Inorganic and stable isotope geochemistry of tropical Atlantic/Caribbean planktonic foraminifera : implications for the reconstruction of upper ocean temperatures and stratification

• Main Author: Regenberg, Marcus
• Other Authors: Nürnberg, Dirk, Dullo, Wolf-Christian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2006
• Subjects: ddc:550; thesis; Atlantischer Ozean; Foraminiferen; Isotopengeochemie; Mg/Ca ratios; oxygen isotope values; planktonic foraminifera; dissolution; carbonate ion concentration; temperature calibration; calcification depth; diagenesis; stratification; laser ablation; Planktonic foraminifera
• Online Access: https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-19627; https://macau.uni-kiel.de/receive/diss_mods_00001962; https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00001962/d1962.pdf

Planktonic foraminifera from tropical Atlantic and Caribbean sediment-surface samples (0-1 cm) show general westward-directed increasing calcification depths depending on the east-west increase in thermocline depth. Positively related planktonic foraminiferal Mg/Ca and carbonate ion concentration in the Caribbean show well preserved Mg/Ca down to depths about 1.5 km above the lysocline, which equals a carbonate ion concentration of 26-18 µmol/kg. Species-specific calibrations of Mg/Ca with d18O-derived calcification temperatures reveal similar exponential and differing preexponential constants for shallow- and thermocline-dwelling compared to deep-dwelling species. For multispecies, a "warm water" and a "cold water" calibration was derived. Alteration of deep-sea sediments in the vicinity of the Bahama platform results in micro-scale inorganic crystallites on planktonic foraminiferal tests, which synchronize the absence of high Mg-calcite from the sediments. Mg/Ca and Sr/Ca of the crystallites are 4-6 times elevated and 2-3 times depleted, respectively, compared to the original foraminiferal test.