L edge Sr mapping of growth regions in stony coral primary polyps, exposed to dial (day/night) enriched Sr water: a nano XRF mapping study

Stony corals grow in seawater, where they successfully isolate Ca to precipitate CaCO3 mineral, mostly in the form of aragonite however Sr is often incorporated in small amounts in the skeleton, possibly alongside amorphous mineral. Previous low-resolution XRF mapping on mySpot with a 20 µm diameter beam did not provide sufficient information on the spatial distribution of Sr in relation to the mineral deposits. We propose to use the nm-sized beam of ID21 and to excite XRF L lines of Sr to image the distribution of Sr and within Ca in newly forming corals, grown under different Sr water concentrations. The low energy of Sr L edge excitation (ca. 1805 eV) will help us pinpoint where this element is found. This information will help characterize zones of primary polyp growth important to understand fundamental aspects of coral biomineralization in which the stable mineral phases formed are not fully understood.