3D modelling of upwelling around a headland

Hydrodynamic

Discord in the family Sparidae (Teleostei): divergent phylogeographical patterns across the Atlantic-Mediterranean divide

The Strait of Gibraltar has been proposed to be the divide between two marine biogeographical regions, the Mediterranean Sea and the Northeast Atlantic. Intraspecific studies have shown, for several of the examined species, a reduction of gene flow between the two basins. The present study examines genetic variation at nuclear and mitochondrial loci in five marine teleost species belonging to the family Sparidae. Four samples for each species were analysed spanning the Northeast Atlantic and the Mediterranean. For all individuals 17 allozyme loci were scored and a combined single strand conformation polymorphism-sequencing approach was used to survey approximately 190 bp of the mitochondrial DNA (mtDNA) D-loop region. All five species share similar biological features. For three species, namely Lithognathus mormyrus, Spondyliosoma cantharus, and Dentex dentex, large mtDNA divergence was observed between Atlantic and Mediterranean samples. Little or no mtDNA differentiation was found in the other two species, Pagrus pagrus and Pagellus bogaraveo. Allozyme data revealed strong differentiation when comparing Atlantic and Mediterranean samples of L. mormyrus and D. dentex, moderate for P. pagrus, and no differentiation for P. bogaraveo and S. cantharus. These results provide evidence for a sharp phylogeographical break (sensu Avise) between the Atlantic and the Mediterranean for two (or possibly three) sparid species of the five investigated. At the same time, the obtained results for the other two species raise the question on which ecological/historical factors might have caused the observed discrepancy in the geographical distribution of genetic variation among otherwise biologically similar species.info:eu-repo/semantics/publishedVersio

Modelling the long term dispersion of radioactive liquid effluent and dose from marine pathways using a grid model

A grid model was developed to combine small-scale grid resolution and long-term predictions of radionuclide dispersion in shallow seas. A predictor-corrector algorithm ensures an unconditional stability of the model. Four modules calculate the concentration of suspended sediments, the dispersion of radionuclides in the marine environment, and the doses to members of the public and marine biota. The model was applied to the dispersion of liquid effluent in the Irish Sea from the Sellafield nuclear reprocessing plant, Cumbria (UK). The concentration factors and partition coefficients have been calibrated for biota species and local conditions. The validation against environmental samples for twenty-two radionuclides shows a good agreement between predicted and measured values

A computer model of sediment dynamics and radionuclide dispersion in a macrotidal estuary

In macrotidal, partially mixed estuaries, tidal pumping can become a dominant mechanism that progressively accumulates sediment in the upper part of the estuary. This mechanism is also reinforced by different mixing behaviour during flood and ebb, due to significantly different stratification patterns. The flux and retention of particle reactive radionuclides within an estuary is complicated by their adsorption onto suspended silts and clays that may then accumulate in an estuary due to these tidal pumping processes. Predicting the accumulation of radionuclides in an estuary is further complicated by radioactive decay processes where daughter products may have distinctly different geochemical properties to those of the parent. The VERSE model has been recently developed in order to replicate the sediment transport and the advection-dispersion of dissolved and particle bound radionuclides with up to nine daughter products. The model is two-dimensional laterally averaged and uses finite difference schemes on a fixed grid. It contains four modules that compute the hydrodynamics, the cohesive sediment dynamics, and the advection-dispersion of conservative and non-conservative contaminants. VERSE has been developed to provide industry and regulatory authorities with a tool that can predict the transport of sediment and the dispersion of contaminants in estuaries, under various hydrodynamic conditions. This paper provides an overview of the model structure and results are compared to field data collected in a macrotidal estuary during several measurement campaigns

Scoping assessment of groundwater doses to biota at the Sellafield site, UK

In investigating the impact of discharges from the nuclear industry on non-human biota, much attention has been given to biota in marine and terrestrial environments. Relatively little attention to date has been given to the exposure of biota to groundwater containing man-made radionuclides. This area of interest is growing especially in the field of nuclear waste repositories. A scoping assessment has been performed to determine the impacts due to radiological contamination on organisms living within or coming into contact with groundwater at the Sellafield site, UK. for time periods up to 2120, modelling of contaminant release from in-ground inventories and transport in groundwater was carried out using a relatively simple assessment methodology with the MONDRIAN modelling suite. Calculated equivalent dose rates to freshwater and marine biota were significantly higher at groundwater sites within the Sellafield boundary than at locations offsite. In general, the total weighted absorbed dose rates calculated in this scoping assessment were of no radiological significance in relation to the England and Wales Environment Agency freshwater ecosystem trigger level (40 µGy h-1). The one exception to this was for bacteria, although the calculated exposure rate is believed to be inconsequential due to the very small size of bacteria

Estimating sediment and caesium-137 fluxes in the Ribble Estuary through time-series airborne remote sensing

High spatial and temporal resolution airborne imagery were acquired for the Ribble Estuary, North West England in 1997 and 2003, to assess the application of time-series airborne remote sensing to quantify total suspended sediment and radionuclide fluxes during a flood and ebb tide sequence. Concomitant measurements of suspended particulate matter (SPM) and water column turbidity were obtained during the time-series image acquisition for the flood and ebb tide sequence on the 17th July 2003 to verify the assumption of a vertically well mixed estuary and thus justifying the vertical extrapolation of spatially integrated estimate of surface SPM. The 137Cs activity concentrations were calculated from a relatively stable relationship between SPM and 137Cs for the Ribble Estuary. Total estuary wide budgets of sediment and 137Cs were obtained by combining the image-derived estimates of surface SPM and 137Cs with estimates of water volume from a two-dimensional hydrodynamic model (VERSE) developed for the Ribble Estuary. These indicate that around 10,000 tonnes of sediment and 2.72 GBq of 137Cs were deposited over the tidal sequence monitored in July 2003. This compared favourably with bed height elevation change estimated from field work. An uncertainty analysis on the total sediment and 137Cs flux yielded a total budget of the order of 40% on the final estimate. The results represent a novel approach to providing a spatially integrated estimate of the total net sediment and radionuclide flux in an intertidal environment over a flood and ebb tide sequence

Observations of a western alborán gyre migration event

Publicado

Progress from 1989 to 1992 in understanding the circulation of the Western Mediterranean Sea

The present paper describes the major results obtained from 1989 to 1992 by the EUROMODEL group in studying the circulation in the Western Mediterranean Sea. Particular emphasis has been given to the physical processes responsible for seasonal and mesoscale variabilities. Observations (in situ and satellite), together with theoretical, physical and numerical models, have been widely used in the course of these studies. Attention has been focused on the dynamics of the northern basin (deep water formation, dynamics of the Northern Mediterranean Current, circulation and shelf/slope interaction in the Balearic Sea) and of the southern basin (Alboran Sea circulation, instabilities of the Algerian Current). The straits dynamics have been studied with particular reference to the Corsica channel. Preliminary runs of a basin-scale circulation model of the Western Mediterranean Sea forced by the straits are also presented. They are shown to be capable of generating a cyclonic circulation in the western basin