Fig. 4: Direct imaging of ¹⁸O-enrichments in foraminifera tests after incubation.

NanoSIMS images of Ammonia sp., H. germanica, and A. lessonii tests after incubation for 6 days at 90 °C in seawater analogue with a ¹⁸O/¹⁶O ratio of 0.30. a–c Surfaces exposing the interior of test walls show high ¹⁸O-enrichments occurring as thin parallel bands following the curvature of the test walls and elongated zones of variable thickness running perpendicular to the test surface. d–f Same view of the same samples showing the ³¹P/¹⁶O ratio, which reveals P-rich bands following the curvature of the test walls. g–i Surfaces from the interior of the same samples, but cut parallel to the wall surface, show ¹⁸O-enrichments occurring as thin, tortuous and cogwheel-shaped lines in Ammonia sp. and H. germanica, which merge into patchy areas of higher ¹⁸O enrichment in A. lessonii.