Is silt the most influential soil grain size fraction?

The contribution of individual grain size fractions (2000–500, 500–250, 250–63, 63–2 and < 2 μm) to bulk soil surface area and reactivity is discussed with reference to mineralogical and oxalate and dithionite extractions data. The 63–2 μm fraction contributed up to 56% and 67% of bulk soil volume and BET surface area, respectively. Consideration of these observations and the mineralogy of this fraction suggest that the 63–2 μm fraction may be the most influential for the release of elements via mineral dissolution in the bulk soil.     

Drainage evolution in south and east England during the Pleistocene

Two major river systems operated in southern and eastern England throughout the Pleistocene: the river Thames and the Solent river. Both rivers are axial streams of comparable size draining major basinal structures comprising similar Tertiary and Mesozoic rocks. Although the modem Thames flows broadly W-E in the London Basin, upstream of Reading it flows from the north to drain the south Midlands. It was diverted to its present course through London by glaciation in the Anglian (Elsterian) before which it flowed across East Anglia into the southem North Sea. The Solent river no longer exists since most of its course was drowned by eustatic sea-level rise during the Flandrian Stage (Holocene). Previously, it flowed eastwards across SE Dorset and S Hampshire as an extension of the modem river Frome in the Hampshire Basin. During periods of low sea-level (cold stages) it was a tributary of the 'Channel River'. Fluvial aggradations provide evidence of the former courses of these substantial rivers and their tributaries. The facies and sedimentary structures indicate that the bulk of the deposits in both systems accumulated in braided river environments under periglacial climates. Fossiliferous sediments provide biostratigraphical frameworks. During temperate periods the rivers adopted singlethread courses. Evolution of both rivers reflect their responses to climatic change, local geological structure and long-term tectonic activity. Both rivers are undoubtedly of considerable antiquity, their records potentially extend from the Early Pleistocene or Late Pliocene, but they may have originated in the early Tertiary.     

Polar wander on Triton and Pluto due to volatile migration

Polar wander may occur on Triton and Pluto because of volatile migration. Triton, with its low obliquity, can theoretically sublimate volatiles (mostly nitrogen) at the rate of ∼10¹³ kg year⁻¹ from the equatorial regions and deposit them at the poles. Assuming Triton to be rigid on the sublimation timescale, after ∼10⁵ years the polar caps would become large enough to cancel the rotational flattening, with a total mass equivalent to a global layer ∼120-250 m in depth. At this point the pole wanders about the tidal bulge axis, which is the line joining Triton and Neptune. Rotation about the bulge axis might be expected to disturb the leading side/trailing side cratering statistics. Because no such disturbance is observed, it may be that Triton’s surface volatile inventory is too low to permit wander. On the other hand, its mantle viscosity might be low, so that any uncompensated cap load might be expected to wander toward the tidal bulge axis. In this case, the axis of wander passes through the equator from the leading side to the trailing side; rotation about this wander axis would not disturb the cratering statistics. Low-viscosity polar wander may explain the bright southern hemisphere: this is the pole which is wandering toward the sub-Neptune point. In any case the “permanent” polar caps may be geologically very young. Polar wander may possibly take place on Pluto, due to its obliquity oscillations and perihelion-pole geometry. However, Pluto is probably not experiencing any wander at present. The Sun has been shining strongly on the poles over the last half of the obliquity cycle, so that volatiles should migrate to the equator, stabilizing the planet against wander. Spacecraft missions to Triton and Pluto which measure the dynamical flattening could give information about the accumulation of volatiles at the poles. Such information is best obtained by measuring gravity and topography from orbiters, as was done for Mars with the highly successful Mars Global Surveyor.     

Knowledge gaps in our perceptual model of Great Britain's hydrology

There is a no lack of significant open questions in the field of hydrology. How will hydrological connectivity between freshwater bodies be altered by future human alterations to the hydrological cycle? Where does water go when it rains? Or what is the future space–time variability of flood and drought events? However, the answers to these questions will vary with location due to the specific and often poorly understood local boundary conditions and system properties that control the functional behaviour of a catchment or any other hydrologic control volume. We suggest that an open, shared and evolving perceptual model of a region's hydrology is critical to tailor our science questions, as it would be for any other study domain from the plot to the continental scale. In this opinion piece, we begin to discuss the elements of and point out some knowledge gaps in the perceptual model of the terrestrial water cycle of Great Britain. We discuss six major knowledge gaps and propose four key ways to reduce them. While the specific knowledge gaps in our perceptual model do not necessarily transfer to other places, we believe that the development of such perceptual models should be at the core of the debate for all hydrologic communities, and we encourage others to have a similar debate for their hydrologic domain.     

Extragalactic integral field spectroscopy on the Gemini telescopes

We have been undertaking a programme on the Gemini 8‐m telescopes to demonstrate the power of integral field spectroscopy, using the optical GMOS spectrograph, and the new CIRPASS instrument in the near‐infrared. Here we present some preliminary results from 3D spectroscopy of extra‐galactic objects, mapping the emission lines in a 3CR radio galaxy and in a gravitationally lensed arc, exploring dark matter sub‐structure through observations of an Einstein Cross gravitational lens, and the star formation time‐scales of young massive clusters in the starburst galaxy NGC 1140. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nickel sulphide fire assay for the collection of the platinum group elements and gold from chromitites using reduced bead size

Summary Fire assay is a classical method for the separation of the platinum group elements and gold (PGE + Au). In nickel sulphide fire assay nickel and sulphur are used for the preconcentration of PGE + Au. In the past the authors have successfully reduced the weight of the collectors used without affecting the recovery of the elements from silicate material and eliminated the reagent blank problem. In this work the authors have applied the small bead size to chromitites. Chromitites can be difficult to fuse, and the authors have applied their modified technique to improve the dissolution of chromitites. This paper describes the application of the reduced bead size to the preconcentration of the PGE + Au from chromitites, by using only 0.5 g of nickel compared to the 10 g used by other fire assay workers.

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Nickelsulfid Fire assay zur Anreicherung von Platingruppenelementen und Gold aus Chromititen

Zusammenfassung Fire assay ist die klassische Methode um Platingruppenelemente und Gold (PGE + Au) vor der Analyse anzureichern und von der Matrix abzutrennen. Zum Sammeln der PGE und Au wird Nickelsulfid verwendet. Durch Verwendung möglichst kleiner Mengen konnte das Problem eventueller Verunreinigung der verwendeten Reagenzien ausgeschaltet werden. In der vorliegenden Arbeit wird diese Methode bei Chromititen angewendet, wobei hier ein modifiziertes Verfahren zum Lösen dieser Gesteine verwen det wird. Es werden 0.5 g Nickel zum Abtrennen der PGE und Au von Chromititen verwendet, was einer 20-fachen Mengenreduktion des Kollektormaterials gegenüber herkömmlichen Methoden entspricht.