Stratigraphic hiatuses and solution unconformities in the subsurface of Enewetak Atoll, northern Marshall Islands, record periods of atoll emergence during low stands of sea level. Changes in sea level are also recorded in the atoll subsurface by variations in the rate of sediment accumulation relative to the subsidence rate of the underlying volcanic edifice. Past sea levels can be derived from atoll stratigraphy by correcting the present depth of dated subsurface horizons for thermal subsidence and lithospheric flexure since the time of deposition. A correction for depositional paleodepth may also be necessary. As a result of erosion and nondeposition during periods of emergence, the history of sea level derived in this manner is discontinuous. Past sea levels derived from atoll stratigraphy can only be estimated to within ¿50 m relative to present sea level owing to uncertainities in the corrections for subsidence and flexure; however, the minimum magnitude of sea level falls estimated from stratigraphic hiatuses can be estimated to within ¿10 m. Owing to limited fossil-based age resolution, only long-term sea level trends can be deduced from sediments dated by means of biostratigraphy. Based on the biostratigraphic ages of subsurface horizons at Enewetak, we can discem very little long-term change in sea level from late Eocene through late Oligocene, a rise to ~110 m above present sea level in the early Miocene, a long-term fall of ~170 m through middle and late Miocene time, and a long-term rise of ~60 m from the end of the Miocene to present.

Resolution of the sea level history recorded beneath mid-ocean atolls may be improved by determining the age of shallow-marine carbonates by means of strontium isotope stratigraphy. Our interpretation of past sea levels based on 87Sr/86Sr chronostratigraphy from Enewetak confirms the long-term sea level trends inferred from biostratigraphic subsurface ages. In addition, we interpret three Oligocene sea level falls with minimum magnitudes of 30--50 m at ~35, 33--30, and ~25 Ma and four Miocene sea level falls greater than 30--95 m at 16--14, ~12, ~10, and ~5 Ma. These estimates of the timing and magnitude f Oligocene and Miocene sea level changes, derived from Enewetak Atoll stratigraphy, are compared with sea level histories derived from continental margin stratigraphy and from ice volume changes inferred from deep-sea foraminifera Δ18O records. ¿American Geophysical Union 1991