Cretaceous Sea Level Fall Caused by Tectonics, not Cooling

About 80 million years ago—a time when dinosaurs ruled the Earth—global sea levels were roughly 560 feet (170 meters) higher than they are today, according to a new study.

[...]

The finding stems from more than a decade of effort to virtually reconstruct ancient ocean basins to understand how their size and depth have changed since the Cretaceous, which lasted from 145.5 to 65.5 million years ago.

The result is a dramatic image of historic sea level change that goes beyond what is expected in the coming decades due to rapid global warming-induced ice cap melting.

"There're natural processes that also contribute to sea level change and are in fact independent of ice cap melting," said Dietmar Müller, a geologist at the University of Sydney in Australia.

In fact, the data reveal that the long-term trend in sea levels since the Cretaceous has been downward, said Müller, who led the study appearing in tomorrow's issue of the journal Science.

[...]

According to the new study, a key factor in sea level change is the creation and spreading of new ocean crust along underwater mountain chains called mid-ocean ridges, Müller said.

"As the ocean floor moves away from the hot and shallow mid-ocean ridges into parts of the abyssal plains, it cools and sinks," he explained.

Currently the mid-ocean ridges lie, on average, 1.6 miles (2.5 kilometers) beneath sea level, while the abyssal plains sit 3.7 miles (6 kilometers) deep.

"That's a huge difference, and if you change the relative proportion of mid-ocean ridges and abyssal plains in the ocean basins, you change [the ocean's] volume, and this is what we have tried to reconstruct," he said.

The team found that, during the late Cretaceous, huge mid-ocean ridges wrapped around the planet, making the global ocean much shallower on average than it is today.

In particular, a mid-ocean ridge system in an ancient ocean called Panthalassa—the precursor to the Pacific—was a crucial force driving sea level change through time, Müller said.

Much of that system no longer exists, which largely explains why sea levels have fallen over the last 80 million years.

So...the retreat of the Intra-American sea had nada to do with cooling at the end of the Cretaceous. hmmm. That seems to completely disagree with past posters and does agree with...


For fun they do an extrapolation of the world's maps with sea level rise and fall.