\(\delta \)\textsuperscript{44/40}Ca and Mg/Ca Ratios of \textit {N. Pachyderma} (sin.) in the Western Nordic Seas: Indications of Changing Carbonate Chemistry Controlled by Water Mass Effects or Foraminiferal Metabolism

HR: 0800h
AN: B21B-0865 [Abstracts]
TI: \(\delta \)\textsuperscript{44/40}Ca and Mg/Ca Ratios of \textit {N. Pachyderma} (sin.) in the Western Nordic Seas: Indications of Changing Carbonate Chemistry Controlled by Water Mass Effects or Foraminiferal Metabolism
AU: * Kozdon, R
EM: rkozdon@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: * Kozdon, R
EM: rkozdon@ifm-geomar.de
AF: Christian-Albrechts-Universitaet zu Kiel, Ludewig-Meyn-Strasse 10, Kiel, 24118 Germany
AU: Eisenhauer, A
EM: aeisenhauer@ifm-geomar.de
AF: IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, 24148 Germany
AU: Hippler, D
EM: hippler@geo.unibe.ch
AF: Isotopengeologie/Universitaet Bern, Erlachstrasse 9a, Bern, 3012 Switzerland
AU: Meland, M
EM: marius.meland@geo.uib.no
AF: Bjerknes Centre for Climate Research, AllＨaten 55, Bergen, 5007 Norway
AU: Weinelt, M
EM: mw@gpi.uni-kiel.de
AF: Christian-Albrechts-Universitaet zu Kiel, Ludewig-Meyn-Strasse 10, Kiel, 24118 Germany
AU: Sarnthein, M
EM: ms@gpi.uni-kiel.de
AF: Christian-Albrechts-Universitaet zu Kiel, Ludewig-Meyn-Strasse 10, Kiel, 24118 Germany
AB: The high temperature sensitivity of the \(\delta \)\textsuperscript{44/40}Ca signature in the polar to subpolar planktonic foraminifer of \textit {N. pachyderma} (sin.) (\(\delta \)\textsuperscript{44/40}Ca=0.21*SST(\textsuperscript{o}C)-0.61) found by previous workers has turned out to be solid and reproducible in the North Atlantic and Norwegian Sea. In this area, calcium isotopic compositions provide the possibility to resolve the amplitude of sea surface temperature (SST) changes as well as absolute SST estimates. Here we present a multi proxy record from a sediment core near the Denmark Strait, spanning the time interval from the LGM to the late Holocene. The comparison of \(\delta \)\textsuperscript{44/40}Ca, Mg/Ca, \(\delta \)\textsuperscript{18}O and foraminiferal transfer functions highlights the potential of \(\delta \)\textsuperscript{44/40}Ca as an additional SST-proxy, especially at the 'cold end' with its higher statistical uncertainties. However, in the western part of the Nordic Seas which is characterized by polar and Arctic waters, \(\delta \)\textsuperscript{44/40}Ca ratios of \textit {N. pachyderma} (sin.) are insensitive to temperature variations, reflecting the low temperature dependency found in most planktonic foraminifer species. This observed change in the calcium isotopic composition coincide with unusual high Mg/Ca ratios in \textit {N. pachyderma} (sin.) in polar and Arctic waters as published in previous works. Mg/Ca calculated temperatures in these water masses overestimate existing SSTs by more than 10\textsuperscript{o}C. Diagenetic effects, ice cover, dissolution or sample contamination were considered to influence the Mg/Ca ratio. Simultaneous measurements of Mg/Ca and \(\delta \)\textsuperscript{44/40}Ca in samples of \textit {N. pachyderma} (sin.) indicate that the change in the \(\delta \)\textsuperscript{44/40}Ca temperature sensitivity is directly linked to this unusual high Mg/Ca ratios. This failure of existing temperature calibrations of two independent carbonate-chemistry proxies in polar and Arctic waters suggests that either water mass chemistry or selective processes controlled by the foraminiferal metabolism may be responsible.
DE: 4870 Stable isotopes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting