Reconciliation of sea-level observations in the Western North Atlantic during the last glacial cycle

A south to north gradient of increasing marine isotope substage (MIS) 5a (∼80 ka BP) sea level has been recorded across the Caribbean and surrounding region. Relative to present, MIS-5a sea levels range from −19 m to more than +3 m between Barbados, Haiti, the Bahamas, Florida, Bermuda and the US Atlantic Coast. In contrast, no gradient in sea level is observed for the last interglacial period MIS-5e (∼128–118 ka BP) at tectonically stable localities in the same region, with deposits generally lying several metres above present. We demonstrate here that these controversial observations are reconciled by taking into account the isostatic response of the Earth to glacial loading and unloading – a fundamental effect that is commonly overlooked in the interpretation of sea-level observations from different locations to define a ‘global sea-level curve’. Furthermore, the observed gradient can be used to place constraints on Earth rheology and is an important indicator of the behaviour of the North American ice sheets during the last glacial cycle.