LA-ICP-MS-derived U-concentrations and microstructural domains within biogenic aragonite of Arctica islandica shell

Helama S., Heikkila P., Rinne K., Nielsen J. K., Nielsen J. K.

ENVIRONMENTAL MONITORING AND ASSESSMENT, cilt.187, sa.5, 2015 (SCI-Expanded, Scopus)

Özet

Understanding of the uranium uptake processes (both in vivo and post-mortem) into the skeletal structures of marine calcifiers is a subject of multidisciplinary interest. U-concentration changes within the molluscan shell may serve as a paleoceanographic proxy of the pH history. A proxy of this type is needed to track the effects of fossil fuel emissions to ocean acidification. Moreover, attaining reliable U-series dates using shell materials would be a geochronological breakthrough. Picturing the high-resolution changes of U-concentrations in shell profiles is now possible by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Here, we analyzed in situ U-concentration variations in sub-fossilized shells of ocean quahog (Arctica islandica), a commonly studied bivalve species in Quaternary geoscience, using LA-ICP-MS. Microstructural details of the shell profiles were achieved by the scanning electron microscopy (SEM). Comparison of the shell aragonite microstructure with the changes in U-concentration revealed that uranium of possibly secondary origin is concentrated into the porous granular layers of the shell. Our results reinforce the hypothesis that U-concentration variations can be linked with microstructural differences within the shell. A combination of LA-ICP-MS and SEM analyses is recommended as an interesting approach for understanding the U-concentration variations in similar materials.