HR: 17:00h
AN: PP44A-05    [Abstracts]
TI: Post-depositional Mn-Mg-rich carbonates: Implications for foraminiferal Mg/Ca paleothermometry
AU: * Pena, L D
EM: lpena@ub.edu
AF: GRC GeociŠncies Marines, Department of Stratigraphy, Paleontology and Marine Geosciences, University of Barcelona, Faculty of Geology, Martˇ i Franqu‚s s/n, Barcelona, 08028 Spain
AU: Calvo, E
EM: ecalvo@cmima.csic.es
AF: Research School of Earth Sciences, The Australian National University, Canberra, 0200 Australia
AU: Calvo, E
EM: ecalvo@cmima.csic.es
AF: Centre Mediterrani d'Investigacions Marines i Ambientals, CMIMA-CSIC, Passeig Mary'tim de la Barceloneta, 37-49, Barcelona, 08003 Spain
AU: Cacho, I
EM: icacho@ub.edu
AF: GRC GeociŠncies Marines, Department of Stratigraphy, Paleontology and Marine Geosciences, University of Barcelona, Faculty of Geology, Martˇ i Franqu‚s s/n, Barcelona, 08028 Spain
AU: Cacho, I
EM: icacho@ub.edu
AF: Godwin Laboratory, Department of Earth Sciences, Pembroke Street, Cambridge, CB2 3SA United Kingdom
AU: Eggins, S
EM: stephen.eggins@anu.edu.au
AF: Research School of Earth Sciences, The Australian National University, Canberra, 0200 Australia
AU: Pelejero, C
EM: pelejero@cmima.csic.es
AF: Research School of Earth Sciences, The Australian National University, Canberra, 0200 Australia
AU: Pelejero, C
EM: pelejero@cmima.csic.es
AF: Centre Mediterrani d'Investigacions Marines i Ambientals, CMIMA-CSIC, Passeig Mary'tim de la Barceloneta, 37-49, Barcelona, 08003 Spain
AB: The use of foraminiferal Mg/Ca ratios as an indicator of past temperatures in which these organisms dwelt has been widely employed by the paleoceanographic community during the last two decades. However, it was also early recognized that there are many potential contamination sources that may bias the `natural' Mg/Ca relationship within foraminiferal carbonates. In this work, we have analyzed the geochemical composition of foraminifera shells from an Ocean Drilling Program Site in the Panama Basin. A broad array of different analytical techniques has been used (LA-ICP-MS, ICP-MS, XRD, SEM, EDX and Electron Microprobe) in order to identify and evaluate the occurrence of contaminant phases. Laser Ablation ICP-MS profiles prove the presence of Mn-Mg-rich contaminant phases at the inner surfaces of the foraminifera shells. X-ray diffraction analysis further reveals that this Mn-Mg-rich phase is a carbonate known as kutnahorite (Ca(Mn, Mg)(CO3)2). Our results demonstrate that the presence of kutnahorite-like minerals can bias Mg/Ca ratios towards higher values (by 7-36%) and lead to significant overestimation of past sea water temperatures (by 0.9 up to 6.2°C, in the case of these Panama Basin samples). New collected data have proved that these contaminant phases are likely biasing other trace elements ratios in foraminiferal calcites as for example the U/Ca and Ba/Ca ratios. We have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included. The analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high Mn values are associated with at least two different contaminant phases, of which only one is linked to high Mg values.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4924 Geochemical tracers
DE: 4994 Instruments and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005