HR: 0800h
AN: PP11B-1453    [Abstracts]
TI: The Influence of Light on U, Sr, and Mg Incorporation Into Planktic Foraminifera, and Other Culture Study Results
AU: * Russell, A D
EM: russell@geology.ucdavis.edu
AF: Dept of Geology, University of California, Davis, CA 95616 United States
AU: Hoenisch, B
EM: hoenisch@ldeo.columbia.edu
AF: LDEO, 61 Route 9W, Palisades, NY 10964 United States
AU: Spero, H J
EM: spero@geology.ucdavis.edu
AF: Dept of Geology, University of California, Davis, CA 95616 United States
AU: Lea, D W
EM: lea@geol.ucsb.edu
AF: Dept of Geological Sciences, University of California, Santa Barbara, CA 93106 United States
AB: The processes of photosynthesis and respiration influence pH gradients from the calcifying shell wall of foraminifera to the bulk fluid, since photosynthesis consumes CO₂ (increasing pH), and respiration releases CO₂ (lowering pH). Previous laboratory culture experiments with O. universa (a symbiont-bearing species) and G. bulloides (which lacks symbionts) demonstrated that shell U/Ca in both species decreased exponentially and Sr/Ca increased linearly as seawater pH increased from pH = 7.7 to 8.7. Whereas the form of the U/Ca-pH relationship was similar for both species, U/Ca in G. bulloides (at the same pH) was 40% higher than in O. universa. Mg/Ca decreased with pH (at pH<8.2), and was lower in G. bulloides (Russell et al., GCA 2004). The direction of the U/Ca and Mg/Ca species offsets is consistent with the relatively low pH surrounding the shell of G. bulloides, in which the influence of respiratory carbon on pH is not counteracted by the effects of photosynthesis. Here we report results of laboratory culture experiments in which we grew O. universa under low light conditions (LL) (50-73 μmol photons/m²/sec) in seawater over a range of pH. Based on the pH dependencies and species offsets above, we hypothesized that inhibition of photosynthesis would lead to higher U/Ca and lower Mg/Ca and Sr/Ca ratios in shells of O. universa compared to those cultured under high light (HL) conditions. Contrary to our expectations, U/Ca ratios in shells of individuals cultured under LL were approximately 50% lower than those cultured under HL at similar pH. At low and ambient pH, Sr/Ca and Mg/Ca in the LL shells was not significantly different from the HL shells, but in a single LL high pH group, both Sr/Ca and Mg/Ca was elevated relative to the HL shells. We suggest that the composition of these metals in shells of O. universa may be affected by the competing influences of symbiont activity and bulk solution pH over calcification rate.
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 4875 Trace elements (0489)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005