ALBERT

Description: The plasma membrane protein CaRch1p of Candida albicans , homologous to the human solute carrier protein SLC10A7, is involved in the regulation of calcium homeostasis. C. albicans cells lacking CaRCH1 are hypersensitive to high extracellular Ca 2+ concentrations and show increased tolerance to ketoconazole (KCZ). We assume a higher basal Ca 2+ influx in the rch1/rch1 mutant strain at low extracellular Ca 2+ concentrations which is not detrimental to C. albicans cells but may be sufficient to activate calcineurin, finally resulting in an increased tolerance to KCZ. However, at 8 µg/ml KCZ plus 3 mM Ca 2+ the rch1/rch1 mutant and the wild type strains showed identical growth. By further increasing the Ca 2+ concentration to 30 mM this phenotype completely reversed and the rch1/rch1 mutant strain became extremely sensitive to 8 µg/ml KCZ, probably due to synergistic toxic effects of Ca 2+ and KCZ under these conditions. Furthermore, we aimed to clarify if CaRch1p interacts with the Cch1p component of the voltage-gated calcium influx channel Cch1p/Mid1p in C. albicans cells. As disruption of the two alleles of CCH1 in the rch1 / rch1 mutant strain did not alter its hypersensitivity to high extracellular Ca 2+ , and, as this phenotype was completely abolished by low amounts of Mg 2+ in the rch1/rch1 mutant as well as in the cch1/cch1 rch1/rch1 double mutant, we conclude that CaRch1p is a functional component of the low-affinity calcium uptake system (LACS) system and does not functionally interact with Cch1p. This article is protected by copyright. All rights reserved.

Description: Terra Nova, 23, 220–224, 2011 Abstract The Teide–Pico Viejo stratovolcanoes constitute one of the major potentially active volcanic complexes in Europe but have traditionally been considered to be non-explosive and not to represent a significant threat to the island of Tenerife. However, the reconstruction of their eruptive record is still far from complete, and better knowledge of their volcano-stratigraphy and physical volcanology is required to undertake a comprehensive hazard assessment of these volcanoes. We conducted a detailed field investigation of the northern side of Teide–Pico Viejo, a poorly known area, and identified several deposits of explosive eruptions of phonolitic magmas. Herein we report for the first time the presence of density current deposits, including ignimbrites and block and ash deposits, in the Holocene eruptive history of the Teide–Pico Viejo stratovolcanoes. We discuss the characteristics of these deposits, their eruption mechanisms and their implications for hazard assessment at Teide–Pico Viejo.

Description: El Hierro eruption started on 10 October 2011 after an unrest episode that initiated on 17 July, 2011. This is the first eruption in the Canary Islands that has been tracked in real time. Although being submarine and not directly observable, the data recorded allowed its reconstruction and to identify its causes and mechanisms. Seismicity, surface deformation, and petrological data indicate that a batch of basanitic magma coming from a reservoir located at depth of about 25 km below El Hierro island was emplaced at shallower depth creating a new reservoir about 10–12 km above, where magma evolved till the initiation of the eruption. The characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position, which coincides with the crust/mantle boundary beneath El Hierro, was created in about two months by elastic deformation and magma-driven fracturing of the crust. After this first intrusion episode part of the magma started to migrate laterally toward the south-east for nearly 20 km, always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere. This lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of El Hierro island. The total seismic energy released during the unrest episode was of 8.1x10 11 Joules, and the total uplift previous to the onset of the eruption was of 40 mm. Combining geological, geophysical, petrological data and numerical modeling, we propose a volcanological model of the causes and mechanisms of El Hierro eruption that shows how the stress distribution in the crust beneath El Hierro, which was influenced by rheological contrasts, tectonic stresses, and gravitational loading, controlled the movement and eruption of magma. We also discuss the implications of this model in terms of eruption forecast in the Canary Islands.

Description: Analyses of field observations and numerical model results have identified that sediment transport in the Hudson River estuary is laterally segregated between channel and shoals, features frontal trapping at multiple locations along the estuary, and varies significantly over the spring-neap tidal cycle. Lateral gradients in depth, and therefore baroclinic pressure gradient and stratification, control the lateral distribution of sediment transport. Within the saline estuary, sediment fluxes are strongly landward in the channel and seaward on the shoals. At multiple locations, bottom salinity fronts form at bathymetric transitions in width or depth. Sediment convergences near the fronts create local maxima in suspended-sediment concentration and deposition, providing a general mechanism for creation of secondary estuarine turbidity maxima at bathymetric transitions. The lateral bathymetry also affects the spring-neap cycle of sediment suspension and deposition. In regions with broad, shallow shoals, the shoals are erosional and the channel is depositional during neap tides, with the opposite pattern during spring tides. Narrower, deeper shoals are depositional during neaps and erosional during springs. In each case, the lateral transfer is from regions of higher to lower bed stress, and depends on the elevation of the pycnocline relative to the bed. Collectively, the results indicate that lateral and along-channel gradients in bathymetry and thus stratification, bed stress, and sediment flux lead to an unsteady, heterogeneous distribution of sediment transport and trapping along the estuary rather than trapping solely at a turbidity maximum at the limit of the salinity intrusion.

Description: Element ratios and water stable isotopes reveal the presence of only two independent deep brines in the Kinnarot Basin, Israel: the evaporite dissolution brine of Zemah-1 and the inferred Ha’on mother brine (HMB) with low and high Br/Cl ratios, respectively. HMB is considered to be a representative of the Late Pliocene evaporated Sedom Sea. The freshwater-diluted evaporation brine emerges as Ha’on brine on the eastern shore of Lake Tiberias and is also identified in the pore water of lake sediments. HMB is converted into Tiberias mother brine (TMB) by dolomitization of limestones and alteration of abundant volcanic rocks occurring along the western side of the lake. The Ha’on and Tiberias brines, both characterized by high δD and δ 18 O values, are similar in Na/Cl and Br/Cl ratios but are dissimilar in Br/K ratios because these brines were subjected to different degrees of interactions with rocks and sediments. Excepting the brine from KIN 8, all brines from the Tabigha area including the nearby off-shore Barbutim brine are related to the TMB. The brine KIN 8 and all brines from the Fuliya and Hammat Gader areas are related to the HMB. The brine encountered in wildcat borehole Zemah-1 is generated by halite-anhydrite/gypsum dissolution and is independent from the HMB system.

Description: Well-developed karst aquifers consist of highly conductive conduits and a relatively low permeability fractured and/or porous rock matrix and therefore behave as a dual-hydraulic system. Groundwater flow within highly permeable strata is rapid and transient and depends on local flow conditions, i.e., pressurized or nonpressurized flow. The characterization of karst aquifers is a necessary and challenging task because information about hydraulic and spatial conduit properties is poorly defined or unknown. To investigate karst aquifers, hydraulic stresses such as large recharge events can be simulated with hybrid (coupled discrete continuum) models. Since existing hybrid models are simplifications of the system dynamics, a new karst model (ModBraC) is presented that accounts for unsteady and nonuniform discrete flow in variably saturated conduits employing the Saint-Venant equations. Model performance tests indicate that ModBraC is able to simulate (1) unsteady and nonuniform flow in variably filled conduits, (2) draining and refilling of conduits with stable transition between free-surface and pressurized flow and correct storage representation, (3) water exchange between matrix and variably filled conduits, and (4) discharge routing through branched and intermeshed conduit networks. Subsequently, ModBraC is applied to an idealized catchment to investigate the significance of free-surface flow representation. A parameter study is conducted with two different initial conditions: (1) pressurized flow and (2) free-surface flow. If free-surface flow prevails, the systems is characterized by (1) a time lag for signal transmission, (2) a typical spring discharge pattern representing the transition from pressurized to free-surface flow, and (3) a reduced conduit-matrix interaction during free-surface flow.

Description: [1]  Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 Mt, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that ~2/3 of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms, and only about 1/5 of the new sediment reaching the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.

Description: Karst aquifers exhibit highly conductive features caused from rock dissolution processes. Flow within these structures can become turbulent and therefore can be expressed by nonlinear gradient functions. One way to account for these effects is by coupling a continuum model with a conduit network. Alternatively, turbulent flow can be considered by adapting the hydraulic conductivity within the continuum model. Consequently, the significance of turbulent flow on the dynamic behavior of karst springs is investigated by an enhanced single-continuum model that results in conduit-type flow in continuum cells (CTFC). The single-continuum approach CTFC represents laminar and turbulent flow as well as more complex hybrid models that require additional programming and numerical efforts. A parameter study is conducted to investigate the effects of turbulent flow on the response of karst springs to recharge events using the new CTFC approach, existing hybrid models, and MODFLOW-2005. Results reflect the importance of representing (1) turbulent flow in karst conduits and (2) the exchange between conduits and continuum cells. More specifically, laminar models overestimate maximum spring discharge and underestimate hydraulic gradients within the conduit. It follows that aquifer properties inferred from spring hydrographs are potentially impaired by ignoring flow effects due to turbulence. The exchange factor used for hybrid models is necessary to account for the scale dependency between hydraulic properties of the matrix continuum and conduits. This functionality, which is not included in CTFC, can be mimicked by appropriate use of the Horizontal Flow Barrier package for MODFLOW.

Description: ABSTRACT The outflowing currents from tidal inlets are influenced both by the morphology of the ebb-tide shoal and interaction with incident surface gravity waves. Likewise, the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current. The 3D COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) modeling system is applied to numerically analyze the interaction between currents, waves, and bathymetry in idealized inlet configurations. The bathymetry is found to be a dominant controlling variable. In the absence of an ebb shoal and with weak wave forcing, a narrow outflow jet extends seaward with little lateral spreading. The presence of an ebb-tide shoal produces significant pressure gradients in the region of the outflow, resulting in enhanced lateral spreading of the jet. Incident waves cause lateral spreading and limit the seaward extent of the jet, due both to conversion of wave momentum flux and enhanced bottom friction. The interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume. For weak outflows, the outflow jet is actually enhanced by strong waves when there is a channel across the bar, due to the “return current” effect. For both strong and weak outflows, waves increase the along-shore transport in both directions from the inlet due to the wave-induced set-up over the ebb shoal. Wave-breaking is more influenced by the topography of the ebb shoal than by wave-current interaction, although strong outflows show intensified breaking at the head of the main channel.