Raman microprobe study of synthetic diaplectic plagioclase feldspars

Raman microprobe spectra were made on three post shock, diaplectic plagioclase feldspars. Optical and X-ray diffraction studies indicated that feldspars maintained a partially or totally crystalline state after having passed through the mixed phase zone of Hugoniot response to shock waves (15–38 GPa). The appearance of uniquely glass-type spectra occurs at different shock pressures for each specimen according to its atomic structural arrangement, below 38 GPa for mosaic structured labradorite, near 40 GPa for anorthite and above 50 GPa for the highly ordered low albite. The diaplectic anorthite and labradorite glasses give spectra which indicate the presence of two glass types. Shifts in the band envelope frequencies compared to spectra of fused glass and statically pressure densified glass suggest that these glasses have specific structural arrangements. These differences suggest that the shock and fusion glass-forming processes are not exactly identical. The results from material shocked in the mixed phase region of Hugoniot response show that the phase transitions are effected at different pressures depending upon the feldspar structural type.     

Raman microprobe (RMP) determinations of natural and synthetic coesite

Raman microprobe (RMP) spectra of synthetic coesiste and three natural coesites from eclogite — facies rocks are provided and evaluated for characterisation purposes. The main coesite line lies at 521 cm^?1 and the other characteristic lines attributed to coesite occur at 117, 177 and 271 cm^?1. Two petrologically useful applications were (a) the confirmation of the coesite structure in very small natural crystals deduced to be coesite from petrographic observations only, and (b) the recognition of sub-microscopic crystallites of quartz in incipiently — transformed coesite in all the natural samples.     

Theoretical studies of charge relaxation effects on the statics and dynamics of oxides

Inclusion of spherical charge relaxation in response to the long-range electrostatic potential (potential induced breathing, or PIB) gives improved results for the static and dynamic properties of oxides. PIB is a Gordon-Kim type model, in which the crystal charge density is estimated by overlapping ionic charge densities. No experimental data are used, except for the values of universal constants, and in this sense the results are from first principles. In contrast to earlier models which include some form of charge relaxation, we explicitly include the breathing effects on the self-energy and pair potentials in the model Hamiltonian. PIB is a many-body effect that couples the long-and short-range forces in a way that is not present in any other first principles or empirical models. It leads to the observed violations of the Cauchy relations for the elastic constants whereas central force rigid ion models cannot violate the Cauchy relations. PIB also reduces the predicted LO-TO splitting because the breathing effect introduces dynamical effective charges that are lower in magnitude than the ionic charges. Some results are shown and discussed for MgO (periclase), BeO (bromellite), Al₂O₃ (corundum), TiO₂ (rutile) and SiO₂ (quartz and stishovite).     

Indirect Hurricane Effects on Resource Availability and Microbial Communities in a Subtropical Wetland-Estuary Transition Zone

Three sequential hurricanes made landfall over the South Florida peninsula in August and September 2004. The storm systems passed north of the Everglades wetlands and northeastern Florida Bay, but indirect storm effects associated with changes in freshwater discharge during an otherwise drought year occurred across the wetland–estuary transition area. To assess the impacts of the 2004 hurricane series on hydrology, nutrients, and microbial communities in the Everglades wetlands to Florida Bay transition area, results are presented in the context of a seasonal cycle without hurricane activity (2003). Tropical activity in 2004 increased rainfall over South Florida and the study area, thereby temporarily relieving drought conditions. Not so much actual rainfall levels at the study site but more so water management practices in preparation of the hurricane threats, which include draining of an extensive freshwater canal system into the coastal ocean to mitigate inland flooding, rapidly reversed hypersalinity in the wetlands-estuary study area. Although annual discharge was comparable in both years, freshwater discharge in 2004 occurred predominantly during the late wet season, whereas discharge was distributed evenly over the 2003 wet season. Total organic carbon (TOC), ammonium ( \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} ), and soluble reactive phosphorus (SRP) concentrations increased during the hurricane series to concentrations two to five times higher than long-term median concentrations in eastern Florida Bay. Spatiotemporal patterns in these resource enrichments suggest that TOC and SRP originated from the Everglades mangrove ecotone, while \operatornameNH ⁺ ₄ \operatorname{NH} ^{ + }_{4} originated from the bay. Phytoplankton biomass in the bay increased significantly during storm-related freshwater discharge, but declined at the same time in the wetland mangrove ecotone from bloom conditions during the preceding drought. In the bay, these changes were associated with increased nanophytoplankton and decreased picophytoplankton biomass. Heterotrophic bacterial production increased in response to freshwater discharge, whereas bacterial abundance decreased. Hydrochemical and microbial changes were short-lived, and the wetland–bay transition area reverted to more typical oligotrophic conditions within 3 months after the hurricanes. These results suggest that changes in freshwater discharge after drought conditions and during the hurricane series forced the productivity and P-enriched characteristics of the wetland’s mangrove ecotone, although only briefly, to the south into Florida Bay.     

Tropical seagrass-associated macroalgae distributions and trends relative to water quality

Tropical coastal marine ecosystems including mangroves, seagrass beds and coral reef communities are undergoing intense degradation in response to natural and human disturbances, therefore, understanding the causes and mechanisms present challenges for scientist and managers. In order to protect our marine resources, determining the effects of nutrient loads on these coastal systems has become a key management goal. Data from monitoring programs were used to detect trends of macroalgae abundances and develop correlations with nutrient availability, as well as forecast potential responses of the communities monitored. Using eight years of data (1996–2003) from complementary but independent monitoring programs in seagrass beds and water quality of the Florida Keys National Marine Sanctuary (FKNMS), we: (1) described the distribution and abundance of macroalgae groups; (2) analyzed the status and spatiotemporal trends of macroalgae groups; and (3) explored the connection between water quality and the macroalgae distribution in the FKNMS. In the seagrass beds of the FKNMS calcareous green algae were the dominant macroalgae group followed by the red group; brown and calcareous red algae were present but in lower abundance. Spatiotemporal patterns of the macroalgae groups were analyzed with a non-linear regression model of the abundance data. For the period of record, all macroalgae groups increased in abundance (Ab_i) at most sites, with calcareous green algae increasing the most. Calcareous green algae and red algae exhibited seasonal pattern with peak abundances (Φ_i) mainly in summer for calcareous green and mainly in winter for red. Macroalgae Ab_i and long-term trend (m_i) were correlated in a distinctive way with water quality parameters. Both the Ab_i and m_i of calcareous green algae had positive correlations with NO₃⁻, NO₂⁻, total nitrogen (TN) and total organic carbon (TOC). Red algae Ab_i had a positive correlation with NO₂⁻, TN, total phosphorus and TOC, and the m_i in red algae was positively correlated with N:P. In contrast brown and calcareous red algae Ab_i had negative correlations with N:P. These results suggest that calcareous green algae and red algae are responding mainly to increases in N availability, a process that is happening in inshore sites. A combination of spatially variable factors such as local current patterns, nutrient sources, and habitat characteristics result in a complex array of the macroalgae community in the seagrass beds of the FKNMS.     

Influence of morphological changes on suspended sediment dynamics in a macrotidal estuary: diachronic analysis in the Seine Estuary (France) from 1960 to 2010

Ocean Dynamics - Estuaries are subject to extensive morphological changes through human activities, such as deepening and narrowing via dredging and channelization. The estuary sediment load,...     

The AMANDES tidal model for the Amazon estuary and shelf

The AMANDES project aims to study transports from the Andean mountains to the Atlantic Ocean through the Amazon system. This requires realistic estuarine modelling in this area strongly forced by tides and river discharge. As none of the existing models for this region would fit the actual needs of the project, a specific new generation model has been implemented.The model is based on the hydrodynamic finite element model T-UGOm. In a first step, we limit our investigations to tidal dynamics. As the Amazon estuary is a very shallow macro-tidal area, it is necessary to improve the available bathymetries and to develop a precise bottom friction parametrisation.In this paper, we discuss the implementation of a high resolution regional model. This allows us to develop a precise and accurate tidal model: for instance, the overall root mean square error on complex differences is reduced from 54 cm in a standard model to 27 cm in our best model. Such precise and accurate tidal modelling is a prerequisite for modelling particle transport.