Incorporation of hydrothermal elements in foraminiferal calcite: Results from culturing experiments

The trace race element chemistry of foraminiferal tests reflect the environment in which they grew. Thus geochemical data can be used as paleo-proxies constraining environmental conditions in ancient seas [e.g.: 1]. Seawater chemistry may be influenced by local sources such as hydrothermal activity. However, for elements considered diagnostic for hydrothermalism, reliable experimental data is rare [e.g. 2]. To provide a solid basis for a more complete understanding of trace element partitioning between foraminiferal calcite and seawater, we carried out culture experiments under controlled laboratory conditions. This is the main objective of our study.For our experiment we grew freshly collected benthic foraminifera (Ammonia tepida) in seawater, containing a cocktail of Mn, Co, Ni and Cu, at defined trace element levels.Measurements of the culture solutions were carried out regularly by HR-ICP-MS whereas the calcite of newly grown chambers of the cultured foraminifera was detected by a non-destructive technique - µSy-XRF [3]. To confirm the data LA-ICP-MS measurements have been performed. To distinguish between old and new chambers the calcein labeling technique [4] was applied.First results demonstrate that especially Ni and Cu could be determined with high precission and accuracy using µSy-XRF measurements. We determined trace element/Ca ratios and DNi as well as DCu using LA ICP-MS

Heavy metal incorporation in foraminiferal calcite: results from multi-element enrichment culture experiments with Ammonia tepida

The incorporation of heavy metals into carbonate tests of the shallow water benthic foraminifer <i>Ammonia tepida</i> was investigated under controlled laboratory conditions. Temperature, salinity, and pH of the culture solutions were kept constant throughout the duration of this experiment, while trace metal concentrations were varied. Concentrations of Ni, Cu, and Mn were set 5-, 10-, and 20 times higher than levels found in natural North Sea water; for reference, a control experiment with pure filtered natural North Sea water was also analysed. The concentrations of Cu and Ni from newly grown chambers were determined by means of both μ-synchrotron XRF and Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS). The results of both independent analytical techniques agreed within the analytical uncertainty. In general, the concentration of the analysed elements in the tests increased in line with their concentration in the culture solutions. Potential toxic and/or chemical competition effects might have resulted in the decreased incorporation of Ni and Cu into the calcite of the specimens exposed to the highest elemental concentrations. Mn incorporation exhibited large variability in the experiment with the 20-fold increased element concentrations, potentially due to antagonistic effects with Cu. The partition coefficients of Cu and Ni were calculated to be 0.14 ± 0.02 and 1.0 ± 0.5, respectively, whereas the partition coefficient of Mn was estimated to be least 2.4. These partition coefficients now open the way for reconstructing past concentrations for these elements in sea water