Solar Si XI Line Ratios Observed by the Normal Incidence Spectrometer on SOHO CDS

New measurements of line intensity ratios in the Be-like ion Si xi are presented for observations of the quiet Sun, active regions, coronal holes and above-limb regions obtained using the Coronal Diagnostic Spectrometer on the Solar and Heliospheric Observatory. A model ion, constructed using the best available atomic data, is used to predict the line intensity ratios for a wide range of electron temperatures and densities. Comparisons of the theoretical ratios with the new intensity ratios as well as with those from previous solar observations and laboratory measurements are given. The usefulness of the ratios for electron temperature and density diagnostics, as well as for spectrometer calibration, is discussed.     

Biologically induced mineralization of dypingite by cyanobacteria from an alkaline wetland near Atlin,British Columbia,Canada

Background  

This study provides experimental evidence for biologically induced precipitation of magnesium carbonates, specifically dypingite (Mg₅(CO₃)₄(OH)₂·5H₂O), by cyanobacteria from an alkaline wetland near Atlin, British Columbia. This wetland is part of a larger hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) playa. Abiotic and biotic processes for magnesium carbonate precipitation in this environment are compared.     

An Improved Mean-Gravity Model for GPS Hydrostatic Delay Calibration

The determination of global positioning system (GPS) heights with submillimeter accuracy needs proper correction of tropospheric delay. In this letter, the modeling of zenith hydrostatic delay (ZHD) was addressed, considering that wet delay must be treated separately. ZHD is traditionally estimated from Saastamoinen's formula using a mean-gravity model and surface pressure observations. The uncertainty in ZHD associated with the mean-gravity model is about 0.3 mm. An improved parametric model is derived here, which yields an uncertainty in the ZHD less than 0.1 mm when the surface altitude lies in the range of 0-9 km. A second parametric model is derived for higher altitudes (such as above radiosonde observations or atmospheric models). Both parametric models depend on latitude, height, and time variables. This dependence is due to the link between the mean gravity and temperature profiles between the surface and ~80-km altitude. The uncertainty in the parametric models due to short-term temporal variability of the temperature profiles is shown to produce an uncertainty in ZHD smaller than 0.1 mm     

Climatological aspects of convective parameters from the NCAR/NCEP reanalysis

Annual cycles of convectively important atmospheric parameters have been computed for a variety of from the National Center for Atmospheric Research (NCAR)/National Centers for Environmental Prediction (NCEP) global reanalysis, using 7 years of reanalysis data. Regions in the central United States show stronger seasonality in combinations of thermodynamic parameters than found elsewhere in North America or Europe. As a result, there is a period of time in spring and early summer when climatological mean conditions are supportive of severe thunderstorms.The annual cycles help in understanding the large-scale processes that lead to the combination of atmospheric ingredients necessary for strong convection. This, in turn, lays groundwork for possible changes in distribution of the environments associated with possible global climate change.     

Biogeochemical exploration for tungsten at Barrytown,New Zealand

Biogeochemical prospecting for tungsten was carried out at a mineralised area near Barrytown, New Zealand. The tungsten content of the ash of the shallow-rooted tree ferns Cyathea medullaris and Dicksonia squarrosa correlated well with the concentrations of this element in the soil. Sampling of these species therefore provides a possible method of detecting general soil anomalies and moreover is considerably faster than soil sampling under local conditions.Trend surface analysis of the concentrations of tungsten in the trunks of all species of common large evergreen trees sampled on belt transects, could be used to delineate extensions of known tungsten mineralisation in bedrock, and was to some extent superior to soil geochemistry in this respect.     

Petrogenesis of syenites at a rifted continental margin: origin,contamination and interaction of alkaline mafic and felsic magmas in the Astrophyllite Bay Complex,East Greenland

The Astrophyllite Bay Complex in East Greenland (part of the Palaeogene North Atlantic Igneous Province) consists of an alkaline diorite plug, with detached trachyandesitic pillows, surrounded by co-magmatic syenite that was emplaced into Archaean basement. The diorite intrusion has yielded a 47.11 ± 0.68 Ma Rb-Sr isochron age. Saw-cut profiles through pillow-syenite-gneiss sections have been taken to resolve close spatial elemental and isotopic (Sr-Nd-Hf-Pb-O) variations. The diorite and syenite formed from alkaline basaltic, mantle-derived, melts with complex histories of prolonged assimilation and fractional crystallisation. Each evolved to different extents in separate magma chambers during the establishment of new plumbing systems in the Kangerlussuaq area. The diorite is dominated by lower crustal, granulite facies contamination, whereas the syenite shows evidence for greater degrees of upper crustal amphibolite facies contamination, indicating stalling and fractionation of magmas at different levels within the crust. The syenite and diorite magmas were subsequently emplaced as separate pulses into the basement gneisses at Astrophyllite Bay giving rise to superimposed local contamination trends between pillow/syenite and syenite/gneiss, respectively.     

Organic carbon flow in the Ob, Yenisey Rivers and Kara Sea of the Arctic region

Stable carbon isotope and elemental C/N ratios of the organic fraction of a set of samples along a transect in the Ob and Yenisey Rivers into the Kara Sea in the Arctic were measured. Previously, the concentrations of 239,240Pu and 137Cs in these same samples had been determined. The coupled measurements were carried out to assess possible connectivity between organic carbon flow into the Kara Sea and transport of radioactive nuclides in this marine environment. Organic carbon flow into the Kara Sea is influenced significantly by terrigenous sources carried by the Ob and Yenisey Rivers. The carbon isotope-organic carbon relationship provides evidence that a rich source of terrigenous carbon exists in the riverine system. A weak, but significant relationship between stable carbon isotope ratio and 137Cs suggests that most of the 137Cs is derived from riverine particles, as compared to Pu which is also derived from in situ scavenging within the water column.     

Temporal Variability of Iron Speciation in Coastal Rainwater

Iron occurs in rain as particulateand dissolved Fe and includes both Fe(II) and Fe(III)species. Model calculations and correlation analysisindicate Fe(II)(aq) occurs almost exclusively as thefree ion whereas Fe(III)(aq) occurs as both ironoxalate and Fe(OH)₂ ⁺(aq) with largevariations over the pH range from 4.0 to 5.0. Complexation with humic-like compounds may also beimportant for Fe(III)(aq); however, the concentrationand structural characteristics of these compounds haveyet to be determined. 112 rain samples were collectedfor iron analysis in Wilmington, North Carolina,between 1 July 1997, and 30 June 1999. Total iron,particulate iron and Fe(III)(aq) were higher inconcentration in summer and spring rain relative towinter and autumn rain. Fe(II)(aq) concentrations, incontrast, did not vary seasonally. Particulate iron,which was approximately half the total rainwater iron,was highest between noon and 6 p.m. (EST), probably dueto more intense regional convection including land-seabreezes during that time. The ratio ofFe(II)(aq)/Fe(III)(aq) was also highest in rainreceived between noon and 6 p.m., which most likelyreflects photochemical reduction of Fe(III)(aq)complexes to form Fe(II)(aq). A conceptual modeldepicting the interplay between iron species, lightintensity and organic ligands in rainwater ispresented.     

The influence of lithology on surface water sources

Understanding the temporal and spatial variability of water sources within a basin is vital to our ability to interpret hydrologic controls on biogeochemical processes and to manage water resources. Water stable isotopes can be used as a tool to determine geographic and seasonal sources of water at the basin scale. Previous studies in the Coastal Range of Oregon reported that the variation in the isotopic signatures of surface water did not conform to the commonly observed “elevation effect,” which exhibits a trend of increasing isotopic depletion with rising elevation. The primary purpose of this research is to investigate the mechanisms governing seasonal and spatial variations in the isotopic signature of surface waters within the Marys River Basin, located in the leeward side of the Oregon Coastal Range. Surface water and precipitation samples were collected every 2–3 weeks for isotopic analysis for 1 year. Our results confirmed the lack of elevational variation of surface water isotopes within this leeward basin. Although we find elevational variation in precipitation in the eastern portion of the watershed, this elevation effect is counteracted by rainout with distance from the Pacific coast. In addition, we found significant variation in surface water isotope values between catchments underlain predominantly by basalt or sandstone. The degree of separation was strongest during the summer when low flows reflect deeper groundwater sources. This indicates that baseflow within streams drained by each lithology is being supplied from two distinctly separate water sources. In addition, the flow of the Marys River is dominated by water originating from the sandstone water source, particularly during the low‐flow summer months. We interpreted that the difference in water source results from sandstone catchments having highly fractured geology or locally tipping to the east facilitating cross‐basin water exchange from the windward to the leeward side of the Coast Range. Our results challenge topographic derived watershed boundaries in permeable sedimentary rocks; highlighting the overwhelming importance of underlying geology.