AbstractResults of palaeomagnetic measurements of a core from Mururoa atoll, French Polynesia, led us to document for the first time the atoll's magnetostratigraphy. Periods of slow aggradation, correlated with sea‐level low‐stands, show that atolls are accurate recorders of sea level fluctuations. The timing and amplitude of sea level fluctuations may be reconstructed on the basis of precise dating of atolls and shallow‐water platforms. Magnetostratigraphy is therefore a first step towards a quantitative calibration of the eustatic records of coral a