The development of freshwater science in Britain, and British contributions abroad, 1900-2000

This article outlines the development of freshwater science between 1900 and 2000 and in particular traces British contributions, both to a deepened knowledge of specifics and to their interrelation as environmental and ecological science. The author provides a selected bibliography of important publications relevant to the topic of the article

Advisory report on nutrient levels and related ecology of Malham Tarn

Aspects of reported nutrient levels and their ecological implications for Malham Tarn are discussed. Discussion centres upon the data given here as appendices, involving possible evidence of a long-term increase in the concentrations of some nutrients (especially nitrate) of significance for the Tarn's ecology and conservation. Further comparative tests of some methods of chemical analysis employed in obtaining those data are reported

Africa: the FBA connection

Since its inception in the 1930's the Freshwater Biological Association at Windermere, England has been involved in research on African lakes and rivers. Research has included general and multidisciplinary surveys of many lakes including Lake Victoria, Lake Tanganyika, Lake Nyasa (Lake Malawi) and Lake George. The hydrobiology of the River Nile has also been studied. Research into physical and chemical limnology, phytoplankton ecology and primary productivity, invertebrate biology, freshwater fish and fisheries

Deformation mechanisms of Gum metal

Gum metal (Ti-36Nb-2Ta-3Zr-0.3O) is a recently developed multifunctional bcc titanium (p Ti) alloy that exhibits high strength (> 1 GPa), high ductility (>10%) and high yield strain (~2.5%). In addition, this alloy possesses the invar and elinvar properties, and is highly cold workable. The encouraging mechanical properties and workability of Gum metal mean that it is a candidate material in a range of applications, from biomedical implants to aerospace and military applications. The deformation mechanisms of Gum metal have previously been reported to involve ideal shear. The rational for this suggestion is that Gum metal was designed on first principles, such that the value of the shear modulus (C') assumes a very low value. This implies that the ideal shear stress is comparable to the actual strength, such that deformation can proceed via ideal shear. Furthermore, the observation of ‘giant shear steps’ in transmission electron microscopy (TEM), whose orientation does not correspond to any bcc slip or twin systems is considered to be consistent with this hypothesis. However, the existence of a deformation mechanism involving ideal shear is against metallurgical wisdom. Many other titanium alloys of similar composition are also known to exhibit a low C. However, these alloys deform via a stress induced superelastic martensitic transformation. Therefore the aim of this work is to improve our understanding of the micromechanisms of this alloy. The single crystal elastic constants (C¡¡) of Gum metal were acquired with the aid of in- situ synchrotron X-ray diffraction (SXRD) and an Eshelby-Kroner-Kneer self consistent model. The results showed that although C is low in this alloy, the ideal shear strength (>2 GPa) is still above the material’s tensile strength, implying deformation cannot occur via ideal shear. Furthermore, analysis of the SXRD spectra during cyclic loading suggests that Gum metal undergoes a stress-induced superelastic martensitic (a") transformation. The SXRD results were complemented with TEM characterisation, which showed the presence of the a" phase, and the © phase, which exhibited a plate-like morphology. In addition, deformation twins of the type {1 12} were identified. Structures similar to the giant shear steps were observed and their formation is believed to be due to a" variants nucleating from co plates or twin boundaries. The effect of processing route and chemical composition on the deformation mechanisms and mechanical properties of Gum metal were also investigated. A more cost effective processing route involving ingot metallurgy was trialled and the mechanical properties were comparable to the alloys produced via powder metallurgy. Oxygen was found to suppress the amount of transformation strain in Gum metal (by increasing C'); and hence the majority of the observed superelastic strain was due to the low Young’s modulus and high yield strain of the p phase. However, oxygen increased the stress for permanent deformation, thus allowing more stable superelasticity. Prior deformation (extrusion or cold rolling) was found to increase the amount of transformation strain. This was considered to be a result of mechanical working providing nucleation sites, such as the co phase and twins, from which, the a" phase was able to nucleate. The amount of transformation strain could be increased through control of specimen texture. The specimens produced via the ingot metallurgy processing route, involving casting and extrusion were found to exhibit the greatest transformation strain

Implications of reduced turbidity current and landslide activity for the Initial Eocene Thermal Maximum - evidence from two distal, deep-water sites

Previous studies propose that submarine landslides and turbidity currents may become more likely due to future rapid global warming. Determining whether global warming increases likelihood assists in assessment of landslide-triggered tsunami hazards and risk to seafloor structures. Other studies propose that landslides helped to trigger past rapid climate change due to sudden release of gas hydrates. Two deep-water turbidite records show prolonged hiatuses in turbidity current activity during the Initial Eocene Thermal Maximum (IETM) at ∼55 Ma. The IETM represents a possible proxy for future anthropogenically-induced climate change. It is likely that our records mainly represent large and fast moving disintegrative submarine landslides. Statistical analysis of long term (>2.3 Myr) records shows that turbidity current frequency significantly decreased after the IETM. Our results indicate that rapid climate change does not necessarily cause increased turbidity current activity, and do not provide evidence for landslides as a primary trigger for the IETM

Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?

Subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet, and it is important to understand how they are linked offshore from river mouths. Previously, it was thought that slope failures or direct plunging of river floodwater (hyperpycnal flow) dominated the triggering of turbidity currents on delta fronts. Here we reanalyze the most detailed time‐lapse monitoring yet of a submerged delta; comprising 93 surveys of the Squamish Delta in British Columbia, Canada. We show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes, rather than landslides or hyperpycnal flows. Turbidity currents triggered by settling plumes occur frequently, run out as far as landslide‐triggered events, and cause the greatest changes to delta and lobe morphology. For the first time, we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

Preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord-head delta

Rivers and turbidity currents are the two most important sediment transport processes by volume on Earth. Various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths, including direct plunging of river discharge, delta mouth bar flushing or slope failure caused by low tides and gas expansion, earthquakes and rapid sedimentation. During 2011, 106 turbidity currents were monitored at Squamish Delta, British Columbia. This enables statistical analysis of timing, frequency and triggers. The largest peaks in river discharge did not create hyperpycnal flows. Instead, delayed delta-lip failures occurred 8–11 h after flood peaks, due to cumulative delta top sedimentation and tidally-induced pore pressure changes. Elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water. Elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta-lip, which is the most significant of all controls on flow timing in this setting

Hybrid event beds dominated by transitional-flow facies: character, distribution and significance in the Maastrichtian Springar Formation, north-west Vøring Basin, Norwegian Sea

Hybrid event beds comprising clay-poor and clay-rich sandstone are abundant in Maastrichtian-aged sandstones of the Springar Formation in the north-west Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction in total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay-poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay-poor sandstone (non-stratified or stratified) overlain by banded sandstone, with clay-rich non-stratified sandstone at the bed top. The dominant type of clay-poor sandstone at the base of these beds varies spatially; non-stratified sandstone is thickest and most common proximally, whereas stratified sandstone becomes dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non-cohesive at the front, through a region of transitional behaviour (fluctuating non-cohesive and cohesive flow), to cohesive behaviour at the rear. Spatial variation in the dominant type of clay-poor sandstone at the bed base suggests that the front of the flow remained non-cohesive, and evolved from high-concentration and turbulence-suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fallout. This research may be applicable to other hybrid event bed prone systems, and emphasizes the dynamic nature of hybrid flows