Seasonal Distributions of Foraminifera and their Implications for Sea-Level Studies, Cowpen Marsh, U.K.
Benjamin P. Horton, Robin J. Edwards, 2003. "Seasonal Distributions of Foraminifera and their Implications for Sea-Level Studies, Cowpen Marsh, U.K.", Micropaleontologic Proxies for Sea-Level Change and Stratigraphic Discontinuities, Hilary Clement Olson, R. Mark Leckie
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Analyses of total abundance of dead foraminifera from a twelve-month study of surface samples (0–1 cm) from Cowpen Marsh shows no definite seasonal pattern, but significant seasonal variations are evident in the relative abundance of agglutinated and calcareous taxa. Agglutinated species are most dominant in the winter months whilst calcareous foraminifera reach their peak relative abundances during the summer. We identify three cluster zones: a high-marsh and middle-marsh zone of Jadammina macrescens and Trochammina inflata; a low-marsh zone of Miliammina fusca and Jadammina macrescens; and a mudflat zone of calcareous foraminiferal species, notably Elphidium williamsoni, Haynesina germanica, and Quinqueloculina spp. The variations of contemporary foraminiferal distribution across the intertidal zone during an annual cycle modify the elevation of the zonal boundaries by as much as 0.9 m. Consequently, a contemporary sample taken in one month can significantly underestimate (0.35 m) or overestimate (0.48 m) the elevation range of a zone. Hence, the value of cluster zones as indicators of former sea levels can be assessed only following a consideration of the elevation errors induced by the seasonal variability in saltmarsh foraminiferal distributions.
We developed monthly and annual foraminifera-based transfer functions using weighted averaging regression and calibration. Results suggest that precise reconstructions of former sea levels are possible (r2 ≥ 0.82) but that the accuracy of these reconstructions varies during the course of the year. Greatest precision is achieved using samples collected in the winter months (± 0.29 m) and weakest during the summer (± 0.35 m) because the foraminiferal assemblages are dominated by agglutinated and calcareous species, respectively. We conclude that an investigation of contemporary saltmarsh foraminifera that recovers a complete set of samples in the winter, spring, summer, and autumn will provide the best-quality data for use in sea-level investigations (error = ± 0.21 m). If only one set of measurements can be obtained, sampling in the winter months may represent the most reliable alternative.