New model reveals dramatic swings in Earth's sea levels

Sea levels have risen and fallen since Earth first held oceans. Until recently, scientists could only measure these shifts over million-year increments.

Now, researchers from Utrecht, the UK, and the United States have mapped sea level changes across much shorter timeframes – spanning thousands of years and covering the last 540 million years.

Published in the journal Earth and Planetary Science Letters, the study combines paleoclimate data, sediment records, and orbital modeling.

“Taking these rapid sea level variations into account is important for understanding the structure of the subsurface and the applications to green energy resources,” said Dr. Douwe van der Meer, guest researcher at Utrecht University and lead author of the study.

Measuring sea level rise

Sea level changes depend on two main factors: plate tectonics and land ice. Tectonics control the shape of ocean basins. Ice determines how much water fills them.

Previously, scientists could detect 200-meter (656 feet) swings in sea level over million-year periods using fossil and rock records.

“In time steps of about a million years, you can derive an average sea level for as far back as there are fossils, about 540 million years,” said Van der Meer.

“That varied by as much as 200 meters. We suspected that sea level could go up and down enormously in much shorter periods as well, but there is not enough data to make those shorter time steps.”

Earth’s orbit affects sea level

To track faster changes, researchers used a clever method. They matched sediment records with Earth’s orbital cycles, called Milankovitch cycles, that change climate on scales of 20,000 to 400,000 years. These wobbles trigger glacial and interglacial phases, which affect sea levels.

“We see alternations, especially when the global climate is cold, and there is ice on the poles,” said Van der Meer.

“Then, the rhythmic wobbling of Earth’s spin axis creates ice ages that last only tens of thousands of years, during which the sea level can go up and down by as much as 100 meters (328 feet).”

This new approach calculated how much ice volume could change due to orbital variations. Then, the researchers estimated how those changes would affect sea level during the last 540 million years.

Greenhouse vs. icehouse worlds

During warm, ice-free periods like the mid-Cretaceous, sea levels stayed relatively stable. In contrast, colder times like the late Carboniferous or modern ice age showed huge sea level swings.

Modeling showed that orbital cycles in the icehouse phases could cause sea levels to shift by over 328 feet within a few thousand years.

During the Permo-Carboniferous, for example, global temperatures may have ranged from 17°C (62.6°F) during interglacials to 10°C (50°F) during glacials.

Such shifts drove large expansions and retreats of ice sheets, influencing sediment layers and fossil patterns.

Past sea level rise helps planning

Knowing when and how sea levels changed helps scientists better understand Earth’s climate and geography. These findings can also improve models for geothermal energy, hydrogen storage, and radioactive waste disposal.

“High or low sea levels, it’s all happened before in the geological past,” said Van der Meer.

Sandstone, laid down during low sea levels, makes a good reservoir for storing gases or heat. Claystone, formed during high sea levels, can seal these reservoirs. Mapping these layers globally can help in safe subsurface use.

“If we know that at a certain time global sea level was high, we also know that a relatively continuous layer of claystone would have been deposited,” said Van de Meer.

“We can use that information to create a global layer map of sand and claystone, which helps us in the safe use of the subsurface.”

Ancient sea level rise patterns

The researchers tested their new model against known sedimentary records. For the Silurian, their orbital-scale sea level variation estimates – around 230 feet – match compiled data from five paleo-continents.

Similar matches appear in Cretaceous and Devonian records, with fluctuations ranging from 50 to 230 feet.

The model shows especially large short-term sea level swings during the late Ordovician, Permo-Carboniferous, and the past few million years.

In contrast, during the Jurassic and mid-Cretaceous, the shifts were much smaller, generally under 164 feet.

Some older reconstructions show higher variability, up to 328 feet, even during greenhouse phases. The new study argues that such large estimates may be inflated and not supported by physical models or isotope data.

Instead, this new work provides more grounded estimates using physics-based ice models, stratigraphy, and isotope geochemistry.

Future climate and geology research

This approach can help resolve long-standing questions about ancient climates, sedimentary patterns, and biodiversity changes. It also offers new tools for identifying reliable storage sites in the subsurface.

The authors suggest refining the method with non-linear models and more paleoclimate simulations. For now, their work marks a turning point in how we study ancient sea levels.

It is not just about history. It is a guide to understanding our dynamic planet.

The study is published in the journal Earth and Planetary Science Letters.

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