BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-7-2193-2010 Technical Note: On methodologies for determining the size-normalised weight of planktic foraminifera Beer C. J. 1 Schiebel R. 1 2 Wilson P. A. 1 National 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, Angers CEDEX, 49045, France 16 07 2010 7 7 2193 2198 Copyright: © 2010 C. J. Beer et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/7/2193/2010/bg-7-2193-2010.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/7/2193/2010/bg-7-2193-2010.pdf

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 the SNW data produced as part of this study 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.

 References Archer, D., Winguth, A., Lea, D., and Mahowald, N.: What caused the glacial/interglacial atmospheric <i>p</i>CO<sub>2</sub> cycles?, Rev. Geophys., {38}(2), 159–189, 2000. Barker, S.: Planktic foraminiferal proxies for temperature and CO<sub>2</sub>, Ph.D.&nbsp;thesis, University of Cambridge, 2002. Barker, S. and Elderfield, H.: Foraminiferal calcification response to glacial-interglacial changes in atmospheric CO<sub>2</sub>, Science, {297}(5582), 833–836, 2002. Beer, C. J., Schiebel, R., and Wilson, P. A.: Examination of planktic foraminiferal test weight as a surface water [CO$_{2}^{-3}$] proxy, Geology, 38(2), 103–106, 2010. Bijma, J.,&nbsp;Spero, H., and&nbsp;Lea, D.: Reassessing foraminiferal stable isotope geochemistry: Imapct of the ocean carbonate system (experimental results), in: Uses of Proxies in Paleoceanography: Examples from the South Atlantic, edited by:&nbsp;Fischer, G. and&nbsp;Wefer, G., Springer-Verlag, Berlin, Heidelberg, 489–512, 1999. Bijma, J.,&nbsp;Hönisch, B., and Zeebe, R.&nbsp;E.: Impact of the ocean carbonate chemistry on living foraminiferal shell weight: Comment on "Carbonate ion concentration in glacial-age deep waters of the Caribbean Sea", edited by: Broecker, W. S. and Clark, E., Geochem. Geophy. Geosy., {3}(11), 1064, https://doi.org/10.1029/2002GC000388, 2002. Bollmann, J., Quinn, P. S., Vela, M., Brabec, B., Brechner, S., Cortés, M. Y., Hilbrecht, H., Schmidt, D. N., Schiebel, R., and Thierstein, H. R.: Automated particle analysis: Calcareous microfossils, in: Image Analysis, Sediments and Paleoenvironments, edited by:&nbsp;Francus, P., Kluwer Academic Publishers, Dodrecht, 229–252, 2004. Broecker, W. and&nbsp;Peng, T.: Tracers in the Sea, Eldigo Press, New York, 1982. Broecker, W.&nbsp;S. and&nbsp;Clark, E.: An evaluation of Lohmann's foraminifera weight dissolution index, Paleoceanography, {16}(5), 431–434, 2001a. Broecker, W.&nbsp;S. and&nbsp;Clark, E.: Reevaluation of the CaCO<sub>3</sub> size index paleocarbonate ion proxy, Paleoceanography, {16}(6), 669–671, 2001b. Broecker, W.&nbsp;S. and&nbsp;Clark, E.: CaCO<sub>3</sub> dissolution in the deep sea: paced by insolation cycles, Geochem. Geophy. Geosy., {4}(7), 1059, https://doi.org/10.1029/2002GC000450, 2003. Broecker, W.&nbsp;S. and&nbsp;Clark, E.: Shell weights from the South Atlantic, Geochem. Geophy. Geosy., {5}(3), Q03003, https://doi.org/10.1029/2003GC000625, 2004. Caldeira, K. and Wickett, M. E.: Oceanography: Anthropogenic carbon and ocean pH, Nature, 425(6956), 365–-365, https://doi.org/10.1038/425365a 10.1038/425365a, 2003. de Moel, H., Ganssen, G. M., Peeters, F. J. C., Jung, S. J. A., Kroon, D., Brummer, G. J. A., and Zeebe, R. E.: Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification?, Biogeosciences, 6, 1917–1925, https://doi.org/10.5194/bg-6-1917-2009, 2009. Hecht, A.&nbsp;D.: An ecological model for test size variation in recent planktonic foraminifera: applications to the fossil record, J. Foramin. Res., {6}(4), 295–311, 1976. Lohmann, G.&nbsp;P.: A model for variation in the chemistry of planktonic-foraminifera due to secondary calcification and selective dissolution, Paleoceanography, {10}(3), 445–457, 1995. Moy, A. D., Howard, W. R., Bray, S. G., and Trull, T. W.: Reduced calcification in modern Southern Ocean planktonic foraminifera, Nat. Geosci., 2(4), 276-–280, https://doi.org/10.1038/ngeo460, 2009. Orr, J. C., Fabry, V. J., Aumont, O., Bopp, L., Doney, S. C., Feely, R. A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., Key, R. M., Lindsay, K., Maier-Reimer, E., Matear, R., Monfray, P., Mouchet, A., Najjar, R. G., Plattner, G. K., Rodgers, K. B., Sabine, C. L., Sarmiento, J. L., Schlitzer, R., Slater, R. D., Totterdell, I. J., Weirig, M. F., Yamanaka, Y., and Yool, A.: Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms, Nature, {437}(7059), 681–686, 2005. Peacock, S.,&nbsp;Lane, E., and Restrepo, J.&nbsp;M.: A possible sequence of events for the generalized glacial-interglacial cycle, Global Biogeochem. Cy., {20}(2), GB2010, https://doi.org/10.1029/2005GB002448, 2006. Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P., Riebesell, U., Shepherd, J., Turley, C., and Watson, A.: Acidification due to increasing carbon dioxide, Tech. rep., The Royal Society, 2005. Russell, A. D., Hönisch, B., Spero, H. J., and Lea, D. W.: Effects of seawater carbonate ion concentration and temperature on shell U, Mg, and Sr in cultured planktonic foraminifera, Geochim. Cosmochim. Ac., 68(21), 4347–-4361, https://doi.org/10.1016/j.gca.2004.03.013, 2004. Schiebel, R., B.&nbsp;Hiller, and C.&nbsp;Hemleben: Impacts of storms on recent planktic foraminiferal test production and CaCO<sub>3</sub> flux in the North Atlantic at 47&nbsp;degrees&nbsp;N, 20&nbsp;degrees&nbsp;W ({JGOFS}), Mar. Micropaleontol., 26(1–4), 115–129, 1995. Schiebel, R., Barker, S., Lendt, R., Thomas, H., and Bollmann, J.: Planktic foraminiferal dissolution in the twilight zone, Deep Sea Res. Pt.&nbsp;II, 54, 670–686, 2007. Schmidt, D., Renaud, S., Bollmann, J., and Thierstein, H.: Environmental dependence of size in planktic foraminifers, Geochim. Cosmochim. Ac., {66}(15A), A680–A680, suppl.&nbsp;1, 2002. Schmidt, D.&nbsp;N., Lazarus, D., Young, J.&nbsp;R., and Kucera, M.: Biogeography and evolution of body size in marine plankton, Earth-Sci. Rev., {78}(3–4), 239–266, 2006. Sigman, D.&nbsp;M. and Boyle, E.&nbsp;A.: Glacial/interglacial variations in atmospheric carbon dioxide, Nature, {407}(6806), 859–869, 2000. Zeebe, R. and Wolf-Gladrow, D.: CO<sub>2</sub> in Seawater: Equilibrium, Kinetics, Isotopes, Elsevier Oceanography Series, vol.&nbsp;65, Elsevier, 2001. Zeebe, R.&nbsp;E., Zachos, J.&nbsp;C., Caldeira, K., and Tyrrell, T.: Oceans: Carbon emissions and acidification, Science, {321}(5885), 51–52, 2008.