms.

Current meters documented three unique types of storms: frontal passages, southwest storms, and northeast storms. In general, the current meter results indicate that frontal passages and southwest storms were responsible for bringing sediment towards the shore, while northeast storms resulted in a net movement of sediment away from the beach. During the 1999–2000 winter, there were a greater percentage of frontal passages and southwest storms, while during the 2000–2001 winter, there were more northeast storms. The sediment that was transported landward during the 1999–2000 winter was reworked into the berm along moderately and highly developed beaches during the next summer.

A northeast storm on March 5–6, 2001, resulted in currents in excess of 1 m s−1 and wave heights that reached six meters. The storm persisted over 10 high tides and caused coastal flooding and property damage. Topographic profiles made before and after the storm demonstrate that developed beaches experienced a loss of sediment volume during the storm, while sediment was redistributed along the profile on moderately developed and undeveloped beaches. Two months after the storm, the profiles along the developed beaches had not reached their pre-storm elevation. In comparison, the moderately developed and undeveloped beaches reached and exceeded their pre-storm elevation and began to show berm buildup characteristic of the summer months.  相似文献   


8.
Surface and water column profiles of suspended matter collected during April-May 2002, and satellite images were used to study factors influencing suspended sediment concentrations (SSCs) and dispersal in the northern Andaman Sea and Gulf of Martaban, one of the largest highly turbid areas of the world's oceans. Perennial high SSC in the Gulf of Martaban is due to a combination of factors including resuspension of sediments by strong tidal currents, shallow bathymetry and seasonal sediment influx from rivers. From satellite images, it was observed that in the central portion of the Gulf of Martaban, the turbidity front oscillates about 150 km in phase with spring-neap tidal cycles and the area covered by the turbid zone (SSC>15 mg l−1) increases from less than 15 000 km2 during neap tide to more than 45 000 km2 during spring tide. The sediment discharged by the Ayeyarwady River is transported mainly eastward, along the coast, into the Gulf of Martaban. Occasionally, during the winter monsoon period, sediment plumes are seen heading westward into the Bay of Bengal. Turbidity profiles show that bottom nepheloid layers are actively transporting some of the sediments into the deep Andaman Sea via the Martaban canyon.  相似文献   

9.
Over the past three to four decades, there has been a growing awareness of the important controls exerted by large-scale meteorological events on coastal systems. For example, definitive links are being established between short-term (timescales of 5–10 years) beach dynamics and storm frequency. This paper assesses temporal variability of coastal storms (both tropical and extratropical) and the wave climatology in the North Atlantic Basin (NAB), including the Gulf of Mexico. With both storm types, the empirical record shows decadal scale variability, but neither demonstrates highly significant trends that can be linked conclusively to natural or anthropogenic factors. Tropical storm frequencies have declined over the past two or three decades, which is perhaps related to recent intense and prolonged El Niños. Some forecasts predict higher frequencies of tropical storms like that experienced from the 1920s to the 1960s to occur in coming decades. Results from general circulation models (GCMs) suggest that overall frequencies of tropical storms could decrease slightly, but that there is potential for the generation of more intense hurricanes. These data have important implications for the short-term evolution of coastal systems.

There is strong suggestion that extratropical systems have declined overall over the past 50–100 years, but that there is an increase in frequency of very powerful storms, especially at higher latitudes. Both ENSO and the North Atlantic Oscillation (NAO) are shown to have associations with frequencies and tracking of these systems. These empirical results are in general agreement with GCM forecasts under global warming scenarios. Analyses of wave climatology in the NAB show that the last two to three decades have been rougher at high latitudes than several decades prior, but this more recent sea state is similar to conditions from about 100 years ago. The recent roughness at sea seems to be related to high NAO index values, which are also expected to increase with global warming. Thus, when coupled to an anticipated continued rise in global sea level, this trend will likely result in increasing loss of sediment from the beach-nearshore system resulting in widespread coastal erosion.  相似文献   


10.
The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.  相似文献   

11.
Beach-nearshore profiles combined with beach and surficial sediment samples were analyzed in conjunction with wave, current, littoral drift and sea-level data to determine the effect of bedrock on morphodynamic processes within the littoral zone of Alexandria on the Mediterranean coast of Egypt. This 14.5-km-long littoral cell is bounded by pronounced embayments and pocket beaches separated by headlands which prevent bypassing of beach sands, in effect making this cell a large, semi-closed basin. The compartmented nature of this cell acts together with the rough irregularity of the rocky seafloor to trap a thin veneer of sediment (<3 m thick), showing proportional mixing between two sedimentary provinces. A modern fine-grained sediment facies consisting of mixed carbonate/siliciclastic sand flanks most of the nearshore zone down to a depth of 8–10 m. Beyond this depth, considered to be the depth of closure, a relict late Pleistocene to mid-Holocene coarse-grained facies composed of biogenic carbonate sand is found. Along a short section of the coastline (km 3–6), the coarser sediment also occupies the nearshore zone. Over most of the study area the two sediment types are mixed in various proportions, largest mixing coinciding with poorest sorting. Profile analyses revealed seasonal changes in sediment volume along the coast which closely follow the cyclicity of seasonal changes in wave climate. The present shoreline orientation, headlands and rough, irregular rocky seabed are reflected in the erosion/accretion pattern, sediment characteristics, and the reversibility of longshore currents and littoral drift. Although there is a marked deficiency in the sediment balance, the sand budget for this cell, including artificial material (2.339*106 m3) has increased slightly by 0.041*106 m3 year–1 as a result of engineering works carried out to widen the coastal road (Corniche). In addition to the physical properties of the bedrock (degree of induration), the accelerating sea-level rise during the Holocene and human influences, the modern morphology of the coast, the erosional seabed features in the nearshore zone, and the texture of seabed sediments are all controlled by the original geometry of the coast which consisted of an elevated subaerial ridge.  相似文献   

12.
全球热带风暴时空分布特点   总被引：2，自引：0，他引：2  
对全球三大洋热带风暴的统计分析表明,全球热带风暴在时空分布上具有明显的统计特性.各海域热带风暴都具有季节集中性.在太平洋和印度洋,风暴发生频繁的时间在地理位置上有沿逆时针移动的分布.全球风暴总数在8月、9月份明显偏多,在4月、5月份明显偏少.北半球风暴扩展范围和分布密度大于南半球,并以东北太平洋和西北太平洋风暴分布密度为最大.各海域热带风暴发生频数在统计长度(33a)内都表现年际和10年际“振荡”,不同程度地存在2～3a,6～7a,11～12a及21～23a的重复性变化.较强的风暴,往往寿命也较长.在月份之间比较,风暴在多发月份,一般平均寿命较长,强度也较大;而在年度之间比较,风暴在多发年度,平均寿命却往往较短,强度也较小.风暴在大尺度环境中较好地沿反气旋路径向高纬度运动.  相似文献   

13.
The tectonically active islands of the Indo-Pacific Archipelago deliver much sediment to the ocean margins. In the Gulf of Papua on the south coast of Papua New Guinea (PNG), the chemical composition of surface sediment from grab samples indicates that Fly River muds are dispersed to the north and east, where they are joined by sediment plumes from the other large rivers along the south coast of PNG. This is the likely source of terrestrial sediment on the Papuan Plateau and the northern Coral Sea Abyssal Plain. The sediment is transported through submarine troughs and canyons offshore, far to the east of the riverine inputs. Immediately south and 30–50 km offshore from the Fly and Purari deltas is a platform of algal and reef carbonate materials, containing little or no terrestrial surface sediment.  相似文献   

14.
Stable isotope ratios (δ13C) of total organic carbon were measured in surface sediments from the continental margins of the northern and western Gulf of Mexico, the north coast of Alaska and the Niger Delta. Gulf of Mexico outer-shelf isotope ratios were in the same range as has been reported for Atlantic coastal shelf sediments, ?21.5 to ?20‰. Off large rivers including the Mississippi, Niger and Atchafalaya (Louisiana), δ13C values increased from terrigenous-influenced (around ?24‰) to typically marine (～?20‰) within a few tens of kilometers from shore. This change was accompanied by a decrease in the amount of woody terrigenous plant remains in the sediment. Alaskan continental margin samples from the cold Beaufort Sea had isotopically more negative carbon (?25.5 to ?22.6‰) than did warmer-water sediments. The data indicate that the bulk of organic carbon in Recent sediments from nearshore to outer continental shelves is marine derived.  相似文献   

15.
受限于海洋动力条件的复杂性,基于陆架泥质沉积重建的古气候或古环境一直存在争议。为此,本文在北黄海地区沿沉积物输运路径采集3根柱样,通过沉积物粒度及其端元组分和基于器测数据的东亚冬季风指数和黄海暖流强度,分析了不同泥区沉积物粒度端元组分对冬季风暴和黄海暖流变化的响应机理和强度,揭示了上述变化在不同区域产生的沉积效应。结果表明,近百年以来黄河远端泥北支的沉积物组分变化受到了自然因素和人类活动的共同影响。1980年以后,人类活动对黄河沉积物入海通量及其组成的影响开始增强,并掩盖了自然演化信息。而1980年以前,不同泥区的不同端元组分对冬季风暴和黄海暖流的响应机理和强度存在差异,具有显著的区域沉积效应：粗端元组分受冬季风暴强度变化主导,能够反映山东半岛北岸跨锋面物质输运强度的变化;细端元组分受到黄海暖流强度变化主导,反映沉积物从北黄海西部泥区到辽东半岛东岸泥区的输运过程。上述结论说明,虽然粒度是表征古气候和古环境变化的重要标志物,但应根据不同泥区沉积物来源和沉积动力环境的特点,谨慎选择敏感端元组分,正确地使用粒度指标。  相似文献   

16.
Washovers, dune scarps and flattened beach profiles with concentrations of coarse-grained sediment or heavy minerals are the diagnostic geological signatures of large storms on barriers today. It is clear that storms are a major force driving transgressive barriers onshore, but what is not as well understood is the role these powerful erosive events play in the evolution of prograding barriers. Application of ground-penetrating radar (GPR) and a combination of coring techniques have significantly improved our ability to image barrier architecture. Results of these studies reveal a more complex evolution than previously recognized. It is now possible to precisely locate and map storm deposits within prograded barrier lithosomes.

A comprehensive study of northern Castle Neck, Massachusetts was performed using 15 km of GPR surveys, a 120-m-long seismic line, 11 cores, and several radiocarbon dates. Storm-related layers are the most prominent horizons contained in the barrier stratigraphy. The geometry and sedimentology of these layers closely resembles those of a present-day post-storm beach. Twenty closely spaced, curvilinear heavy mineral layers imaged in the landward portion of the barrier suggest that the Castle Neck barrier was heavily influenced by storms during its initial phase of progradation beginning 4000 years BP. Approximately 1800 years BP, two intense storms impacted the coast depositing two extensive coarse-grained units. These layers mimic the flat-lying sand and gravel deposits that occur in front of a nearby eroding till outcrop following major storms. The great number of storm deposits in the early history of Castle Neck is related to either a period of greater storm activity and/or a slow rate of barrier progradation. The occurrence and preservation of these earlier storm layers are likely a product of the exposure of nearby drumlins resulting in greater availability of iron oxide and ferromagnesian sands. The supply of heavy-mineral sands has gradually diminished as the barrier prograded and the proximal drumlin source was buried by beach and dune sands.  相似文献   


17.
Results are presented from the deployment of three bottom-mounted instrumentation systems in water depths of 6–9 m on the sandy inner shelf of Louisiana, USA. The 61-day deployment included nine cold front passages that were associated with large increases in wind speed. Two of the most energetic cold front passages were characterized by distinct meteorological, hydrodynamic, bottom boundary layer, and sedimentary responses and may potentially be treated as end-member types on a continuum of regional cold front passages. Arctic surges (AC storms) have a very weak pre-frontal phase followed by a fairly powerful post-frontal phase, when northeasterly winds dominate. Migrating cyclones (MC storms) are dominated by a strong low-pressure cell and have fairly strong southerly winds prior to the frontal passage, followed by strong northwesterly winds.

On the basis of measurements taken during this study, AC storms are expected to have a lower average significant wave height than MC storms and are dominated by short-period southerly waves subsequent to the frontal passage. Currents are weak and northerly during the pre-frontal phase, but become very strong and southwesterly following the passage. Sediment transport rate during AS storms was not as high as during MC storms, and the mean and overall direction tended to be southwesterly to westerly, with low-frequency flows producing easterly transport, and wind-wave flows producing southeasterly transport.

MC storms had the most energetic waves of any storm type, with peaks in significant wave height occurring during both the pre- and post-frontal phases. The wave field during MC storms tended to be more complex than during AS storms, with an energetic, northerly swell band gradually giving way to a southerly sea band as the post-frontal phase progressed. Currents during MC storms were moderate and northerly during the pre-frontal phase, but became much stronger and southeasterly during the post-frontal phase. Shear velocity was high during both the pre- and post-frontal phases of the storm, although sediment transport was highest following the frontal passage. Mean and overall sediment transport was directed southeasterly during MC storms, with low-frequency and wind-wave flows producing northerly transport. In summary, the data sets presented here are unique and offer insight into the morphosedimentary dynamics of mid-latitude, micro-tidal coasts during extratropical storms.  相似文献   


18.
Using the hierarchical clustering method, we present comprehensive analyses of water masses and their seasonal variations based on substantial in situ observations in the eastern Beibu Gulf, a shallow sea with a depth mostly less than 100 m. Besides traditional physical parameters (salinity and temperature), chemical and biological parameters are also used for the water mass classification and analyses, which include dissolved oxygen, alkalinity, nitrite, reactive silicate, and chlorophyll a. Consequently, the eastern Beibu Gulf water is classified into five water masses in the study area, namely the diluted water, the mixed water, the surface water, the subsurface water, and the bottom water. The diluted water is located in the area along the Guangxi coast; the mixed water mainly occupies the northern study area; the surface water resides in the central and southern study area; the subsurface water exists just near the Gulf mouth; and the bottom water appears in the lower layer east of Bailongwei Island, which is different from the Beibu Gulf cold water mentioned in previous studies. The parameter properties and spatial distribution of most water masses in the eastern Beibu Gulf exhibit strong seasonal variability which is mainly modulated by circulations and solar radiation.  相似文献   

19.
A review on the South China Sea western boundary current   总被引：7，自引：2，他引：5  
The advances in understanding the South China Sea (SCS) western boundary current (SCSwbc) have been reviewed since the works of Dale (1956) and Wyrtki (1961) in the middle of the 20th century. The features of the pattern of SCSwbc and the oceanic phenomena associated with it are focused on. The current is driven mainly by monsoon over the SCS and partially by winds over the tropical Pacific governed by the island rule. The SCSwbc exhibits strong seasonal variation in its direction and patterns. In winter, the current is strong and flows southwestward along the South China shelf and slope from the east of Dongsha Islands to the northern central Vietnamese coast, then turns to the south along the central and southern Vietnamese coast, and finally partially exits the SCS through the Karimata Strait. In summer and early fall, the SCSwbc can be divided into three segments based on their characteristics. The southern segment is stable, flowing northward from the Karimata Strait up to about 11 N, where it separates from the coast forming an eastward offshore current. The separation of the current from Vietnamese coast induces some striking features, such as upwelling and cold sea-surface temperature. The middle segment off the central Vietnamese coast may have a bimodal behavior: northward coastal current and meandering current in early summer (June-July), and cyclonic gyre in later summer and early fall (August-September). The northern segment is featured by the summer SCS Warm Current on the South China shelf and a southwestward subsurface current along the continental slope.  相似文献   

20.
G. Gelfenbaum  Gregg R. Brooks   《Marine Geology》2003,200(1-4):273-289
A series of migrating shore-normal sandbars with wavelengths of 75–120 m and heights up to 2 m have been identified off the northern tip of Anna Maria Island, a barrier island on the west-central Florida coast. Similar features have been described elsewhere since the 1930s and termed ‘transverse bars’. The transverse bars identified off Anna Maria Island are found for about 3 km along the coast and extend 4 km offshore, well outside the normal surf-zone width. No cusps or any other associated beach expression is evident despite the fact that the bars come to within about 75 m of the beach. Sediments on the crests of the bars are a well-sorted fine quartz sand, whereas sediments in the troughs are a poorly sorted coarse carbonate shell hash. Historical aerial photographs and repeated high-resolution bathymetric surveys provide a means of quantifying the migration of the transverse bars. Analyses of orthorectified aerial photographs from the early 1940s through the mid 1990s clearly show movement or migration taking place in the bar field. In the 40-yr period from 1951 to 1991, the southern edge of the bar field moved 200–350 m to the south, with an average long-term migration rate of 8 m/yr. Repeated bathymetric surveys over an 8-month period give an average short-term migration rate of 21 m/yr to the south. Wave and current measurements suggest that southerly winds associated with the passage of cold fronts drive near-bed currents to the south that are strong enough to initiate sediment transport and cause the southerly migration of the transverse bars.  相似文献   

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