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Blooming coccolithophores
Goldschmidt Conference Abstracts 2006
Blooming coccolithophores R.E.M. RICKABY1, H. STOLL2, J. HENDERIKS3, S. SHAW4, H. ELDERFIELD5 1
Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, USA ([email protected]) 2 Williams College Department of Geosciences, Clark Hall, 947 Main Street, Williamstown, MA 01267, USA (hstoll@ williams.edu) 3 Department of Geology and Geochemistry, Stockhom University, SE-106 91 Stockhom, Sweden (jorijntje.henderiks@ geo.su.se) 4 School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK ([email protected]) 5 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, USA ([email protected]) Coccolithophores play a critical role in the balance between the chemistry of the atmosphere, ocean and sediments. Over geological time, amongst the population of coccolithophore species present, particular bloom forming species have risen to dominance. Every species of coccolithophore initiates the growth of calcite liths with a protococcolith ring consisting of calcite crystals with alternating vertically or radially oriented c-axes, the V/R model (Young et al., 1992). But the modern bloom species, Emiliania huxleyi, appears to exploit the faster propagation of radial calcite crystals which grow largely with obtuse kink sites parallel to the c-axis (Paquette and Reeder, 1995) to produce liths consisting almost entirely of radial calcite. Cations larger than calcium are preferentially incorporated into the less spatially restricted obtuse kink sites of calcite with a radially oriented c-axis, and cations smaller than calcium are preferentially incorporated into the acute sites of calcite with a vertically oriented c-axis. We hypothesis that the different orientations of crystal growth may also have implications for the stable isotopic composition of the calcite liths. Sediment records from the global ocean reveal an inverse relationship between coccolith fraction Mg/Ca and Sr/Ca during the last 1 Myr with a strong resonance of bloom species production at 100 and 400 kyr periods at times of low eccentricity. We propose that these trace metal and isotopic records demonstrate a relationship between orbital eccentricity and the production of bloom species growing radial calcite liths in the Pleistocene ocean (Rickaby et al.), perhaps as a result of the inverse relationship between growing season length and insolation under conditions of high eccentricity. We shall explore, with a geological perspective, the complex interplay between atmospheric chemistry, ocean saturation and the evolution of coccolithophores and their geochemistry.
References Paquette, J., Reeder, R.J., 1995. Geochim. Cosmochim. Acta 59, 735–749. Rickaby, R.E.M., Bard, E., et al., Earth Planet. Sci. Lett., submitted for publication. Young, J.R., Didymus, J.M., Brown, P.R., Prius, B., Mann, S., 1992. Nature 356, 516–518.
A533
Characteristics of mackinawite, tetragonal FeS D. RICKARD School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff CF103YE, UK (rickard@cardiff.ac.uk) Mackinawite, tetragonal FeSm, is a key mineral in ore deposits and in sediments. It is possibly the last widespread simple sulfide mineral discovered. FeSm is metastable and its relatively rapid formation from aqueous solution (Rickard, 1995) is an example of a modified Ostwald’s Step Rule (Luther and Rickard, 2005). Its textbook composition is Fe1+xS. However, the non-stoichiometry is caused by the substitution of metals such as Cu, Ni and Cr in mackinawite associated with the monosulfide solid solution in magmatic ore deposits. Analyses of the synthetic phase has been plagued by a lack of reproducibility. The problems include: (a) FeSm dissolution in acid can produce black rhombic sulfur which leads to under estimation of FeS:S. This can be overcome with the addition of a reductant like Ti(III) citrate; (b) Low analytic totals which are caused partly by (a) but may also be due to contaminants involved in the syntheses. The composition is stoichiometric Fe1.00±0.01S, in agreement with precision XRD results. The material is not hydrated (Rickard et al.). The solubility of FeSm is described by a pH-dependent reaction and a pH-independent reaction. The intrinsic solubility product is 105.7 for the pH-independent reaction FeSm ¼ FeS0 where FeS0 is a monomeric representation of aqueous FexSx clusters (Rickard). The pH-independent reaction describes FeSm solubility in environmentally important neutral to alkaline solutions. The free Fe2+ concentration in sulfidic solutions at pH 8 in equilibrium with FeSm is <0.1% of the total dissolved Fe (II). FeSm only forms where {Fe(II)}{S(II)} is high and thus its distribution in normal marine sediments appears limited (Rickard and Morse). Precipitated FeSm is nanoparticulate and occurs as tabulate crystals, 2–11 nm long and 2–4 nm thick. The smallest particles contain ca. 150 FeS molecules and may represent the first condensed phase in the system. The material is not amorphous, as has been widely reported. Apparent XRPD amorphism is due to small particle size. The mean specific surface area is 380 ± 10 m2 g1. The d100 lattice expansion is 63% of the bulk consistent with lattice relaxation in the nanoparticles (Ohfuji and Rickard, 2006).
References Luther III, G.W., Rickard, D., 2005. J. Nano. Res. 7, 389–407. Ohfuji, H., Rickard, D., 2006. Earth Planet. Sci. Lett. 241, 227–233. Rickard, D., 1995. Geochem. Cosmochim. Acta 59, 4367–4379. Rickard, D., Morse, J.W., Mar. Chem. 97, 141–197. Rickard, D., Griffith A., Oldroyd A., Butler I.B., Lopez-Capel E., Manning D.A.C., Apperley, D.C., Chem. Geol., submitted for publication. Rickard, D., Geochem. Cosmochim. Acta, in press.
doi:10.1016/j.gca.2006.06.982 doi:10.1016/j.gca.2006.06.983
Blooming coccolithophores R.E.M. RICKABY1, H. STOLL2, J. HENDERIKS3, S. SHAW4, H. ELDERFIELD5 1
Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, USA ([email protected]) 2 Williams College Department of Geosciences, Clark Hall, 947 Main Street, Williamstown, MA 01267, USA (hstoll@ williams.edu) 3 Department of Geology and Geochemistry, Stockhom University, SE-106 91 Stockhom, Sweden (jorijntje.henderiks@ geo.su.se) 4 School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK ([email protected]) 5 Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, USA ([email protected]) Coccolithophores play a critical role in the balance between the chemistry of the atmosphere, ocean and sediments. Over geological time, amongst the population of coccolithophore species present, particular bloom forming species have risen to dominance. Every species of coccolithophore initiates the growth of calcite liths with a protococcolith ring consisting of calcite crystals with alternating vertically or radially oriented c-axes, the V/R model (Young et al., 1992). But the modern bloom species, Emiliania huxleyi, appears to exploit the faster propagation of radial calcite crystals which grow largely with obtuse kink sites parallel to the c-axis (Paquette and Reeder, 1995) to produce liths consisting almost entirely of radial calcite. Cations larger than calcium are preferentially incorporated into the less spatially restricted obtuse kink sites of calcite with a radially oriented c-axis, and cations smaller than calcium are preferentially incorporated into the acute sites of calcite with a vertically oriented c-axis. We hypothesis that the different orientations of crystal growth may also have implications for the stable isotopic composition of the calcite liths. Sediment records from the global ocean reveal an inverse relationship between coccolith fraction Mg/Ca and Sr/Ca during the last 1 Myr with a strong resonance of bloom species production at 100 and 400 kyr periods at times of low eccentricity. We propose that these trace metal and isotopic records demonstrate a relationship between orbital eccentricity and the production of bloom species growing radial calcite liths in the Pleistocene ocean (Rickaby et al.), perhaps as a result of the inverse relationship between growing season length and insolation under conditions of high eccentricity. We shall explore, with a geological perspective, the complex interplay between atmospheric chemistry, ocean saturation and the evolution of coccolithophores and their geochemistry.
References Paquette, J., Reeder, R.J., 1995. Geochim. Cosmochim. Acta 59, 735–749. Rickaby, R.E.M., Bard, E., et al., Earth Planet. Sci. Lett., submitted for publication. Young, J.R., Didymus, J.M., Brown, P.R., Prius, B., Mann, S., 1992. Nature 356, 516–518.
A533
Characteristics of mackinawite, tetragonal FeS D. RICKARD School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff CF103YE, UK (rickard@cardiff.ac.uk) Mackinawite, tetragonal FeSm, is a key mineral in ore deposits and in sediments. It is possibly the last widespread simple sulfide mineral discovered. FeSm is metastable and its relatively rapid formation from aqueous solution (Rickard, 1995) is an example of a modified Ostwald’s Step Rule (Luther and Rickard, 2005). Its textbook composition is Fe1+xS. However, the non-stoichiometry is caused by the substitution of metals such as Cu, Ni and Cr in mackinawite associated with the monosulfide solid solution in magmatic ore deposits. Analyses of the synthetic phase has been plagued by a lack of reproducibility. The problems include: (a) FeSm dissolution in acid can produce black rhombic sulfur which leads to under estimation of FeS:S. This can be overcome with the addition of a reductant like Ti(III) citrate; (b) Low analytic totals which are caused partly by (a) but may also be due to contaminants involved in the syntheses. The composition is stoichiometric Fe1.00±0.01S, in agreement with precision XRD results. The material is not hydrated (Rickard et al.). The solubility of FeSm is described by a pH-dependent reaction and a pH-independent reaction. The intrinsic solubility product is 105.7 for the pH-independent reaction FeSm ¼ FeS0 where FeS0 is a monomeric representation of aqueous FexSx clusters (Rickard). The pH-independent reaction describes FeSm solubility in environmentally important neutral to alkaline solutions. The free Fe2+ concentration in sulfidic solutions at pH 8 in equilibrium with FeSm is <0.1% of the total dissolved Fe (II). FeSm only forms where {Fe(II)}{S(II)} is high and thus its distribution in normal marine sediments appears limited (Rickard and Morse). Precipitated FeSm is nanoparticulate and occurs as tabulate crystals, 2–11 nm long and 2–4 nm thick. The smallest particles contain ca. 150 FeS molecules and may represent the first condensed phase in the system. The material is not amorphous, as has been widely reported. Apparent XRPD amorphism is due to small particle size. The mean specific surface area is 380 ± 10 m2 g1. The d100 lattice expansion is 63% of the bulk consistent with lattice relaxation in the nanoparticles (Ohfuji and Rickard, 2006).
References Luther III, G.W., Rickard, D., 2005. J. Nano. Res. 7, 389–407. Ohfuji, H., Rickard, D., 2006. Earth Planet. Sci. Lett. 241, 227–233. Rickard, D., 1995. Geochem. Cosmochim. Acta 59, 4367–4379. Rickard, D., Morse, J.W., Mar. Chem. 97, 141–197. Rickard, D., Griffith A., Oldroyd A., Butler I.B., Lopez-Capel E., Manning D.A.C., Apperley, D.C., Chem. Geol., submitted for publication. Rickard, D., Geochem. Cosmochim. Acta, in press.
doi:10.1016/j.gca.2006.06.982 doi:10.1016/j.gca.2006.06.983