HR: 0800h
AN: PP11A-0547    [Abstracts]
TI: New Insights into Inferring Climate Variability from Records of Planktonic Foraminiferal Mg/Ca, Oxygen Isotope and Shell Weight in the Southern Ocean
AU: * Greaves, M
EM: mg109@esc.cam.ac.uk
AF: University of cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Barker, S
EM: na
AF: Lamont Doherty Earth Observatory of Columbia University, Palisades, New York, 10964 United States
AU: Tripati, A
EM: n.a
AF: University of cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Elderfield, H
EM: he101@esc.cam.ac.uk
AF: University of cambridge, Department of Earth Sciences Downing Street, Cambridge, CB2 3EQ United Kingdom
AU: Hall, I
EM: n.a
AF: School of Earth, Ocean, Planet. Sci., Cardiff University, Cardiff, CF10 3YE United Kingdom
AU: Pahnke, K
EM: n.a
AF: School of Earth, Ocean, Planet. Sci., Cardiff University, Cardiff, CF10 3YE United Kingdom
AU: Zahn, R
EM: n.a
AF: ICREA, University of Barcelona, Barcelona, E-08193 Spain
AB: Temperature is the dominant control on foraminiferal Mg/Ca, although other factors are important and can bias paleoceanographic reconstructions. In order to investigate the controls on Mg/Ca, we compare records from two sites at different water depths located north and south of the Subtropical Convergence in the Southern Ocean (ODP Site 1123 and MD97-2120). Mg/Ca, d18O, and shell weight were obtained from two narrow size fractions (250-300 and 300-355 um) of the planktonic foraminifer Globigerina bulloides. Combining these data allows us to investigate the effects of hydrography, dissolution and foraminiferal habitat as controls on Mg/Ca. Differences are observed between the records from these locations. Comparison of Mg/Ca records from both size fractions at MD97-2120 implies similar calcification temperatures. In contrast, Mg/Ca-derived paleotemperatures from the 250-300 um fraction at ODP Site 1123 are higher than in the larger size fraction. Mg/Ca records from both size fractions at MD97-2120 are similar across Termination 1 and imply a glacial-interglacial temperature change of 8 degrees C. The temperature record from the 250-300 um fraction from ODP Site 1123 shows a glacial-interglacial temperature change of 4 degrees across Termination 1, whereas in the 300-355 um fraction no temperature change is observed. At ODP Site 1123, the contrast between size fractions in Mg/Ca-derived temperatures is even more striking across Termination 2. The differences in Mg/Ca records are associated with offsets in d18O and shell weight records from both size fractions. The larger fraction exhibits heavier d18O and larger weight variability. Possible explanations for these observations include hydrographic differences between the two sites, foraminiferal habitat, dissolution susceptibility, and preservation history.
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting