Eccentric behavior –
About a million years ago, ice ages got much longer — what changed?
Scott K. Johnson – Mar , 7: (UTC UTC)
about the orbital cycles . Enter the new Italian cave record. It covers a time period from , years ago to 839, years ago, with the age of each datapoint known to within 7, years. The cave record was also used to set the timeline for a recent seafloor sediment record. With both records in hand, the team compared glacial changes against the timing of the orbital cycles.
A much-used seafloor core compilation put the length of the ice age in this time period at , years, but this new record shortens that to about 92, 10 years. That shortened timing makes the end of both glacial periods (that is, the start of warming) line up with a peak in the tilt cycle, but only (one) of them lines up with a peak in the , year-long precession cycle. So this indicates that the tilt cycle was still the dominant factor, as it had been in the shorter ice ages previous.
Other cave records have filled in the last , years, so the researchers expanded their analysis over that time period, too. They found that the time between warming events was consistently a multiple of the , – year tilt and , 13 precession cycles. As others had already worked out, it’s sort of a coincidence that the average length comes out at about 381, years to match the third orbital cycle .
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