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Technical Note: Determining the size-normalised weight of planktic foraminifera
1National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO14 3ZH, UK
*now at: Laboratoire d'Etude des Bio-indicateurs Actuels et Fossiles, Université d'Angers, 2 Boulevard Lavoisier, 49045 Angers CEDEX, France
Abstract. The size-normalised weight (SNW) of planktic foraminifera, a measure of test wall thickness and density, is potentially a valuable palaeo-proxy for marine carbon chemistry. As increasing attention is given to developing this proxy it is important that methods are comparable between studies. Here, we compare SNW data generated using two different methods to account for variability in test size, namely i) the narrow (50 μm range) sieve fraction method and ii) the individually measured test size method. Using specimens from the 200–250 μm sieve fraction range collected in multinet samples from the North Atlantic, we find that sieving does not constrain size sufficiently well to isolate changes in weight driven by variations in test wall thickness and density from those driven by size. We estimate that these SNW data are associated with an uncertainty, or error bar, of about ±11%. Errors associated with the narrow sieve fraction method may be reduced by decreasing the size of the sieve window, by using larger tests and by increasing the number tests employed. In situations where numerous large tests are unavailable, however, substantial errors associated with this sieve method remain unavoidable. In such circumstances the individually measured test size method provides a better means for estimating SNW because, as our results show, this method isolates changes in weight driven by variations in test wall thickness and density from those driven by size.
Discussion Paper (PDF, 1015 KB) Supplement (10715 KB) Interactive Discussion (Open, 1 Comment)
Citation: Beer, C. J., Schiebel, R., and Wilson, P. A.: Technical Note: Determining the size-normalised weight of planktic foraminifera, Biogeosciences Discuss., 7, 905-920, 2010. Bibtex EndNote Reference Manager
