Malathion induced biochemical alterations in the liver of the fingerlings of Channa punctatus (BL.)

The effect of a sublethal concentration of malathion (95% E. C.) on the nucleic acids (DNA, RNA) and protein content in the liver of fingerlings of Channa punctatus, a freshwater murrel was investigated. 10 days of exposure brought non-significant alteration (P < 0.05) neither in the nucleic acids nor in protein content. However, significant quantitative decline in the liver's RNA (P < 0.01) and protein (P < 0.001) but not in the DNA content was observed after 20 days of exposure. Possible causes for such decline have been discussed.     

Survivality and Impaired Growth in Arsenic Treated Fingerlings of Channa punctatus,a Fresh Water Murrel

The LC₅₀-values of As³⁺-compounds for Channa punctatus are determined for a 48-h exposure to 19.4 (18.02… 21.3) mg/1 and for a 96-h exposure to 14.3 (13.06… 16.80) mg/1. At a long-time exposure to 7.0 mg/1 As³⁺, during the first seven days there does not occur any change of growth, then the growth in length and the increase in weight decreased by 6.6 and 11.7%, respectively, till the 31st day. At the same time, the RNA content of the muscle decreased by 11.5% to 966.7 μg/g fresh weight and the protein content decreased by 12.5 % to 95.39 mg/g fresh weight.     

The effect of long-term aerial exposure on intertidal mudflat erodibility

Intertidal zones by definition are exposed to air at low tide, and the exposure duration can be weeks (e.g. during neap tides) depending on water level and bed elevation. Here we investigated the effect of varying exposure duration (6 h to 10 days) on intertidal mudflat erosion (measured using the EROMES device), where the effects of water content and biofilm biomass (using chlorophyll-a content as a proxy, Chl-a μg g⁻¹) were taken into account. Sediments were collected between spring and summer (in October 2018, January 2019 and February 2019) from an intertidal site in the Firth of Thames, New Zealand. Longer exposure duration resulted in more stable sediments [higher erosion threshold (Ƭ_cr, N m⁻²) and lower erosion rate (ER, g m⁻² s⁻¹)]. After 10 days, exposure increased Ƭ_cr by 1.7 to 4.4 times and decreased ER by 11.6 to 21.5 times compared with 6 h of exposure. Chl-a and water content changed with exposure duration and were significantly correlated with changes in Ƭ_cr and ER. The stability of sediments after two re-submersion periods following exposure was also examined and showed that the stabilizing effect of exposure persisted even though water content had increased to non-exposure levels. Re-submersion was associated with an increase in Chl-a content, which likely counteracted the destabilizing influence of increased water content. A site-specific model, which included the interplay between evaporation and biofilm biomass, was developed to predict water content as a function of exposure duration. The modelled water content (W_Mod.) explained 98% of the observed variation in water content (W_Obs.). These results highlight how the exposure period can cause subtle changes to erosion regimes of sediments. An understanding of these effects (e.g. in sediment transport modelling) is critical to predicting the resilience of intertidal zones into the future, when sea-level rise is believed to exacerbate erosion in low-lying areas. © 2020 John Wiley & Sons, Ltd.     

微囊藻群体总RNA提取方法的比较

微囊藻群体富含多糖类物质是影响微囊藻RNA提取的关键因素.为了获得高质量的微囊藻群体总RNA,对比分析4种针对多糖含量较高的方法——方法 1 PGTX-bead法、方法 2 CTAB-bead法、方法 3 Fast RNAPro Blue Kit和方法 4RNeasy Mini Kit对微囊藻群体总RNA的提取效果.采用琼脂糖凝胶电泳检测微囊藻群体RNA的完整性,Nanodrop ND1000分光光度计检测RNA纯度及浓度,并采用q PCR检测DNA污染情况.结果表明,4种方法都能从微囊藻群体中提取获得RNA,并在去除DNA后都可以进行RT-PCR等后续实验.方法 1 PGTX-bead提取的RNA产量最高,纯度好,DNA污染小,成本低,适合从微囊藻群体中大量提取RNA;方法 2 CTAB-bead提取的RNA样品产量也较高,但DNA污染严重,适合需要同时提取DNA和RNA的样本;方法 3 Fast RNAPro Blue Kit和方法 4 RNeasy Mini Kit提取的RNA产量都较低,但方法 4操作简单,耗时短,所检测目的基因的相对表达量较高,更适合从少量的微囊藻群体中提取总RNA.     

The summertime 12-h wind oscillation with zonal wavenumber s = 1 in the lower thermosphere over the South Pole

Meteor radar measurements of winds near 95 km in four azimuth directions from the geographic South Pole are analyzed to reveal characteristics of the 12-h oscillation with zonal wavenumber one (s = 1). The wind measurements are confined to the periods from 19 January 1995 through 26 January 1996 and from 21 November 1996 through 27 January 1997. The 12-h s = 1 oscillation is found to be a predominantly summertime phenomenon, and is replaced in winter by a spectrum of oscillations with periods between 6 and 11.5 h. Both summers are characterized by minimum amplitudes (5–10 ms^–1) during early January and maxima (15–20 ms^–1) in November and late January. For 10-day means of the 12-h oscillation, smooth evolutions of phase of order 4–6 h occur during the course of the summer. In addition, there is considerable day-to-day variability (±5–10 ms^–1 in amplitude) with distinct periods (i.e., 5 days and 8 days) which suggests modulation by planetary-scale disturbances. A comparison of climatological data from Scott Base, Molodezhnaya, and Mawson stations suggests that the 12-h oscillation near 78°S is s = 1, but that at 68°S there is probably a mixture between s = 1 and other zonal wavenumber oscillations (most probably s = 2). The mechanism responsible for the existence of the 12-h s = 1 oscillation has not yet been identified. Possible origins discussed herein include in situ excitation, nonlinear interaction between the migrating semidiurnal tide and a stationary s = 1 feature, and thermal excitation in the troposphere.     

Variation of Antioxidant System in Pinus armandii under Elevated O3 in an Entire Growth Season

Impact of elevated O₃ (80 nmol mol^?1) was studied on antioxidant system in the previous‐year needles (P‐needles) of Pinus armandii under the background of global climate change. CAT (catalase) did not play an important role in defensing O₃ pollution, as no significant change was observed in its activity in P‐needles exposed to elevated O₃ during the entire growth season. Ascorbate (AsA) was more sensitive to elevated O₃, as the O₃‐induced decrease in its content was observed at Day 45. It suggests that AsA consumption was a crucial way for protecting against O₃ pollution. After 75 days of O₃ exposure, increase in superoxide dismutase and ascorbate peroxidase activities occurred in P‐needles (p < 0.05), whereas glutathione reductase activity was significantly increased after 105 days of O₃ treatment (p < 0.05). Dehydroascorbate reductase and monoascorbate reductase activities also increased after 75 days of elevated O₃ exposure. However, the elevated antioxidant capability did not suppress the generation of reactive oxygen species, and as a result, increase in malondialdehyde content was noted (p < 0.05). Noticeably, no change was observed in electrolyte leakage during the entire growth season under elevated O₃ fumigation. It indicates that O₃‐induced oxidative stress was not severe in the needles of P. armandii. In other words, P. armandii has certain tolerance to O₃ pollution.     

Treatment of anchor pixels in the METRIC model for improved estimation of sensible and latent heat fluxes

Abstract

Reliable estimation of sensible heat flux (H) is important in energy balance models for quantifying evapotranspiration (ET). This study was conducted to evaluate the value of adding the Priestley-Taylor (PT) equation to the METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. METRIC was used to estimate energy fluxes for 10 Landsat images from the 2005, 2006 and 2007 crop growing seasons in south-central Nebraska, USA, where each image owing to recent rainfall exhibited high residual moisture content even at the hot pixel. The METRIC model performed satisfactorily for net radiation (R_n ) and soil heat flux (G) estimation with a root mean square error (RMSE) of 52 and 24 W m^-2, respectively. A RMSE of 122 W m^-2 for H indicated the limitation of the METRIC model in estimating H for high residual moisture content of the hot pixel (Alfalfa reference ET fraction, ET _r F > 0.15). The modified METRIC model (wet METRIC or wMETRIC) incorporating the PT equation was applied to calculate H at the anchor pixels (hot and cold) for high residual moisture content of the hot pixel. The α coefficient of the PT equation was locally calibrated using hourly meteorological data from an automatic weather station and R_n and G data from a Bowen ratio flux tower. The mean α coefficient value was 1.14. The wMETRIC model reduced the RMSE of H from 122 to 64 W m^-2 and that of latent heat flux, LE, from 163 to 106 W m^-2. The RMSE of daily ET decreased from 1.7 to 1.1 mm d^-1 with wMETRIC. The results indicate that treatment of anchor pixels for high residual moisture content with the PT approach gives improved estimation of H, LE and daily ET. It is recommended that the wMETRIC model be used for estimating ET if the hot pixel has high residual moisture (i.e. reference ET fraction > 0.15).

Citation Singh, R. K. & Irmak, A. (2011) Treatment of anchor pixels in the METRIC model for improved estimation of sensible and latent heat fluxes. Hydrol. Sci. J. 56(5), 895–906.     

Planktonic algae and epiphyton of the littoral in lake Peipsi, Estonia

The littoral plankton of Lake Peipsi (3555 km², mean depth 7.1 m) was studied in summer 1980 and 2000–2002, and the epiphyton was studied on two dominating macrophytes, Phragmites australis (Cav.) Trin. ex Steud. and Potamogeton perfoliatus L., in 2000. The purpose of the study was to estimate to what extent the littoral phytoplankton and epiphytic algae (their biomass, chlorophyll a content and dominant species) can be used as a criterion for the trophic state of the lake. In wind-open areas, phytoplankton biomass in the littoral is commonly more than ten times higher than in open water due to the presence of the macroscopic cyanobacterium Gloeotrichia echinulata (J.S. Smith) P. Richter. This alga is abundant in the moderately eutrophic northern lake's part and rare in the strongly eutrophic southern part; hence also biomass in the southern part is considerably lower. In open water, phytoplankton biomass increases southward with increasing trophy. Algal biomass in the littoral depends on wind direction and can change completely in a few days. Epiphyton biomass and Chla content increased southward with increasing trophic state. They both revealed significant Spearman correlations (P < 0.05) with wind index and transparency (negative), and with abundance of the host plant, both reed and pondweed (positive). The phytoplankton biomass of the littoral of the large and shallow Lake Peipsi can not be used as a criterion of trophic state, however, the species composition of the dominants, particularly cyanobacteria, is well applicable for this purpose. The biomass and Chla content of the epiphyton can be used as a criterion for trophic state.     

Estimation of tree water stress from stem and soil water monitoring with time‐domain reflectometry in two small forested basins in Spain

Soil‐tree water relationships were studied using time domain reflectometry (TDR) in two small forested basins in Spain. The stem water content of two Mediterranean Quercus species (Quercus pyrenaica and Quercus rotundifolia) was measured using previously constructed species‐specific equations. To monitor soil moisture, a TDR station network was used in both cases. Sixteen Q. pyrenaica and six Q. rotundifolia individuals were selected to install two TDR probes in their trunks (at 20 and 120 cm above the ground) to monitor stem water content. Stem and soil water contents were measured fortnightly. The stem water content of both species showed a similar temporal trend for the period studied. A spring maximum (0·654 cm³ cm^?3 for Q. pyrenaica and 0·568 cm³ cm^?3 for Q. rotundifolia) was found to be associated with high transpiration and no soil moisture deficit, and a late‐summer minimum (0·520 cm³ cm^?3 for Q. pyrenaica and 0·426 cm³ cm^?3 for Q. rotundifolia) was associated with the end of the dry season. This drop in stem water content occurs when the available water in the soil decreases. This seasonal difference presumably reflects water withdrawn from stem storage to support the transpirational demands of the tree. Since plant water stress results in reduced stem water content and since this drop can be measured by TDR, it may be concluded that this technology offers a suitable tool for detecting plant water stress. Copyright © 2007 John Wiley & Sons, Ltd.     

The role of wavegroup velocity in the blocking problem

Considering the blocking problem as a baroclinic instability problem in a dispersive wave system with diabatic heating effects, it is of great interest to investigate the role of wavegroup velocityv _gr in blocking processes, becausev _gr controls the energy transfer in the wave field. Using a Newtonian Cooling —type of forcing with a phase differencek to the main field and taking the linearized version of a two-level model, the phase speedc _r, the group velocityv _gr and the growth ratekc _i have been obtained as analytical functions of the mean zonal windU, the thermal windU _T, the coefficient of diabatic heating x, the phase differencek and the wavelengthL. Now the hypothesis is introduced, that a blocking should be expected, ifv _gr has a maximum value in the vicinity ofL _o, for whichc _r vanishes and thee-folding timet=1/kc _i (kc _i>0) is smaller than 6 days (see condition (20) in the text). One finds, that for special parameter combinations (U _T, U, ), where 15 m/secU _T25m/sec,U=10m/sec, 0.8·10^–51.5·10^–5 [sec^–1], certain valuesL _o with an appropriate phase differencek exist, which satisfy the conditions mentioned above (for values see Table 2). TherebyL _o varies within the range 8500 km <L _o<11000 km corresponding to the preferred planetary blocking wavenumber 2 in middle latitudes 50°<<70° N.     

Structure and evolution of the terrestrial planets

Geo-scientific planetary research of the last 25 years has revealed the global structure and evolution of the terrestrial planets Moon, Mercury, Venus and Mars. The evolution of the terrestrial bodies involves a differentiation into heavy metallic cores, Fe-and Mg-rich silicate mantles and light Ca, Al-rich silicate crusts early in the history of the solar system. Magnetic measurements yield a weak dipole field for Mercury, a very weak field (and local anomalies) for the Moon and no measurable field for Venus and mars. Seismic studies of the Moon show a crust-mantle boundary at an average depth of 60 km for the front side, P- and S-wave velocities around 8 respectively 4.5 km s^–1 in the mantle and a considerable S-wave attenuation below a depth of 1000 km. Satellite gravity permits the study of lateral density variations in the lithosphere. Additional contributions come from photogeology, orbital particle, x-and -ray measurements, radar and petrology.The cratered surfaces of the smaller bodies Moon and Mercury have been mainly shaped by meteorite impacts followed by a period of volcanic flows into the impact basins until about 3×10⁹ yr before present. Mars in addition shows a more developed surface. Its northern half is dominated by subsidence and younger volcanic flows. It even shows a graben system (rift) in the equatorial region. Large channels and relics of permafrost attest the role of water for the erosional history. Venus, the most developed body except Earth, shows many indications of volcanism, grabens (rifts) and at least at northern latitudes collisional belts, i.e. mountain ranges, suggesting a limited plate tectonic process with a possible shallow subduction.List of Symbols and Abbreviations a=R _e mean equatorial radius (km) - A(r, t) heat production by radioactive elements (W m^–3) - A, B equatorial moments of inertia - b polar radius (km) - complex amplitude of bathymetry in the wave number (K) domain (m) - C polar moment of inertia - C _Fe moment of inertia of metallic core - C _Si moment of inertia of silicate mantle - C _p heat capacity at constant pressure (JK^–1 mole^–) - C _nm,J _nm,S _nm harmonic coefficients of degreen and orderm - C/(MR _e ² ) factor of moment of inertia - d distance (km) - d nondimensional radius of disc load of elastic bending model - D diameter of crater (km) - D flexural rigidity (dyn cm) - E Young modulus (dyn cm^–2) - E maximum strain energy - E energy loss during time interval t - f frequency (Hz) - f flattening - F magnetic field strength (Oe) (1 Oe=79.58A m^–1) - g acceleration or gravity (cms^–2) or (mGal) (1mGal=10^–3cms^–2) - mean acceleration - g _e equatorial surface gravity - complex amplitude of gravity anomaly in the wave number (K) domain - g free air gravity anomaly (FAA) - g Bouguer gravity anomaly - g _t gravity attraction of the topography - G gravitational constant,G=6.67×10^–11 m³kg^–1s^–2 - GM planetocentric gravitational constant - h relation of centrifugal acceleration (² R _e ) to surface acceleration (g _e ) at the equator - J magnetic flux density (magnetic field) (T) (1T=10⁹ nT=10⁹ =10⁴G (Gauss)) - J ₂ oblateness - J _nm seeC _nm - k ₍₀₎ (zero) pressure bulk modulus (Pa) (Pascal, 1 Pa=1 Nm^–2) - K wave number (km^–1) - K ^* thermal conductivity (Jm^–1s^–1K^–1) - L thickness of elastic lithosphere (km) - M mas of planet (kg) - M _Fe mass of metallic core - M _Si mass of silicate mantle - M(r) fractional mass of planet with fractional radiusr - m magnetic dipole moment (Am²) (1Am²=10³Gcm³) - m _b body wave magnitude - N crater frequency (km^–2) - N(D) cumulative number of cumulative frequency of craters with diameters D - P pressure (Pa) (1Pa=1Nm^–2=10^–5 bar) - P _z vertical (lithostatic) stress, see also _z (Pa) - P _n ^m (cos) Legendre polynomial - q surface load (dyn cm^–2) - Q seismic quality factor, 2E/E - Q _s ,Q _p seismic quality factor derived from seismic S-and P-waves - R=R ₀ mean radius of the planet (km) (2a+b)/3 - R _e =a mean equatorial radius of the planet - r distance from the center of the planet (fractional radius) - r _Fe radius of metallic core - S _nm seeC _nm - t time and age in a (years), d (days), h (hours), min (minutes), s (seconds) - T mean crustal thickness from Airy isostatic gravity models (km) - T temperature (°C or K) (0°C=273.15K) - T _m solidus temperature - T sideral period of rotation in d (days), h (hours), min (minutes), s (seconds), =2/T - U external potential field of gravity of a planet - V volume of planet - V _p ,V _s compressional (P), shear (S) wave velocity, respectively (kms^–1) - w deflection of lithosphere from elastic bending models (km) - z, Z depth (km) - z (K) admittance function (mGal m^–1) - thermal expansion (°C^–1) - viscosity (poise) (1 poise=1gcm^–1s^–1) - co-latitude (90°-) - longitude - Poisson ratio - density (g cm^–3) - mean density - ₀ zero pressure density - _m , _Si average density of silicate mantle (fluid interior) - average density of metallic core - _t , _top density of the topography - density difference between crustal and mantle material - electrical conductivity (^–1 m^–1) - _r , radial and azimuthal surface stress of axisymmetric load (Pa) - _z vertical (lithostatic) stress (seeP _z ) - _II second invariant of stress deviation tensor - latitude - angular velocity of a planet (=2/T) - ages in years (a), generally 0 years is present - B.P. before present - FAA Free Air Gravity Anomaly (see g - HFT High Frequency Teleseismic event - LTP Lunar Transient Phenomenon - LOS Line-Of-Sight - NRM Natural Remanent Magnetization Contribution No. 309, Institut für Geophysik der Universität, Kiel, F.R.G.     

Fractal approach of the temporal earthquake distribution in the Hellenic arc-trench system

The time clustering of earthquakes occurring in the Hellenic arc-trench system is quantitatively analyzed by means of the fractal dimension,D, of their time distribution in the time intervals of 1950–1985 (M _s >-4.5) and 1964–1985 (M _s 4.0). The results obtained imply that scale-invariant clustering holds over very large scale lengths of time,T, with 2²–2⁸T (in min) 2²⁰–2²², depending on the seismotectonic segment considered. In all segments a common feature is the relation between theD ₁,D ₂ andD ₃-values found for shallow, intermediate-depth and all-depth shocks, respectively:D ₃>D₁>D₂. TheD-values found for shallow shocks range between 0.137 and 0.191 with the exception of the Ionian Islands and Cretan segments where anomalously high values (D=0.221–0.251) have been determined. We discuss possible seismotectonic interpretations of the results.     

Energy flux partitioning and evapotranspiration in a sub‐alpine spruce forest ecosystem

In this study, we examined the year 2011 characteristics of energy flux partitioning and evapotranspiration of a sub‐alpine spruce forest underlain by permafrost on the Qinghai–Tibet Plateau (QPT). Energy balance closure on a half‐hourly basis was H + λE = 0.81 × (R_n ? G ? S) + 3.48 (W m^?2) (r² = 0.83, n = 14938), where H, λE, R_n, G and S are the sensible heat, latent heat, net radiation, soil heat and air‐column heat storage fluxes, respectively. Maximum H was higher than maximum λE, and H dominated the energy budget at midday during the whole year, even in summer time. However, the rainfall events significantly affected energy flux partitioning and evapotranspiration. The mean value of evaporative fraction (Λ = λE/(λE + H)) during the growth period on zero precipitation days and non‐zero precipitation days was 0.40 and 0.61, respectively. The mean daily evapotranspiration of this sub‐alpine forest during summer time was 2.56 mm day^?1. The annual evapotranspiration and sublimation was 417 ± 8 mm year^?1, which was very similar to the annual precipitation of 428 mm. Sublimation accounted for 7.1% (30 ± 2 mm year^?1) of annual evapotranspiration and sublimation, indicating that the sublimation is not negligible in the annual water balance in sub‐alpine forests on the QPT. The low values of the Priestley–Taylor coefficient (α) and the very low value of the decoupling coefficient (Ω) during most of the growing season suggested low soil water content and conservative water loss in this sub‐alpine forest. Copyright © 2013 John Wiley & Sons, Ltd.     

A model of the Phlegraean Fields magma chamber in the last 10,500 years

Volcanological and petrological data suggest that the Phlegraean Fields volcanic activity has been fed, at least in the last 10,500 years, by a not-refilled magma chamber where trachytic residual liquids were produced by fractionation of a trachybasaltic magma. Using estimated volumes of the erupted products andP–T data obtained through petrological studies, a conductive thermal model of the chamber was built up in order to estimate its past and present size. Results suggest a volume decrease from approximately 14 to 1.4 km³ of the trachybasaltic magma in 10,500 years. Trachytic liquid would also be present in the chamber in a minimum amount of 0.4 km³. The model allowed some insights on the petrogenesis of the Phlegraean trachytes, suggesting that they were erupted as liquids because thermally buffered within the magma chamber.     

The effect of the number of charges carried by the argon ion on the darkening of ilford Q2 emulsion as ion detectors in mass-spectrometer

Summary The darkening (S) of Illford Q₂ photographic plates as ion detectors in mass spectrometer has been investigated. The dependence of the darkening (S) on the ion density (n=ions/mm²) i.e.S=S(n)E for constant energy (E)=z U ranging from 4U20 Kv of the impinging⁴⁰A⁺¹-,⁴⁰A⁺²- and⁴⁰A⁺³-ions whenS does not exceed the value 0.15 and the second relationn=n(z U) _S for darkening 0.05S0.15 constructed from the above relationS=S(n) _E has been determined. The darkening was found to increase with increasing ion-density which inturn decreases with the ionenergy. For⁴⁰A⁺¹-,⁴⁰A⁺²-, and⁴⁰A⁺³-ion of equal energy and ion-density the darkening effect was independent of the number of the charges carried by the argon ion.     

Amendment of Copper Toxicity in Alluvial Soil Using Iron: Effect on Growth and Yield of Triticum aestivum L.

Pot experiments were conducted in glasshouse under controlled conditions. The effect of copper in alluvial soil on the growth and yield of Triticum aestivum L. (wheat) was worked out. Copper was applied in soil at 5–100 mg L^?1, along with iron supplement. Inhibitory response of copper was significant (p < 0.05) confirmed by the plant growth parameters viz., plant height, fresh and dry weight, moisture content, pigment contents, protein, sugar contents followed by increased catalase and peroxidase activity in the harvest at 30, 60, and 90 days, of treatment, respectively. The plants grown on copper treated soil along with 5 mg L^?1 Cu and iron application showed significant effects (p < 0.05) regarding the increase in plant biomass, plant height (shoot only), pigment contents, protein, sugar contents, grain yield followed by decreased catalase and peroxidase activity in wheat after 30, 60, and 90 days of treatment, respectively. The accumulation of metal in plant tissues was found in order of Fe > Cu coupled by less translocation in grain as compared to the whole plant.     

Meridional Turner angles and density compensation in the upper ocean

The World Ocean Atlas 1998 is used to determine the global field of the meridional density ratio R ^hy =T/S, where temperature and salinity changes T and S are evaluated along meridians, in and below the mixed layer. The focus of the analysis is the identification of regions where the R ^hy field matches the values R =2 sometimes suggested as the commonly perceived state of the ocean and R =1, the condition of density compensation. Results are presented through fields of the meridional Turner angle Tu ^hy =arctan(R ^hy ) and through histograms of Tu ^hy for the Pacific, Atlantic and Indian Oceans at the ocean surface and at 300 m depth. At the 300-m depth level, which in the subtropics is representative of conditions in the permanent thermocline, the most frequently encountered values of the meridional density ratio are R ^hy =3.2 in the North and South Pacific, R ^hy =2.0 in the South Atlantic and Indian and R ^hy =1.6 in the North Atlantic Ocean. Conditions in the mixed layer are more variable and show seasonal differences, but R ^hy =2.0 occurs prominently in all ocean regions during winter and in all regions but the Atlantic during summer. Summer values for the Atlantic Ocean are R ^hy =3.2 in the Northern Hemisphere and R ^hy =2.4 in the Southern Hemisphere. Detailed analysis of R ^hy across the Subtropical Front (STF) confirms the most frequently observed values but shows zonal variation along the front in some oceans. Nearly complete density compensation (R ^hy =1) in the mixed layer is encountered in the STF of the eastern North Pacific, the eastern South Pacific and the eastern Indian Ocean. The eastern Indian Ocean south of Australia is also the only region where complete density compensation in the STF occurs below the mixed layer.Responsible Editor: Neville Smith AcknowledgementWe thank Dan Rudnick for helpful comments and discussion during the preparation of this paper.     

Uncertainties in field-line tracing in the magnetosphere. Part II: the complete internal geomagnetic field

The discussion in the preceding paper is restricted to the uncertainties in magnetic-field-iine tracing in the magnetosphere resulting from published standard errors in the spherical harmonic coefficients that define the axisymmetric part of the internal geomagnetic field (i.e. g_n⁰ ± g_n⁰). Numerical estimates of these uncertainties based on an analytic equation for axisymmetric field lines are in excellent agreement with independent computational estimates based on stepwise numerical integration along magnetic field lines. This comparison confirms the accuracy of the computer program used in the present paper to estimate the uncertainties in magnetic-field-line tracing that arise from published standard errors in the full set of spherical harmonic coefficients, which define the complete (non-axisymmetric) internal geomagnetic field (i.e. g_n^m ± g_n^m and h_n^m ± h_n^m). An algorithm is formulated that greatly reduces the computing time required to estimate these uncertainties in magnetic-field-line tracing. The validity of this algorithm is checked numerically for both the axisymmetric part of the internal geomagnetic field in the general case (1 n 10) and the complete internal geomagnetic field in a restrictive case (0 m n, 1 n 3). On this basis it is assumed that the algorithm can be used with confidence in those cases for which the computing time would otherwise be prohibitively long. For the complete internal geomagnetic field, the maximum characteristic uncertainty in the geocentric distance of a field line that crosses the geomagnetic equator at a nominal dipolar distance of 2 R_E is typically 100 km. The corresponding characteristic uncertainty for a field line that crosses the geomagnetic equator at a nominal dipolar distance of 6 R_E is typically 500 km. Histograms and scatter plots showing the characteristic uncertainties associated with magnetic-field-line tracing in the magnetosphere are presented for a range of illustrative examples. Finally, estimates are given for the maximum uncertainties in the locations of the conjugate points of selected geophysical observatories. Numerical estimates of the uncertainties in magnetic-field-line tracing in the magnetosphere, including the associated uncertainties in thelocations of the conjugate points of geophysical observatories, should be regarded as first approximations in the sense that these estimates are only as accurate as the published standard errors in the full set of spherical harmomic coefficients. As in the preceding paper, howerver, all computational techniques developed in this paper can be used to derive more realistic estimates of the uncertainties in magnetic-field-line tracing in the magnetosphere, following further progress in the determination of more accurate standard errors in the spherical harmonic coefficients.Also Visiting Reader in Physics, University of Sussex, Palmer, Brighton, BN1 9QH, UK     

Effect of Single Species or Mixed Algal (Chlorella vulgaris and Scenedesmus acutus) Diets on the Life Table Demography of Brachionus calyciflorus and Brachionus patulus (Rotifera: Brachionidae)

We tested the effect of two algal diets (Chlorella vulgaris at 1 · 10⁶ cells mL^?1and Scenedesmus acutus at 0.57 · 10⁶ cells mL^?1) offered alone or in combination (50 % each, 75 % or 25 % of either alga), at a total dry weight of 14.2 μg mL^?1on the life table demography of two rotifer species, Brachionus calyciflorus and Brachionus patulus. Data on fecundity indicated that, for any given algal food type or combination of food types, B. calyciflorus had a higher rate of offspring production than B. patulus. Regardless of the rotifer species, the average lifespan varied from 4 to 6 days. The gross and net reproductive rates were higher for B. calyciflorus than for B. patulus. These values ranged from 45 to 71 offspring female^?1 lifespan^?1 and 15 to 24 offspring female^?1 lifespan^?1, respectively, for B. calyciflorus. Generation times (around 4…5 days) were similar for both rotifer species in most of the treatments. Whatever the algal food combination, the rate of population increase (d^?1) of B. patulus was less than half (i.e. 45 %) of that for B. calyciflorus. The observed differences in the life history variables of Brachionus probably explain species‐specific adaptations to the changing phytoplankton composition occurring seasonally in natural waterbodies.