Global Changes in Postglacial Sea Level: A Numerical Calculation

TLDR

Sea‑level rise from ice‑sheet melt has varied globally because Earth's surface and geoid deform under changing ice and water loads. A numerical model of a spherical viscoelastic Earth simulates global relative sea‑level changes as northern‑hemisphere ice sheets melt and meltwater fills ocean basins. The model explains most of the global sea‑level variance, partitions oceans into six zones with distinct relative sea‑level curves, predicts beaches in four zones and submergence in the others, and its close agreement with data suggests no net ocean‑volume change in the past 5,000 years, though local predictions need refinement.

Abstract

The sea-level rise due to ice-sheet melting since the last glacial maximum was not uniform everywhere because of the deformation of the Earth's surface and its geoid by changing ice and water loads. A numerical model is employed to calculate global changes in relative sea level on a spherical viscoelastic Earth as northern hemisphere ice sheets melt and fill the ocean basins with meltwater. Predictions for the past 16,000 years explain a large proportion of the global variance in the sea-level record, particularly during the Holocene. Results indicate that the oceans can be divided into six zones, each of which is characterized by a specific form of the relative sea-level curve. In four of these zones emerged beaches are predicted, and these may form even at considerable distance from the ice sheets themselves. In the remaining zones submergence is dominant, and no emerged beaches are expected. The close agreement of these predictions with the data suggests that, contrary to the beliefs of many, no net change in ocean volume has occurred during the past 5000 years. Predictions for localities close to the ice sheets are the most in error, suggesting that slight modifications of the assumed melting history and/or the rheological model of the Earth's interior are necessary.