Enigmatic Efflorescence in Kärkevagge, Swedish Lapland: The Key to Chemical Weathering?

The second marvel to catch the eye of the visitor to Kärkevagge, after the impressive boulder deposit on the floor of the valley, is the series of prominent white stripes running down the valley's dark cliffs. Streams and springs descending the eastern flank of Kärkevagge are marked by the presence of whitish coatings on the black rock surfaces and on cobbles lining ephemeral waterways. These were referred to as 'lime crusts' by early investigators, but they are not reactive to HCl. We believe that they are a precipitate resulting from acid attack on the local rocks. Pyrite is common in many of the rocks in the valley and its oxidation produces sulfuric acid. As the dissolved mineral elements are carried in the drainage water, efflorescence forms on the surfaces where the water flows due to evaporation or to changes in temperature. The exact mineralogy of the white crusts is unknown, but the crusts are dominated by Al, S, and O, and in some cases by Ca, depending on the substrate and local conditions. Gypsum, illite, and chlorite have been identified by X–ray diffraction of some scrapings of white–coated rocks. However, we believe that some unidentified oxy–hydroxy aluminum sulfates make up the bulk of the precipitates.     

Schorlomite: a discussion of the crystal chemistry, formula, and inter-species boundaries

Examination of schorlomite from ijolite at Magnet Cove (USA) and silicocarbonatite at Afrikanda (Russia), using electron-microprobe and hydrogen analyses, X-ray diffraction and Mössbauer spectroscopy, shows the complexity of substitution mechanisms operating in Ti-rich garnets. These substitutions involve incorporation of Na in the eightfold-coordinated X site, Fe²⁺ and Mg in the octahedrally coordinated Y site, and Fe³⁺, Al and Fe²⁺ in the tetrahedrally coordinated Z site. Substitutions Ti⁴⁺Fe³⁺Fe³⁺_–1Si_–1 and Ti⁴⁺Al³⁺Fe³⁺_–1Si_–1 are of major significance to the crystal chemistry of schorlomite, whereas Fe²⁺ enters the Z site in relatively minor quantities (<3% Fe). There is no evidence (either structural or indirect, such as discrepancies between the measured and calculated Fe²⁺ contents) for the presence of ^[6]Ti³⁺ or ^[4]Ti⁴⁺ in schorlomite. The simplified general formula of schorlomite can be written as Ca₃Ti⁴⁺₂[Si_3-x(Fe³⁺,Al,Fe²⁺)_xO₁₂], keeping in mind that the notion of end-member composition is inapplicable to this mineral. In the published analyses of schorlomite with low to moderate Zr contents, x ranges from 0.6 to 1.0, i.e. Ti⁴⁺ in the Y site is <2 and accompanied by appreciable amounts of lower-charged cations (in particular, Fe³⁺, Fe²⁺ and Mg). For classification purposes, the mole percentage of schorlomite can be determined as the amount of ^[6]Ti⁴⁺, balanced by substitutions in the Z site, relative to the total occupancy in the Y site: (^[6]Ti⁴⁺–^[6]Fe²⁺–^[6]Mg²⁺– ^[8]Na⁺)/2. In addition to the predominant schorlomite component, the crystals examined in this work contain significant (>15 mol.%) proportions of andradite (Ca₃Fe³⁺₂Si₃O₁₂), morimotoite (Ca₃Fe²⁺TiSi₃O₁₂), and Ca₃MgTiSi₃O₁₂. The importance of accurate quantitative determination and assignment of Fe, Ti and other cations to the crystallographic sites for petrogenetic studies is discussed.

The hard solar X-ray burst of 18 September 1963

A hard solar X-ray burst was observed by J-P. Legrand on 18 September 1963, 13:56 UT, at balloon altitude. It lasted a few minutes; a steep increase was followed by an exponential decay. During its declining phase a weak radio burst was observed on 3 and 10 cm, not on longer wavelengths.Maximum radio intensity occurred two minutes after that of the X-ray burst. The X-ray and radio bursts ended almost simultaneously. Optically a small shortlived (some minutes) flare point occurred simultaneously with the X-ray burst in a magnetically interesting part of the active region of September 1963. The X-burst photons seem to have had an energy of about 0.5 MeV. The burst was therefore of a fairly rare type, since very few other bursts with similar photon energies have been detected up to now.It is suggested that a mass of gas, magnetically confined to a volume of about 5·10²⁵ cm³ in the low corona, containing about 3·10³⁵ electrons was accelerated to energies of about 0.5 MeV. The gas gradually expanded, partly also to higher levels. The gyro-synchrotron radiation, emitted by the plasma became observable after about two minutes. At the lower radio frequencies the radiation was absorbed by overlying undisturbed coronal matter. Quantitative computations justify this model. A detailed summary of the events, and some numerical data are given in the concluding Section 8 and in Table V.     

Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs

Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs were characterized using ³²P as a nutrient tracer. Larrea tridentata's horizontal zone of influence was sparse near the plant's stem base, with a maximum probability of accessing ³²P (P_max) of 41%. However, its horizontal zone of influence extended beyond 5 m, and the distance from the stem base at which the probability of accessing ³²P was half P_max (L₅₀3 m) was significantly greater than the other three shrubs. Ambrosia dumosa's zone of influence was dense near the plant's stem base (P_max78%), but was rare at distances >2 m (L₅₀1 m). Zones of influence for Lycium andersonii and Lycium pallidum were intermediate between those of L. tridentata and A. dumosa. For vertical zones of influence, L. tridentata was more likely to obtain ³²P from 5 m soil depths than A. dumosa, but L. pallidum was not significantly different from either A. dumosa or L. tridentata. Horizontal zones of influence did not change with treatments that altered soil water and nitrogen availability, but vertical zones of influence increased with a flood irrigation treatment that increased water availability to 5 m soil depth. These differences among species likely reflect compromises between their shoot growth strategies and their need to acquire spatially and temporally limited soil resources, especially through competitive interactions.     

Heavy rare gases from Rabbit Lake (Canada) and the Oklo mine (Gabon): natural spontaneous chain reactions in old uranium deposits

Xenon isotopic studies confirm natural spontaneous chain reactions at the Oklo mine site (Republic of Gabon) with an integrated neutron flux of approximately 4 × 10²⁰n/cm² and a duration between 14,000 and 70,000 years. Similar studies for the Rabbit Lake deposit (Saskatchewan), a slightly younger site with some evidence of continued geologic activity, shows no evidence of self-supporting reactions.     

Understanding the surface hydrology of the Lake Eyre Basin: Part 1—Rainfall

This is the first of two papers that describe the surface hydrology of the Lake Eyre Basin (LEB) (1,140,000 km²) in central Australia and compares some key characteristics with those observed from arid regions globally. This paper concentrates on annual rainfall, whereas the second paper is devoted to streamflow. The first part describes the LEB's climate (arid to semi-arid), which is dominated by a subtropical high pressure ridge stretching latitudinally across central Australia. Then follow major analyses that include the characteristics of rainfall, wet and dry spell lengths and cumulative surpluses and deficiencies, rainfall trends and intra- and inter-decadal fluctuations, and the relationship between rainfall and El Niño-Southern Oscillation (ENSO). The paper concludes with six conclusions, the key ones being: the variability of the annual rainfall (based on the coefficient of variation) in the LEB is approximately 60% greater than that found for stations located in arid regions in the rest of the world; there is a bias towards longer lengths of dry years than observed in the rest of Australia; and, there is a significant lag correlation between rainfall and ENSO, particularly in the east and in the latter part of a year.