Fig. 2.

Foraminifera tests after isotope re-equilibration experiments. a–e SEM images showing the overall morphologies and ultrastructures of the foraminifera tests (G. bulloides) after their ultrasonic cleaning in pure ethanol. f Backscattered SEM image of a polished section of a test embedded in epoxy. g, h EDXS maps showing the spatial distributions of carbonates (Ca appears in yellow) and clays (Si appears in pink). i, j NanoSIMS maps showing the ¹⁸O/¹⁶O ratio distributions in carbonates and clays. Carbonates exhibit a ¹⁸O/¹⁶O ratio ranging from 0.1 to 0.8, while clays exhibit a ¹⁸O/¹⁶O ratio ranging from 0.9 to greater than 1.0. Note that the isotope exchange occurred very heterogeneously, leading to areas that are more or less enriched in ¹⁸O. The red rectangles in f, g indicate the locations of i, j. The red rectangle in i indicates the location of h. Scale bars are 100 µm (a, b, f, g), 50 µm (c), 20 µm (d, i) and 10 µm (e, h, j)