Large fluctuations in sea level throughout the last ice age challenge understanding of past climate

Greenland ice sheet (east coast) [credit: Hannes Grobe @ Wikipedia]

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What was supposed to be settled science has turned out not to be. More long-term variability exists in the Earth’s ice sheets than previously assumed. Researchers say it’s a paradigm shift in their understanding of such matters, with new ideas needed to replace the outdated theories.
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From Phys.org: Large changes in global sea level, fueled by fluctuations in ice sheet growth and decay, occurred throughout the last ice age, rather than just toward the end of that period, a study published in the journal Science has found.

The findings represent a significant change in researchers’ understanding of how the Pleistocene—the geological period from about 2.6 million to 11,700 years ago and commonly known as the last ice age—developed, said Peter Clark, a paleoclimatologist at Oregon State University and the study’s lead author.

“This is a paradigm shift in our understanding of the history of the ice age,” said Clark, a university distinguished professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences.
. . .
When the first reconstruction of global sea level over the last ice age was published nearly 50 years ago, science suggested there was a transition period about 1.25 million to 700,000 years ago, known as the middle Pleistocene transition, when the size of the ice sheets and the cycle of forming and melting changed.

“Before that transition, the glaciation cycles occurred about every 41,000 years, and after the transition, the cycles were every 100,000 years and were larger in amplitude,” said Clark.

“All theories developed to explain this transition were focused on an increase in the size of the ice sheets through this transition. Every sea level reconstruction since that initial study produced the same storyline, until now.”
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In the new study, researchers reconstructed sea level changes for the past 4.5 million years. They found that many of the glaciation cycles during the early Pleistocene, when the cycles were 41,000 years in duration, were as large as the more recent cycles.

“Having those large ice sheets present throughout that time means that their formation and decay were likely influenced by internal feedbacks in the climate system, rather than external dynamics,” Clark said.

“This finding challenges the conventional wisdom on the middle Pleistocene transition and forces us to develop new explanations.”

Full article here.
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Image: Greenland ice sheet (east coast) [credit: Hannes Grobe @ Wikipedia]