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1.
The hydrographic structure in the east central Arabian Sea during premonsoon period undergoes significant temporal change in the thermal field of upper 100 m, wherein temperature rises by about 0–5°C on an average from May to June. The major contribution in increasing the surface layer temperature comes from surface heat exchange processes, while the horizontal advective process tends to remove the heat from the upper layer. The geostrophic flow patterns are similar from May to June in the major part of the study area while in the coastal areas off Goa a southerly current sets in June in response to coastal upwelling.  相似文献   

2.
Time variation of surface fluxes of heat, moisture and momentum over a sea station (20°N 89°E) in the north Bay of Bengal has been computed by profile method for the period 18th–25th August 1990 using meteorological data of MONTBLEX-90 from ORVSagarkanya. The fluxes showed synoptic and diurnal variations which are marked during depression (20th–21st August) compared to their variation prior to and after this period. Variations of heat and water vapour fluxes were in phase. Night time fluxes are relatively high compared to day time. Average momentum transfer during depression was two to three times large. Variations in Bowen ratio were relatively large during day time. During depression, it varied between 0·2 in day time and about 0·3 at night and in the undisturbed period between ?0·1 and 0·2 during day time and 0·2 and 0·25 at night. The study shows that the assumptionC D=CH=CE of the exchange coefficients normally used in estimating the fluxes by the bulk aerodynamic method is not appropriate becauseC H/CD≈2,C E/CD≈1·5 andC H/CE≈1·4.  相似文献   

3.
The sedimentary succession of piston core RC26-16, dated by 14C accelerator mass spectrometry, provides a nearly continuous palaeoceanographic record of the northeastern South China Sea for the last 15000 yr. Planktic foraminiferal assemblages indicate that winter sea-surface temperatures (SSTs) rose from 18°C to about 24°C from the last glacial to the Holocene. A short-lived cooling of 1°C in winter temperature centred at about 11000 14C yr ago may reflect the Younger Dryas cooling event in this area. Summer SSTs have remained between 27°C and 29°C throughout the record. The temperature difference between summer and winter was about ca. 9°C during the last glacial, much higher than the Holocene value of ca. 5°C. During the late Holocene a short-lived cooling event occurred at about 4000 14C yr ago. Oxygen and carbon isotopic gradients between surface (0–50 m) and subsurface (50–100 m) waters were smaller during the last glacial than those in the Holocene. The fluctuation in the isotopic gradients are caused most likely by changes in upwelling intensity. Smaller gradients indicate stronger upwelling during the glacial winter monsoon. The fauna-derived estimates of nutrient content of the surface waters indicate that the upwelling induced higher fertility and biological productivity during the glacial. The winter monsoon became weaker during the Holocene. The carbonate compensation depth and foraminiferal lysocline were shallower during the Holocene, except for a short-lived deepening at about 5000 14C yr ago. A preservation peak of planktic foraminifera and calcium carbonate occurred between 13400 and 12000 14C yr ago, synchronous to the global preservation event of Termination I.  相似文献   

4.
Radiocarbon analyses were carried out in the annual bands of a 40 year old coral collected from the Gulf of Kutch (22.6°N, 70°E) in the northern Arabian Sea and in the annual rings of a teak tree from Thane (19°14′N, 73°24′E) near Bombay. These measurements were made in order to obtain the rates of air-sea exchange of CO2 and the advective mixing of water in the Gulf of Kutch. The Δ14C peak in the Thane tree occurs in the year 1964, with a value of ∼630‰, significantly lower than that of the mean atmospheric Δ14C of the northern hemisphere (∼ 1000‰). The radiocarbon time series of the coral was modelled considering the supply of carbon and radiocarbon to the gulf through air-sea exchange and advective water transport from the open Arabian Sea. A reasonable fit for the coral data was obtained with an air-sea CO2 exchange rate of 11–12 mol m−2 yr−1, and an advective velocity of 28 m yr−1 between the Arabian Sea and the Gulf of Kutch; this was based on a model generated time series for radiocarbon in the Arabian Sea. The deduced velocity (∼ 28 m yr−1) of the advective transport of water between the gulf and the Arabian Sea is much lower than the surface tidal current velocity in this region, but can be understood in terms of net fluxes of carbon and radiocarbon to the gulf to match the observed coral Δ14C time series.  相似文献   

5.

Numerical simulations of groundwater flow and heat transport are used to provide insight into the interaction between shallow groundwater flow and thermal dynamics related to permafrost thaw and thaw settlement at the Iqaluit Airport taxiway, Nunavut, Canada. A conceptual model is first developed for the site and a corresponding two-dimensional numerical model is calibrated to the observed ground temperatures. Future climate-warming impacts on the thermal regime and flow system are then simulated based on climate scenarios proposed by the Intergovernmental Panel on Climate Change (IPCC). Under climate warming, surface snow cover is identified as the leading factor affecting permafrost degradation, including its role in increasing the sensitivity of permafrost degradation to changes in various hydrogeological factors. In this case, advective heat transport plays a relatively minor, but non-negligible, role compared to conductive heat transport, due to the significant extent of low-permeability soil close to surface. Conductive heat transport, which is strongly affected by the surface snow layer, controls the release of unfrozen water and the depth of the active layer as well as the magnitude of thaw settlement and frost heave. Under the warmest climate-warming scenario with an average annual temperature increase of 3.23 °C for the period of 2011–2100, the simulations suggest that the maximum depth of the active layer will increase from 2 m in 2012 to 8.8 m in 2100 and, over the same time period, thaw settlement along the airport taxiway will increase from 0.11 m to at least 0.17 m.

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6.
Western tropical Indian Ocean, Arabian Sea, and the equatorial Pacific are known as regions of intense bio-chemical-physical interactions: the Arabian Sea has the largest phytoplankton bloom with seasonal signal, while the equatorial Pacific bloom is perennial with quasi-permanent upwelling. Here, we studied three dimensional ocean thermodynamics comparing recent ocean observation with ocean general circulation model (OPYC) experiment combined with remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS). Using solar radiation parameterization representing observations that a higher abundance of chlorophyll increases absorption of solar irradiance and heating rate in the upper ocean, we showed that the mixed layer thickness decreases more than they would be under clear water conditions. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994-1995 Arabian Sea experiment and epi-fluorescence microscopy (EFM) on samples collected during Equatorial Pacific Ocean Climate Study (EPOCS) in November, 1988. In the Arabian Sea, as the chlorophyll concentrations peak in October (3 mg/m3) after the summer plankton bloom induced by coastal upwelling, the chlorophyll induced biological heating enhanced the sea surface temperature (SST) by as much as 0.6‡C and sub-layer temperature decreases and sub-layer thickness increases. In the equatorial Pacific, modest concentrations of chlorophyll less than 0.3 mg/m3 is enough to introduce a meridional differential heating, which results in reducing the equatorial mixed layer thickness to more than 20 m. The anomalous meridional tilting of the mixed layer bottom enhances off equatorial westward geostrophic currents. Consequently, the equatorial undercurrent transports more water from west to east. We proposed that these numerical model experiments with use of satellite andin situ ocean observations are consistent under three dimensional ocean circulation theory combined with solar radiation transfer process.  相似文献   

7.
This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has motivated a new interest for renewable sources, such as the use of ground-source heat pumps for domestic heating and cooling. The vertical variability of the groundwater temperature between the ground surface and 10–20 m was detected: deeper temperatures were higher than shallow temperatures in spring, while a decrease with depth occurred in autumn. These variations are connected with the heating and cooling cycles of the ground surface due to the seasonal temperature oscillation. Variations below the seasonal oscillation are likely to be connected with the presence of advective heat transport due to the groundwater flow, according to the hydraulic features of a shallow aquifer. Temperature values mostly ranged between 12 and 14 °C in rural areas, while the values were between 14 and 16 °C below the Turin city. This groundwater warming is attributed to a widespread urban heat island phenomenon linked to warmer land surface temperatures in Turin city. Sparse warm outliers are connected with point heat sources and site-specific conditions of land and subsurface use, which may cause the aquifer temperature to rise. A relatively stable temperature below the seasonal fluctuation zone combined with high productivity and legislated limits for deeper groundwater use represent favourable conditions for a large-scale diffusion of groundwater heat pumps within the shallow aquifer. Moreover, this heat surplus should be regarded as a resource for future geothermal installations.  相似文献   

8.
Heat flow variations with depth in Europe can be explained by a model of surface temperature changes >10°C. New heat flow map of Europe is based on updated database of uncorrected heat flow values to which paleoclimatic correction is applied across the continent. Correction is depth dependent due to a diffusive thermal transfer of the surface temperature forcing of which glacial–interglacial history has the largest impact. It is obvious that large part of the uncorrected heat flow values in the existing heat flow databases from wells as shallow as few hundreds of meters is underestimated. This explains some very low uncorrected heat flow values 20–30 mW/m2 in the shields and shallow basin areas of the craton. Also, heat flow values in other areas including orogenic belts are likely underestimated. Based on the uncorrected and corrected heat flow maps using 5 km × 5 km grid, we have calculated average heat flow values (uncorrected heat flow: 56.0 mW/m2; SD 20.3 mW/m2 vs. corrected heat flow: 63.2 mW/m2; SD 19.6 m/Wm2) and heat loss for the continental part. Total heat loss is 928 E09 W for the uncorrected values versus corrected 1050 E09 W.  相似文献   

9.
The mechanism of hydrogen-deuterium isotopic exchange was studied in crystalline layer forms of silica (hydrous and cation-substituted SiO2-X2 and SiO2-Y varieties) and alumina (hydrargillite and boehmite) in contact with liquid D2O at temperatures of 20–200°C and saturated vapor pressure. Extensive exchange was observed between adsorbed H2O and D2O molecules via the self-diffusion mechanism in all silica varieties and boehmite at a temperature of 20°C. Deuterium substitution for hydrogen in structural OH groups was observed at 20°C only in the H-form of SiO2-Y (0.7%) and boehmite (1.2 or 17% with molecular deuteration). When the temperature of the hydrothermal treatment of samples was raised up to 200°C, the degree of structural deuterium exchange increased up to 12% (35% with molecular deuteration) in the former case and up to 34% in the latter case. In the former case, the process of isotopic exchange occurred by the nucleophile substitution SNi near surface silicon atoms, and in the latter case, the electrophile substitution ENi in surface OH groups.  相似文献   

10.
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   

11.
南海西部夏季冷涡的季节变化特征   总被引：5，自引：0，他引：5  
兰健  洪洁莉  李丕学 《地球科学进展》2006,21(11):1145-1152
基于美国海军的空间分辨率为0.5°×0.5°月平均的GDEM(Generalized Digital Environmental Model )三维温盐资料,采用P Vector方法,计算了南海西部夏季冷涡及附近海域的三维环流,分析了此冷涡的水平结构和垂向结构及其季节变化规律。结果表明南海西部夏季冷涡所占据的海域为一上升流区,对应的是低温区和气旋式环流,其温度场具有明显的垂向层化结构,冷涡随深度增加而减弱。冷涡中心在上层靠近越南沿岸,在温跃层以下有离岸的趋势。此冷涡具有明显的季节性变化：在5、6月份冷涡开始形成,其范围达到110.75°E,最大切向流速为8 cm/s;在7、8月份冷涡达到强盛,其范围向东扩展至112.50°E,冷涡中心也向东移至(110.50°E,13.25°N),最大切向流速增加为30 cm/s;在9、10月份冷涡开始衰减。  相似文献   

12.
Thermal structure of the lithosphere studies the partition of crustal and mantle heat flow of the continental area and is of significant importance to understand various energy‐related geodynamic processes. The study addresses the spatial distribution of the Meso‐Cenozoic mantle heat flow and Moho temperatures in the region of the Bohai Bay Basin based on the thermal history of the sedimentary basin, radioactive heat production rate and thickness of crustal layering. The results show that the ratio of the mantle and surface heat flow (qm/qs) experienced two peaks in the late period of the Early Cretaceous (qm/qs ~ 68%) and the Middle to Late Palaeogene (qm/qs ~ 75%), respectively. Based on the qm/qs ratio, the lithosphere of the Bohai Bay Basin transformed its thermal structure during the Meso‐Cenozoic, from the ‘cold mantle but hot crust’ stage in the Triassic–Jurassic to the ‘hot mantle but cold crust’ stage in the Cretaceous and Cenozoic. The Moho temperatures (Tm) during the Meso‐Cenozoic were also calculated by using the equation of one‐dimensional heat conduction, and the result shows that there exist three Tm peaks occurring in the late period of the Early Cretaceous (930–1080 °C), the Middle‐Late Palaeogene (820–890 °C) and the Early Neogene (770–810 °C). The qm/qs ratio began to exceed 50%, and the Moho temperature started to go over 700 °C from the Cretaceous to the present day, which revealed that the activity of the upper mantle in the eastern North China Craton (NCC) increased significantly accompanied by the strong crustal movement in the Cretaceous. The thermal structure revealed the Cretaceous to be a revolutionary period during the evolution of the Bohai Bay Basin, and this paper may provide some thermal evidence for the studies of the geodynamic evolution during the destruction of the NCC. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

13.
Pore water profiles of Ca, Mg, F, PO4?3 and Mn in the Galapagos Mounds Hydrothermal Field are believed to reflect, in part, upwelling of hydrothermal solutions through the sediments. Concentration-depth profiles in a low heat flow area just north of the Mounds Field display diagenetic changes typical of those found in pore waters underlying highly productive surface waters, consistent with the inference of no water flow or very slow downwelling (w < 5 cm/yr) of bottom water through these sediments. Rates of upward advection calculated from Mounds Field pore water profiles of Ca, Mg, and F profiles agree well with each other, averaging about 1 cm/yr in the pelagic sediments near the mounds and 15–30 cm/yr within the hydrothermal mounds themselves. The upward advection also modifies the shape of PO4?3 and Mn profiles.Advection rates inferred from the pore water data are generally in reasonable agreement with those made from heat flow data.The higher Ca and lower Mg, F, PO4?3 and Mn concentrations in Mounds Field pore waters (compared with those of the low heat flow area) suggest chemical exchange between the solution and basalt prior to upwelling. Li+, K+, Rb+, Sr++ and SO4? concentrations are indistinguishable from bottom water. This suggests very high effective water/rock ratios during the reactions which produced the upwelling solutions, perhaps due to extensive prior alteration of basalt adjacent to the flow path of water through the crust Inferred reaction temperatures are between 70–150°C.  相似文献   

14.
This study uses zircon and apatite fission‐track (FT) analyses to reveal the exhumation history of the granitoid samples collected from the Lesser Hinggan Mountains, northeast China. A southeast to northwest transect across the Lesser Hinggan Mountains yielded zircon FT ages between 89.8 ± 5.7 and 100.4 ± 8.6 Ma, and apatite FT ages between 50.6 ± 13.8 and 74.3 ± 4.5 Ma with mean track lengths between 11.7 ± 2.0 and 12.8 ± 1.7 µm. FT results and modelling identify three stages in sample cooling history spanning the late Mesozoic and Cenozoic eras. Stage one records rapid cooling from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110 °C) during ca. 95 to 65 Ma. Stage two records a period of relative slow cooling (∼110–60 °C) taking place between ca. 65 and 20 Ma, suggesting that the granitoids had been exhumed to the depth of ∼1−2 km. Final stage cooling (60–20 °C) occurred since the Miocene at an accelerated rate bringing the sampled rocks to the Earth's surface. The maximum exhumation is more than 5 km under a steady‐state geothermal gradient of 35 °C/km. Integrated with the tectonic setting, this exhumation is possibly led by the Pacific Plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

15.
The near-solidus transition from garnet lherzolite to spinel lherzolite   总被引：20，自引：1，他引：19  
The position of the transition from spinel lherzolite to garnet lherzolite in the system CaO-MgO-Al2O3-SiO2 (CMAS) has been determined experimentally at near-solidus temperatures. In reversed experiments, the transition occurs between 18 and 20 kbar at 1200 °C and between 26 and 27 kbar at 1500 °C, corresponding to higher pressures than previously envisaged. A position for the transition deeper within the Earth further complicates the explanation of the so-called garnet signatures in the trace element and isotope patterns of mid-ocean ridge basalts. If melting during adiabatic upwelling beneath a mid-ocean ridge begins at the depth required for the stability of garnet in peridotitic compositions, simple melting models predict that the amount of melt produced should be much greater than the observed thickness of the oceanic crust. A partial solution to the apparent conflict might be that (1) the rather simplistic melting models are in error, (2) that melting begins in garnet pyroxenite veins that are believed to be stable at lower pressures than garnet lherzolite or (3) that melting does not involve garnet at all, but it is clinopyroxene causing the trace element patterns observed in basalts erupted at mid-ocean ridges. A second set of reversal experiments were conducted to investigate the solubility of alumina in both orthopyroxenes and clinopyroxenes at the high temperatures near the solidus in the system CMAS. The results are compatible with most previous studies, and may be used as a starting point to calibrate thermodynamic models for pyroxenes in chemical systems, approximating upper mantle chemistry. Received: 9 August 1999 / Accepted: 29 October 1999  相似文献   

16.
《Applied Geochemistry》1988,3(2):153-163
A simulated nuclear waste glass, developed by the Power Reactor and Nuclear Fuel Development Corporation of Japan, was leached at 50, 75, 95, 110, 160, 210 and 240°C under saturated vapor pressure in groundwater from a granitic terrain. Depth profiles of insoluble components in reacted glass surface were measured by EPMA, together with time-excursion of the solution composition. Except at 160 and 210°C, B, Na, Mo (as MoO42−), Li, K, Si and Cs were leached out readily, with increasing rate of leaching in this order, at all other temperatures. At the intermediate temperatures of 160 and 210°C, however, the leaching rates of the soluble components were significantly lowered. Surface layers formed on the reacted glass surface thickened and changed in composition and structure with increasing temperature of reaction. During 312 h leaching at 110°C, a leached layer, about 5 μm thick, formed which is depleted in the soluble components and enriched in immobile metals such as Ni, Mn and Fe, and in precipitated components such as Ca and Mg. At 160 and 210°C, the secondary layer is composed of two sharply defined sublayers: an inner leached layer and an outer KSiAlrich layer, probably formed on the leached layer by precipitation from solution. The 50-μm thick layer formed during 508 h of leaching at 240°C is composed of three broadly defined sublayers, an inner leached layer, an outer precipitation layer and a middle layer of intermediate composition between the former two. The significant suppression in leaching rate at 160 and 210°C is interpreted as a result of rapid formation of the precipitation layer on the glass surface which slowed the diffusive migration of solution species responsible for glass dissolution through the surface layer. At 240°C, the leaching rate of soluble species except for silica increased significantly after an initial stage of slow leaching. At this temperature, coarse crystalline analcime precipitated from solution probably in expense of the surface precipitate, thus preventing the formation of surface precipitation layer as impermeable to solution species migration as that formed at 160 and 210°C.  相似文献   

17.
《Quaternary Science Reviews》2007,26(1-2):155-169
Diatom abundance and assemblage composition determined for 47 surface sediment samples from the Southeast Pacific (50°S–15°N), combined with existing data for the Peru and Chile margins, demonstrate responses to regional temperature, upwelling, and productivity. High diatom abundances (# valves/g) mark the eastern equatorial Pacific upwelling and the coastal upwelling areas, in particular the upwelling centers off Peru. Freshwater diatoms reflect the low-salinity tongue off the Chilean fjords. Diatom species composition distinguishes between coastal and eastern equatorial Pacific upwelling conditions, and records sea-surface temperatures. Q-mode factor analysis defines five floral assemblages. Factors 1 and 4 determined by the genus Chaetoceros (F1) and Thalassionema (F4) reflect coastal and equatorial upwelling conditions, respectively. Factors 2 and 3 characterized by the genus Thalassiosira and Azpetia nodulifera can be associated with El Niño conditions. A 5th factor, described by Paralia sulcata, records a near-shore upwelling center off Point Concepción, central Chile. Statistical transfer functions relate diatom species percentages to sea-surface temperature and productivity with error estimates of ±0.9 °C and ±23 gC/m2 yr, respectively, and provide new tools for estimating past temperature and productivity along the west coast of South America.  相似文献   

18.
The surface energy budget on the debris-covered Koxkar Glacier in China   总被引：1，自引：1，他引：0  
Energy fluxes were measured by using the eddy covariance system plus an automatic weather station at the debris-covered area on Koxkar Glacier from March to August, 2009. The coldest month of the glacier was January, and air temperature reached a maximum in July and August. Wind velocity at 2.0 m was higher in summer and lower in winter as a whole. Precipitation was concentrated from May to September and accounted for about 80 % of the total. Daily latent heat fluxes were higher than daily sensible heat fluxes during the observation period. The main reason for higher latent heat fluxes from March to April was snow cover. From June to August, latent heat fluxes during the daytime were limited by surface water content, and were lower than sensible heat fluxes, but latent heat fluxes were higher than sensible heat fluxes during summer nights because of air convection in the debris layer. Summer evaporation was higher than in the spring, and evaporation was 53.7 % of the precipitation from 19 June to 23 August. The Bowen ratio ranged from ?2.0 to 2.0 at the site.  相似文献   

19.
This study focuses on the water and gas chemistry of the northeastern Algerian thermal waters. The helium gas was used to detect the origin of the geothermal fluid. In the Guelma Basin, the heat flow map shows an anomaly of 120 ± 20 mW/m2 linked to the highly conductive Triassic extrusion. The chemical database reveals the existence of three water types, Ca-SO4/Na-Cl, which are related to evaporites and rich in halite and gypsum minerals. The third type is Ca (Na)-HCO3, which mostly characterizes the carbonated Tellian sector. The origin of thermal waters using a gas-mixing model indicates a meteoric origin, except for the El Biban hot spring (W10), which shows a He/Ar ratio of 0.213, thus suggesting the presence of batholith. The helium distribution map indicates a lower 3He/4He ratio between 0 Ra and 0.04 Ra in the W10 and W15 samples, which is compatible with the crustal ratio. Reservoir temperatures estimated by silica geothermometers give temperatures less than 133 °C. The geothermal conceptual model suggests that a geothermal system was developed by the deep penetration of infiltrated cold waters to a depth of 2.5 km and then heated by a conductive heat source (batholith for El Biban case). The thermal waters rise up to the surface through the deep-seated fractures. During their ascension, they are mixed with shallow cold groundwater, which increase the Mg content and cause the immature classification of the water samples.  相似文献   

20.
Air pollution predictions often require the height of atmospheric mixed layer in time especially in big cities. Here, the variation of the height of this layer is estimated from direct measurements and also from a numerical forecast model with a high resolution boundary layer scheme. The height of the daytime mixed layer for the city of Zanjan (48.5°N, 36.7°E, 1700m above sea level) is measured using a LIDAR (532 nm) system, which works based on aerosols scattering of laser light. The mixed layer height (z i ) for Zanjan city, well above mean sea level compared to other major cities in the world, is found to be between 1.4 km typically in spring and 2.2 km in summer, for synoptic calm conditions. Also, the MM5 forecast model with a proper boundary layer scheme (MRF) is used to estimate z i which shows rather good agreement with direct observations using the LIDAR system. The entrainment zone of the mixed layer was also found to undergo some occasional temporal growth that may be attributed to shear instability that led to more mixed layer growth.  相似文献   

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