North American ice sheets drove the final surge in sea-level rise at the end of the last deglaciation

The end of the last glacial period transformed Earth’s geography. Between about 20 000 and 7 000 years ago, retreating ice raised global sea levels by more than 120 m (394 feet). Yet scientists have struggled to identify which ice sheets melted fastest and when. For decades, reconstructions pointed toward Antarctica as the main contributor to the final surge, but the new study overturned that view.

By combining high-resolution sea-level data from the Mississippi Delta with global records and glacial isostatic adjustment modeling, Mukherjee’s Team found that most of the 14 m (45 feet) rise between 9 000 and 7 000 years ago came from the North American ice sheets. This is between 4–10 m (13–33 feet) more meltwater than earlier estimates, enough to cover an area nearly twice the size of Greenland.

The data come from radiocarbon-dated layers of basal peat buried beneath coastal sediments. These organic layers form where the land meets rising seas, preserving a natural record of local sea-level change. The team integrated dozens of such measurements to reconstruct how the Gulf Coast responded to melting far to the north.

Once those records were compared with similar sites around the world, the picture became clear. Antarctica’s contribution was modest, no more than a third of the total. North America was the real driver of the ocean’s last great climb.

A continent in collapse

The North American ice complex, once stretching from the Arctic to the upper Midwest, was dominated by two major domes of ice. Between them lay a lower corridor of frozen terrain over Hudson Bay known as the “saddle.” The new research suggests that this saddle collapsed rapidly near the close of deglaciation.

Such a collapse would have drained enormous volumes of meltwater southward through the Great Lakes and eastward through the St. Lawrence valley into the North Atlantic. This deluge likely happened over several centuries, not millennia, and it left a measurable fingerprint in sea-level curves worldwide.

Geophysical models that simulate how Earth’s crust and gravity respond to ice loss reproduce the 14-meter global rise only when North America’s contribution dominates. If Antarctic melt were increased, the pattern no longer fits the data. This finding implies that the late-deglacial landscape of North America changed far more violently than previously thought.

The rate of sea-level rise during this time likely reached several millimeters per year, rivaling the upper range of modern projections. In other words, the planet has seen similar speeds of ocean rise before—but only when entire ice sheets were disintegrating.

The cold that followed the flood

Around 8 200 years ago, the Northern Hemisphere experienced a brief but sharp cooling, lasting roughly 150 to 200 years. Climate records from Greenland ice cores and North Atlantic sediments show temperatures falling by about 1–3°C (1.8–5.4°F). Scientists have long suspected that a massive pulse of meltwater disrupted the Atlantic’s circulation, reducing heat transport toward Europe.

Mukherjee’s study adds new weight to that theory. If 14 m (45 feet) of sea-level rise were dominated by North American melt, much of that freshwater would have flowed directly into the North Atlantic. Computer models published in Scientific Reports in 2021 found that a discharge equivalent to about 5.3 m (17 feet) of sea-level rise over 1 000 years, including a rapid 2.2 m (7 feet) pulse over just 130 years, could reproduce the cooling seen in proxy data.

The link between North American ice collapse and the 8.2 ka event suggests that even a modest perturbation in ocean salinity can have global consequences. The study therefore offers a rare natural experiment: a time when a single continent’s meltwater altered the entire climate system.

Lessons from the ancient tide

The Mississippi Delta archive used in this research represents one of the most precise natural sea-level datasets on Earth. Each layer of peat marks the elevation where vegetation once grew before rising seas drowned it. When radiocarbon-dated, these layers reveal both the speed and magnitude of local sea-level change.

By comparing those observations with numerical models, scientists can estimate how much global ice had to vanish to produce the observed rise. The results show that previous models underestimated the North American component because they relied on fewer coastal records and simplified Earth-rebound physics.

Yet there are caveats. Translating local sea-level rise into global ice volume requires assumptions about Earth’s mantle viscosity, crustal rebound, and water routing. Even small differences in these parameters can shift the final number by several meters. Future studies may refine the total, but the trend is unlikely to reverse: North America’s ice sheets were the main player in the planet’s last great melt.

This refined picture closes part of the long-standing “missing ice” problem, where earlier budgets could not account for all observed sea-level rise since the last glacial maximum. The new data bring the global balance closer to closure and provide a stronger baseline for testing ice-sheet models.

References:

¹ Sea-level rise at the end of the last deglaciation dominated by North American ice sheets – October 9, 2025 –https://doi.org/10.1038/s41561-025-01806-0

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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