共查询到20条相似文献，搜索用时 46 毫秒
1.
Errol Wiles Andrew Green Mike Watkeys Wilfried Jokat Ralf Krocker 《Geo-Marine Letters》2014,34(6):525-540
Although global thermohaline circulation pathways are fairly well known, the same cannot be said for local circulation pathways. Within the southwest Indian Ocean specifically there is little consensus regarding the finer point of thermohaline circulation. We present recently collected multibeam bathymetry and PARASOUND data from the northern Natal Valley and Mozambique Ridge, southwest Indian Ocean. These data show the Ariel Graben, a prominent feature in this region, creates a deep saddle across the Mozambique Ridge at ca. 28°S connecting the northern Natal Valley with the Mozambique Basin. Results show a west to east change in bathymetric and echo character across the northern flank of the Ariel Graben. Whereby eroded plastered sediment drifts in the west give way to aggrading plastered sediment drift in the midgraben, terminating in a field of seafloor undulations in the east. In contrast, the southern flank of the Ariel Graben exhibits an overall rugged character with sediments ponding in bathymetric depressions in between rugged sub/outcrop. It is postulated that this change in sea-floor character is the manifestation of deep water flow through the Ariel Graben. Current flow stripping, due to increased curvature of the graben axis, results in preferential deposition of suspended load in an area of limited accommodation space consequently developing an over-steepened plastered drift. These deposited sediments overcome the necessary shear stresses, resulting in soft sediment deformation in the form of down-slope growth faulting (creep) and generation of undulating sea-floor morphology. Contrary to previous views, our works suggests that water flows from west to east across the Mozambique Ridge via the Ariel Graben. 相似文献
2.
Gamak Bay is one of the largest aquaculture areas in the South Sea of Korea and exhibits hypoxia conditions during the summer. The harmful effects of hypoxia on aquaculture fish stock have not been elucidated. This study describes the biochemical effects of low levels of dissolved oxygen (DO) on cultivated juvenile Sebastes schlegeli in Gamak Bay. The hypoxia-inducible factor 1α (HIF1α) gene was induced significantly in S. schlegeli collected from low oxygen level areas, which suggests that fluctuations in the DO induces the expression of HIF1α. The level of antioxidant enzyme exhibited significantly higher activities in fish obtained from station F2 in which low levels of DO were shown in 2010 and 2011. The results of this study demonstrate that cultivated S. schlegeli are affected by the low levels of DO in Gamak Bay and superoxide dismutase enzymes operate dependently with HIF1α. The plasma glucose level did not exhibit significant difference in the fish among the sampling stations. We noted that HIF1α and the superoxide dismutase enzymes are useful biomarkers that might enable the detection of otherwise unnoticed hypoxic stress. 相似文献
3.
Equilibrium conditions in anf-plane ocean evolve as follows after the sudden onset of winds parallel to a coast. At first the flow is two-dimensional-spatial variations are confined to a plane perpendicular to the coast-and the salient features in the forcing region are acceleration of a coastal jet in the surface layers in the wind direction, and offshore Ekman drift that causes coastal upwelling. Kelvin waves excited at the edge of the forced region establish equilibrium conditions by creating an alongshore pressure gradient that balances the wind so that the acceleration stops. The vertical structure corresponding to each vertical mode differs from that of the wind-driven coastal jet so that the arrival of the barotropic Kelvin wave starts to accelerate a coastal undercurrent in a direction opposite to that of the wind. Subsequent baroclinic Kelvin waves modify the vertical structure of the coastal current so that the undercurrent in the subsurface layer is accelerated. In an inviscid model there is a singularity in the surface layers at the coast ast→∞ because the Kelvin modes with small offshore and vertical scales travel slowly and take a very long time to make their contribution to the establishment of equilibrium conditions. A modest amount of friction eliminates this problem. Nonlinearities are important in the heat equation and affect sea surface temperatures significantly but their effect on the momentum balance is secondary. 相似文献
4.
S. A. Beisel V. K. Gusiakov L. B. Chubarov Yu. I. Shokin 《Izvestiya Atmospheric and Oceanic Physics》2014,50(5):508-519
Results of a numerical simulation of the action of distant tsunamis on the coast of the Russian Far East are presented. It is shown that waves generated by focuses of the strongest M9 earthquakes in the region of South Chilean coast, as well as in the region of Papua New Guinea and Solomon Islands, are most dangerous for this coast. Other tsunamigenic zones of the Pacific Ocean, by virtue of their geographical position, orientation of focuses, and absence of pronounced channels (submarine ridges) along paths of tsunami propagation are not dangerous for it even at a limit magnitude of submarine subduction earthquakes. The simulation results are compared with historical data about manifestations of distant tsunamis on the Russian Far East coast. 相似文献
5.
The breakup of western margin of Australia from Greater India started around 155 Ma and progressed southwards. After the separation, the interceding intraplate region experienced large volumes of submarine volcanism, extending over 100 Myrs. The Christmas Island Seamount Province (CHRISP, as it has been dubbed) lies south of the Java-Sunda Trench, and contains numerous submerged volcanic seamounts, and two sub-aerially exposed island groups—Cocos (Keeling) Islands, and Christmas Island. While recent geochronological investigations have shed light on the diverse eruption ages of the volcanics of this region, some islands/seamounts have demonstrated protracted volcanic histories, and it is not clear how the volcanic loading, tectonic subsidence, and subsequent emergence history of the islands relates to these discrete volcanic episodes. This study utilises a number of geophysical techniques to determine the crustal structure, loading and subsidence history, and last sub-aerial exposure age for the CHRISP. The study shows that flexural and subsidence modelling are reliable techniques in constraining the age of the seamounts when geochronological techniques are not possible. Utilising regional gravity signatures, we model the crustal structure underneath the Cocos (Keeling) Island, and constrain the thickness of the limestone cover between 900 and 2,100 m. Using age-depth subsidence curves for oceanic lithosphere the time since these seamounts were exposed above sea-level was determined, and a trend in exposure ages that youngs towards the west is observed. Two episodes of volcanism have been recorded at Christmas Island and they are of different origin. The younger phase in the Pliocene is a manifestation of flexure induced cracks produced in the lithosphere as it rides the subduction fore-bulge, whereas a low velocity seismic zone rising from the lower mantle, and tectonic reorganization, may be associated with the older Eocene volcanic phase, as well as much of the rest of the province. Our modelling also supports the existence of an older, undated volcanic core to Christmas Island, based on the loading ages from flexural modelling. 相似文献
6.
Volcanic rocks collected from the Solomon Sea Basin are mostly ferrobasalt lavas similar to evolved MORB; an exception is a single sample of basaltic crystal tuff invaded by later basalt. The rocks contain labradorite, aluminous diopsidic augite, and titanomagnetite, with olivine and pigconite in the more vitrophyric samples, and segregation vesicles in some. Cobbles dredged from Gudaraba Canyon, south of the Solomon Sea Basin, include both MORB-like glassy lava and K-metasomatised basalt and andesite(?). Two small pieces of volcanic glass from the southern Bismarck Sea are more primitive MOR-type basalts. 相似文献
7.
Severe red tides due toChattonella antiqua occur sporadically during summer in the Seto Inland Sea, Japan, and cause significant damage to the fishing industry. In order to assess the chemical environment with respect to the outbreak ofC. antiqua, environmental factors that affect the growth ofC. antiqua were monitored around the Ie-shima Islands, the Seto Inland Sea, in the summer of 1986. In addition, a growth bioassay of the seawater usingC. antiqua was conducted under a semicontinuous culture system. Although temperature, salinity and light intensity were optimum for the growth ofC. antiqua, red tides by this species did not occur. Concentrations of NH 4 + , NO 3 ? and PO 4 3? were low (<0.4, <0.2, <0.06 µM, respectively) above the thermocline (8–12 m) and high below it (0.6–2, 4–8, 0.4–0.8 µM, respectively). Vitamin B12 concentrations did not change significantly between the surface (0 m) and below the thermocline (25 m) in the level of 2–4 ng·l?1. The growth bioassay revealed that in the surface waters, concentrations of N- as well as P- nutrients were too low to support a rapid growth ofC. antiqua. At the depth of 25 m, neither N, P nor B12 limited the growth rate. In order to obtain more quantitative information on the growth rate as a function of the concentrations of N- and P- nutrients,C. antiqua was grown in a semicontinuous culture system by changing nutrient concentrations systematically. The observed growth rate (μ) can be approximated as follows: $$\mu = \mu _{\max } .\frac{{S_N }}{{K_g ^N + S_N }}.\frac{{S_{PO4} }}{{K_g ^P + S_{PO4} }},$$ whereS N is the concentration of NO 3 ? plus NH 4 + (0–6 µM),S PO, the concentration of PO 4 3? (0–0.6 µM), μmax (0.97 d?1) the maximal growth rate,K 0 N (1.0 µM) andK 0 P (0.11 µM) the half saturation constants for NO 3 ? and PO 4 3? , respectively. Using the above equation with nutrient concentrations measured, the rate at which seawater supports the growth ofC. antiqua can be estimated and this can be used for the assessment of chemical environments with respect to the outbreak ofC. antiqua. 相似文献
8.
This paper is focused on the hydrophysical state of the western basin of the Large Aral Sea in its present conditions of ecological crisis. The investigation is based on the direct observations carried out during a field survey in the Aral Sea in October of 2013. The analysis of the distribution of the temperature values across the western basin is given. Time series of the water currents variability were recorded at four mooring stations. The pattern of the basin-scale circulation response to the wind forcing was described. Based on the in situ measurements of the time variability of the temperature fields, the principal characteristics of the internal waves were specified for the present-day Aral Sea for the first time. 相似文献
9.
Effects of the longshore variation of the coastline geometry and the bottom topography on coastal upwelling are discussed. Longshore variations of the topography cause local enhancing or weakening of upwelling in the process of the generation and propagation of internal Kelvin and the shelf waves. 相似文献
10.
Charcoal column chromatography and a dialysis system using a Visking tube were used for the concentration and separation of dissolved carbohydrates in seawater. Recoveries of mono-, oligo-, and polysaccharides were 46–74, 61–89 and 70%, respectively, relative to the total amount of sugars initially submitted to analysis. The combined charcoal column chromatography and dialysis system was used to separate dissolved carbohydrates in seawater samples from Mikawa Bay into mono-, oligo- and polysaccharide fractions. The polysaccharides are separated into two fractions with molecular weights of <4,000 and >4,000 using Sephadex G-25 column chromatography. Monosaccharides, oligosaccharides, polysaccharides with M.W.<4,000 and polysaccharides with M.W. >4,000 accounted for 7–9, 15–26, 7–13 and 20–33% of total dissolved carbohydrates, respectively. However, 32–38% of dissolved carbohydrates were lost during the analytical procedures. Glucose, galactose, mannose, xylose, arabinose, ribose, fucose, and rhamnose were found upon acid hydrolysis of the oligo- and polysaccharide fractions, while fucose and rhamnose were not present in the monosaccharide fraction. Possible sources of the carbohydrates in these fractions are discussed with reference to the monosaccharide composition of cellular carbohydrate in marine algae. 相似文献
11.
Accurate and rapid determination of inorganic carbon constituents in ocean environments is important for understanding the carbon cycle, especially in the context of ocean-acidification research. A microsensor capable of directly measuring carbonate ion (CO3 2–) concentrations would be desirable. In this study, a carbonate microsensor with a polymeric liquid membrane was fabricated, and two calibration methods were used to evaluate its performance. The first method was based on continuous titration. Small increments of HCl were added to seawater or Na2CO3 solution to adjust the total alkalinity and pH values and thus obtain a series of carbonate concentrations. The second method used a series of discrete standards. Varying amounts of HCl or NaOH were added to separate seawater aliquots, and the CO3 2– concentration of each standard was calculated from the resulting total alkalinity and total dissolved inorganic carbon. Both methods were found to be adequate for achieving accurate calibration of the CO3 2– sensor, and both are suitable for field work. The discrete standards method, however, is more convenient and may provide a better linear range at low CO3 2– concentrations (detection range: 2–300 μmol/kg) than the continuous titration method in seawater (detection range: 10–250 μmol/kg). This CO3 2– microsensor can be used for 5–7 d and detects changes in carbonate concentration as low as 2 μmol/kg in the inorganic carbon constituents of the environments where marine calcareous organisms grow. The CO3 2– microelectrode was further assessed by applying it to the measurement of pore-water CO3 2– concentration profiles in a marine sediment core. 相似文献
12.
Comparison of modern submarine fans and ancient turbidite sequences is still in its infancy, mainly because of the incompatibility of study approaches. Research on modern fan systems mainly deals with morphologic aspects and surficial sediments, while observations on ancient turbidite formations are mostly directed to vertical sequences. The lack of a common data set also results from different scales of observation. To review the current status of modern and ancient turbidite research, an international group of specialists formed COMFAN (Committee on Fans) and met in September 1982 at the Gulf Research and Development Company research facilities in Pennsylvania. 相似文献
13.
A large number of tar globules with sessile organisms were collected from the surface tows taken with larval nets in the waters around the Ryukyu Islands during November and December, 1973. Bryozoans (one species), tubeworms (Serpulidae,Janua (Dexiospira) foraminosa (Moore &Bush)) and goose barnacles (Lepas pectinata Spengler,L. anatifera Linné) were the most important species of sessile animals found on these tar globules. Sinking of tar globules byLepas of middle or large size was suggested from the differences in their specific gravity. 相似文献
14.
In this model, we apply a nonlinear three-dimensional sigma-coordinate model to study the waves and currents in the Sea of Azov generated by different fields of wind forcing: a constant wind, a quickly varying real wind obtained using the data of reanalysis applying the SKIRON model, and the wind resulting from their combined forcing. This mathematical model was also applied to study the transformation of the passive admixture appearing under the influence of wind fields in the Sea of Azov considered here. We compared the results of numerical calculations with the field data obtained under the wind forcing at a number of hydrological stations. We found the regularities of the water transport driven by onshore and offshore winds, the velocities of the currents, and the characteristics of the evolution of polluted regions at different depths as functions of the nonstationary wind intensity and the velocities of the stationary currents. 相似文献
15.
Monterey Fan is the largest modern fan off the California shore. Two main submarine canyon systems feed it via a complex pattern of fan valleys and channels. The northern Ascension Canyon system is relatively inactive during high sea-level periods. In contrast, Monterey Canyon and its tributaries to the south cut across the shelf and remain active during high sea level. Deposition on the upper fan is controlled primarily by the relative activity within these two canyon systems. Deposition over the rest of the fan is controlled by the oceanic crust topography, resulting in an irregular fan shape and periodic major shifts in the locus of deposition. 相似文献
16.
During periods of sunspot maxima (approximately every 11 years) the mean winter position of the center of the Aleutian Low pressure system shifts from the Gulf of Alaska to the western Aleutian Islands, and mean, cyclonic, wind-stress transport in the Gulf of Alaska is reduced by roughly 20%. Coastal sea level data in the gulf do not reflect an 11-year cycle but spectral energy densities indicate an approximate 6-year periodicity also present in transpacific annual mean sea surface temperatures that, in the last one or two decades, parallels large year classes of Pacific herring in southeastern Alaska, large escapements of sockeye salmon fry in the Bristol Bay area, and maxima in the January catch of Dungeness crab in Alaska. 相似文献
17.
18.
Won Duk Yoon Hye Eun Lee Changhoon Han Soo-Jung Chang Kyunghoon Lee 《Ocean Science Journal》2014,49(3):183-192
Nemopilema nomurai have appeared massively since 2003 in Korean waters, and regular offshore monitoring has been performed since 2005 in the eastern Yellow Sea (YS), northwestern East China Sea (ECS), Korean southern waters (Ksw), and western East Sea (ES). Korea Jellyfish Monitoring Network (KoJEM) was established in 2006 for coastal jellyfish monitoring. From these, sight survey monitoring data were gathered and analyzed to extract the yearly and seasonal fluctuation of N. nomurai’s abundance and distribution. The first massive annual appearance of N. nomurai occurred in the northwestern ECS, off Shanghai, China, in mid May of 2005–2008 and of 2012–2013. In other years or concurrently with the appearance in the northwestern ECS in the same year, several individuals were found in the mid-eastern YS and Ksw, and southwestern ES. The population of N. nomurai at the northwestern ECS moved to the southeastern YS and Jeju Strait in June, and from the July to August it extended its distribution all around the Korean peninsula and persisted till October. Since October, the distribution was retracted into the southern YS and Ksw, and disappeared slowly. N. nomurai’s yearly abundance varied a lot, from nearly 0 inds 10?4m?2 in 2010 to 62.4 inds 10?4m?2 in 2005. The highest abundance was recorded in 2005, followed by 2007 and 2009, and the least abundance was in 2008 and 2010–2013. The results were compared with those of the Liaoning Bay, Bohai Sea, which led to speculation about a new seeding place of N. nomurai, and mortality during the early planktonic phase of N. nomurai was proposed as the determinant of the yearly variation in abundance. 相似文献
19.
Bengal Submarine Fan, with or without its eastern lobe, the Nicobar Fan, is the largest submarine fan known. Most of its sediment has been supplied by the Ganges and Brahmaputra Rivers, probably since the Early Eocene. The “Swatch-of-No-Ground” submarine canyon connects to only one active fan valley system at a time, without apprent bifurcation over its 2500-km length. The upper fan is comprised of a complex of huge channel-levee wedges of abandoned and buried older systems. A reduction of channel size and morphology occurs at the top of the middle, fan, where meandering and sheet flow become more important. 相似文献
20.
Both spatial and spatiotemporal distributions of the sources of tsunamigenic earthquakes of tectonic origin over the last 112 years have been analyzed. This analysis has been made using tsunami databases published by the Institute of Computational Mathematics and Mathematical Geophysics (Siberian Branch, Russian Academy of Sciences) and the National Aeronautics and Space Administration (United States), as well as earthquake catalogs published by the National Earthquake Information Center (United States). It has been found that the pronounced activation of seismic processes and an increase in the total energy of tsunamigenic earthquakes were observed at the beginning of both the 20th (1905–1920) and 21st (2004–2011) centuries. Studying the spatiotemporal periodicity of such events on the basis of an analysis of the two-dimensional distributions of the sources of tectonic tsunamis has made it possible to determine localized latitudinal zones with a total lack of such events (90°?75° N, 45°–90° S, and 35°?25° N) and regions with a periodic occurrence of tsunamis mainly within the middle (65°?35° N and 25°–40° S) and subequatorial (15° N–20° S) latitudes of the Northern and Southern hemispheres. The objective of this work is to analyze the spatiotemporal distributions of sources of tsunamigenic earthquakes and the effect of the periodic occurrence of such events on the basis of data taken from global tsunami catalogs. 相似文献