Determination of intratest variability of trace elements in foraminifera by laser ablation inductively coupled plasma-mass spectrometry

We have developed a technique to determine the variability of trace elements (including Li, B, Na, Mg, Mn, Cu, Zn, Sr and Ba) within foraminifera tests using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). This technique has a high spatial resolution (width 40–80 μm, depth >0.5 μm), is reproducible (<8% external reproducibility) and has low detection limits (generally <0.05 μg g−1). We demonstrate that normalization of data to a calcite standard usually gives results that are more consistent with solution ICP-MS data than normalization to NIST 612. Rastering into the wall of the final chamber of Globigerinoides sacculifer shows that the outermost ∼1.5 μm of the test is enriched in trace elements, including Mn, relative to the interior, indicating the presence of a contaminant surface phase. Pustule calcite close to the aperture of Globorotalia tumida has different Sr/Ca and Ba/Ca compared to other parts of the test. Sr/Ca and Ba/Ca partition coefficients suggest that the pustule calcite is diagenetic and/or formed in a more open system. Multiple analyses of Orbulina universa tests recovered from a latitudinal transect in the North Atlantic give a relationship between Mg/Ca and sea surface temperature similar to that reported elsewhere in the literature. These initial data demonstrate the validity of this technique, and show that it is potentially an extremely powerful microanalytical tool for palaeoceanographic and palaeontological studies