Fossil corals reveal that sea-level rise occurs in rapid bursts

Sea-level rise isn’t always slow and steady. Fossil corals from the Seychelles show that it has surged in quick bursts in the past – rising much faster than most people would expect.

The fossilized corals, once living just below the surface, captured a snapshot of a world much like today, but with oceans jumping higher in sudden leaps.

Researchers from the University of Wisconsin–Madison and the University of Florida led the project, working with colleagues at the University of Sydney, the University of Minnesota Twin Cities, Victoria University of Wellington, and the University of Massachusetts Amherst.

“This is not good news for us as we head into the future,” said Andrea Dutton, a professor of geoscience at Wisconsin.

Sea level climbed in bursts, not gradually

The team studied two dozen fossil corals lodged at different heights above present sea level. Because these corals only grow in shallow, sun-lit water and the Seychelles sit far from ancient ice sheets, the skeletons provide clean snapshots of past oceans.

Precise dating shows the peak of the Last Interglacial high stand came 122,000 – 123,000 years ago – when global temperatures resembled those we see now.

The surprise lay in how the sea level reached that peak. The record shows three bursts of rapid rise, each followed by a drop, over just 6,000 years.

“That says there’s potential for this very rapid, dynamic change in both ice sheet volume and sea level change,” said Dutton. “This is hugely important for coastal planners, policy makers and those in the business of risk management.”

Ice sheets out of step

The sea-level swings hint that Greenland and Antarctic ice did not melt in sync. According to Professor Dutton, the swings suggest that the polar ice sheets were growing and shrinking out of phase with each other as a result of temperature changes in the two hemispheres that were not aligned.

“So even though sea level rose at least several meters higher than present during this past warm period, if temperature rises simultaneously in both hemispheres as it is today, then we can expect future sea level rise to be even greater than it was back then,” explained Professor Dutton.

Hidden contribution from Antarctica

One pulse matches the collapse of the last fragments of the North American ice sheet, based on earlier Atlantic Ocean studies.

“But if ice was still present in North America several thousand years into this past warm period, then some of the rise we’ve documented would have required more meltwater from another ice sheet, such as Antarctica,” said Dutton.

“This would suggest that Antarctica was even more sensitive to warming than we previously recognized, because the full extent of sea-level rise flowing from the continent was masked by a remnant ice sheet in North America.”

Corals predict greater sea level rise

Together, the coral data indicate that today’s warming could lock in far higher seas than current forecasts.

“We could be looking at upward of 10 meters of global average sea-level rise in the future just based on the amount of warming that has already occurred,” noted Professor Dutton.

“The more we do to draw down our greenhouse gas emissions, and the faster we do so, could prevent the worst scenarios from becoming our lived reality.”

Cutting emissions now cannot freeze the oceans in place, but it can slow the pace – and give coastal planners, and the millions who live near the shore, a fighting chance.

The dangers of sea level rise

The danger of rising sea levels isn’t just theoretical – it’s already becoming a reality for millions of people.

Coastal cities and island nations are seeing higher tides, more frequent flooding, and increased erosion. In some places, communities are being forced to relocate as seawater creeps further inland.

These changes also put critical infrastructure at risk. Roads, power plants, ports, and wastewater systems in low-lying areas weren’t built to withstand repeated saltwater exposure.

When sea level rises even a small amount, it raises the baseline for storm surges, making hurricanes and typhoons more destructive than they used to be. The economic impact is massive. Flood insurance costs are climbing, while property values in vulnerable areas are falling.

Governments are spending billions on sea walls, drainage systems, and other short-term fixes. If the past is any indication – as the fossil coral record shows – sea levels may not rise slowly enough for these defenses to keep up.

The full study was published in the journal Science Advances.

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