Science· 2025Q1
Global mean sea level over the past 4.5 million years
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- Q1SCImago
- 2025year
Short summary
Global mean sea level (GMSL) reconstructions reveal highstands up to 20m above present between 4.5-3 Ma, with the first lowstands below present suggesting Northern Hemisphere glaciation onset at 4 Ma.
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Key points
- GMSL was up to 20m above present between 4.5-3 Ma.
- Northern Hemisphere glaciation onset suggested at 4 Ma by first lowstands below present.
- Intensified glaciation from 3-2.5 Ma produced Last Glacial Maximum-like lowstands.
- Middle Pleistocene ice sheet variability transition linked to CO₂ modulating obliquity forcing.
AI-generated from the title and abstract; the full text is not read.
Abstract
Changes in global mean sea level (GMSL) during the late Cenozoic remain uncertain. We use a reconstruction of changes in δ 18 O of seawater to reconstruct GMSL since 4.5 million years ago (Ma) that accounts for temperature-driven changes in the δ 18 O of global ice sheets. Between 4.5 and 3 Ma, sea level highstands remained up to 20 m above present whereas the first lowstands below present suggest onset of Northern Hemisphere glaciation at 4 Ma. Intensification of global glaciation occurred from 3 Ma to 2.5 Ma, culminating in lowstands similar to the Last Glacial Maximum lowstand at 21,000 years ago and that reoccurred throughout much of the Pleistocene. We attribute the middle Pleistocene transition in ice sheet variability (1.2 Ma to 0.62 Ma) to modulation of 41-thousand-year (kyr) obliquity forcing by an increase in ~100-kyr CO 2 variability.
The authors' abstract, as published at the source. Science, 2025 · DOI ↗
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Field: Atmospheric Science
Atmospheric ScienceEarth and Planetary Sciences