The filtering capacity of a tropical riverine wetland: I. Water balance

Wetlands in the coastal catchments adjacent to the Great Barrier Reef lagoon play an important role in local hydrological processes and provide important ecological habitats for terrestrial and aquatic species. Although many wetlands have been removed or degraded by agricultural expansion, there is now great interest in their protection and restoration as important aquatic ecosystems and potential filters of pollutant runoff. However, the filtering capacity of tropical wetlands is largely unknown, so the current study was established to quantify the water, sediment and nutrient balance of a natural riverine wetland in tropical north Queensland. Surface and groundwater fluxes of water, sediment and nutrients into and out of the wetland were monitored for a 3‐year period. This paper focuses on the water balance of this natural wetland and a companion paper presents its sediment and nutrient balance and estimates of water quality filtering. Wetland inflows and outflows were dominated by surface flows which varied by 3–4 orders of magnitude through the course of the year, with 90% of the annual flow occurring during the period January to March. Although groundwater inputs to the wetland were only 5% of the annual water balance, they are very important to sustaining the wetland during the dry season, when they can be the largest input of water (up to 90%). Water retention times in this type of wetland are very short, particularly when most of the flow and any associated materials are passing through it (i.e. 1–2 h), so there is little time to filter most of the annual flux of water through this wetland. Longer retention times occur at the end of the dry season (up to 8·5 days); but this is when the lowest fluxes of water pass through the wetland. Copyright © 2011 John Wiley & Sons, Ltd.     

Role of the atmospheric mean state on the initiation of the Madden-Julian oscillation in a tropical channel model

Tropical channel models, defined as models that are global in the zonal direction but bounded in the meridional direction, are particularly useful for simulating the Madden-Julian oscillation (MJO) and understanding its physical and dynamical basis. Influences from the extratropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain MJO events. This led to a hypothesis that multi-year simulations using a tropical channel model would reproduce reasonable MJO statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses. Interestingly, the MJO statistics in such a multi-year simulation by a high-resolution tropical channel model are not better than those from global climate models. The error in the atmospheric mean state is found to be a possible reason for the poor MJO statistics in the simulation. Nevertheless, even with a large error in the mean state, the multi-year simulation captures two MJO events previously found to be initiated by extratropical influences. However, the model does not reproduce a third event, whose initiation is not directly influenced by the extratropics. This implies that in the absence of dynamical interactions between the MJO and the lateral boundary conditions, the error in the mean state could be sufficient to prevent the MJO initiation. To explore this third MJO event further, a series of sensitivity tests are conducted. These tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed, nor the initial conditions when the model is integrated 2?weeks prior to the MJO initiation. The model captures this event when the MJO signal is already present in the initial conditions. The use of high-resolution sea surface temperature does not improve the simulation of the third MJO event. A higher-resolution nested domain covering the Indo-Pacific warm pool region and including a cloud-system resolving domain over the Indonesian Maritime Continent has little effect on the MJO initiation over the Indian Ocean. In <2?weeks the error in the simulation is comparable to the climate error. The role of the simulated MJO on the mean state is also explored. Implications and limitations of these results are discussed.     

Seismic reliability of traditional and innovative concentrically braced frames

Structural engineering problems are always affected by many sources of uncertainty, such as aleatory of material properties, applied loads and earthquake intensity, therefore, seismic assessment of structures should be based on probabilistic methods. Since PBSD (Performance‐based Seismic Design) philosophy was formulated, many researches have been conducted in this field in order to develop simple and accurate procedures for evaluating structural reliability. An important contribution has been provided by Jalayer and Cornell, who have developed a closed‐form expression to evaluate the mean annual frequency of exceeding a defined limit state. In this paper, by assuming the record‐to‐record variability as the only source of uncertainty, the seismic reliability of concentrically braced frames designed according to traditional and innovative methodologies is investigated, and a comparison between their performances is presented. In particular, two design methodologies have been applied: Eurocode 8 provisions and a new design methodology based on a rigorous application of ‘capacity design’ criteria. The innovative reduced section solution strategy, based on the reduction of cross sections at bracing member ends, has also been analysed. Copyright © 2011 John Wiley & Sons, Ltd.     

Jurassic microbial communities in hydrothermal manganese crust of the Rifian Calcareous Chain,Northern Morocco

The stratigraphic record of the Middle and Upper Jurassic in the Western Tethys is characterized by successive eustatic and tectonic events recorded as stratigraphic unconformities, which are revealed by hardgrounds, palaeokarsts, palaeosoils, and by the deposition of Fe–Mn crusts. The study of a Mn crust from the Middle-Upper Jurassic discontinuity in the Jbel Moussa Group (Rifian Cordillera), from stratigraphic, geomicrobiologic, mineralogical, and geochemical standpoints allows us to establish its hydrothermal origin. The manganese crust is composed by Ca-birnessite, cryptomelane and coronadite. Major- and trace-elements analyses of the whole crust show high contents in MnO (> 70 wt.%), a negative Ce anomaly and a positive Eu anomaly. Analysis of the microstructures under scanning electron microscopy reveals crystalline and microbial laminations, probably owing to fungal mycelium. Mineralogical and geochemical composition, together with microbial structures, suggest that this Mn crust formed as a result of venting hydrothermal fluids through synsedimentary faults. Chemosynthetic microbes were probably involved in the precipitation of Mn.     

Regionalization of the Gulf of Mexico from space-time chlorophyll-<Emphasis Type="Italic">a</Emphasis> concentration variability

Regions in the Gulf of Mexico are determined based on the statistical behavior of the long-term monthly means of chlorophyll-a concentration from SeaWiFS satellite estimations. An analysis based on the four largest modes of an empirical orthogonal decomposition, which account for 84.9% of the variance, results in nine spatial patterns with different statistical behavior representing 14 connected regions. The time evolution (or principal component) of the first two modes resemble the annual cycle, but each one with a different phase; the third mode represents a semiannual period and the fourth mode shows three maxima and minima. A map of the resulting regions is obtained and the oceanographic processes taking place in each region are discussed. The largest region covers most of the deep Gulf and the continental slope. Other regions in the deep Gulf are located southeast of the Mississippi River mouth and off-shelf of southern Texas and Tabasco, all associated with seasonal offshore cross-shelf transports. The shelves are associated with specific regions, but in wide shelves the inner and outer continental platforms are separated. Among the causes that determine different regions are topographic characteristics and the seasonal variability of physical processes, mainly entrainment caused by heat and momentum fluxes, upwelling, river plumes, and cross-shelf transports associated with the convergence of the along-coast currents.     

Cycle 23 Variation in Solar Flare Productivity

The NOAA listings of solar flares in cycles 21?–?24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975?–?2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M- or X-flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004?–?2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24.