HR: 08:30h
AN: PP41E-03 INVITED    [Abstracts]
TI: Controls on Mg/Ca variation in planktonic foraminifera: insights from microanalysis of laboratory cultured Orbulina universa
AU: * Eggins, S
EM: Stephen.Eggins@anu.edu.au
AF: Research School of Earth Sciences The Australian National University, Mills Road, Canberra, ACT 0200, Australia
AU: Spero, H
EM: spero@geology.ucdavis.edu
AF: Department of Geology University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
AU: Russell, A D
EM: russell@geology.ucdavis.edu
AF: Department of Geology University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
AU: Alford, S
EM: sealford@umich.edu
AF: Dept of Geological Sciences University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AU: Doo, S
AF: Department of Geology University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
AU: Kuroyanagi, A
EM: a-kuroyanagi@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, the University of Tokyo, 1-15-1, Minamidai, Tokyo, 164-8639, Japan
AU: da Rocha, R E
EM: rrocha@awi-bremerhaven.de
AF: Alfred Wegner Institute, Am Handelschafen 12, Bremerhaven, D-27570, Germany
AU: Sadekov, A Y
EM: Aleksey.sadekov@anu.edu.au
AF: Research School of Earth Sciences The Australian National University, Mills Road, Canberra, ACT 0200, Australia
AB: The bulk shell Mg/Ca composition of foraminifera (including Orbulina universa) increase exponentially with seawater temperature at ~10% per °C, however, individual O. universa exhibit large-amplitude internal Mg/Ca growth banding that suggests factors in addition to temperature may influence foraminiferal calcite Mg/Ca composition. To shed light on the origin of Mg/Ca banding in O. universa we have performed high resolution compositional profiling of single shells grown in laboratory-cultures under a 12 hour high-light (day)-12 hour dark (night) cycle, synchronized with transfer of living foraminifers between trace element or isotopically spiked and natural seawater. These experiments confirm that the Mg/Ca banding reflects a diel cycle and specifically that high Mg/Ca bands form at night and low-Mg/Ca bands form during the day. Our results, together with existing models for and measured daily changes in [CO₃^2-] and calcite saturation state within the foraminiferal microenvironment, point to the important interplay between day-time photosynthesis (by algal symbionts) and night-time respiration in determining the Mg/Ca composition of foraminiferal calcite. They are also consistent with previously reported increases in bulk Mg/Ca composition with decreasing seawater [CO₃^2-] and pH. The results of other experiments undertaken to elucidate the effects of seawater properties on the nature of both compositional banding and the development of gametogenic calcite within O. universa will also be discussed.
DE: 4808 Chemical tracers
DE: 4872 Symbiosis
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4924 Geochemical tracers
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting