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 31 毫秒
1.
Uptake rates of NH4+, NO3− and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3− was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO3− uptake rate in the ice algal communities was light-limited The in situ NO3− and NH4− uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH4+ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO3− uptake rate.  相似文献   

2.
Summary. The luni-solar forced nutations and body tide are believed to be resonant at frequencies near (1 + 1/460) cycle sidereal day−1 as seen from the rotating Earth. This resonance is due to the Earth's rotating, elliptical fluid core. We show here that tides in the open ocean and the Earth's response to those tides must also be resonant at (1 + 1/460) cycle day−1. We examine these resonant oceanic effects on the Earth's nutational motion and on the body tide. Effects on the forced nutations might be as large as 0.002 arcsec at 18.6 yr. The effects on the observed resonance in the body tide are more important. For tidal gravity, for example, the difference between K 1 and 0 1 which is usually used to determine the resonance, can be perturbed by 30 per cent or more due to the oceanic resonance effects.  相似文献   

3.
10 m and 2.3 m ice cores were obtained on Austre Brøggerbreen, Spitsbergen in Svalbard (78°53 ' N, 11°56 ' E, 450 m a.s.l.) in September 1994 and in March 1995, respectively. Stratigraphy, bulk density, pH, electrical conductivity, and major ions were obtained from the core samples.
The chemical effect of meltwater percolation through snow/ice is examined. Good correlation between Cl− and Na+ was obtained. The ratio of Cl− to Na+ was 1.14 which was nearly the same value as in bulk sea water. However, the variation of Cl−/Na+ shows that higher ratio occured in the bubble-free ice. Furthermore the Cl− ions remain in higher concentration than SO 4 2− or Na+ ions.  相似文献   

4.
Summary. The viscoelastic response of the Earth to the mass displacements caused by late Pleistocene deglaciation and concomitant sea level changes is shown to be capable of producing the secular motion of the Earth's rotation pole as deduced from astronomical observations. The calculations for a viscoelastic Earth yield a secular motion in the direction of 72° W meridian which is in excellent agreement with observed values. The average Newtonian viscosity and the relaxation time obtained from polar motion data are about (1.1 ± 0.6)1023 poise (P) and 104 (1 ± 0.5) yr. The non-tidal secular acceleration of the Earth can also be attributed to the viscoelastic response to deglaciation and results in an independent viscosity estimate of 1.6 × 1023 P with upper and lower limits of 1.1 × 1023 and 2.8 × 1023 P. These values are in agreement with those based on the polar drift analysis and indicate an average mantle viscosity of 1–2 × 1023 P.  相似文献   

5.
Oxygen consumption by rotifers Macrotrachela musculosa and Trichotria truncata from Spitsbergen tundra (77°N) was measured using the method of Cartesian divers. The metabolic rate of M. musculosa was: 0.205 10−3mm3 02 per g 10−6 per hour at 2°C, 0.201 10−6mm3 at 6°C and 0.616 10−3mm3 02 per g 10−6 per hour at 10°C. The metabolic rate of Trichotria truncata at 6° was 0.103 10−3mm3 per g 10−6 per hour. The relation between body weight and oxygen consumption by M. musculosa at 2°C is expressed with the equation R = 0.18W0.67, with R – oxygen consumption in mm310−3 per individual per hour and W – wet weight of an animal in g 10−6.  相似文献   

6.
Seismic sources with observable glut moments of spatial degree two   总被引：1，自引：0，他引：1  
Let ζΛ and r Λ. be the hypocentral position and time of an extended indigenous seismic source. Backus showed that the force moment tensors of the source, Γ( m +1, n )(ζΛ, r Λ), determine and are determined by the motion which the source produces. For small m + n , only the long-period motion is relevant. The glut moment tensor Λ( m,n ) (ζΛ, r Λ.) can be calculated uniquely from γ( m +1, n )(ζΛ r Λ) only if m = 0 or m = 1. The tensor G =Λ(2,0)(ζΛ) gives the spatial variance tensor WΛ of the source, and WΛ. roughly describes the size, shape and orientation of the source region. Therefore the failure of the observed F =Γ(3,0)(ζΛ) to determine G uniquely is of seismological interest. In the present paper we show that F determines G uniquely if we assume the source to be a simple straight line source (SSLS) or an ideal fault in an isotropic medium with isotropic prestress (IFIMIP). We give tests on F which determine whether it can come from a SSLS, from an IFIMIP or from a simple plane surface source (SPSS). If we assume the source to be a SPSS then knowing F and the fault plane determines G to within an unknown scalar multiple of a certain tensor tangent to the fault plane. Moreover F determines the fault plane uniquely unless F can come from a SSLS. If it can, then F determines this virtual source line uniquely, and F permits the fault plane to be any plane containing the virtual source line.  相似文献   

7.
The ecophysiology of under-ice fauna   总被引：2，自引：0，他引：2  
During exposure to low salinity, the under-ice amphipods Gammarus wilkitzkii and Onisimus glacialis appeared as euryhaline osmoregulators, displaying regulation of haemolymph concentrations of sodium and chloride. Free amino acids took part in the regulation. During freezing and brine formation, the amphipods were freeze-sensitive and did not tolerate being frozen into solid ice. However, they could stay in the vicinity of the ice, conforming osmotically to the ambient brine and thus lowering the melting point of the amphipods' body fluids. This prevented internal ice formation in the absence of antifreeze agents (THF) in the haemolymph. When G. wilkitzkii, O. glacialis and Apherusa glacialis were exposed to dilute seawater, elevated rates of oxygen consumption and ammonia excretion were observed. The O:N atomic ratio was kept nearly constant during hyposmotic stress, indicating protein/lipids as metabolic substrate. Rates of oxygen consumption and ammonia excretion increased with increasing osmotic differences between the haemolymph and the medium, indicating higher energy requirements for osmotic and ionic regulation at low salinities. A minor decrease in haemolymph sodium concentrations coincided with the increased ammonia output during hyposmotic stress, indicating a possible counter ion regulation of NH+4 and Na+. An increased rate of oxygen consumption, ammonia excretion and 0:N ratio versus temperature was observed for all species.  相似文献   

8.
Glaciers in Svalbard: mass balance, runoff and freshwater flux   总被引：4，自引：1，他引：4  
Gain or loss of the freshwater stored in Svalbard glaciers has both global implications for sea level and, on a more local scale, impacts upon the hydrology of rivers and the freshwater flux to fjords. This paper gives an overview of the potential runoff from the Svalbard glaciers. The freshwater flux from basins of different scales is quantified. In small basins (A < 10 km2), the extra runoff due to the negative mass balance of the glaciers is related to the proportion of glacier cover and can at present yield more than 20% higher runoff than if the glaciers were in equilibrium with the present climate. This does not apply generally to the ice masses of Svalbard, which are mostly much closer to being in balance. The total surface runoff from Svalbard glaciers due to melting of snow and ice is roughly 25 ± 5 km3 a−1, which corresponds to a specific runoff of 680 ± 140 mm a−1, only slightly more than the annual snow accumulation. Calving of icebergs from Svalbard glaciers currently contributes significantly to the freshwater flux and is estimated to be 4 ± 1 km3 a−1 or about 110 mm a−1.  相似文献   

9.
We present an approximate method to estimate the resolution, covariance and correlation matrix for linear tomographic systems Ax = b that are too large to be solved by singular value decomposition. An explicit expression for the approximate inverse matrix A − is found using one-step backprojections on the Penrose condition AA −≈ I , from which we calculate the statistical properties of the solution. The computation of A − can easily be parallelized, each column being constructed independently.
The method is validated on small systems for which the exact covariance can still be computed with singular value decomposition. Though A − is not accurate enough to actually compute the solution x , the qualitative agreement obtained for resolution and covariance is sufficient for many purposes, such as rough assessment of model precision or the reparametrization of the model by the grouping of correlating parameters. We present an example for the computation of the complete covariance matrix of a very large (69 043 × 9610) system with 5.9 × 106 non-zero elements in A . Computation time is proportional to the number of non-zero elements in A . If the correlation matrix is computed for the purpose of reparametrization by combining highly correlating unknowns x i , a further gain in efficiency can be obtained by neglecting the small elements in A , but a more accurate estimation of the correlation requires a full treatment of even the smaller A ij . We finally develop a formalism to compute a damped version of A −.  相似文献   

10.
Summary. As part of integrated marine geophysical studies in the Western Somali Basin, we performed 118 sonobuoy experiments to define better the crustal structure of the margins and basin created by the separation of Madagascar and Africa. After using T 2/ X 2, conventional slope-intercept methods, and slant-stacked t-p techniques to analyse the data, we combined our solutions with all previous velocity information for the area. Velocity functions were derived for the sediment coiumn, and we detected a high-velocity (4.58 ± 0.29 km s–1) sediment layer overlying acoustic basement. We confirmed that the crust is indeed seismically oceanic, and that it may be considered either in terms of a layered model – layers 2B (5.42 ± 0.19 km s–1), 2C (6.23 ± 0.22 km s–1), 3 (7.03 ± 0.25 km s–1), and mantle (7.85 ± 0.32 km s–1) were identified – or a more complex gradient model in which layer 2 is marked by a steeper velocity gradient than underlying layer 3. Integrated igneous crustal thicknesses (1.62 ± 0.22 s, 5.22 ± 0.64 km) are significantly less than what is considered normal. We present a revised seismic transect across the East African margin, as well as total sediment thickness, depth to basement and crustal thickness maps.  相似文献   

11.
Carbon fluxes in the Arctic Ocean—potential impact by climate change   总被引：1，自引：0，他引：1  
Because of its ice cover the central Arctic Ocean has not been considered as a sink of atmospheric carbon dioxide. With recent observations of decreasing ice cover there is the potential for an increased air–sea carbon dioxide flux. Though the sensitivity of the carbon fluxes to a climate change can at present only be speculated, we know the responses to some of the forcing, including: melting of the sea ice cover make the air–sea flux operate towards equilibrium; increased temperature of the surface water will decrease the solubility and thus the air-sea flux; and an open ocean might increase primary production through better utilization of the nutrients.
The potential change in air-sea CO2 fluxes caused by different forcing as a result of climate change is quantified based on measured data. If the sea ice melts, the top 100 m water column of the Eurasian Basin has, with the present conditions, a potential to take up close to 50 g C m−2. The freshening of the surface water caused by a sea ice melt will increase the CO2 solubility corresponding to an uptake of ∼ g C m−2, while a temperature increase of 1°C in the same waters will out-gas 8 g C m−2, and a utilization of all phosphate will increase primary production by 75 g C m−2.  相似文献   

12.
Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and quantity of snow all affect microbial activity, thus influencing CO2 production in soil. In this study annual and seasonal emissions of CO2 were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real-time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained from different snow regimes in order to evaluate the effect of snow depth on winter CO2 effluxes. Total annual emissions of CO2 from the sub-Arctic site (0.662–1.487 kg CO2 m–2 yr–1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO2 m–2 yr–1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO2 effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004–0.248 kg CO2 m–2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by 2 weeks and decreased the annual CO2 emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.  相似文献   

13.
Micromonas pusilla (Butcher) Manton & Parke appears to be a prominent member of the Barents Sea picoplankton community as revealed by the serial dilution culture method. Cell numbers frequently exceeded 107 cells 1−1, though they usually varied between 103and 106 cells l−1. A number of other identified and unidentified taxa were recorded and quantified. Distribution relative to the marginal ice zone is reported.  相似文献   

14.
we have obtained one year of measurements from a subsurface instrumented mooring carrying two current meters and one bottom pressure recorder in the strait between Nordaustlandet and Kvitøya in the northeastern Svalbard archipelago. The observations show a mixed tide with typical amplitudes 0.4 db and 10cm sec−1. The semidiurnal tide is characterized by a progressive wave propagating toward the south. together with a cross-channel baroclinic mode. The annual average (non-tidal) current is less than 2cm sec−1 toward the north-east, suggesting that the transport into the Arctic Ocean is approximately 0.2 × 106m3s−1.  相似文献   

15.
Summary. Asymptotic expressions for components of the electromagnetic field of a grounded electric dipole are considered for the model consisting of a thin surface-layer overlapping a stratified medium with a highly resistive screen on the roof. It is shown that the method of spatial derivatives makes it possible to obtain proper estimates of the impedance at distances of r ≥|λ0| from the nearest edge of the surface anomaly (|λ0| being the effective depth of the field penetration in the underlying section). the magnetotelluric methods allow one to obtain the true values of impedance, provided r ≥ max {|λ0|, |/( S −1+ Z −0|1/2} where S is the integrated conductivity of the surface layer, is the transverse resistance of the screen, and Z −0 is the Tikhonov—Cagniard impedance for the medium underlying the surface layer.  相似文献   

16.
Summary. The statistical capability of the m b: M s discriminant for the discrimination of earthquake and explosion populations is examined by application of discriminant functions to a group of 83 explosions and 72 earthquakes in Eurasia. Equations are derived for the probability that an event is an earthquake or an explosion. The positive sign of DIS in the decision index equation, DIS i = 34.3383 – 11.9569 mb t + 7.1161 M si , indicates that the event i is an earthquake. Its negative sign indicates that event i is an explosion. The probability of correct classification for an event, P i , is related to its DIS i value, by P i = [1-exp (DIS i )]−1, where a large, positive DIS indicates a high probability that an event is an earthquake and a large, negative DIS indicates a high probability that an event is an explosion. The discrimination line M s = 1.680 m b– 4.825, or m b= 0.595 M s+ 2.872 very successfully separates the explosion population from the earthquake population. The points on this line have an equal chance of being an earthquake or an explosion; moreover, for any event, the distance parallel to the M s-axis from the point representing that event in the m b: M s plane to this line is a measure of the probability for the correct classification of that event.  相似文献   

17.
Approaches to Modelling the Surface Albedo of a High Arctic Glacier   总被引：1，自引：0，他引：1  
Broadband surface albedo measurements, made during the summer melt season at three weather stations on John Evans Glacier (79°40 ' N, 74°00 ' W), varied strongly with the solar zenith angle ( θ z ). Tests were carried out to assess the impact of diurnal variations in surface albedo on seasonal net shortwave radiation ( K * ) totals. Removing the diurnal signal from albedo measurements by daily averaging of hourly measurements, or by applying midday measurements to all hours of the day, changed K * by up to 16%. Ignoring measurements made at θ z & 75°, to account for measurement (cosine) error at high θ z , decreased K * by between 5 and 18%. Given the sensitivity of K * to diurnal patterns in surface albedo, experiments were carried out with two albedo models. One model accounted for albedo variations with θ z and one did not. The model driven by θ z , when implemented within a surface energy balance model for John Evans Glacier, produced better melt estimates. This suggests that diurnal variations in surface albedo should be accounted for in energy balance models of glacier melt.  相似文献   

18.
Magnetic susceptibility ( χ ) variations and the behaviour of the ratio of susceptibility to saturation magnetization ( χ/J s ) along the loess/palaeosol section at Koriten (NE Bulgaria) are used to deduce climatic changes during the Pleistocene in southeastern Europe. A good correlation of susceptibility variations with the astronomically tuned oxygen isotope record from ODP site 677 enables us to propose a more precise dating of the upper part of the Bulgarian loess complex. Close correspondence between susceptibility and δ 1 8 O records demonstrates the global significance of the palaeoclimatic signal recorded, although differences in relative amplitudes of χ and χ/J s and δ 1 8 O create difficulties in making quantitative estimates of the climatic humidity in the past. The role of local factors affecting the palaeoclimatic mineral magnetic record deduced from the profile studied in Bulgaria is discussed.  相似文献   

19.
Primary production of the northern Barents Sea   总被引：7，自引：0，他引：7  
The majority of the arctic waters are only seasonally ice covered; the northern Barents Sea, where freezing starts at 80 to 81°N in September, is one such area. In March, the ice cover reaches its greatest extension (74-75°N). Melting is particularly rapid in June and July, and by August the Barents Sea may be ice free. The pelagic productive season is rather short, 3 to 3.5 months in the northern part of the Barents Sea (north of the Polar Front, 75°N), and is able to sustain an open water production during only half of this time when a substantial part of the area is free of ice. Ice algal production starts in March and terminates during the rapid melting season in June and July, thus equalling the pelagic production season in duration.
This paper presents the first in situ measurements of both pelagic and ice-related production in the northern Barents Sea: pelagic production in summer after melting has started and more open water has become accessible, and ice production in spring before the ice cover melts. Judged by the developmental stage of the plankton populations, the northern Barents Sea consists of several sub-areas with different phytoplankton situations. Estimates of both daily and annual carbon production have been based on in situ measurements. Although there are few sampling stations (6 phytoplankton stations and 8 ice-algae stations), the measurements represent both pelagic bloom and non-bloom conditions and ice algal day and night production. The annual production in ice was estimated to 5.3 g Cm-2, compared to the pelagic production of 25 to 30 g Cm-2 south of Kvitøya and 12 to 15 g Cm-2 further north. According to these estimates ice production thus constitutes 16% to 22% of the total primary production of the northern Barents Sea, depending on the extent of ice-free areas.  相似文献   

20.
We examine quantitatively the ranges of applicability of the equation Ω= A+B [1− t/t f ] m for predicting 'system-sized' failure times t f in the Earth. In applications Ω is a proxy measure for strain or crack length, and A , B and the index m are model parameters determined by curve fitting. We consider constitutive rules derived from (a) Charles' law for subcritical crack growth; (b) Voight's equation; and (c) a simple percolation model, and show in each case that this equation holds only when m < 0. When m > 0, the general solution takes the form Ω = A + B [1 + t / T  ] m , where T   is a positive time constant, and no failure time can be defined. Reported values for volcanic precursors based on rate data are found to be within the range of applicability of time-to-failure analysis ( m < 0). The same applies to seismic moment release before earthquakes, at the expense of poor retrospective predictability of the time of the a posteriori -defined main shock. In contrast, reported values based on increasing cumulative Benioff strain occur in the region where a system-sized failure time cannot be defined ( m > 0; commonly m ≈ 0.3). We conclude on physical grounds that cumulative seismic moment is preferred as the most direct measure of seismic strain. If cumulative Benioff strain is to be retained on empirical grounds, then it is important that these data either be re-examined with the independent constraint m < 0, or that for the case 0 < m + 1 < 1, a specific correction for the time-integration of cumulative data be applied, of the form ΣΩ = At + B '{1 − [1 − t/t f ] m+1 }.  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