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Wilke, Iris; Peeters, Frank J C; Bickert, Torsten (2006): Stable isotope record of Globorotalia inflata. PANGAEA,, Supplement to: Wilke, I et al. (2006): The influence of seawater carbonate ion concentration [CO32-] on the stable isotope composition of planktic foraminifera species Globorotalia inflata. Marine Micropaleontology, 58(4), 243-258,

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We sampled the upper water column for living planktic foraminifera along the SW-African continental margin. The species Globorotalia inflata strongly dominates the foraminiferal assemblages with an overall relative abundance of 70-90%. The shell delta18O and delta13C values of G. inflata were measured and compared to the predicted oxygen isotope equilibrium values (delta18O(eq)) and to the carbon isotope composition of the total dissolved inorganic carbon (delta13C(DIC)) of seawater. The delta18O of G. inflata reflects the general gradient observed in the predicted delta18O(eq) profile, while the delta13C of G. inflata shows almost no variation with depth and the reflection of the delta13C(DIC) in the foraminiferal shell seems to be covered by other effects. We found that offsets between delta18O(shell) and predicted delta18O(eq) in the surface mixed layer do not correlate to changes in seawater [CO3[2-]].
To calculate an isotopic mass balance of depth integrated growth, we used the oxygen isotope composition of G. inflata to estimate the fraction of the total shell mass that is grown within each plankton tow depth interval of the upper 500 m of the water column. This approach allows us to calculate the DELTA delta13C(interval added-DIC); i.e. the isotopic composition of calcite that was grown within a given depth interval. Our results consistently show that the DELTA delta13C(IA-DIC) correlates negatively with in situ measured [CO3[2-]] of the ambient water. Using this approach, we found DELTA delta13C(IA-DIC)/[CO3[2-]] slopes for G. inflata in the large size fraction (250-355 µm) of -0.013 per mil to 0.015 per mil (µmol/kg)**-1 and of -0.013 per mil to 0.017 per mil (µmol/kg)**-1 for the smaller specimens (150-250 µm). These slopes are in the range of those found for other non-symbiotic species, such as Globigerina bulloides, from laboratory culture experiments. Since the DELTA delta13C(IA-DIC)/[CO3[2-]] slopes from our field data are nearly identical to the slopes established from laboratory culture experiments we assume that the influence of other effects, such as temperature, are negligibly small. If we correct the delta13C values of G. inflata for a carbonate ion effect, the delta13C(shell) and delta13C(DIC) are correlated with an average offset of 2.11.
Related to:
Wilke, Iris (2005): The influence of seasonal distribution patterns, ecological preferences and calcification process on the incorporation of stable oxygen and carbon isotopes in planktic foraminiferal clacite shells. PhD Thesis, Elektronische Dissertationen an der Staats- und Universitätsbibliothek Bremen, Germany, urn:nbn:de:gbv:46-diss000012356
Median Latitude: -31.123518 * Median Longitude: 15.095797 * South-bound Latitude: -33.475833 * West-bound Longitude: 12.335667 * North-bound Latitude: -29.202333 * East-bound Longitude: 17.169500
Date/Time Start: 2003-01-23T13:03:00 * Date/Time End: 2003-02-03T18:27:00
GeoB8305-3 * Latitude: -33.475833 * Longitude: 17.169500 * Date/Time: 2003-01-23T13:03:00 * Elevation: -709.5 m * Campaign: M57/1 * Basis: Meteor (1986) * Method/Device: CTD/Rosette (CTD-RO) * Comment: 17 x 10 L, Sampling interval: 10, 4 x 30, 50, 4 x 75, 100, 150, 200, 250, 300, 400, 500, 600m. Sample for d13C, d18O, Total alkalinity, Bottle No 17 not closed (sampling interval 30)
GeoB8305-4 * Latitude: -33.475333 * Longitude: 17.169500 * Date/Time: 2003-01-23T13:56:00 * Elevation: -709.5 m * Campaign: M57/1 * Basis: Meteor (1986) * Method/Device: Multiple opening/closing net (MSN) * Comment: 17x 10L, Sampling interval: 0-50, 50-100, 100-200, 200-300, 300-500m
GeoB8305-5 * Latitude: -33.467500 * Longitude: 17.169167 * Date/Time: 2003-01-23T14:51:00 * Elevation: -100.0 m * Campaign: M57/1 * Basis: Meteor (1986) * Method/Device: Multiple opening/closing net (MSN) * Comment: 5x cubs, Sampling interval: 0-20, 20-40, 40-60, 60-80, 80-100m
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