Earth’s 40,000-year tilt cycle links Antarctic ice growth to subtropical productivity

Earth’s Axial Tilt, or Obliquity [Credit: Wikipedia]

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A reminder that orbital effects and cycles can and do play a significant part in Earth’s climate system, which may or may not be reflected in climate models that claim to ‘project’ potential climate futures. A researcher comments: “And when the ice sheet became large enough to extend to the Southern Ocean, the 40,000-year obliquity rhythm of the marine-based ice sheets impacted the delivery of nutrients to our subtropical site”.
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Cycles in the growth and decay of Antarctica’s ice sheets once shaped marine biological productivity thousands of miles away in the subtropical ocean, according to new research led by scientists at the University of Wisconsin-Madison.

The study, published in the Proceedings of the National Academy of Sciences, found that the obliquity cycle—a 40,000-year astronomical cycle tied to changes in Earth’s axial tilt—influenced ocean productivity in subtropical latitudes about 34 million years ago, when the Antarctic ice sheet was first expanding, says Phys.org.

The finding surprised researchers because the 40,000-year cycle, while an important factor in the conditions at Earth’s poles, typically has a more limited influence on climate and ocean conditions near the equator.

“We generally expect other astronomical cycles to have a greater influence,” says Stephen Meyers, a professor of geoscience at UW-Madison and one of the study’s lead authors.

Yet the researchers noted a strong, singular influence of the 40,000-year cycle on the ancient subtropical ocean’s bioproductivity, across a 1-million-year interval of time that is associated with the first expansion of the Antarctic ice sheets around 34 million years ago.

“This tells us that bioproductivity is being influenced by a distant high-latitude process, through nutrient delivery to the lower latitudes,” Meyers says.

Reconstructing ancient ocean productivity
The team arrived at this conclusion by analyzing chemical signals preserved in ocean sediment that record past biological productivity.

The sediments were collected during ocean drilling expeditions from 2020–2022 aboard the now-retired scientific drilling vessel JOIDES Resolution.

For decades, the vessel recovered ocean sediment cores to study Earth’s oceans and their geological history.

“The vessel has provided archives that ground huge scientific discoveries related to global climate events, evolution of life and plate tectonics,” says Alexandra Villa, who co-led the research with Meyers as a Ph.D. student at UW-Madison, and was a shipboard scientist on the drilling expedition.
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Global teleconnections in Earth’s climate
The new research builds on previous UW-Madison studies that showed how strongly the 40,000-year obliquity cycle affects marine-based ice sheets.

Now, scientists are able to connect this cycle to global ocean dynamics with far-ranging effects. Indeed, the new findings highlight how tightly connected Earth’s climate system is.

“Earth’s system is so interconnected, and changes in one part of the planet can ripple out in surprising ways,” Meyers says. “The polar ice sheets and global ocean circulation are important ways this manifests, impacting marine food webs far from the ice sheet. Our study shows how dynamic, variable and sometimes surprising, these ‘global teleconnections’ can be.”

Full article here.
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Image: Earth’s Axial Tilt, or Obliquity [Credit: Wikipedia]