首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The surface water of the Japan Sea contained226Ra of70 ± 4dpm m−3 which was nearly equal to that of the surface water in the North Pacific. The concentration of226Ra in the Japan Sea deep water below 500 m was151 ± 8dpm m−3, showing a vertically and regionally small variation. This concentration of226Ra in the deep water is unexpectedly high, because the Japan Sea deep water has a higher Δ14 C value by about 50‰ than the Atlantic deep water containing the same226Ra. One of the causes to be considered is larger contribution of226Ra from biogenic particles dissolving in the Japan Sea deep water, but the Japan Sea is not so fertile in comparison to the Bering Sea. The other more plausible cause is the internal ventilation of the Japan Sea water, which means that the residence time of the Japan Sea Proper water is considerably long although the water is vertically mixed fairly well especially in winter. The ventilation may supply some amounts of radiocarbon and oxygen but does not change the inventory of226Ra. The residence times of the Japan Sea deep water and of water within the Japan Sea are calculated by solving simultaneous equations for226Ra and14C with a three-box model to be 300–400 years and 700–1000 years, respectively.  相似文献   

2.
From 1979 to 1984, the overall water balance of the Dead Sea was characterized by a water deficit. However, an excess of freshwater inflow during the 1979/80 rainy season resulted in a 3-year-long meromictic phase. This was followed by three consecutive overturns of the water column in December 1982, 1983 and 1984. The buildup and dissipation of the seasonal thermocline and halocline is followed throughout this period which covers a wide range of water balance situations. The gravitational stabilities of the summer pycnoclines, measured in terms of N2 3×10−2 s−2, are at least one order of magnitude greater than the values reported in freshwater lakes and oceans. The contributions of temperature and salinity to N2 and to the integrated stability W are examined separately, and their interdependence is pointed out. Two irreversible effects in the evolution of the properties of the water masses are identified: (1) a monotonic increase in the density of the deep waters; and (2) a monotonic shift of the NaCl saturation curve towards higher salinities.  相似文献   

3.
The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANICE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m−2 day−1, which has the potential to promote primary productivity of 5.3 mmol C m−2 day−1. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km−1, i.e. 0.19 mmol N m−2 day−1 which has the potential to promote primary productivity of 1.2 mmol C m−2 day−1. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NOx and NH3 are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m−2 day−1, i.e. 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m2 is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem.  相似文献   

4.
Measurement of228Ra activities in the upper 300 m water column was conducted at two stations in the South China Sea using an MnO2-fiber extraction/β-counting technique of228Ac. Results showed that228Ra activities ranged from 0.38 to 3.60 Bq · m-3. The vertical profiles of228Ra at the time-series station favored a steady state assumption. Based on a one-dimensional steady state model,228Ra-nitrate coupled approach was applied to stations NS97-43, NS99-53 (T1), NS99-53 (T2). New production thus quantified were 4.4, 5.1 and 5.7 mmolC · m-2 · d-1, respectively,f ratios in the South China Sea were estimated from the derived new production and the documented primary productivity in the regime, to be 0.12–0.15.  相似文献   

5.
We examined the effects of freshwater flow and light availability on phytoplankton biomass and production along the Louisiana continental shelf in the region characterized by persistent spring–summer stratification and widespread summer hypoxia. Data were collected on 7 cruises from 2005 to 2007, and spatially-averaged estimates of phytoplankton and light variables were calculated for the study area using Voronoi polygon normalization. Shelf-wide phytoplankton production ranged from 0.47 to 1.75 mg C m−2 d−1 across the 7 cruises. Shelf-wide average light attenuation (kd) ranged from 0.19–1.01 m−1 and strongly covaried with freshwater discharge from the Mississippi and Atchafalaya Rivers (R2=0.67). Interestingly, we observed that the euphotic zone (as defined by the 1% light depth) extended well below the pycnocline and to the bottom across much of the shelf. Shelf-wide average chlorophyll a (chl a) concentrations ranged from 1.4 to 5.9 mg m−3 and, similar to kd, covaried with river discharge (R2=0.83). Also, chl a concentrations were significantly higher in plume versus non-plume regions of the shelf. When integrated through the water-column, shelf-wide average chl a ranged from 26.3 to 47.6 mg m−2, but did not covary with river discharge, nor were plume versus non-plume averages statistically different. The high integrated chl a in the non-plume waters resulted from frequent sub-pycnocline chl a maxima. Phytoplankton production rates were highest in the vicinity of the Mississippi River bird's foot delta, but as with integrated chl a were not statistically different in plume versus non-plume waters across the rest of the shelf. Based on the vertical distribution of light and chl a, a substantial fraction of phytoplankton production occurred below the pycnocline, averaging from 25% to 50% among cruises. These results suggest that freshwater and nutrient inputs regulate shelf-wide kd and, consequently, the vertical distribution of primary production. The substantial below-pycnocline primary production we observed has not been previously quantified for this region, but has important implications about the formation and persistence of hypoxia on the Louisiana continental shelf.  相似文献   

6.
The first224Ra (t1/2 = 3.64days) measurements from mixing zones of estuarine systems are presented for the Pee Dee River-Winyah Bay and Delaware Bay Estuaries. High-resolution gamma-ray spectrometry was used to determine224Ra,228Ra (t1/2 = 5.7years), and226Ra (t1/2 = 1622years) activity ratios. Desorption and diffusion from suspended and bottom sediments contributes to the non-conservative increases of the three isotopes in each systems. In Delaware Bay224Ra concentrations were nearly constant over the 2.5‰ to 15‰ salinity range where two turbidity maximum zones are located.228Th scavenging onto the suspended particles in the turbid zones may supply a regenerative source of224Ra in this system. Samples collected on the ebb and flood tide from a salt marsh along Delaware Bay have a 5-fold increase in224Ra from flood to ebb and 3- and 2-fold increases for228Ra and226Ra respectively, indicating salt marshes are another source of radium to estuarine waters.  相似文献   

7.
Measurements of the228Ra/226Ra activity ratio in the waters of the Greenland, Norwegian and Labrador Seas and Baffin Bay reveal strong horizontal gradients in the surface waters. The coastal waters are dominated by228Ra injection from nearshore sediments. There is an inverse correlation between the228Ra/226Ra activity ratio and salinity in the 30–36‰ salinity range. Vertical profiles indicate that the228Ra/226Ra activity ratio is also strongly coupled toσθ except for some regions where228Ra is being injected into higher density water as these isopycnals intersect coastal areas. We use these measurements in the area of formation of North Atlantic Deep Water to estimate that this water mass forms with a228Ra/226Ra activity ratio of 0.10.  相似文献   

8.
We have measured Ba in Dead Sea samples collected before and after the 1979 overturn, and226Ra in nine samples collected after the overturn. Before this overturn, Ba and the226Ra data measured by Chung and Craig [4] show that a distinct two-layer structure existed, with higher concentrations in the upper layer. After the overturn, both elements were uniformly distributed in the water column. The inventories of Ba and Ra calculated from these data are the same for the periods before and after the overturn. If the inventories were constant during the last meromictic phase then the input rate must be balanced by the removal rate, and a mass balance model can be constructed to estimate physical parameters based on known or deduced sources and sinks. The sources include inputs from the Jordan River, springs around the Dead Sea, and submerged springs or seepages, etc. The sinks include coprecipitation with aragonite, gypsum, precipitation of barite, coprecipitation of Ra with barite, particulate scavenging, and radioactive decay for Ra. Our data include measurements of Ba and226Ra in gypsum, aragonite and halite from the Dead Sea, as well as in some of the inflowing rivers and springs.The inclusion of particulate scavenging as a sink is a major element of the model. We find that, without inclusion of a Ba scavenging term in the deep water, the lake volume at the previous overturn as calculated from the Ba data would be unrealistically high in comparison with historical records. The inclusion of particulate scavenging for Ra in the model reduces the calculated duration of the last meromictic phase significantly.Our model excludes internal mixing between the upper and lower water masses. With this restriction, various sets of model parameters were calculated as a function of theRa/Ba scavenging rate ratio. If the ratio is one, the calculated age of the last meromictic phase is about a hundred years. A substantial increase in the Ra input rate is required to balance the removal rate by particulate scavenging as well as decay. If the ratio is zero, i.e. no particulate scavenging for Ra, the age is about 260 years, as obtained by Stiller and Chung [2].  相似文献   

9.
Thermal springs of the Boundary Creek hydrothermal system in the southwestern part of Yellowstone Park outside the caldera boundary vary in chemical and isotopic composition, and temperature. The diversity may be accounted for by a combination of processes including boiling of a deep thermal water, mixing of the deep thermal water with cool meteoric water and/or with condensed steam or steam-heated meteoric water, and chemical reactions with surrounding rocks. Dissolved-silica, Na+, K+ and Ca2+ contents of the thermal springs could result from a thermal fluid with a temperature of 200 ± 20°C. Chloride-enthalpy and silica-enthalpy mixing models suggest mixing of 230°C, 220 mg/l Cl− thermal water with cool, low-Cl− components. A 350 to 390°C component with Cl− ≥ 300 mg/l is possibly present in thermal springs inside the caldera but is not required to fit observed spring chemical and isotopic compositions. Irreversible mass transfer models in which a low-temperature water reacts with volcanic glass as it percolates downward and warms, can account for observed pH and dissolved-silica, K+, Na+, Ca2+ and Mg2+ concentrations, but produces insufficient Cl− or F− for measured concentrations in the warm springs. The ratio of aNa/aH, and Cl− are best accounted for in mixing models. The water-rock interaction model fits compositions of acid-sulfate waters observed at Summit Lake and of low-Cl− waters involved in mixing.The cold waters collected from southwestern Yellowstone Park have δD values ranging from −118 to −145 per mil and δ18O values of −15.9 to −19.4 per mil. Two samples from nearby Island Park have δD values of −112 and −114 per mil and δ18O values of −15.1 and −15.3 per mil. All samples of thermal water plot significantly to the right of the meteoric water line. The low Cl− and variable δD values of the thermal waters indicate isotopic compositions are derived by extensive dilution with cold meteoric water and by steam separation on ascent to the surface. Many of the hot springs with higher δD values may contain in addition a significant amount of high-D, low-Cl−, acid-sulfate or steam-heated meteoric water. Mixing models, Cl− content and isotopic compositions of thermal springs suggest that 30% or less of a deep thermal component is present. For example, the highest-temperature springs from Three Rivers, Silver Scarf and Upper Boundary Creek thermal areas contain up to 70% cool meteoric water and 30% hot water components, springs at Summit Lake and Middle Boundary Creek spring 57 are acid-sulfate or steam-heated meteoric water; springs 27 and 48 from Middle Boundary Creek and 49 from Mountain Ash contain in excess of 50% acid-sulfate water; and Three Rivers spring 46 and Phillips could result from mixing hot water with 55% cool meteoric water followed by mixing of acid-sulfate water. Extensive dilution by cool meteoric water increases the uncertainties in quantity and nature of the deep meteoric, thermal component.  相似文献   

10.
During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 101 km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area.Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m− d−1 and 75 mg m−, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO3-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a−1 h−1), high mean α (14 mg C mg Chl a−1 Ein−1 m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters.The results imply a seasonal (June to August) middle shelf production of 150 g C m−1, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area.  相似文献   

11.
The distributions of dimethylsulfide (DMS) and its precursor, dimethylsulfoniopropionate (DMSP), were examined in the surface microlayer and corresponding subsurface water of the Yellow Sea, China, in April 2006. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were 5.42 (1.78–12.75), 9.22 (2.85–19.73) and 17.50 (4.33–36.09) nmol L−1 in the subsurface water, and those in the surface microlayer were 4.92 (1.69–10.66), 17.08 (3.13–38.82) and 22.54 (4.85–47.24) nmol L−1, respectively. The enrichment factor (EF) of DMS in the microlayer ranged from 0.47 to 2.24 with a mean of 0.98. In contrast, DMSPd and DMSPp appeared to be enriched in the microlayer with average EFs of 1.98 and 1.39, respectively. A close correlation of integrated DMS, DMSPp and chlorophyll a concentrations for compiled data from all stations in the microlayer and the subsurface water indicated that phytoplankton biomass might play an important role in controlling the distributions of biogenic sulfurs in the study area. Moreover, a statistically significant relationship was found between the microlayer concentrations of DMS, DMSP and chlorophyll a and their subsurface water concentrations, suggesting a close linkage between these two water compartments. Interestingly, we observed higher biological production rates and consumption rates of DMS in the microlayer relative to the subsurface water. Furthermore, the DMS production rates were closely correlated both with DMSPd and chlorophyll a concentrations. Our study showed that the major sink of DMS in microlayer was escape into the atmosphere, which greatly exceeded its bacterial consumption. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 6.41 μmol m−2 d−1 during spring.  相似文献   

12.
We used regression analyses of water samples from 18 lakes, nine rivers, and one spring in Ethiopia to (a) test the hypothesis that water bodies of relatively higher salinity (K25>1000 μS cm−1) have a different conductivity to salinity relationship than waters of lower salinity (K25 < 1000 μS cm−1), and (b) develop models to predict total cations and salinity from conductivity that can be used for Ethiopian waters and other African aquatic systems of similar chemical composition. We found no statistical difference in the bilogarithmic relationships (total cations vs. conductivity; salinity vs. conductivity) for waters of higher salinity (K25 > 1000 μS cm−1) and waters of lower salinity (K25 < 1000 μS cm−1). However, comparison among our models and models from the literature suggests that developing separate equations for low and high salinity water bodies has some merit. We believe that the equations developed in this study can be used for Ethiopian waters and other African waters within the range of conductivity in this study.  相似文献   

13.
In light of the current problems facing the Yellow River and surrounding areas (e.g., periods of zero river discharge, increasing nitrate concentrations of the Bohai Sea), we examined the coastal mixing dynamics around the mouth of the Yellow River. Naturally occurring radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) and other geochemical tracers (Ba, Si, and salinity) were employed to determine river plume transport scales and rates. Barium and radium exhibit elevated concentrations within the salinity gradient where they are desorbed from particles via ion-exchange. Once they are added to the system, they decrease offshore from dilution with lower concentration Bohai Sea water, and in the case of 224Ra and 223Ra, by radioactive decay. Using radium “ages” to assess the dissolved material transport scales and rates proved to be a useful tool in this environment. The ages based on the 224Ra/228Ra activity ratio increased gradually until salinities reached ∼25 when they rapidly increased due to decreased mixing at higher salinities. Integrated net transport rates through the salinity front ranged from 1.4 to 1.6 cm/s and did not vary significantly with river discharge. Thus, tidal mixing appears to dominate in this system, at least over the range of discharges investigated (80–600 m3/s). Determining the temporal scale of flow across the coastal zone in this region is a valuable first step toward examining whether the Yellow River is contributing to the increasing inorganic nitrogen concentrations in the central Bohai Sea.  相似文献   

14.
The Ischia geothermal system is hosted by silicic rocks of the Quaternary Potassic Roman Province, in southern Italy. Exploration drilling down to 1156 m depth in the mid-1950s provided information on boiling profiles (up to 250°C) and on the depth and permeability of the potential reservoirs. Discharge fluid samples were collected and analyzed to define the inflow of surrounding seawater (C1 ranges from 2.5 to 20 g/kg) into the system.Analyses of samples from surface manifestations and shallow wells collected during 1983 and 1988 point to the existence of three distinct mixing regimes, involving three water components. A dishomogeneous body of diluted water (Cl less than 2.5 g/kg), that occurs at depths > 700 m and reequilibrates at 240°C at least, is overlain by an aquifer of groundwater variably mixed with variably seawater (Cl from 4 to 10 g/kg), which tends to reequilibrate at 160°C. Steam-heated waters locally develop and act as dilutants of the rising geothermal fluids.Dilution, mixing, and evaporation of the ascending chloride fluids are supported by oxygen and hydrogen isotopic data the thermal waters being enriched in 18O and D with respect to local meteoric water by up to 7 and 30‰, respectively. The relative composition of the major cations in thermal solutions was used to discriminate the two main groups of thermal waters, the reservoir temperatures of which are estimated from the Na/K-gethermometer. K-Mg geothermometer indicates reequilibration in near-surface conditions.The isotopic composition of the fumarolic steam varies from −7 to −12‰ in ∂8O and from − 35 to − 70‰ in ∂D, in agreement with a deep mixed fluid that boils adiabatically from 240 to 80°C. The deuterium content of the H2O-H2 pair gives enrichment factor of about 830‰, corresponding to equilibrium temperature conditions slightly higher than the surface boiling temperatures. The ∂13C of CO2is almost constant at −4.5‰ (1δ=0.4), suggesting an important magmatic contribution, and the ∂18O values of CO2appears to in equilibrium with accompanying steam at the measured temperatures.The CO2/Ar and H2/Ar chemical ratios have been used to derive aquifer temperatures, the values obtained being consistent with those of solute geothermometers.  相似文献   

15.
The Valles caldera in New Mexico hosts a high-temperature geothermal system, which is manifested in a number of hot springs discharging in and around the caldera. In order to determine the fluid pathways and the origin of chloride in this system, we measured 36Cl/Cl ratios in waters from high-temperature drill holes and from surface springs in this region. The waters fall into two general categories: recent meteoric water samples with low Cl− concentrations (< 10 mg/L) and relatively high 36Cl/Cl ratios [(300–1000) × 10−15]; and geothermal brines with high Cl− concentrations (800–9400 mg/L) but low 36Cl/Cl ratios [(11–26) × 10−15]. The 36Cl/Cl ratios for meteoric waters are slightly higher than expected for this region, suggesting a small addition of anthropogenic 36Cl. Because of low 36Cl/Cl ratios and high Cl− concentrations in the brines, chloride in these waters must be derived from subsurface sources. A comparison between the observed 36Cl/Cl ratios in the brines and those calculated for potential source formations in this region indicates that the present host formations, mainly volcanic tuffs, cannot be major sources of chloride, and that formations at greater depth, such as the Paleozoic and Precambrian formations are more likely to be sources of chloride in the brines. The results suggest that brines are meteoric waters which penetrated into the basement where they derive chloride from leaching of basement rocks and/or from saline pore fluids trapped there, along with likely addition of chloride from Paleozoic strata. Although these fluids have since come to reside in the intracaldera volcanic sequence after convective upwelling, they do not derive much Cl− from the volcanic strata; and residence times of fluids in the volcanics are < 100,000 years.  相似文献   

16.
Strontium stable isotopes fractionate in the soil environments?   总被引：1，自引：0，他引：1  
This study shows that the stable isotopic composition of strontium (the 88Sr/86Sr ratio expressed as δ88/86Sr value relative to the NBS987 standard) varies significantly in sedimentary terrestrial environments. The abundances of 86Sr, 88Sr isotopes were analyzed by MC-ICP-MS “Nu Plasma”. All studied rocks and waters show δ88/86Sr values that are distinctly different from the measured NBS987 standard (yielding 0.01 ± 0.05‰, all errors are reported as 2σ). Modern corals from the northern Gulf of Aqaba, Red Sea yielded significantly different value than seawater (δ88/86Sr = 0.22 ± 0.07‰, compared to 0.35 ± 0.06‰, respectively), in an excellent correlation with the δ88/86Sr analyses reported by Fietzke and Eisenhauer [Fietzke, J., Eisenhauer, A., 2006. Determination of temperature-dependent stable strontium isotopes (88Sr/86Sr) fractionation via bracketing standard MC-ICP-MS. Geochm. Geophys. Geosyst. 7 (no. 8)] on other coral samples. All carbonate samples that originated in the marine environment: corals (porites and acropora from the northern Gulf of Aqaba); Cretaceous limestone and runoff from the Judea Mountains as well as lacustrine evaporitic aragonite (Dead Sea); and Red Sea and Atlantic seawater yield an average δ88/86Sr value of 0.26 ± 0.1‰. On the other hand, secondary materials (products of chemical weathering) from the terrestrial environment of the Judea Mountain such as terra rossa soil and speleothem calcite (that derives its Sr from the above-lying soil) yielded significantly lower δ88/86Sr value of − 0.17 ± 0.06‰. This indicates that strontium isotopes fractionate in the soil environment calling for a possible development of strontium isotopes as a tracer for processes of chemical weathering and pedogenesis.  相似文献   

17.
Recent radium measurements from the near-surface Caribbean Sea are presented. The surface horizontal and vertical distributions of226Ra are essentially the same as reported by Szabo et al. (1967) for the early 1960's. The226Ra activity at the surface is relatively uniform across the Caribbean, with an average of8.2±0.4dpm/100kg. The subsurface distribution to ～200 m averages7.8±0.4dpm/100kg and increases slowly below 200 m. reaching ～9.5 dpm/100 kg at 560 m. In contrast to226Ra, the surface concentration of228Ra was much more variable in both time and space. An average increase of 33% was found between 1968 and 1976 in the western Caribbean and during both years an anomalously high228Ra activity was found in the eastern Caribbean. These data support previous hypotheses that water entering the eastern Caribbean has been enriched in228Ra prior to entry and that variable mixing of the Atlantic water masses found to the northeast and southeast of the Lesser Antilles may produce temporal variations in the near-surface228Ra activity. Scatter plots of228Ra vs. salinity and sigma-t indicate that the near-surface vertical distribution of228Ra in the Caribbean Sea is predominantly influenced by advection. Thus228Ra cannot be used to study near-surface vertical mixing rates in this region.  相似文献   

18.
228Ra concentrations were measured in 12 subsurface water samples collected during August–September 1970 in the North Atlantic at the Second Geosecs Intercalibration Station.228Ra concentrations ranged from 1.5 to 2.1 dpm/100 kg in the water layer between 100 and 600 m depth, above the main thermocline, but decreased with increasing depth to less than 0.5 dpm/100 kg at 1.5 km, below the main thermocline. The two deepest samples, collected below 4 km depth, indicated that the228Ra concentration increased again to at least 1.2 dpm/100 kg as the interface with the sea floor sediments was approached. Above the 4 km level, the228Ra profile was roughly similar to the tritium profile measured by Roether and Münnich.  相似文献   

19.
Loading by atmosphere and by the Baltic Sea cause gravity change at Metsähovi, located 15 km from the open sea. Gravity is changed by both the Newtonian attraction of the loading mass and by the crustal deformation. We have performed loading calculations using appropriate Green's function for both gravity and deformation, for both atmospheric and Baltic loading. The loading by atmosphere has been computed using a detailed surface pressure field from high resolution limited area model (HIRLAM) for north Europe up to 10° distances. Baltic Sea level is modelled using tide gauge records. Calculations show that 1 m of uniform layer of water corresponds to 31 nm s−2 in gravity and −11 mm in height. Modelled loading is compared with observations of the superconducting gravimeter T020 for years 1994–2002. The combination of HIRLAM and a tide gauge record decreases RMS of gravity residuals by 14% compared to single admittance in air pressure corrections without sea level data. Regression of gravity residuals on the tide gauge record at Helsinki (at 30 km distance) gives a gravity effect of 26 nm s−2 m−1 for Baltic loading.The gravity station is co-located with a permanent GPS station. We have also associated the loading effects of the atmosphere and of the Baltic Sea with temporal height variations. The range of modelled vertical motion due to air pressure was 46 mm and that due to sea level 18 mm. The total range was 38 mm. The effects of the Baltic Sea and of the atmosphere partly cancel each other, since at longer periods the inverse barometer assumption is valid. Regression of the modelled height on local air pressure gives −0.37 mm hPa−1, corresponding approximately to width 6° for pressure system.We have tested the models using one year of daily GPS data. Multilinear regression on local air pressure and sea level in Helsinki gives the coefficient −0.34 mm hPa−1 for pressure, and −11 mm m−1 for sea level. These match model values. Loading by air pressure and Baltic Sea explains nearly 40% of the variance of daily GPS height solutions.  相似文献   

20.
An intense but short-lived phytoplankton bloom develops in the low-salinity melt waters at the edge of the Bering Sea ice as the ice melts and retreats each spring. In spring 1988 we followed the development of this bloom by sampling every 3 h while following a freely drifting drogue in the marginal ice-edge zone for two four-day periods. The first period (29 April–3 May) was at an early stage of the bloom while the second period (10–13 May) was at the peak of the bloom. Early in the bloom, the phytoplankton consumed all the nitrate (400 mmoles m−2) initially present in the surface water producing large accumulations of particulate carbon (>1000 mmoles C m−2). By the time of peak chlorophyll concentrations (35 mg M−3), nitrate concentrations had been depleted so that the sustained high productivity depended on either recycled or imported nutrients. After this point, there was little net additional accumulation of biomass. From these data plus cruise data from previous years, we find that the Bering Sea ice-edge bloom typically begins in the last week of April and appears to precede blooms in the adjacent ice-free waters by days to weeks. The variability in bloom onset observed over several years is not linked very closely to the large scale climatic variations found in this region, but rather appears to be related to local weather during the end of April and the first part of May, with calm, sunny weather being required to initiate the blooms.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号