An overview of climatic variability and its causal mechanisms

A variance spectrum of climatic variability is presented that spans all time scales of variability from about one hour (10⁻⁴ years) to the age of the Earth (4 × 10⁹ years). An interpretive overview of the spectrum is offered in which a distinction is made between sources of variability that arise through stochastic mechanisms internal to the climatic system (atmosphere-ocean-cryosphere) and those that arise through forcing of the system from the outside. All identifiable mechanisms, both internal and external, are briefly defined and clarified as to their essential nature. It is concluded that most features of the spectrum of climatic variability can be given tentatively reasonable interpretations, whereas some features (in particular the quasi-biennial oscillation and the neoglacial cycle of the Holocene) remain fundamentally unexplained. The overall spectrum suggests the existence of a modest degree of deterministic forms of climatic change, but sufficient nonsystematic variability to place significant constraints both on the extent to which climate can be predicted, and on the extent to which significant events in the paleoclimatic record can ever manage to be assigned specific causes.     

Silt- and Bioclastic-Rich Flocs and Their Relationship to Sedimentary Structures: Modern Observations from the Petitcodiac River Estuary

Fine-grained sediment deposition is often conceived to happen in still water conditions and to represent slow sedimentation rates. However, it has been increasingly noted that mud sedimentation commonly occurs under high-energy conditions. The macrotidal Petitcodiac River estuary is used as an example to investigate the significance of flocculation as an important process in the rapid removal of large amounts of sediments from suspension under turbulent flow conditions. A range of physical sedimentary structures was observed at the Petitcodiac River estuary intertidal flats and bars, including low-angle and horizontal planar lamination, current and climbing ripples, surficial fluid mud, soft-sediment deformation, microfaults, and mud rip-up clasts. Fluid mud within the study area contains considerable proportions of clay (21–67%) and contributes to the formation of creeping fluid-mud sheets and streams. Detailed examination of the naturally occurring clay flocs shows that they contain up to 77% of the entangled silt- and sand-sized grains. SEM and microscopic imaging of fluid mud reveal a substantial amount of bioclastic material within the flocs and dispersed among the sediments. These observations show that physicochemical and biological processes influence silt, plankton, and clay aggregation. Water samples and observations from the Petitcodiac River estuary confirm that flocs form in the water column and then settle to the tidal-channel floor and flanking intertidal flats. Laboratory experiments, using Petitcodiac sediment, show how the clay flocs have the potential to sweep the water of silt-sized suspended grains. Additionally, diatoms and their associated extracellular polymeric substance (EPS) sheaths might play a role in mineral aggregation and increased sediment cohesiveness.     

Lower and Middle Ordovician conodonts of Laurentian affinity from blocks of limestone in the Rosroe Formation,South Mayo Trough,western Ireland and their palaeogeographic implication

The Middle Ordovician Rosroe Formation consists of some 1350 m of coarse, mainly siliciclastic to volcaniclastic sedimentary rocks, deposited in a submarine fan environment, and is restricted to the southern limb of the South Mayo Trough, western Ireland. Discrete allochthonous blocks, reaching 5 m in size, are present in the formation at several localities. Conodonts recovered from these blocks, collected from two separate locations, are of late Early and mid Mid Ordovician age. The conodonts have high conodont‐alteration indices (CAI 5) indicative of temperatures as high as 300^o to max. 480 °C; some found in the Lough Nafooey area have abnormally high indices (CAI 6), which correspond to temperatures of about 360^o to max. 550 °C. The oldest fauna is dominated by Periodon aff. aculeatus and characterized by Oepikodus evae typical of the Oepikodus evae Zone (Floian Stage; Stage Slices Fl2–3, Lower Ordovician). The younger conodont assemblage, characterized by Periodon macrodentatus associated with Oistodella pulchra, is referred to the P. macrodentatus conodont Biozone (lower Darriwilian; Stage Slices Dw1–2). The Rosroe conodont assemblages are of Laurentian affinity; comparable faunas are well known from several locations along the east to south‐eastern platform margin of Laurentia and the Notre Dame subzone of central Newfoundland, Canada. The faunal composition from the limestone blocks suggests a shelf edge to slope (or fringing carbonate) setting. The faunal assemblages are coeval with, respectively, the Tourmakeady Formation (Floian–Dapingian) and Srah Formation (Darriwilian) in the Tourmakeady Volcanic Group in the eastern part of the South Mayo Trough and probably are derived from the same or similar laterally equivalent short‐lived carbonate successions that accumulated at offshore ‘peri‐Laurentian’ islands, close to and along the Laurentian margin. During collapse of the carbonate system in the late Mid Ordovician, the blocks were transported down a steep slope and into deep‐water by debris flows, mixing with other rock types now found in the coarse polymict clastics of the Rosroe Formation. The faunas fill the stratigraphical ‘gap’ between the Lower Ordovician Lough Nafooey Volcanic Group and the upper Middle Ordovician Rosroe Formation in the South Mayo Trough and represent a brief interval conducive to carbonate accumulation in an otherwise siliciclastic‐ and volcaniclastic‐dominated sedimentary environment. Copyright © 2015 John Wiley & Sons, Ltd.     

Youth empowerment and information and communication technologies: a case study of a remote Australian Aboriginal community

In spite of a ‘digital divide’, Aboriginal groups in Australia, as internationally, are increasingly using information and communication technologies (ICTs) to maintain their cultures, communicate, archive knowledge, empower their communities, develop skills and generate income. Each community uses the technologies differently in accordance with their particular needs and the opportunities available. The use of ICTs in Aboriginal youth empowerment is illustrated through a case study of an initiative undertaken by the Walkatjurra Cultural Centre in Leonora, remote Western Australia. A participatory process was used to engage the Centre’s young people and they were given individual assistance to develop their ICT related capacity. The community conceives this youth empowerment to be part of a broader youth participation process that will contribute to the Centre’s overall objectives.     

Development and Testing of a Field Screening Method Based on Bubbling Extraction and Photoionization Detection for Measurement of Benzene and Total VOCs

A field screening method was developed for rapid measurement of benzene and gasoline range total petroleum hydrocarbons (TPHg) concentrations in groundwater. The method is based on collecting photoionization detector (PID) measurements from vapor samples. The vapor samples are collected by bubbling air through groundwater samples (air sparging) with a constant volume, temperature and sparging rate. The level of accuracy, sensitivity, precision, and statistical significance of the estimated concentrations, derived from the screening method, are comparable to conventional laboratory analytical results at concentrations equal to or greater than 150 µg/L for benzene and greater than 50 µg/L for TPHg. The method's concentration estimations can assist in making real‐time decisions regarding location of dissolved plumes and light nonaqueous phase liquid (LNAPL) source zones at many fuel release sites. The screening method was tested in the laboratory and in the field with 208 and 107 samples, respectively. The study concludes that the screening method can be used as a tool to aid in completing a site conceptual model as well as analyzing groundwater from monitoring wells.     

Recent shifts in coastline change and shoreline stabilization linked to storm climate change

Since cuspate coastlines are especially sensitive to changes in wave climate, they serve as potential indicators of initial responses to changing wave conditions. Previous work demonstrates that Cape Hatteras and Cape Lookout, North Carolina, which are largely unaffected by shoreline stabilization efforts, have become increasingly asymmetric over the past 30 years, consistent with model predictions for coastline response to increases in Atlantic Ocean summer wave heights and resulting changes in the distribution of wave‐approach angles. Historic and recent shoreline change observations for Cape Fear, North Carolina, and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment, produce comparable differences in shoreline change rates in response to changes in wave climate. Results suggest that the effect of beach nourishment is to compensate for – and therefore to mask – natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone. Therefore, this case study suggests that the effects of wave climate change on human‐modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities. Similar analyses of cuspate features in areas where the change in wave climate is less pronounced (i.e. Fishing Point, Maryland/Virginia) and where local geology appears to exert control on coastline shape (i.e. Cape Canaveral, Florida), suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave‐dominated coastlines where the change in wave climate has been most pronounced. However, if hurricane‐generated wave heights continue to increase, large‐scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger‐scale coastline shape comes into equilibrium with changing wave conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

The termination of the last major phase of aeolian sand movement,coastal dunefields,Denmark

Optically stimulated luminescence (OSL) dating of sand samples from stabilized (or inactive) coastal dunes in Denmark provides information on the age of the termination phase of the last major aeolian activity period. A total of 26 sand samples were taken from four different coastal dunefields around the North Sea, Skagerrak and Kattegat coasts of Denmark. The OSL dates indicate that the last major phase of aeolian activity terminated between ad 1860 and 1905. Most of the dunes examined in this study were active around 1820, during a period documented to have been very stormy. A dune management scheme started around 1792, and this no doubt was a major cause of dunefield stabilization, but an overall decline of storminess, particularly spring and summer storminess, around the end of the 19th century must also have contributed to the increasing inactivity of coastal dunes. The new OSL dates on aeolian sand movement agree well with historical data and data from topographic maps on dune movement. This agreement supports the observation from earlier work that OSL dating of recent aeolian sand movement is accurate over the last few decades to centuries. Copyright © 2005 John Wiley & Sons, Ltd.     

New evidence on the hydrothermal system in Long Valley caldera, California, from wells, fluid sampling, electrical geophysics, and age determinations of hot-spring deposits

Data collected since 1985 from test drilling, fluid sampling, and geologic and geophysical investigations provide a clearer definition of the hydrothermal system in Long Valley caldera than was previously available. This information confirms the existence of high-temperature (> 200°C) reservoirs within the volcanic fill in parts of the west moat. These reservoirs contain fluids which are chemically similar to thermal fluids encountered in the central and eastern parts of the caldera. The roots of the present-day hydrothermal system (the source reservoir, principal zones of upflow, and the magmatic heat source) most likely occur within metamorphic basement rocks beneath the western part of the caldera. Geothermometer-temperature estimates for the source reservoir range from 214 to 248°C. Zones of upflow of hot water could exist beneath the plateau of moat rhyolite located west of the resurgent dome or beneath Mammoth Mountain. Lateral flow of thermal water away from such upflow zones through reservoirs in the Bishop Tuff and early rhyolite accounts for temperature reversals encountered in most existing wells. Dating of hot-spring deposits from active and inactive thermal areas confirms previous interpretations of the evolution of hydrothermal activity that suggest two periods of extensive hot-spring discharge, one peaking about 300 ka and another extending from about 40 ka to the present. The onset of hydrothermal activity around 40 ka coincides with the initiation of rhyolitic volcanism along the Mono-Inyo Craters volcanic chain that extends beneath the caldera's west moat.