Modern diatom and sponge δ30Si calibrations. (a) Diatom δ30Si vs. surface water silicic acid concentration in the Southern Ocean. Diatoms filtered from the top 100 m of the water column during in situ studies (crosses, triangles and stars; Cardinal et al., 2007; Fripiat et al., 2011a, 2011c, ; Varela et al., 2004) and core top diatom opal (circles, Egan et al., 2012). (b) Sponge δ30Si vs. ambient silicic acid concentration (Hendry and Robinson, 2012). Sponge spicules from modern sponges (open symbols) and core tops (solid symbols).
water column
100 m
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