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1.
S. Prasanna Kumar M. Madhupratap M. Dileep Kumar M. Gauns P. M. Muraleedharan V. V. S. S. Sarma S. N. De Souza 《Journal of Earth System Science》2000,109(4):433-441
Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological
productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian
Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast
of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized
by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection
of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand,
is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and
increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea
remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing
during winter resulted in one-and-a-half times higher production in 1997 than in 1995. 相似文献
2.
A coupled physical-biological-chemical model has been developed at C-MMACS. for studying the time-variation of primary productivity
and air-sea carbon-dioxide exchange in the Indian Ocean. The physical model is based on the Modular Ocean Model, Version 2
(MOM2) and the biological model describes the nonlinear dynamics of a 7-component marine ecosystem. The chemical model includes
dynamical equation for the evolution of dissolved inorganic carbon and total alkalinity. The interaction between the biological
and chemical model is through the Redfield ratio. The partial pressure of carbon dioxide (pCO2) of the surface layer is obtained from the chemical equilibrium equations of Penget al 1987. Transfer coefficients for air-sea exchange of CO2 are computed dynamically based on the wind speeds. The coupled model reproduces the high productivity observed in the Arabian
Sea off the Somali and Omani coasts during the Southwest (SW) monsoon. The entire Arabian Sea is an outgassing region for
CO2 in spite of high productivity with transfer rates as high as 80 m-mol C/m2 /day during SW monsoon near the Somali Coast on account of strong winds. 相似文献
3.
M. R. Ramesh Kumar S. Sathyendranath N. K. Viswambharan L. V. Gangadhara Rao 《Journal of Earth System Science》1986,95(3):435-446
Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali and Arabian coasts are associated with good monsoon rainfall over India. The strong monsoonal cooling in these regions can be attributed to strong low level winds and intense upwelling. The reappearance of 27°C isotherm off Somali coast in May/June coincides with the onset of southwest monsoon over India. Further, the influence of zonal anomaly of SST off Somalia Coast (SCZASST) and Central Indian Ocean Zonal Anomaly of SST (CIOZASST) with monsoon rainfall over India is brought out. The former is negatively related to the monsoon rainfall over western and central parts of India, whilst CIOZASST is positively related. 相似文献
4.
We review the geological and geophysical structural framework of the deep Black Sea and Caspian Sea basins. Based on seismic evidence and subsidence history, we conclude that the deep basins have an oceanic crust formed in a marginal sea environment. We propose that the present deep basins are remnants of a much greater marginal sea formed during three separate episodes during the Mesozoic: in the Middle Jurassic, Upper Jurassic and Late Cretaceous. A tentative sketch of the geologic evolution of the area is presented. The marginal sea reached its greatest extent in the Early Tertiary when it was about 900 km wide and 3000 km long. The central part of the marginal sea has since disappeared during the collision between the Arabian promontory and the Eurasian margin. 相似文献
5.
The summer cooling of the Arabian Sea has been reviewed in relation to the dynamic and thermodynamic processes. The differences in the quantum of cooling in the coastal regions have been attributed to the variations in the strength of coastal upwelling along the respective coasts. In the central portions of the Arabian Sea, the thickness of the surface layer and the thermal structure appear to be predominantly governed by the turbulent mixing of cold waters entrained into the surface layer in association with the deepening of current shear zone. The surface heat losses during the passage of a cyclone over the east central Arabian Sea account for only 40% of the total heat change in the surface layer while the rest is lost into the interior. Also presented are climatological mean patterns of the forcing parameters and their variations during certain years. 相似文献
6.
全球大洋深海有孔虫碳同位素(δ13C)记录中广泛发现40万年周期,这一周期可能与偏心率长周期的轨道驱动有关.1.6 Ma以来,δ13C的这一长周期拉长到50万年,且重值期不再与偏心率低值对应.目前对δ13C 40万年周期的成因及其周期拉长的机制还不明确.这里使用了包含9个箱体的箱式模型,用于研究热带过程与冰盖相互作用及其对大洋碳循环的影响.模拟结果显示当北半球高纬海区海冰迅速增大时冰盖迅速融化,进入冰消期,而当海冰快速消失后,冰盖则重新缓慢增长.冰盖变化具有冰期长,间冰期短的非对称形态.在季节性太阳辐射量的驱动下冰盖变化具有10万年冰期-间冰期旋回.当冰盖融化速率受北半球高纬夏季太阳辐射量控制时,冰盖变化的岁差周期明显加强,相位与地质记录一致,说明轨道驱动可以通过非线性相位锁定机制使冰盖变化与其在相位上保持一致.海冰的阻隔效应使大气中CO2在冰消期时增多.冰期时大洋环流减弱使大气中CO2逐渐减少.当模型只有ETP驱动的风化作用而不考虑冰盖变化时,模拟的δ13C记录显示极强的40万年周期,体现了大洋碳储库对热带风化过程的响应.当同时考虑冰盖变化和风化作用时,模拟的δ13C结果中40万年周期减弱而10万年周期加强,并且40万年周期上碳储库与偏心率的相位与不考虑冰盖变化时的相位也存在差异,反映了冰盖变化引起的洋流改组压制了大洋碳循环对热带过程的响应. 相似文献
7.
8.
The crustal and upper mantle compressional-wave velocity structure across the southwestern Arabian Shield has been investigated by a 1000-km-long seismic refraction profile. The profile begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, trends southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan, and terminates at the outer edge of the Farasan Bank in the southern Red Sea. More than 500 surveyed recording sites were occupied, and six shot points were used, including one in the Red Sea.Two-dimensional ray-tracing techniques, used to analyze amplitude-normalized record sections indicate that the Arabian Shield is composed, to first order, of two layers, each about 20 km thick, with average velocities of about 6.3 km/s and 7.0 km/s, respectively. West of the Shield-Red Sea margin, the crust thins to a total thickness of less than 20 km, beyond which the Red Sea shelf and coastal plain are interpreted to be underlain by oceanic crust.A major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition. Elsewhere along the profile, several high-velocity anomalies in the upper crust correlate with mapped gneiss domes, the most prominent of which is the Khamis Mushayt gneiss. Based on their velocities, these domes may constitute areas where lower crustal rocks have been raised some 20 km. Two intracrustal reflectors in the center of the Shield at 13 km depth probably represent the tops of mafic intrusives.The Mohorovičić discontinuity beneath the Shield varies from a depth of 43 km and mantle velocity of 8.2 km/s in the northeast to a depth of 38 km and mantle velocity of 8.0 km/s depth in the southwest near the Shield-Red Sea transition. Two velocity discontinuities occur in the upper mantle, at 59 and 70 km depth.The crustal and upper mantle velocity structure of the Arabian Shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the Precarnbrian. The Shield is currently flanked by the active spreading boundary in the Red Sea. 相似文献
9.
Fresh water supplied to Djibouti town is essentially groundwater located inthe fractured Gulf and Somali basalt aquifers. About 30 wells (3 to 6 km inland from the sea) are exploited and provide water of rather poor quality (TDS between 1000 mg 1−1 and 2800 mg 1−1). A sea water interface has been recognized locally some 3.8 km from the sea at 35 m below sea level. However, a well at Hidka Gisiyed, some 11 km from the sea, also contains water with high salinity (TDS=14,000 mg 1−1) at depth. The over-exploitation of the aquifer and the high pumping rate are contributing to an increase in the salinity due to the intrusion of sea water, as shown by the chemical results. The Hidka Gisiyed saline water is another possible source of saline water at depth.The isotopic results from part of the Djibouti aquifer have shown that current recharge from local rain or surface runoff is occurring. An understanding of factors influencing the evolution of the salinity will allow the better management of the aquifer. 相似文献
10.
Claus Prodehl 《Tectonophysics》1985,111(3-4)
In February 1978 seismic-refraction profiles were recorded by the U.S. Geological Survey along a 1000 km line across the Arabian Shield in western Saudi Arabia. This report presents a traveltime and relative amplitude study in the form of velocity-depth functions for each individual profile assuming horizontally flat layering. The corresponding cross section of the lithosphere showing lines of equal velocity reaches to a depth of 60–80 km.The crust thickens abruptly from 15 km beneath the Red Sea Rift to about 40 km beneath the Arabian Shield. The upper crust of the western Arabian Shield yields relatively high-velocity material at about 10 km depth underlain by velocity inversions, while the upper crust of the eastern Shield is relatively uniform. The lower crust with a velocity of about 7 km/s is underlain by a transitional crust-mantle boundary. For the lower lithosphere beneath 40 km depth the data indicate the existence of a laterally discontinuous lamellar structure where high-velocity zones are intermixed with zones of lower velocities. Beneath the crust-mantle boundary of the Red Sea rift most probably strong velocity inversions exist. Here, the data do not allow a detailed modelling, velocities as low as 6.0 km/s seem to be encountered between 25 and 44 km depth. 相似文献
11.
Meteorological fields variability over the Indian seas in pre and summer monsoon months during extreme monsoon seasons 总被引：1，自引：0，他引：1
U. C. Mohanty R. Bhatla P. V. S. Raju O. P. Madan A. Sarkar 《Journal of Earth System Science》2002,111(3):365-378
In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields
and heat budget components) over monsoon region (30‡E-120‡E, 30‡S30‡N) during the pre-monsoon month of May and summer monsoon
season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for
42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for
Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon
years in the surface meteorological fields are also examined by Student’s t-test at 95% confidence level.
Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the
pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2 m) in the
month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea
that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2 m) in the
month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region
is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed
over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows
positive anomalies over NW India and north Arabian Sea.
There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent
heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive
anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered as an advance indicator of the
possible behavior of the subsequent monsoon season. The distribution of net heat flux is predominantly negative over eastern
Arabian Sea, Bay of Bengal and Indian Ocean. Anomaly between the two extreme monsoon years in post 1980 (i.e., 1988 and 1987)
shows that shortwave flux, latent heat flux and net heat flux indicate reversal in sign, particularly in south Indian Ocean.
Variations of the heat budget components over four smaller sectors of Indian seas, namely Arabian Sea, Bay of Bengal and west
Indian Ocean and east Indian Ocean show that a small sector of Arabian Sea is most dominant during May and other sectors showing
reversal in sign of latent heat flux during monsoon season. 相似文献
12.
An interpretation of deep seismic sounding measurements across the ocean-continent transition of the Red Sea-Saudi Arabian Shield is presented. Using synthetic seismograms based on ray tracing we achieve a good fit to observed traveltimes and some of the characteristic amplitudes of the record sections. Crustal thickness varies along the profile from 15 km in the Red Sea Shelf to 40–45 km beneath the Asir Mountains and the Saudi Arabian Shield. Based on the computation of synthetic seismograms our model requires a velocity inversion in the Red Sea-Arabian Shield transition. High-velocity oceanic mantle material is observed above continental crust and mantle, thereby forming a double-layered Moho. Our results indicate a thick sedimentary basin in the shelf area, and zone of high velocities within the Asir Mountains (probably uplifted lower crust). Prominent secondary low-frequency arrivals are interpreted as multiples. 相似文献
13.
Indu Jain P. Chittibabu Neetu Agnihotri S. K. Dube P. C. Sinha A. D. Rao 《Natural Hazards》2007,42(1):67-73
The northeastern sector of the Arabian Sea, which covers the Gujarat coast of India and western coast of Pakistan, is a region
vulnerable to extreme sea levels associated with tropical cyclones (TCs). Although the frequency of tropical cyclones in the
Arabian Sea is not high, the coastal regions of India and Pakistan suffer in terms of loss of life and property caused by
the surges. In view of this a location-specific fine resolution model is developed for the Gujarat coast of India and adjoining
Pakistan coast. The east–west and north–south grid distance is about 3.0 km. Using this model, numerical experiments are carried
out to simulate the surges generated by 1999 and 2001 cyclones which struck the Pakistan coast. The model computed surges
are in agreement with the available observational estimates. 相似文献
14.
Upper reaches of the Arabian Gulf consist of different types of fine sediments including the vast Mesopotamia Plain sediments, tidal flat sediments and estuarine sabkha sediments. The height of the plain starts from zero meter and increases northwards to three meters with extremely gentle gradient. The vast plain to the north of the Arabian Gulf is drained by Shat Al-Arab (Shat means river in Iraqi slang language) and Khor Al-Zubair (Khor means estuary). The former drains the extreme eastern part of the plain; whereas, the latter drains the western part. Shat Al-Arab is the resultant of confluence of the Tigris and Euphrates rivers near Al-Qurna town; about 160 km north of the Arabian Gulf mouth at Al-Fao town; whereas, the length of Khor Al-Zubair is about 50 km; as measured from Um Qasir Harbor. The drainage system around Khor Al-Zubair is extremely fine dendritic; whereas around Shat Al-Arab is almost parallel running from both sides of the river towards the river; almost perpendicularly. The fine dendritic drainage around Khor Al-Zubair shows clear recent erosional activity, beside water divides, abandoned irrigation channels and dislocated irrigational channels and estuarine distributaries; all are good indication for a Neotectonic activity in the region. These may indicate the presence of subsurface anticlines, which may represent oil fields; since tens of subsurface anticlines occur in near surroundings, which are oil fields. 相似文献
15.
Anshu Prakash Mishra A. C. Pandey S. Rai 《Journal of the Geological Society of India》2010,76(5):468-478
In this article, the authors examine Sea surface temperature (SST), Sea surface circulation (SSC) and Vertical velocity (VV) fields from simulation of 25 layers coarse resolution Modular ocean model (MOM version 3.0) with prescribed wind forcing for the region 74.25°S to 65°N, 180°W-180°E. It is found that distribution of SST simulated by the model shows its consistency with the observed climatology. However, simulated SST in the areas of Arabian Sea, Bay of Bengal, Indonesian Throughflow (ITF) region and east of North America near equator exhibit slight warming with respect to observation, which may be due to model deficiency and forcing problems. Circulation features suggest that one of the strongest current viz. Antarctic circumpolar current (ACC) along with other major current systems viz. Gulf stream current, North and South Pacific current, Agulhas current, Labrador current, Canary current, etc are captured well by the model. In the Indian Ocean and other ocean basins, current patterns are well captured by the model simulation. Intense upwelling as well as downwelling areas is marked in the horizontal distribution of VV, which is as expected. VV show quasi-stagnant and convergent regions suggesting that floating materials may be accumulated during January/July in the real ocean and wind driven circulation may act as an important contribution for such transport of floating materials in these regions. An attempt has also been made to understand the fluctuations of the SST in NINO 3.4 region during the period of model simulation using SST anomalies. 相似文献
16.
17.
The crustal structure of the western Arabian platform is derived using the spectral analysis of long-period P-wave amplitude ratios. The ratio of the vertical to the horizontal component is used to obtain the crustal transfer function based on thickness variations, crustal velocities, densities and the angle of emergence at the lower crust and upper mantle interface. Eleven well-defined earthquakes recorded at the long-period RYD station during the period from 1985 to 1994 were selected for analysis based on the following criteria: focal depths with a range between 7 and 89 km, body-wave magnitudes greater than 4.7, epicentral distances with a range from 8.8° to 26.5°, and back azimuthal coverage from 196° to 340°. Spectral analysis calculations were based on the comparison of the observed spectral ratios with those computed from theoretical P-wave motion obtained using the Thomson–Haskell matrix formulation for horizontally layered crustal models. The selection of the most suitable model was based on the identification of the theoretical model which exhibits the highest cross-correlation coefficient with the observed transfer function ratio. By comparing the spectral peak positions of the observed and theoretical values, the thickness and velocity can be resolved within 3 km and 1 km/s, respectively, of the observed values. The spectral analysis of long-period P-waves can detect a thin layer near the surface of about 1.6 km thick and a velocity contrast of about 10% with that of the underlying layer. A strong velocity gradient of about 0.05 km/s per km was found in the upper crust and 0.02 km/s per km in the lower crust. The derived crustal model is not unique due to the theoretical assumptions (horizontal layering, constant densities and velocities in each layer), quality of the data and complexities of the crustal structure. The crustal model suggests that the crust consists of five distinct layers. The upper crustal layer has a P-wave velocity of about 5.6 km/s and is about 1.6 km thick. The second layer has a velocity of about 6.2 km/s and is 10.2 km thick. The third layer shows a velocity of 6.6 km/s and is 6.8 km thick. The fourth layer has a velocity of about 6.8 km/s and is 12.3 km thick. The lower crustal layer has a velocity of about 7.5 km/s and is 9.3 km thick. The Mohorovicic discontinuity beneath the western Arabian platform indicates a velocity of 8.2 km/s of the upper mantle and 42 km depth. 相似文献
18.
The spectral characteristics of shallow water waves were studied at two locations along the eastern Arabian Sea during 2011. Wave spectra were single-peaked from June to October and predominantly double-peaked during the rest of the year. Even though both locations were subjected to open sea conditions, the percentage of single-peaked spectra was large (63 %) in the southern location compared to a location 350 km north (46 %), because of variation in local winds. Throughout the year, the double-peaked spectra were mostly swell dominated in the southern location. In the northern location, the double-peaked spectra during January to May and December were sea dominated due to the strong local winds blowing from north-west. For the double-peaked wave spectra, the average difference between the spectral peaks was 0.11 Hz, and the average ratio of the spectral energy density at the two peaks was 0.5. Significant wave heights up to 4.2 m and a maximum wave height of 7 m were observed during the south-west monsoon period. Fifty per cent of the waves recorded had spectral peak wave periods between 6 and 12 s. The narrowest directional spectra were found for waves with 10–12-s peak wave periods. Inverse wave age values were biased towards lower values with peaks in the range of 0.2–0.6, indicating a swell-driven wave regime along the eastern Arabian Sea. 相似文献
19.
《Journal of African Earth Sciences》2000,30(1):149-168
A petrological model for the upper mantle and lower crust under the northern part of the Arabian Plate (Syria) has been derived on the basis of petrology of upper mantle and lower crustal xenoliths occurring in the Neogene to Quaternary alkali basalts of the Shamah volcanic fields. The xenolith suite has been classified by texture mineralogy and chemistry into the following groups: (1) Type I metasomatised and dry Cr diopside xenoliths with protogranular to porphyroclastic textures; (2) Type II Al augite spinal and garnet pyroxenite and websterite which have igneous and/or porphyroclastic textures and abundant phlogopite and/or amphibole; (3) Cr-poor megacrysts; and (4) mafic lower crustal xenoliths. Estimates of Type I xenolith temperatures are 990–1070°C with pressure between 13 and 19 kbar. Type II xenoliths yield temperatures of 930–1150°C and pressures in the range 12—13 kbar. The lower crustal xenolith mineral assemblages and geothermometry based on coexisting minerals suggest equilibration conditions between 6 and 8 kbar and 820–905°C. Mantle plumes, which may be the source of the volatile flux, have implications for melt generation in the Arabian basalt provinces. It is estimated that the lithosphere beneath the Arabian Plate is less than 80 km thick. Xenolith data and geophysical studies indicate that the Moho is located at a depth of 40–37 km and that the crust-mantle transition zone has a thickness of 8–5 km and occurs at a depth of 27–30 km. The boundary between an upper granitic crust and a lower mafic crust occurs at a depth of 19 km. Type I dry xenoliths show a low overall concentration of REE (La/Yb =1–2 and Sm = 0.7–1.1 times chondrite), whereas Type I hydrous xenoliths are LREE enriched (La/Yb=6–9 and Sm=1.1–1.3 times chondrite). Type II xenoliths show high overall LREE enrichment. Petrological and geochemical data for the lower crustal xenoliths indicate that these xenoliths represent basaltic cumulates crystallised at lower crustal pressures. 相似文献
20.
Eastern Anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the Arabian and Eurasian plates. This collisional and contractional zone is being accompanied by the tectonic escape of most of the Anatolian plate to the west by major strike-slip faulting on the right-lateral North Anatolian Transform Fault Zone (NATFZ) and left-lateral East Anatolian Transform Fault Zone (EATFZ) which meet at Karlıova forming an east-pointing cusp. The present-day crust in the area between the easternmost part of the Anatolian plate and the Arabian Foreland gets thinner from north (ca 44 km) to south (ca 36 km) relative to its eastern (EAHP) and western sides (central Anatolian region). This thinner crustal area is characterized by shallow CPD (12–16 km), very low Pn velocities (< 7.8 km/s) and high Sn attenuation which indicate partially molten to eroded mantle lid or occurrence of asthenospheric mantle beneath the crust. Northernmost margin of the Arabian Foreland in the south of the Bitlis–Pötürge metamorphic gap area is represented by moderate CPD (16–18 km) relative to its eastern and western sides, and low Pn velocities (8 km/s). We infer from the geophysical data that the lithospheric mantle gets thinner towards the Bitlis–Pötürge metamorphic gap area in the northern margin of the Arabian Foreland which has been most probably caused by mechanical removal of the lithospheric mantle during mantle invasion to the north following the slab breakoff beneath the Bitlis–Pötürge Suture Zone. Mantle flow-driven rapid extrusion and counterclockwise rotation of the Anatolian plate gave rise to stretching and hence crustal thinning in the area between the easternmost part of the Anatolian plate and the Arabian Foreland which is currently dominated by wrench tectonics. 相似文献