Sediments were prepared following existing techniques (Hendry et al., 2010), which were refined slightly to better suit the microseparation technique utilised here as a convenient alternative to sieving. Initial cleaning with H2O2 and HCl was carried out to concentrate biogenic opal. From this pre-cleaned sample the >100 μm fraction was separated using microseparation (Minoletti et al., 2009) and between 50 and 100 spicules were hand-picked. A range of spicule morphotypes were included, as it has been shown that neither spicule morphology nor species composition creates any consistent offset in δ30Si (Hendry et al., 2010, 2011). Spicules were sonicated in reagent grade methanol and dried down in 200 μL of concentrated HNO3. Sponge δ30Si data presented here are generally in agreement with the data from this site produced by De la Rocha (2003), despite different methodologies and specific sampling intervals (Fig. S2). XRD analysis showed sponge spicules from the Eocene/Oligocene interval of this site to be amorphous opal (De la Rocha, 2003).
fraction
>100 μm
μm
spicules
between 50 and 100
concentrated HNO3
200 μL
μL