Complexing capacity of the nutrient medium and its relation to inhibition of algal photosynthesis by copper

The toxic effect of copper on phytoplankton production is investigated in waters having different complexing capacities. It is demonstrated that a water’s complexing capacity does not guarantee that an equivalent amount of copper could be tolerated without adversely affecting algal production. Possible explanations for these findings are offered and discussed. It is deduced that ionic copper probably is already toxic to planktonic algae at concentrations of about 10^?10 mole/l.     

État actuel des données sur l'âge de la terre

Sans résumé     

Analyzing ice dynamics using Sentinel-1 data at the Solheimajoküll Glacier,Iceland

ABSTRACT

The climate in southern Iceland has warmed over the last 70 years, resulting in accelerated glacier dynamics at the Solheimajoküll glacier. In this study, we compare glacier terminus locations from 1973 to 2018, to changes in climate across the study area, and we derive ice-surface velocities (2015–2018) from satellite remote-sensing imagery (Sentinel-1) using the offset-tracking method. There have been two regional temperature trends in the study period: cooling (1973–1979) and warming (1980–2018). Our results indicate a time lag of about 20 years between the onset of glacier retreat (?53 m/year since 2000) and the inception of the warming period. Seasonally, the velocity time series suggest acceleration during the summer melt season since 2016, whereas glacier velocities during accumulation months were constant. The highest velocities were observed at high elevations where the ice-surface slope is the steepest. We tested several scenarios to assess the hydrological time response to glacier accelerations, with the highest correlations being found between one and 30 days after the velocity estimates. Monthly correlation analyses indicated inter-annual and intra-annual variability in the glacier dynamics. Additionally, we investigate the linkage between glacier velocities and meltwater outflow parameters as they provide useful information about internal processes in the glacier. Velocity estimates positively correlate with water level and negatively correlate with water conductivity between April and August. There is also a disruption in the correlation trend between water conductivity and ice velocity in June, potentially due to a seasonal release of geothermal water.     

The magnetic properties of solar surges

High resolution on- and off-band Hα filtergrams of disk solar surges obtained with the Vacuum Tower Telescope of the Sacramento Peak Observatory have been compared to magnetic data.

1. Surges constitute clusters of very fine dark (sometimes bright) filaments where each thread connects to an Ellerman bomb brightening. If the magnetic map reveals the existence of a satellite polarity as defined by Rust (1968), the bomb(s) lies over it.
2. Although a large fraction of surges is not associated with clearly detectable satellite polarities, events are strongly favored in regions of evolving magnetic features, characterized by dimensions of about 10 000 km and significant flux change over a period of less than a day. A flux change rate of 3 × 10¹⁵ Mx s^?1 has been measured along at least three homologous bomb-surge events in a satellite of region MW 18594. Surges appear to be related to rising flux of one polarity into a region of stronger opposite flux.
3. The trajectories of surges are matched by magnetic lines of force computed in the current-free approximation.

     

A paleoenvironmental reconstruction of Laguna Babícora, Chihuahua, Mexico based on ostracode paleoecology and trace element shell chemistry

Paleoecology of Laguna Babícora, Chihuahua, Mexico was reconstructed using ostracode faunal assemblages and shell chemistry. The paleolimnological record is used to show the magnitude of paleoclimatic changes in the area from 25,000 years to the present.Faunal assemblages consist of four species of the genus Limnocythere: L. sappaensis, L. ceriotuberosa, L. bradburyi and L. platyforma, all associated with Candona caudata, Candona patzcuaro and Cypridopsis vidua. A paleosalinity index developed from these assemblages indicates that the lake's salinity fluctuated frequently from oligo- to meso-haline conditions during the last 25,000 years. This pattern and low salinity range are in good agreement with modern TDS (here used as an indicator of salinity) values recorded from 26 wells and one spring from the area (258–975 mg l^–1). To estimate paleotemperature we examined the trace element content (Mg/Ca ratios) from individual valves of L. ceriotuberosa and L. platyforma, the two species most commonly recorded in Laguna Babícora.Shell Mg/Ca ratios of 204 specimens of these two species were used to estimate water temperature (Mg/Ca) by means of experimental standard coefficients. Our data show that paleowater temperature ranged from 5.6–21.3 °C (with 2 values ranging from 0.2–4.8 °C), which suggest a close correlation with atmospheric temperatures around the lake. These results are in good agreement with a modern mean winter temperature (3.5 °C) and mean summer temperature (20 °C) recorded in the area between 1970 and 1980.     

Discovery of High Proper-Motion Ancient White Dwarfs: Nearby Massive Compact Halo Objects?

We present the discovery and spectroscopic identification of two very high proper-motion ancient white dwarf stars, found in a systematic proper-motion survey. Their kinematics and apparent magnitude clearly indicate that they are halo members, while their optical spectra are almost identical to the recently identified cool halo white dwarf WD 0346+246. Canonical stellar halo models predict a white dwarf volume density that is 2 orders of magnitude less than the rho approximately 7x10-4 M middle dot in circle pc-3 inferred from this survey. With the caveat that the sample size is very small, it appears that a significant fraction, approximately 10%, of the local dark matter halo is in the form of very old, cool, white dwarfs.     

Size Fractionation (Dissolved, Colloidal and Particulate) of Trace Metals in the Thur River, Switzerland

The distribution of some trace metals (Cu, Zn, Ni, Co,Fe, Mn) and of DOC over a particulate (> 1 m),a colloidal (size < 0.45 m and molecular weight > 10 kD) and an ultrafiltered fraction (< 10 kD)was determined at several sites on the Thur River,Switzerland, at various times of the year. Thecomplexation of Cu by strong ligands in theultrafiltrate and in the conventional filtrate (<0.45 m) was compared using a ligand-exchange/CSV method.The <0.45 m concentrations of Cu (from anaverage of 7 nM to 24 nM), Zn (<5–23 nM), Ni (5–13 nM),Co (1.5–3 nM) and Mn (7–92 nM)increased downstream. The major part of Cu, Zn, Niand Co usually occurred in the ultrafiltratefraction at all sites, whereas Fe and Mn were mostlyin the particulate fraction, under conditions of lowsuspended matter content (< 10 mg L^-1) in theriver. The percentage of metal in the colloidalfraction, with respect to the 0.45-m filtrate,decreased in the order: Cu (median 11%) > Zn Ni(median 5–6%) > Mn Co (median < 5%). DOCalso consisted mostly of molecules in the < 10 kDrange.Cu was strongly complexed by natural organic ligandsin all filtrate and ultrafiltrate samples. A largepart of the strong Cu binding ligands consisted ofcompounds in the < 10 kD range, but colloidalligands with similar properties also occurred. Cu wasdistributed among the dissolved and the colloidalligands, roughly in proportion to organic carbon.The colloidal fraction (as defined here) did notincrease in its proportional amount downstream and wasonly of limited significance in transporting traceelements in the Thur River under low discharge conditions.     

Seasonal fluctuations in the deep central equatorial Atlantic Ocean: a data–model comparison

Low-frequency current fluctuations in the deep central equatorial Atlantic are analyzed using current meter measurements recorded from November 1992 to November 1994. Current meters were located at about 14°W of longitude and 1° of latitude on both sides of the equator between 1,700 m depth and the ocean bottom. At all sampling depths, the velocity fluctuations are dominantly zonal and symmetrical with respect to the equator. At 1,700 and 2,000 m, the flow is dominated by annual period fluctuations, at 3,000 m, the velocity field amplitude presents a minimum, and at 3,750 and 3,950 m, the flow is modulated by annual and semiannual period variability. The annual signal exhibits an apparent upward phase propagation. When considering the phase and the amplitude of the seasonal fluctuations, the data compare well with the outputs of a realistic numerical simulation of the Atlantic Ocean. Together with a previous analysis of the model simulations, this supports the idea that the observed annual fluctuations are due to wind-forced vertically propagating Kelvin and Rossby waves. Data and model do not provide deciding evidences of the presence of semiannual equatorial waves deeper than 3,500 m depth in the central equatorial Atlantic Ocean.     

Bioenergy potentials from forestry in 2050

The purpose of this study was to evaluate the global energy production potential of woody biomass from forestry for the year 2050 using a bottom-up analysis of key factors. Woody biomass from forestry was defined as all of the aboveground woody biomass of trees, including all products made from woody biomass. This includes the harvesting, processing and use of woody biomass. The projection was performed by comparing the future demand with the future supply of wood, based on existing databases, scenarios, and outlook studies. Specific attention was paid to the impact of the underlying factors that determine this potential and to the gaps and uncertainties in our current knowledge. Key variables included the demand for industrial roundwood and woodfuel, the plantation establishment rates, and the various theoretical, technical, economical, and ecological limitations related to the supply of wood from forests. Forests, as defined in this study, exclude forest plantations. Key uncertainties were the supply of wood from trees outside forests, the future rates of deforestation, the consumption of woodfuel, and the theoretical, technical, economical, or ecological wood production potentials of the forests. Based on a medium demand and medium plantation scenario, the global theoretical potential of the surplus wood supply (i.e., after the demand for woodfuel and industrial roundwood is met) in 2050 was calculated to be 6.1 Gm³ (71 EJ) and the technical potential to be 5.5 Gm³ (64 EJ). In practice, economical considerations further reduced the surplus wood supply from forests to 1.3 Gm³ year⁻¹ (15 EJ year⁻¹). When ecological criteria were also included, the demand for woodfuel and industrial roundwood exceeded the supply by 0.7 Gm³ year⁻¹ (8 EJ year⁻¹). The bioenergy potential from logging and processing residues and waste was estimated to be equivalent to 2.4 Gm³ year⁻¹ (28 EJ year⁻¹) wood, based on a medium demand scenario. These results indicate that forests can, in theory, become a major source of bioenergy, and that the use of this bioenergy can, in theory, be realized without endangering the supply of industrial roundwood and woodfuel and without further deforestation. Regional shortages in the supply of industrial roundwood and woodfuel can, however, occur in some regions, e.g., South Asia and the Middle East and North Africa.     

Concentration profiles of particles settling in the neutral and stratified atmospheric boundary layer

An expression for the vertical equilibrium concentration profile of heavy particles, including the effects of canopy on the eddy diffusivity as well as corrections for atmospheric stability, is proposed. This expression is validated against measurements of vertical concentration profiles of corn pollen above a corn field. The fitted theoretical profiles show that particle settling is correctly accounted for. The sensitivity to variations in the turbulent Schmidt number, settling velocity and stability corrections are explicitly characterized. The importance of independent measurements of the surface flux of pollen in future experiments is noted.