Variations in the quantity and composition of seston from an estuary in southern Chile on different temporal scales

Estuaries are characterised by highly variable environmental conditions largely driven by tidal and atmospheric forces. This study investigates variation in the physical environment and the composition of the seston on various temporal scales in the Quempillén estuary, southern Chile. The water column was sampled throughout the tidal cycle at various times of the year. Total particulate matter, particulate inorganic matter, particulate organic matter, particle numbers, total particle volume, proximate biochemical composition and energy content of the seston, chlorophyll a and chloropigments were routinely measured. In each of the months in which sampling took place, two or three tidal cycles were examined. The information not only helps to explain the dynamics of the estuary, but is essential for an understanding of the physiology and ecology of the suspension-feeders which exploit the seston as a food source, the most dominant being the gastropod Crepipatella dilatata. Temperature and salinity were generally highest during summer, but seston quality, defined by energy content and biochemical composition (lipid, protein and carbohydrate) was higher at the end of winter and during spring. Chlorophyll a values were greatest in late spring (November). Many of the variables studied changed frequently according to the phase of the tidal cycle, and in several cases significant differences were observed among tidal cycles from the same month of the same year. In general the variables measured did not exhibit consistent patterns linked to the tidal cycle, possibly because any such patterns were masked by atmospheric conditions (wind and rain) that dominate the region and greatly influence the estuary. The quantity and quality of the seston available to suspension-feeders is largely determined by these atmospheric forces, which cause an influx of terrigenous material from adjacent areas and also resuspend bottom sediment. These effects are magnified by the shallowness of the estuary (<2 m depth). The food supply for C. dilatata and other suspension-feeders therefore varies on temporal scales varying from hourly (tidal cycle) to daily/weekly (atmospheric forces) to monthly (seasonal influences), but inhibition of feeding by low salinity sometimes limits the ability of C. dilatata to exploit fully the available organic matter.     

Thermodynamic characterization of boltwoodite and uranophane: Enthalpy of formation and aqueous solubility

Boltwoodite and uranophane are uranyl silicates common in oxidized zones of uranium ore deposits. An understanding of processes that impact uranium transport in the environment, especially pertaining to the distribution of uranium between solid phases and aqueous solutions, ultimately requires determination of thermodynamic parameters for such crystalline materials. We measured formation enthalpies of synthetic boltwoodites, K(UO₂)(HSiO₄)·H₂O and Na(UO₂)(HSiO₄)·H₂O, and uranophane, Ca(UO₂)₂(HSiO₄)₂·5H₂O, by high temperature oxide melt solution calorimetry. We also studied the aqueous solubility of these phases from both saturated and undersaturated conditions at a variety of pH. The combined data permit the determination of standard enthalpies, entropies and Gibbs free energies of formation for each phase and analysis of its potential geological impact from a thermodynamic point of view.     

Acoustic Monitoring of Gas Emission Processes in the Arctic Shelf Seas

Oceanology - The emission of natural gas from the seafloor to the surface in shelf areas of the Arctic seas is of increasing interest among researchers. Recently, various types of acoustic...     

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)

Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.     

Floating and fixed artificial habitats: Spatial and temporal patterns of benthic communities in a coral reef environment

While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column.     

Spatial variation in low-level <Superscript>134</Superscript>Cs in the coastal sediments off central Honshu in the Sea of Japan: implications for delivery,migration, and redistribution patterns

In 2014 and 2015, we examined the spatial distribution of cesium-134 (half-life: 2.06 years) from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in marine sediments within coastal–basin areas (water depths of 40–520 m) off central Honshu Island (the main island of Japan) in the Sea of Japan. The ¹³⁴Cs concentrations in both the surface sediment (0–1 cm depth) and whole-core inventory exhibited wide variations, and were highest at the site closest to the Agano River Estuary area (6.7 Bq/kg-dry and 886 Bq/m², respectively). This indicates that ¹³⁴Cs in coastal areas was delivered by riverine suspended solids (SS). Given the spatial variation in ¹³⁴Cs concentrations, we believe that ¹³⁴Cs partially migrated northeastward within ~50 km along Honshu Island (at water depths shallower than ~140 m), and southwestward, including the Sado Basin area. This is predominantly attributable to the transport of SS by bottom currents and unsteady downward delivery onto the steep slopes of the basin. The total amount of ¹³⁴Cs in the study area in 2014 was estimated at approximately 0.6 TBq (decay-corrected to March 11, 2011, date of FDNPP accident).     

Nonlinear transfer function modelling of beach morphology at Duck,North Carolina

This paper presents a simple nonlinear data-based modelling approach for predicting the beach profile volume at Duck, North Carolina, USA. The state-dependent parameter form of the general transfer function (SDP TF) model is used to describe nonlinearity influencing these morphological data in two case examples. Case 1 investigates the nonlinearity associated with the dependency of wave forcing on the preceding beach volume. Case 2 investigates the ability to model the variables within the well-known diffusion equation for beach volume using this data-based approach. The results of this study show that the SDP TF approach can be used successfully to develop statistically robust models for describing nonlinearity in beach morphological systems. Furthermore, these models are shown to predict the beach volumes over both short (1 month ahead) and long (2 years ahead) time periods, and thus show great potential for practical applications in coastal zone management and engineering.     

TOPEX Constrained Solution of Mean Sea Surface by Joint Processing of TOPEX,ERS-1 and GEOSAT Altimetric Measurements

We present an improved crossover adjustment procedure to determine mean sea surface height using TOPEX, 35-day repeat phase ERS-1, Geosat, and 168-day repeat phase ERS-1 satellite altimeter data. The mean sea surface frame defined by the TOPEX data is imposed as certain constraints in our crossover adjustment procedure rather than held fixed as in some other procedures. The new procedure is discussed in detail. Equations are developed to incorporate the a priori information of Topex data as well as other satellite altimeter data. The numerical computation result shows that the rms crossover discrepancies are reduced by an order of 1 cm when the Topex data is not fixed. Furthermore, the computed mean sea surface is less noisy and more realistic than that computed by the traditional procedure.     

Role of Vertical Resolution in Numerical Models Towards the Intensification,Structure and Track of Tropical Cyclones

The impact of vertical resolution on the evolution and movement of tropical cyclones was studied using NCAR MM5 model with a horizontal resolution of 9 km. Four numerical experiments were performed with different vertical resolutions, that is, with 23 vertical levels as control experiment, and 36 vertical levels with high resolution in the lower troposphere, 33 vertical levels with high resolution in the upper troposphere and 46 vertical levels with increased vertical resolution throughout the troposphere as relative to base experiment. The results indicate that increased vertical resolution in the lower troposphere produces efficient intensification and better structure in terms of eye and eyewall. Increased vertical resolution at lower levels improves the prediction of vertical shear of horizontal wind. Experiments with high resolution in the lower troposphere and high resolution throughout the troposphere simulate better track up to 72 hours.