A clue to why ice ages got much longer

Enlarge / Wee foraminifera, whose shells hold chemical clues to past climates. (credit: Mimi Katz/RPI/NSF)
If you’ve read about the “ice ages” of Earth’s recent history before, you probably learned that the cyclical rhythm of these climate changes is controlled by several reliable cycles in Earth’s orbit. That relationship is pretty clear, but there’s also a fascinating and unsolved puzzle here. For about the last 700,000 years, glacial periods were each about 100,000 years long—lining up with a subtle cycle in the shape of Earth’s orbit around the Sun. If you look at the 500,000 years before that, though, you see shorter glacial periods that line up with a 41,000-year cycle in the tilt of Earth’s axis. Satisfying explanations for this change in Earth’s time signature have proven elusive.
There have been ideas, of course. It could be that the ice sheets of North America and Europe reached a sort of critical mass, becoming too big to fail during the weaker 41,000-year warm-up. The culprit could also lie in the ocean, where circulation changes or increases in the wind-blown dust that fertilizes plankton growth could pull greenhouse gas out of the atmosphere, making the ice ages icier.
A new study led by Adam Hasenfratz and Samuel Jaccard at the University of Bern may have found a piece of the puzzle at the bottom of the ocean around Antarctica.
Read 11 remaining paragraphs | Comments