Seasonal variability in the zooplankton of the Firth of Forth, including mesozooplankton and microplankton, were investigated across a full annual cycle. Grazing rates and prey selectivity by the dominant calanoid copepods (Acartia discaudata, Acartia clausi, Centropages hamatus and Temora longicornis) were also examined. Investigations were conducted upon Acartia discaudata and field collected prey under simulated diatom bloom conditions, using the species Thalassiosira rotula, in order to test the hypothesis of diatom inhibition of calanoid copepod reproductive processes. There were fundamental differences between the spring and autumn blooms, typical of temperate estuaries. The spring bloom was composed of highly abundant, small cells amounting to less than half the biomass of larger, less numerous microplankton present in autumn. Copepods dominated the mesozooplankton undergoing seasonal shifts in species’ dominance primarily in response to physical factors. Results of grazing experiments indicate a disproportionate preference for motile prey compared to ubiquitous concentrations of diatoms. Copepods switch to blooming diatom species when present in concentrations > 80 cells ml-1. Ciliates generally contributed < 25% to copepod carbon ingestion. Acartia discaudata, Acartia clausi, and Centropages hamatus selectively consumed dinoflagellate and ciliate taxa whereas Temora longicornis remained an indiscriminate grazer during the entire study. Despite increasing rates of egg production in Acartia discaudata, at high concentrations (> 1 x 103 cells ml-1), Thalassiosira rotula inhibited hatching success such that recruitment to naupliar stage 2 was severely impaired compared with eggs hatched from females fed ~0.3 x 103 cells ml-1 concentrations of T. rotula. This is the first recorded evidence of embryogenic inhibition in A. discaudata.

During October/November 1978, oceanographic observations were made on the 7/78 Cruise of the R.R.S. "Shackleton" in the N.W. Aegean Sea. The study area is located within 22°30' to 24°30'E of longitude and from 39°15' to 40°25'N of latitude. Data were collected using STD probe, NIO bottles, expendable bathythermographs and surface continuous records of salinity and temperature using a thermosalinograph. The circulation and water masses in the N.W. Aegean Sea are studied in terms of vertical sections of the horizontal distribution of water properties, individual station curves T/S, S/D and T/D, geostrophic speeds and dynamic topography. Isopycnic analyses using relative salinity are made for subsurface water layers. Two main features are observed in the surface waters; these are: (a) A mixed layer of characteristics; depths 15-55m, densities 27.4-28.6 gm/cm, salinities 37.4-38.7°/oo, and temperatures 15.5-17.2°C. (b) A temperature inversion layer of characteristics; depths 35-90m, densities 27.7-28.8 gm/cm, and temperatures 16.3-18.0°C. In the water usually deeper than 75m, three water masses are recognized: (1) Intermediate water characterized by maximum salinity 38.95°/oo, temperatures 16.30-15°C and densities 28.5-29.0 gm/cm. It is present at depths between 75 and 200m. (2) Deep water present at core depth about 350m and is characterized by salinity maximum 38.92°/oo, temperature 14.00°C and density 29.2 gm/cm. (3) Bottom water present deeper than 400m and is characterized by a well-mixed layer of salinity 38.87°/oo, temperature 13.39°C and density 29.32 gm/cm. The horizontal circulation is dominated by a central cyclonic gyre, an intrustion of high salinity water at the east and southeast, and coastal currents associated with freshwater discharge from nearby rivers.

No description available.

This thesis presents a finite element procedure for the solution of the Shallow-Water Equations dealing with tide generated flows in estuaries and coastal areas incorporating a dynamic land-water interface. The flow algorithm employed is an implementation of the explicit Two-Step Taylor-Galerkin finite element method. The 2-dimensional, depth averaged flow domain is discretised into linear triangular 3-noded elements. A background mesh storing the bathymetric information of the domain is generated using a procedure based on the Delaunay Triangulation technique but with the nodes optimally positioned to take into account the contours of the bed. The moving boundary component is separate from the flow computation. They are coupled at the end of each time-step. Nodes on the land-water interface are moved according to the tidal level and bed slope. Elements and nodes are deleted or created along the boundary so as to ensure good quality triangular elements at all stages of the tide. To limit computational time in the moving boundary algorithm, only the affected areas are meshed. The frequency of movement is monitored so that an optimum balance between accurate presentation of the land-water boundary and fast computational needs is achieved. The presence of structures in the intertidal zone is also dealt with.

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The subsurface density of the North Atlantic displays considerable variability on decadal timescales. In this thesis the variability is examined from two directions. First I show direct observations of oceanic Rossby waves, using historical subsurface temperature data in the North Atlantic. Previously, such waves have only been directly observed using satellite data. Subsurface temperature data are used to investigate westward propagating Rossby waves across the North Atlantic at 30.5°N to 34.5°N, during 1970-74 and 1993-97. The latter period is when high resolution satellite altimetry data are available for comparison. The comparison was very favourable, with observed phase speeds east of the mid-Atlantic ridge, 3.6 cm s^-1 in the altimeter data and 3.4 cm s^-1 for the corresponding period in the hydrographic data. The phase speed of Rossby waves (west of the mid-Atlantic ridge) was observed to be 6.1 cm s^-1 in 1970-74, compared with 4.3 cm s^-1 in 1993-00. Interannual variability of the phase speed was also observed in the altimeter data, this variability was greater in the west than the east. Data from a coupled climate model (HadCM3) are used to assess the ability of an assimilation scheme, based on temperature-salinity preservation, to represent salinity given temperature data. The assimilation scheme was amended to account for meridional frontal movements. The adjustment improves the pre-assimilated salinity in comparison to the true-salinity in all areas south of 55°N, in the North Atlantic. Finally initial condition experiments are performed to determine the predictability of sea surface temperature (SST) and heat flux. The temperature and salinity fields resulting from the assimilation scheme are used as initial conditions in a twin experiment of HadCM3. When the temperature and salinity of the initial ocean state are perfectly known, the SST anomaly forecast skill is up to 5 years. When the assimilation scheme is used to provide these initial conditions for a forecast, the skill of predicting the SST anomaly is almost 2 years. There was no skill in predicting the fluxes in HadCM3 on a seasonal or annual timescale. However the average winter flux anomaly, when averaged over 5 years was found to be predictable.

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