Contemporary ecology and stable isotope geochemistry of benthic foraminiferids in the Celtic Sea
The primary aim of this thesis was to assess the value of foraminifera in downcore studies of shelfsea stratification using both assemblage and geochemical characteristics. An examination of the modern distribution of foraminifera in the context of stratification in the Celtic Sea and comparison of these distributions with measured environmental variables was undertaken to this end. In addition, several species were examined for their stable oxygen and carbon isotopic composition with reference to the ambient bottom and porewaters. Cruises were run to the Celtic Sea in July, 1995 and July-August, 1996, during which hydrographic data, water and surface sediment samples were collected from 138 stations. Fifty-three samples were subsequently analysed for grainsize, geochernical and foraminiferal properties, while the water samples were analysed for oxygen isotopic composition. A total of six multicores were extracted and sectioned. Each section was analysed for porewater carbon isotopic composition and foraminiferal content. Selected foraminifera from both the surface and subsurface samples were analysed for the oxygen and carbon isotopic composition of their test calcite. Statistical analyses of the foraminiferal data indentifed four distinct assemblages which have potential for palaeostratification studies. The mixed-type assemblage included Cibicides lobatulus, Ammonia beccarfi, Quinqueloculina seminulum, Textularia bockii and Spiroplectammina, wrightfi. The stratifiedtype assemblages included Bulimina marginata, Hyalinea balthica, Nonionella turgida and Adercotryma glomeratum while Stainforthis fusiformis was diagnostic of the front. Bulimina gibba, Elphidium excavatum forma selseyensis and Eggerelloides scabrus defined an eastern asseblage. It is believed that the true controls on these assemblages are oxygen and food supply. Ammonia beccarii precipitated its test in oxygen isotopic equilibrium while Q. seminulum was consistently, negatively offset by approximately 0.5 O/oo. This demonstrates the potential of these species in palaeo-temperature and particularily, palaeo-stratifcation studies. The 'microhabitat effect' was examined for several species of foraminifera but was not observed.