Very small waves and associated sediment resuspension on an estuarine intertidal flat

Field data from a microtidal estuarine intertidal flat (Tamaki estuary, New Zealand) are used to analyse very small waves (height <10 cm; period 1.0–1.8 s) and associated sediment resuspension under light winds. Mean spectral period at the bed varied over the tidal cycle, driven by changes in surface-wave spectrum and depth-attenuation of orbital motions. Wave-orbital currents exceeded 30 cm/s, disturbing the fine-sand (100–200 μm) matrix of the seabed and resulting in the release of fine silt (particle size <20 μm) at concentrations >120 mg/L. Resuspension was initiated when ∼40% of the maximum zero-downcrossing orbital speeds in a burst exceeded the critical speed for initiation of sediment motion. Sediment concentrations were highest around low tide, when waves were smaller compared to high tide because of a reduced fetch but depth-attenuation of orbital motions was less because the water was shallower. Wave period exerted a control on sediment resuspension through the wave friction factor. There was a hysteresis in the wave Reynolds number such that it was greater on the ebbing tide compared to on the flooding tide: since it did not exceed 3 × 10⁵ the bed was hydraulically smooth, and the wave friction factor therefore is inversely proportional to wave period. Hence, the tidal-cycle hysteresis in wave Reynolds number translated into a smaller wave friction factor on the ebbing tide, and accounting for this caused the ebb and flood sediment concentration data to collapse onto one curve when plotted against wave-induced skin friction. A simple model is presented to evaluate the relative contribution to sediment resuspension of waves associated with weak and strong winds. At the base of the flat (waves competent to resuspend sediment for 5% of the inundation time), waves associated with stronger, infrequent winds dominate resuspension. At the top of the flat (waves competent to resuspend sediment for 30% of the inundation time), waves associated with lighter, frequent winds dominate resuspension. Moderate winds – neither the strongest nor most frequently occurring – dominate resuspension integrated across the profile. The mass of sediment resuspended by waves is greatest towards the top of the flat: shoreward of this, resuspension is smaller because of wave dissipation; seaward of this, resuspension is smaller because of greater depth-attenuation of orbital motions. The location of maximum sediment mass resuspended by waves and the location of maximum duration of resuspension are not necessarily the same.     

Geodiversity,palaeodiversity or biodiversity: where is the place of palaeobiology and an understanding of taphonomy?

While some authors view biodiversity as an integral part of an over-arching geodiversity, most would see them as separate constructs. If that is the case, then the life–death interface marks the critical boundary between those that study organisms in life and the palaeontologists who try to interpret fossils in terms of their palaeobiology. The interface between life and the fossil record is characterised by the processes of taphonomy and, when fossils are collected, care must be taken to ensure that vital taphonomic information is not lost. This does not appear to be highlighted in the various fossil collecting codes and the avoidance of the loss of taphonomic information during collection should be a key feature of collecting policies and geoconservation in general.     

Water–Rock Interactions: An Investigation of the Relationships Between Mineralogy and Groundwater Composition and Flow in a Subtropical Basalt Aquifer

A holistic study of the composition of the basalt groundwaters of the Atherton Tablelands region in Queensland, Australia was undertaken to elucidate possible mechanisms for the evolution of these very low salinity, silica- and bicarbonate-rich groundwaters. It is proposed that aluminosilicate mineral weathering is the major contributing process to the overall composition of the basalt groundwaters. The groundwaters approach equilibrium with respect to the primary minerals with increasing pH and are mostly in equilibrium with the major secondary minerals (kaolinite and smectite), and other secondary phases such as goethite, hematite, and gibbsite, which are common accessory minerals in the Atherton basalts. The mineralogy of the basalt rocks, which has been examined using X-ray diffraction and whole rock geochemistry methods, supports the proposed model for the hydrogeochemical evolution of these groundwaters: precipitation + CO₂ (atmospheric + soil) + pyroxene + feldspars + olivine yields H₄SiO₄, HCO₃ ⁻, Mg²⁺, Na⁺, Ca²⁺ + kaolinite and smectite clays + amorphous or crystalline silica + accessory minerals (hematite, goethite, gibbsite, carbonates, zeolites, and pyrite). The variations in the mineralogical content of these basalts also provide insights into the controls on groundwater storage and movement in this aquifer system. The fresh and weathered vesicular basalts are considered to be important in terms of zones of groundwater occurrence, while the fractures in the massive basalt are important pathways for groundwater movement.     

Effects of multiple stressors on lakes in south-central Ontario: 15 years of change in lakewater chemistry and sedimentary diatom assemblages

Freshwater ecosystems are increasingly affected by human influences. Since the pre-industrial era, lakes of the Muskoka–Haliburton region of south-central Ontario have had increases in shoreline residential development and acid deposition. Previous research on 54 of these lakes, using sediment cores and diatom-based transfer functions, showed changes in lakewater pH and total phosphorus concentration between the preindustrial era and 1992. Since 1992, there has been further change, which we have documented for the same set of lakes, using similar methods. For example, dissolved organic carbon has increased and there have been significant increases in planktonic diatoms (e.g. Cyclotella stelligera) commonly associated with climate warming. More striking diatom changes have occurred in the past 15 years than between pre-industrial times and 1992. Significant changes observed in both chemical (e.g. pH, Ca, DOC) and biological data suggest that novel stressors, such as declines in lake calcium concentrations, acting in conjunction with climate and land-use change, have created ecosystems for which there are no historical analogs.     

Dating Quaternary volcanism and incision by the River Tigris at Diyarbakır,southeast Turkey

New high‐precision Ar‐Ar dating of basalt underlying the city of Diyarbak?r, southeast Turkey, constrains the Quaternary incision history of the River Tigris, strengthening the pre‐existing chronology based on magnetostratigraphy and K‐Ar dates. The basalt, which overlies Tigris terrace gravel 70 m above the river, is part of the Karacada? shield volcano complex centred ca. 60 km to the southwest. The reverse‐magnetised Diyarbak?r basalt, one of relatively few flow units to reach the Tigris valley axis, has been dated to 1196 ± 19 ka (±2σ). Two lower terraces have been recognised in the Diyarbak?r area, 46 and 32 m above the present river, with at least one other further downstream. From this evidence the rate of Middle‐Late Pleistocene incision by the Tigris can be estimated; it probably reached ca. 0.07 mm a^?1, reflecting the characteristic global increase in uplift rates observed at that time. Copyright © 2007 John Wiley & Sons, Ltd.     

Varying Constants, Nuclear Physics and Unification

Precision measurements of gauge couplings at particle accelerators strongly suggest that the standard model fields are unified at about 10¹⁶ GeV. This talk will consist of a brief review of this evidence and also how in such a setting variations in α _em lead to much larger variations in Λ _QCD . I will then describe how variations in the strong force will impact upon nuclear astrophysics, considering in particular the stability of di-nucleons and stellar and primordial nucleosynthesis. (Based upon collaborations with T. Dent and with A. Csoto, H. Oberhummer and H. Schlattl.) This revised version was published online in July 2006 with corrections to the Cover Date.     

Stratigraphic relationships of Cryogenian strata disconformably overlying the Bitter Springs Formation, northeastern Amadeus Basin, Central Australia

Detailed mapping and C and O stable isotopic data from sedimentary carbonate in units both above and below the paleo-erosion surface on the Bitter Springs Formation (BSF) in the northeastern Amadeus Basin, Australia, have clarified the stratigraphy of the area. Isotopic data indicate that the top of the Loves Creek Member of the Bitter Springs Formation is preserved near Corroboree Rock, and is overlain by fenestrate-carbonate-clast breccia, and dolomitic quartz sandstone and chert-pebble conglomerate of the Pioneer Sandstone. The isotopic data, as well as lithologic data, indicate the presence of a 1–2 m-thick cap carbonate preserved between Corroboree Rock and areas 10 km to the northeast. In many places the cap carbonate layer is mostly a syn-sedimentary dolomite-clast breccia, consistent with deposition and disturbance in shallow water. C and O isotopic data also indicate that thin-bedded sandstone and dolomite above the Bitter Springs Formation at Ellery Creek, and a newly discovered massive chert-bearing dolomite at Ross River could both belong to the glaciogenic Olympic Formation. Detailed mapping also provides a more detailed context for the famous black chert microfossil locality in the Bitter Springs Formation at Ross River.     

John Dewey’s metaphysical ground-map and its implications for geographical inquiry

John Dewey was the most significant and influential thinker associated with the American philosophy commonly known as pragmatism. Drawing on Dewey’s writings as well as the work of Deweyan scholars, I endeavor to explain Dewey’s unique contribution to philosophical discourse and how his overlooked scholarship can inform geographical inquiry. After an introduction, I provide a background understanding of Dewey and his context as well as the use of his philosophy in geography and sociology. I then turn to an exposition of Dewey’s metaphysics which are the heart of his philosophy. My discussion breaks his metaphysics into four parts: nature and continuity, contingency and change, situated sociality, and transaction. The subsequent section argues for Dewey’s distinction and value by arguing a particular implication of Dewey’s work for geography—a reconceptualization of place—and more general propositions about what a Dewey-informed geography would, at minimum, entail. A brief conclusion summarizes the Deweyan vision in the context of geographical inquiry.     

The Cold War and geography’s quantitative revolution: Some messy reflections on Barnes’ geographical underworld

A response to a recent paper by Barnes, arguing that the origins of geography’s quantitative revolution were not as monofocused as he suggests.     

Nanogeochemistry of hydrothermal magnetite

Magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million (ppm) of elements such as Ti, Si, V, Al, Ca, Mg, Na, which tend to either structurally incorporate into growth and sector zones or form mineral micro- to nano-sized particles. Here, we report micro- to nano-structural and chemical data of hydrothermal magnetite from the Los Colorados iron oxide–apatite deposit in Chile, where magnetite displays both types of trace element incorporation. Three generations of magnetites (X–Z) were identified with concentrations of minor and trace elements that vary significantly: SiO₂, from below detection limit (bdl) to 3.1 wt%; Al₂O₃, 0.3–2.3 wt%; CaO, bdl–0.9 wt%; MgO, 0.02–2.5 wt%; TiO₂, 0.1–0.4 wt%; MnO, 0.04–0.2 wt%; Na₂O, bdl–0.4 wt%; and K₂O, bdl–0.4 wt%. An exception is V₂O₃, which is remarkably constant, ranging from 0.3 to 0.4 wt%. Six types of crystalline nanoparticles (NPs) were identified by means of transmission electron microscopy in the trace element-rich zones, which are each a few micrometres wide: (1) diopside, (2) clinoenstatite; (3) amphibole, (4) mica, (5) ulvöspinel, and (6) Ti-rich magnetite. In addition, Al-rich nanodomains, which contain 2–3 wt% of Al, occur within a single crystal of magnetite. The accumulation of NPs in the trace element-rich zones suggest that they form owing to supersaturation from a hydrothermal fluid, followed by entrapment during continuous growth of the magnetite surface. It is also concluded that mineral NPs promote exsolution of new phases from the mineral host, otherwise preserved as structurally bound trace elements. The presence of abundant mineral NPs in magnetite points to a complex incorporation of trace elements during growth, and provides a cautionary note on the interpretation of micron-scale chemical data of magnetite.