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Profiling planktonic foraminiferal crust formation
Steinhardt, J.; de Nooijer, L.J.; Brummer, G.-J.A.; Reichart, G.J. (2015). Profiling planktonic foraminiferal crust formation. Geochem. Geophys. Geosyst. 16: 2409-2430. dx.doi.org/10.1002/2015GC005752
In: Geochemistry, Geophysics, Geosystems. American Geophysical Union: Washington, DC. ISSN 1525-2027, more
Peer reviewed article  

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  • Steinhardt, J., more
  • de Nooijer, L.J., more
  • Brummer, G.-J.A., more
  • Reichart, G.J., more

Abstract
    Planktonic foraminifera migrate vertically through the water column during their life, therebygrowing and calcifying over a range of depth-associated conditions. Some species form a calcite veneer,crust, or cortex at the end of their lifecycle. This additional calcite layer may vary in structure, composition,and thickness, potentially accounting for most of their total shell mass and thereby dominating the elementand isotope signature of the whole shell. Here we apply laser ablation ICP-MS depth pro?ling to assess vari-ability in thickness and Mg/Ca composition of shell walls of three encrusting species derived from sedimenttraps. Compositionally, Mg/Ca is signi?cantly lower in the crusts of Neogloboquadrina dutertrei and Globoro-talia scitula, as well as in the cortex of Pulleniatina obliquiloculata, independent of the species-speci?c Mg/Ca of their lamellar calcite shell. Wall thickness accounts for nearly half of the total thickness in both crustalspecies and nearly a third in cortical P. obliquiloculata, regardless of their initial shell wall thickness. Crustthickness and crustal Mg/Ca decreases toward the younger chambers in N. dutertrei and to a lesser extent,also in G. scitula. In contrast, the cortex of P. obliquiloculata shows a nearly constant thickness and uniformMg/Ca through the complete chamber wall. Patterns in thickness and Mg/Ca of the crust indicate that tem-perature is not the dominant factor controlling crust formation. Instead, we present a depth-resolved modelexplaining compositional differences within individuals and between successive chambers as well as com-positional heterogeneity of the crust and lamellar calcite in all three species studied here

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