Emma-Kate Potter

Links between climate and sea levels for the past three million years

The oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on Earth — the ice sheets and the oceans. Since the latest of these oscillations, the Last Glacial Maximum (between about 30,000 and 19,000 years ago), ∼50 million cubic kilometres of ice has melted from the land-based ice sheets, raising global sea level by ∼130 metres. Such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere, oceans, ice sheets and solid earth, all of which have different response timescales. The trigger for the sea-level fluctuations most probably lies with changes in insolation, caused by astronomical forcing, but internal feedback cycles complicate the simple model of causes and effects.

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

Abstract 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.