Uranium series dates from the windy pits of the North York Moors,United Kingdom: implications for late Quaternary ice cover and timing of speleogenesis

Windy pits are open fissures within the Corallian strata of the North York Moors. Here we present nine thermal ionization mass spectrometry (TIMS) U–Th dates on speleothem from the windy pits, the first radiometric dates on calcite for these features and for this region. The dates cluster within three time periods: the interglacial peaks of marine isotope stage (MIS) 7 (～208 to ～190 ka), MIS 5 (～127 ka to ～109 ka) and the Holocene, correlating with the marine isotope record and with the broad pattern of interglacial calcite deposition observed for northern England. However, of the two high‐resolution studies available for comparison, the windy‐pit dates match only the Lancaster Hole dates. The location of the windy pits outside of the Devensian ice limits, within the ice‐free but periglaciated region, suggests that the region has remained ice‐free since some time before MIS 7. The prevalence of widespread and prolonged permafrost conditions suggests a plausible mechanism for these open rift caves in slope‐side periglacial mass movement. Copyright © 2008 John Wiley & Sons, Ltd.     

Differential Effects of Bivalves on Sediment Nitrogen Cycling in a Shallow Coastal Bay

In coastal ecosystems, suspension-feeding bivalves can remove nitrogen though uptake and assimilation or enhanced denitrification. Bivalves may also retain nitrogen through increased mineralization and dissimilatory nitrate reduction to ammonium (DNRA). This study investigated the effects of oyster reefs and clam aquaculture on denitrification, DNRA, and nutrient fluxes (NO _x , NH₄ ⁺, O₂). Core incubations were conducted seasonally on sediments adjacent to restored oyster reefs (Crassostrea virginica), clam aquaculture beds (Mercenaria mercenaria) which contained live clams, and bare sediments from Smith Island Bay, Virginia, USA. Denitrification was significantly higher at oyster reef sediments and clam aquaculture site than bare sediment in the summer; however, DNRA was not enhanced. The clam aquaculture site had the highest ammonium production due to clam excretion. While oyster reef and bare sediments exhibited seasonal differences in rate processes, there was no effect of season on denitrification, or dissimilatory nitrate reduction to ammonium (DNRA) or ammonium flux at the clam aquaculture site. This suggests that farm management practices or bivalve metabolism and excretion may override seasonal differences. When water column nitrate concentration was elevated, denitrification increased in clam aquaculture site and oyster reef sediments but not in bare sediment; DNRA was only stimulated at the clam aquaculture site. This, along with a significant and positive relationship between denitrification and sediment organic matter, suggests that labile carbon limited nitrate reduction at the bare sediment site. Bivalve systems can serve as either net sinks or sources of nitrogen to coastal ecosystems, depending mainly on the type of bivalve, location, and management practices.     

Experimental transport of Si,Al and Mg in hydrothermal solutions: an application to vein mineralization during high-pressure,low-temperature metamorphism in the French Alps

A study of hydrothermal vein mineralization in meta-argillites subjected to high-pressure, low-temperature metamorphism reveals that ferromagnesian (e.g., chlorite) and pure aluminosilicate (e.g., pyrophyllite) mineralization can be correlated with regimes of increasing and decreasing temperature, respectively. An experimental study of the transport of silica, aluminum and magnesium in hydrothermal solutions has been undertaken to simulate variations in the physical conditions during metamorphism and the accompanying mass transport in a closed system. Thermodynamic and kinetic analysis of the experimental results indicates that local equilibrium among aqueous and mineral phases controls the distribution and composition of hydrothermal vein mineralization and that vein mineralogy can be used to infer the sense of variation of pressure and temperature during metamorphism.     

The relationship between freezing and desiccation tolerance in the marine snail Ilyanassa obsoleta (Stimpson)

Temperature acclimation influenced the desiccation tolerance of the marine snail Ilyanassa obsoleta (Nassarius obsoletus). I. obsoleta acclimated to 35‰ seawater at 18°C could survive for 116 hours, and tolerate a 57% loss of body water when desiccated at 15 °C in air with a relative humidity of 35%. In contrast, I. obsoleta acclimated to 3°C seawater survived for only 76 hours, and could not tolerate more than a 37% loss of body water. These results were used to support the proposition that freezing and desiccation tolerance are closely related in I. obsoleta.     

Suspended-Sediment Flux and Retention in a Backwater Tidal Slough Complex near the Landward Boundary of an Estuary

Backwater tidal sloughs are commonly found at the landward boundary of estuaries. The Cache Slough complex is a backwater tidal region within the Upper Sacramento–San Joaquin Delta that includes two features that are relevant for resource managers: (1) relatively high abundance of the endangered fish, delta smelt (Hypomesus transpacificus), which prefers turbid water and (2) a recently flooded shallow island, Liberty Island, that is a prototype for habitat restoration. We characterized the turbidity around Liberty Island by measuring suspended-sediment flux at four locations from July 2008 through December 2010. An estuarine turbidity maximum in the backwater Cache Slough complex is created by tidal asymmetry, a limited tidal excursion, and wind-wave resuspension. During the study, there was a net export of sediment, though sediment accumulates within the region from landward tidal transport during the dry season. Sediment is continually resuspended by both wind waves and flood tide currents. The suspended-sediment mass oscillates within the region until winter freshwater flow pulses flush it seaward. The hydrodynamic characteristics within the backwater region such as low freshwater flow during the dry season, flood tide dominance, and a limited tidal excursion favor sediment retention.     

Assessing municipal vulnerability to predicted sea level rise: City of Satellite Beach, Florida

In the fall of 2009 the City of Satellite Beach (City), Florida, authorized a study designed to assess municipal vulnerability to rising sea level and facilitate discussion of potential adaptation strategies. The project is one of the first in Florida to seriously address the potential consequences of global sea level rise, now forecast to rise a meter or more by the year 2100. Results suggest the tipping point between relatively benign impacts and those that disrupt important elements of the municipal landscape is +?2 ft (0.6 m) above present. Seasonal flooding to an elevation of +?2 ft is forecast to begin around 2050 and thus the City has about 40 years to formulate and implement an adaptation plan. As an initial step, the Comprehensive Planning Advisory Board, a volunteer citizen committee serving as the City??s local planning authority, has recommended a series of updates and revisions to the City??s Comprehensive Plan. If approved by the City Council and Florida??s Department of Community Affairs, the amendments will provide a legal basis for implementing specific policies designed to reduce the City??s vulnerability to sea level rise.     

Shake table tests of stiff,unattached, asymmetric structures

Stiff, unattached structures are highly vulnerable to damage and failure during an earthquake, as evidenced following numerous past events. This class of structures encompasses a wide range of objects and systems such as electrical transformers, radiation shields, office furniture, and marble statues. The vulnerability of these objects is exacerbated when it is highly asymmetric and unattached. Although a number of studies have focused on rigid blocks, few have concentrated on blocks with asymmetric geometries. In an effort to better understand the implications of asymmetries, an extensive shake table testing campaign including more than 150 tests was conducted. These tests incorporate a systematic variation of the mass eccentricities of stiff, unattached structures. The primary modes of rocking, sliding, and twisting as well as interactive modes were recorded for the duration of numerous earthquake motions. The magnitude and direction of response are experimentally correlated with the geometric variations in the various models. These tests indicate that even for symmetric structures with uniaxial shaking, multiple modes and three‐dimensional responses are probable. Furthermore, certain asymmetric geometries exhibited both increased rocking (and overturning) as well as increased sliding when compared with their symmetric counterparts. A final aspect of this study compared the free rocking response of symmetric and asymmetric structures to classical, two‐dimensional rocking analysis. While the theoretical values for the coefficient of restitution yielded a significant overestimation in the simulation (up to ≈90%), reduced coefficients greatly improved the performance of the model. Copyright © 2015 John Wiley & Sons, Ltd.     

Dependence of ground-based Pc5 ULF wave power on F10.7 solar radio flux and solar cycle phase

Utilising fifteen (1990–2005) years of ground-based magnetometer data from four magnetometer stations, we characterise the statistical dependence of the Pc5 ULF wave power spectra on variations in F10.7 solar radio flux and on solar cycle phase. We show that the median Pc5 ULF wave power spectra can be characterised as a power-law with a localised Gaussian centred at a specific frequency superimposed on the power-law spectrum. Further, we demonstrate that the location of the Gaussian in frequency systematically varies with both solar cycle phase and F10.7 and is more pronounced during high-speed solar wind intervals. We postulate that the localised power spectrum enhancement (or Gaussian) is a manifestation of the local eigenfrequency of field line resonances in the Earth's magnetosphere and that the variation in the location of the Gaussian occurs as a result of increased ionospheric outflow during periods of enhanced F10.7 and active solar activity.