The relation between glacial ages and terrestrial magnetism

An attempt is made to show that the change of angular momentum of the earth, caused by glaciations, may compensate the slowing down effect from tidal friction forces and even reverse the polarity in the terrestrial magnetic field.     

Properties of debris flow deposits and source materials compared: implications for debris flow characterization

In the Alps, debris flow deposits generally contain <5% clay‐size particles, and the role of the surface‐charged <2 μm particles is often neglected, although these particles may have a significant impact on the rheological properties of the interstitial fluid. The objective of this study was to compare debris flow deposits and parent materials from two neighbouring catchments of the Swiss Alps, with special emphasis on the colloidal constituents. The catchments are small in area (4 km²), 2·5 km long, similar in morphology, but different in geology. The average slopes are 35–40%. The catchments were monitored for debris flow events and mapped for surface aspect and erosion activity. Debris flow deposits and parent materials were sampled, the clay and silt fractions extracted and the bulk density, <2 mm fraction bulk density, particle size distribution, chemical composition, cation exchange capacity (CEC) and mineralogy analysed. The results show that the deposits are similar to the parent screes in terms of chemical composition, but differ in terms of: (i) particle size distribution; and (ii) mineralogy, reactivity and density of the <2 mm fraction. In this fraction, compared with the parent materials the deposits show dense materials enriched in coarse monocrystalline particles, of which the smallest and more reactive particles were leached. The results suggest that deposit samples should not be considered as representative of source or flow materials, particularly with respect to their physical properties.     

Metamorphism in the Adirondacks: II. The Role of Fluids

Quantitative estimates of metamorphic fluid speciation, stableisotopic analyses, and studies of fluid inclusions all documentthe local complexity of fluids in the deep crustal rocks exposedin the Adirondack Mountains, NY. Estimates of the activity ofH₂O in the granulite facies are substantially lower than inthe amphibolite facies gneisses. The onset of low water activitiesin semi-pelitic gneisses generally correlates with migmatitictextures in the uppermost amphibolite facies, suggesting thatpartial melts absorbed H₂O at the peak of metamorphism. In granulitefacies marbles and calc-silicates, conditions varied from extremelyundersaturated in H₂O-CO₂ fluid to fluid saturated, and _H2Oand _CO2 show sharp gradients within single outcrops. Low valuesof f_O2 and f_H2O, or of f_CO2, and f_H2O indicate fluid-absentconditions for some orthogneisses and marbles, which are inferredto have been ‘dry’ rocks before and during granulitefacies recrystallization. Wollastonite is preserved from earlycontact metamorphism and serves as an index mineral for fluid-absentconditions in granulites where _H2O is low. Values off_O2 rangefrom near the hematite + magnetite buffer in metamorphosed ironformation to substantially below the quartz + magnetite + fayalitebuffer in some orthogneisses. The anorthosite suite is moreoxidized than some associated granitic gneisses. Halogens (Fand Cl) substitute extensively for OH in micas and amphiboles,extending their stability, although F₂, Cl₂, HCl, and HF areminor components in any fluid. Oxybiotite-type exchanges involvingO for OH are also important, extending the stability of biotite.Stable isotopic ratios of O and C demonstrate that premetamorphicwhole-rock compositions are commonly preserved whereas mineralcompositions generally reflect equilibration at the peak ofmetamorphism. The Marcy Anorthosite Massif was intruded as ahigh ¹⁸O magma. The combination of mineral equilibria, stable isotope data,and fluid inclusions is used to identify and to distinguishamong pre-orogenic contact metamorphic/hydrothermal events,peak metamorphic events, and retrograde/postmetamorphic events.Polymetamorphism is documented at skarn zones adjacent to anorthosite,where large volumes of hydrothermal fluid were channeled duringearly, shallow contact metamorphism and where conditions werefluid poor during subsequent regional metamorphism. Peak metamorphicevents are inferred to have been caused primarily by magmaticprocesses of intrusion and anatexis. Partial melting has causedlow values of _H2O in many rocks, but in other cases low valuesof _H2O are recorded in orthogneisses derived from H₂O-poor magmas.Isotopic studies show that maximum fluid/rock ratios were <0?land possibly 0?0 for infiltrating fluids at the peak of metamorphismin many localities. No evidence of pervasive, regional infiltrationby a fluid at the peak of metamorphism has been substantiatedin the Adirondacks. Fluid inclusions containing high-densityCO₂ or CO₂ + H₂O represent conditions from after the peak ofmetamorphism and document isobaric cooling, in agreement withestimates from garnet zoning. Fine-scale retrograde veins arecommon and are associated with high-density CO₂-rich fluid inclusions.     

Measurements of beach pebble attrition in Palliser Bay, southern North Island, New Zealand

The beaches of Palliser Bay, exposed to oceanic waves from the south, are composed of mixed sand and gravel derived from mountain ranges of greywacke and argillite that rise above both sides of the bay. Beach gravel tracer experiments, each using up to 75 tonnes of limestone pebbles, were conducted at three sites. Increase in the roundness of these tracer pebbles at each site during the year of observation was compared with the increase in roundness and rate of weight loss of limestone and greywacke pebbles in a laboratory tumbler. The comparison enabled estimation of the rate of attrition of the natural beach pebbles. A weight loss of 41% per year was found for pebbles at the most exposed site and 15 and 7% at the other two sites.     

Southern Ocean transformation in a coupled model with and without eddy mass fluxes

A coupled air–sea general circulation model is used to simulate the global circulation. Different parameterizations of lateral mixing in the ocean by eddies, horizontal, isopycnal, and isopycnal plus eddy advective flux, are compared from the perspective of water mass transformation in the Southern Ocean. The different mixing physics imply different buoyancy equilibria in the surface mixed layer, different transformations, and therefore a variety of meridional overturning streamfunctions. The coupled‐model approach avoids strong artificial water mass transformation associated with relaxation to prescribed mixed layer conditions. Instead, transformation results from the more physical non‐local, nonlinear interdependence of sea‐surface temperature, air–sea fluxes, and circulation in the model's atmosphere and ocean. The development of a stronger mid‐depth circulation cell and associated upwelling when eddy fluxes are present, is examined. The strength of overturning is diagnosed in density coordinates using the transformation framework.     

Editorial

Abstract

The analysis of geographical information is compared with other production processes in which a user can only accept an end-product if it meets certain quality requirements. Whereas users are responsible for defining the levels of quality they need to use the results of the analyses of geographical information systems in their work, database managers, experts and modellers could greatly assist users to achieve the quality of results they seek by formalizing information on: (1) data collection, level of resolution and quality; (2) the use of the basic analytical functions of the geographical information system; and (3) the data requirements, sensitivity and error propagation in models. These meta-data could be incorporated in a knowledge base alongside the geographical information system where, together with procedures for on-line error propagation, a user could be advised on the best way to achieve a desired aim. If the analysis showed that the original constellation of data, methods and models could not achieve the aim with the desired quality, the intelligent geographical information system would present a range of alternative strategies—better methods, more data, different data, better models, better model calibration, or better spatial resolution—and their costs by which the user's aims could reasonably be achieved.