Recent tectonics of Eratosthenes Seamount: an example of seamount deformation during incipient continental collision

The Eratosthenes Seamount is a continental fragment undergoing collision with Cyprus along the African-Eurasian plate boundary. High-resolution seismic and deep-tow sonar data revealed that extensional deformation is occurring over most of the seamount, whereas compressional deformation was observed within the trench basin to the north and also in the asymmetric basin south of the seamount. This recent tectonic activity has triggered the development of slumps, turbidites and fluid escape structures. Although the 'staircase' bathymetry is similar to that of subducting oceanic seamounts, the distribution and characteristics of structures which develop during collision-subduction are very different.     

Photosynthesis, Respiration and other Factors Influencing the Growth of Laminar/a ochroleuca PYL below 50 Metres in the Straits of Messina

Abstract. The population of Laminaria ochroleuca in the current swept Straits of Messina was investigated regarding its age structure and photosynthesis. Age structure appears to be determined by sporadic recruitment and the limitation of growth due to peak currents decapitating older plants, which is corroborated by drag force resistance calculations. The calculation of a carbon budget from measurements of photosynthesis and dark respiration both in the laboratory and in situ shows that L. ochroleuca cannot satisfy its carbon demands for growth and respiration at 50 m depth and no satisfactory explanation can be given for its rapid growth between 50 and 100 m.     

Soil moisture response to white ash mortality following emerald ash borer invasion

Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive forest insect first identified in southeastern Michigan in 2002, is established in at least 32 US states and three Canadian provinces. Ash (Fraxinus spp.) mortality rates in some forested areas exceed 90%, but to date, little is known about the potential effects of EAB-caused ash mortality on hydrological processes. More broadly, there is a need for information on the timing and magnitude of soil moisture response to species-specific mortality of overstory vegetation in deciduous forest systems. Soil moisture was examined in 28 forested sites where 0–100% of the white ash basal area (Fraxinus americana L.) was killed by EAB. Synoptic measurements of near-surface (0–6 cm depth) soil moisture were collected from 112 plots (18 m radius) within the sites. Three plots were also instrumented with soil moisture sensors at 10 and 25 cm depth to log hourly measurements from May to October. Synoptic data showing white ash mortality and soil moisture were positively correlated in the 34 plots with ≥?5% mortality (by total basal area). In the intensively monitored plots, volumetric soil moisture declined from 37 to 16% between July and September where white ash mortality was low (0.6% of basal area killed), but remained near field capacity (~?30%) throughout the monitoring period in the high mortality plot (8.6% of basal area killed), meriting further investigation to assess effects of white ash mortality on evapotranspiration and soil moisture dynamics in heterogeneous upland forests. Altered soil moisture may have implications for regrowth dynamics, infiltration/runoff partitioning, and nutrient cycling, but additional study to quantify the extent and duration of EAB-related ash mortality on hydrology at the plot and watershed scale is necessary.     

Resolution of bridging oxygen signals from O 1s spectra of silicate glasses using XPS: Implications for O and Si speciation

We used an advanced charge compensation system on an X-ray Photoelectron Spectrometer to yield linewidths from O 1s, Si 2p and Pb 4f spectra of 1.22, 1.35, and 1.10 eV, respectively. These linewidths (eV) are the narrowest obtained for silicate glasses, on any X-ray Photoelectron Spectrometer, to date. The exceptional resolution reveals two O 1s peaks in the PbO-SiO₂ glasses studied. One clearly resolved, high binding energy O 1s peak represents the bridging oxygen signal and the second, lower energy peak represents both non-bridging oxygen and metal-bridging oxygen contributions. These data allow quantification of bridging oxygen contents without detailed deconvolution because both the peak width and intensity are determined solely by the spectral data. The intensity of the bridging oxygen signal decreases systematically with decreased SiO₂ content; however, the measured bridging oxygen abundance is greater than predicted if all Pb atoms in the glass are assumed to be associated with two non-bridging oxygen atoms (i.e., O-Pb-O units). There remains, for example, a significant quantity of bridging oxygen in the glass at the orthosilicate composition (Mol. frac.: 0.67 PbO, 0.33 SiO₂). We demonstrate that bridging oxygen, non-bridging oxygen and metal-bridging oxygen exist at this composition and at all glass compositions studied, including the 0.50 PbO, 0.50 SiO₂ glass. Equilibrium thermodynamic (speciation) calculations indicate that at least three silicate species dominate the glass: a network species (SiO₂), a () monomeric species and a trimeric ring-like species (). With these species, the bridging oxygen contents are accurately modeled in PbO-SiO₂ glasses over the compositional range 0.3 PbO, 0.70 SiO₂ to 0.67 PbO, 0.33 SiO₂, and there is a remarkable agreement between the modeled bridging oxygen and the measured bridging oxygen contents with this study and previous studies. However, we do not intend to imply that the SiO₂, () and () are the only species present in the glass structure. In addition, this study shows that the Si 2p spectrum consists of one peak, fitted with one doublet, which shifts systematically to higher binding energy with increased SiO₂ content. We propose that this shift results from a more intense signal from the networked (more siliceous) species that are located at higher binding energy.     

Transitional, entraining, cloudy, and coastal boundary layers

Atmospheric boundary layers are marvelously varied and complex. Recent research has examined some of that variety. Boundary layers over land undergo drastic changes throughout the day as the sun rises and sets, and as clouds form and dissipate. Air is entrained at the top of the boundary layer at varying rates. As air moves over the coast, the boundary layer reacts to changes in surface forcing. All of these changes affect pollutant transport and weather formation. In this paper, research attempting to understand transitional, cloud-topped, and coastal boundary layers, and boundary-layer top entrainment, is reviewed.     

Evaluation of stony coral indicators for coral reef management

Colonies of reef-building stony corals at 57 stations around St. Croix, US Virgin Islands were characterized by species, size and percentage of living tissue. Taxonomic, biological and physical indicators of coral condition were derived from these measurements and assessed for their response to gradients of human disturbance—a requirement for indicators used in regulatory assessments under authority of the Clean Water Act. At the most intensely disturbed location, five of eight primary indicators were highly correlated with distance from the source of disturbance: Coral taxa richness, average colony size, the coefficient of variation of colony size, total topographic coral surface area, and live coral surface area. An additional set of exploratory indicators related to rarity, reproductive and spawning mode and taxonomic identity were also screened. The primary indicators demonstrated sufficient precision to detect levels of change that would be applicable in a regional-scale regulatory program.     

Diel patterns in coastal‐stream nitrate concentrations linked to evapotranspiration in the riparian zone of a low‐relief,agricultural catchment

Evapotranspiration (ET) can cause diel fluctuations in the elevation of the water table and the stage in adjacent streams. The diel fluctuations of water levels change head gradients throughout the day, causing specific discharge through near‐stream sediment to fluctuate at the same time scale. In a previous study, we showed that specific discharge controls the residence time of groundwater in streambed sediment that, in turn, exerted the primary control on removal from groundwater passing through the streambed. In this study, we examine the magnitude of diel specific discharge patterns through the streambed driven by ET in the riparian zone with a transient numerical saturated–unsaturated groundwater flow model. On the basis of a first‐order kinetic model for removal, we predicted diel fluctuations in stream concentrations. Model results indicated that ET drove a diel pattern in specific discharge through the streambed and riparian zone (the removal zones). Because specific discharge is inversely proportional to groundwater travel time through the removal zones and travel time determines the extent of removal, diel changes in ET can result in a diel pattern in concentration in the stream. The model predictions generally matched observations made during summertime base‐flow conditions in a small coastal plain stream in Virginia. A more complicated pattern was observed following a seasonal drawdown period, where source components to the stream changed during the receding limb of the hydrograph and resulted in diel fluctuations being superimposed over a multi‐day trend in concentrations. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of rainfall on the hygienic quality of blue mussels and water in urban areas in the Inner Oslofjord,Norway

The effects of precipitation on the hygienic quality of water and blue mussels collected from five different localities in the urban areas in the Inner Oslofjord were investigated, with samples analysed for Escherichia coli, Salmonella spp., pathogenic Vibrio spp., Norovirus, Sapovirus, Cryptosporidium spp. and Giardia duodenalis. The sampling sites were located at varying distances from the outlet of combined sewer overflows (CSO)-impacted rivers/streams. In general, 1–3 log₁₀ increases in fecal indicator bacteria and human pathogens were observed after heavy rainfalls. Blue mussels appeared to be a useful indicator of the impact of sewage at these sites, and generally a good correlation was identified between concentrations of E. coli and other human pathogens in the mussels. Provision of general advice to the public of avoiding areas near the outlets of CSO-impacted rivers after heavy rainfall may reduce the risk of gastroenteritis by bathers and others that may swallow water during recreational activities.     

Temporal and spatial variability of fecal indicator bacteria in the surf zone off Huntington Beach, CA

Fecal indicator bacteria concentrations measured in the surf zone off Huntington Beach, CA from July 1998-December 2001 were analyzed with respect to their spatial patterns along 23 km of beach, and temporal variability on time scales from hourly to fortnightly. The majority of samples had bacterial concentrations less than, or equal to, the minimum detection limit, but a small percentage exceeded the California recreational water standards. Areas where coliform bacteria exceeded standards were more prevalent north of the Santa Ana River, whereas enterococci exceedances covered a broad area both north and south of the river. Higher concentrations of bacteria were associated with spring tides. No temporal correspondence was found between these bacterial events and either the timing of cold water pulses near shore due to internal tides, or the presence of southerly swell in the surface wave field. All three fecal indicator bacteria exhibited a diel cycle, but enterococci rebounded to high nighttime values almost as soon as the sun went down, whereas coliform levels were highest near the nighttime low tide, which was also the lower low tide.