Accéder directement au contenu Accéder directement à la navigation
Article dans une revue

Mn / Ca intra-test variability in the benthic foraminifer Ammonia tepida

Abstract :

The adaptation of some benthic foraminiferal species to low-oxygen conditions provides the prospect of using the chemical composition of their tests as proxies for bottom water oxygenation. Manganese may be particularly suitable as such a geochemical proxy because this redox element is soluble in reduced form (Mn2+) and hence can be incorporated into benthic foraminiferal tests under low-oxygen conditions. Therefore, intra- and inter-test differences in foraminiferal Mn∕Ca ratios may hold important information about short-term variability in pore water Mn2+ concentrations and sediment redox conditions. Here, we studied Mn∕Ca intra- and inter-test variability in living individuals of the shallow infaunal foraminifer Ammonia tepida sampled in Lake Grevelingen (the Netherlands) in three different months of 2012. The deeper parts of this lake are characterized by seasonal hypoxia/anoxia with associated shifts in microbial activity and sediment geochemistry, leading to seasonal Mn2+ accumulation in the pore water. Earlier laboratory experiments with similar seawater Mn2+ concentrations as encountered in the pore waters of Lake Grevelingen suggest that intra-test variability due to ontogenetic trends (i.e. size-related effects) and/or other vital effects occurring during calcification in A. tepida (11–25 % relative SD, RSD) is responsible for part of the observed variability in Mn∕Ca. Our present results show that the seasonally highly dynamic environmental conditions in the study area lead to a strongly increased Mn∕Ca intra- and inter-test variability (average of 45 % RSD). Within single specimens, both increasing and decreasing trends in Mn∕Ca ratios with size are observed. Our results suggest that the variability in successive single-chamber Mn∕Ca ratios reflects the temporal variability in pore water Mn2+. Additionally, active or passive migration of the foraminifera in the surface sediment may explain part of the observed Mn∕Ca variability. show less

Type de document :
Article dans une revue
Liste complète des métadonnées

https://hal.univ-angers.fr/hal-02872796
Contributeur : Okina Université d'Angers <>
Soumis le : mercredi 17 juin 2020 - 20:29:35
Dernière modification le : mercredi 14 octobre 2020 - 04:16:59

Lien texte intégral

Identifiants

Collections

Citation

Jassin Petersen, Christine Barras, Antoine Bézos, Carole La, Lennart Jan de Nooijer, et al.. Mn / Ca intra-test variability in the benthic foraminifer Ammonia tepida. Biogeosciences Discussions, European Geosciences Union, 2018, 15, pp.331-348. ⟨10.5194/bg-2017-273⟩. ⟨hal-02872796⟩

Partager

Métriques

Consultations de la notice

25