HR: 16:15h
AN: V54B-02    [Abstracts]
TI: Fractionation Of Silicon Isotopes By Present-Day Demosponges From The Spermonde Shelf, Indonesia.
AU: * Vroon, P Z
EM: vrop@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Beets, K J
EM: beec@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Soenardo, D H
EM: soed@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: van Soest, R W
EM: soest@science.uva.nl
AF: The Zoological Museum of Amsterdam, Mauritskade 61, Amsterdam, 1092 AD Netherlands
AU: Troelstra, S R
EM: tros@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: Schwieters, J
EM: JSchwieters@ThermoFinniganMAT.de
AF: ThermoElectron, Barkhausenstrasse 2, Bremen, 28197 Germany
AU: van Belle, C C
EM: belj@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AU: van der Wagt, B
EM: wagb@geo.vu.nl
AF: Faculty of Earth and Life Sciences, De Boelelaan 1085, Amsterdam, 1081 HV Netherlands
AB: The silicon and carbon biogeochemical cycles are closely linked since diatoms (phytoplankton with an opal skeleton) transport large quantities of silicon and carbon from the surface- to the deep ocean. The silicon isotopic composition of biogenic opal could provide additional information for climate studies, continental weathering and the secular variations of biogenic silica in seawater. So far, only limited data are available for the fractionation factors between dissolved silica in seawater and biogenic opal. De La Rocha et al. (1997) showed that the fractionation factor between dissolved silica and diatom opal is not species dependent. However, other organisms with opal skeletons, such as sponges and radiolarians, have not been investigated in detail so far. We selected three demosponge species from a tropical region (Spermonde Shelf, Sulawesi, East Indonesia), where temperature differences are minimal. Therefore, silicon isotope fractionations induced by temperature, or differences in the dissolved silica isotopic composition are unlikely. The demosponges of this study display a range of $\delta$$^{30}$Si between -2.0 and +0.5$\permil$. This range largely overlaps with previous published data, but extends the range to heavier values. The three species show different $\delta$$^{30}$Si averages: {\it Petrosia hoeksemai}: -0.04 $\pm$ 0.14$\permil$; {\it Stylissa carteri}: 0.20 $\pm$ 0.27$\permil$ and {\it Clathria thalysias basilana}: -1.28 $\pm$ 0.26$\permil$. The results from the studied demosponges suggest that fractionation factors are species dependent, since the sponges display systematic differences at a single locality. We did not observe correlations between $\delta$$^{30}$Si, opal content and water depth. Sponges are probably dissolved silica limited and not food limited in their growth. Consequently, different biological mechanisms for the uptake of dissolved silica and the conversion to sponge opal could be the reason for the different fractionation factors for each species. References De La Rocha et al., (1997) Geochim. Cosmochim Acta 61, 5051-5056.
DE: 4806 Carbon cycling
DE: 4825 Geochemistry
DE: 4835 Inorganic marine chemistry
DE: 4845 Nutrients and nutrient cycling
DE: 4870 Stable isotopes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting