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Meltwater Pulse 1A sea-level-rise patterns explained by global cascade of ice loss

Nature Geoscience volume 18, pages 254–259 (2025)Cite this article

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Abstract

Over the last deglaciation, global sea level rose by ~120–130 m, 10–20 m of which was attributed to a singular, catastrophic event known as Meltwater Pulse 1A (MWP-1A) that spanned at most 500 years approximately 14.6 kyr ago. Given data limitations and simplified models of Earth deformation, previous studies have struggled to determine the ice sources responsible for MWP-1A, its timing and, consequently, the impacts on global climate. With the expansion of palaeo sea-level records and growing consensus that more complex Earth deformation occurs over MWP-1A timescales, revisiting MWP-1A is timely. Here we resolve a sequence of ice loss over MWP-1A using a spatiotemporal sea-level fingerprinting approach constrained by temporal variations across sea-level data that fully models transient viscoelastic deformation, resulting in a space–time melt evolution. Our favoured sequence of ice sheet melting begins with the Laurentide contributing ~3 m (~14.6–14.2 kyr ago), followed by Eurasia and West Antarctica contributing ~7 m and ~5 m, respectively (~14.35–14.2 kyr ago). This scenario is consistent with proxy data that suggest a minimal Laurentide contribution and large retreat of the Eurasian Ice Sheet Complex. Our MWP-1A ice evolution demands the revision of global ice histories and illustrates deformation feedbacks that are relevant for modern ice collapse and sea-level rise.

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Fig. 1: Previous and new interpretations of MWP-1A RSL change.
Fig. 2: Candidate MWP-1A sources.
Fig. 3: Spatiotemporal sea-level fingerprint with transient rheology.
Fig. 4: Distributions of marine and terrestrial ice in Eurasia before and after MWP-1A.

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Data availability

Model outputs from this study are available via Zenodo at https://doi.org/10.5281/zenodo.14231384) (ref. 49). All source data used in this study have been published in previous studies and are publicly available (see Supplementary Section 1 for information about the databases and how to access them).

Code availability

The codes for the forward sea-level model used in this study, as well as the driver program for coupling the forward model with the neighbourhood algorithm sampler, are available via Zenodo at https://doi.org/10.5281/zenodo.14231384 (ref. 49). The repository also includes sample codes for processing the raw outputs of the Bayesian inversion.

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Acknowledgements

We thank F. Hibbert, P. Chutchavaran and A. Dutton for insightful discussions and guidance on the palaeo sea-level data and H. Han for providing source code for the sea-level model. A.N.C. and H.C.P.L. were supported by grant number NSF-EAR 2311897.

Author information

Authors and Affiliations

  1. Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA

    Allie N. Coonin & Harriet C. P. Lau

  2. Department of Earth Sciences, University of New Hampshire, Durham, NH, USA

    Sophie Coulson

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  1. Allie N. Coonin
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  2. Harriet C. P. Lau
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Contributions

H.C.P.L. developed the project. A.N.C. conducted the modelling and analysis with guidance from S.C. and H.C.P.L. The paper was co-written by A.N.C. and H.C.P.L.

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Correspondence to Allie N. Coonin.

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Nature Geoscience thanks Andrew Wickert and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary handling editor: James Super, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Comparison of Relative Sea-Level Predictions to Data.

Predicted RSL outcomes at (A) Tahiti, (B) Barbados, (C) Sunda Shelf, (D) Hydrographer’s Passage (HYD) and (E) Noggin Passage (NOG) within the Great Barrier Reef, and (F) N.W. Scotland for an ensemble of transient viscoelastic models of MWP-1A, sampled within 1\(\sigma\) of the maximum probability value from the posterior probability distributions for each variable in the sea-level fingerprint (onset, duration, and amount of ice loss from each source). Our interpretation of RSL over MWP-1A at each site (Fig. 1d) is marked with squares at each step in the time discretization of the FSL model9. The site-specific uncertainty in RSL (see SM-7) is reflected by the black lines bracketing the data markers. Each transparent orange trace is an RSL prediction with transient viscoelastic Earth rheology18. The individual blue and purple traces for each site indicate the results of the optimum forward model from the spatiotemporal sea-level fingerprint considering transient viscoelastic deformation and that for elastic-only deformation. See SM-11 for further discussion.

Supplementary information

Supplementary Information

Supplementary Sections 1–15, Figs. 1–17 and Tables 1–4.

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Coonin, A.N., Lau, H.C.P. & Coulson, S. Meltwater Pulse 1A sea-level-rise patterns explained by global cascade of ice loss. Nat. Geosci. 18, 254–259 (2025). https://doi.org/10.1038/s41561-025-01648-w

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