The influences of growth rates on planktic foraminifers as proxies for palaeostudies – a review
D. N. Schmidt, T. Elliott, S. A. Kasemann, 2008. "The influences of growth rates on planktic foraminifers as proxies for palaeostudies – a review", Biogeochemical Controls on Palaeoceanographic Environmental Proxies, W. E. N. Austin, R. H. James
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Size dependent changes in element concentrations in planktic foraminifers have long been recognized to influence their reliability as an archive for climate change. Traditionally, these changes have been interpreted as changes in element partitioning during the ontogeny of the organism with faster growth rates in the earlier part of the development. These changes, in the light of new culture experiments, can also be interpreted as changes in growth rate throughout the entire life of the organism, with larger, faster-growing specimens discriminating less efficiently against trace element incorporation into the calcite shell. Growth rates of foraminifera are influenced by the environment and hence change geographically and temporally at various scales, e.g. glacial-interglacial or rapid millennial events such as the Younger Dryas. These changes in growth rate can account for some changes in element to calcium ratio between glacial and interglacials, which were previously linked to changes in seawater element ratios.
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Most of our information about the evolution of Earth’s ocean-climate system comes from the analysis of sediments laid down in the past. For example, the microfossil assemblage reflects the temperature, salinity and nutrient abundance of the water in which the organisms lived, while the chemical and isotopic composition of biogenic carbonates may be used to reconstruct past variations in the operation of the carbon cycle, as well as changes in ocean circulation.
Nevertheless, understanding the link between these sediment variables (or ‘proxies’) and environmental conditions is not straightforward. This volume adopts a novel approach by bringing together palaeontologists, geochemists and palaeoceanographers, who contribute evidence that is required to better constrain these proxies. Topics include: (i) processes of biomineralization, and their effect on the chemical and isotopic composition of different organisms; (ii) proxy validation, including field, laboratory and theoretical studies; (iii) the links between modern and fossil organisms.