![\"An](\"https:\/\/cdn.sci.news\/images\/enlarge13\/image_14551e-Snowball-Earth.jpg\")
<\/a><\/p>\nAn artist\u2019s impression of Earth around 700 million years ago during the Sturtian glaciation. Image credit: Pablo Carlos Budassi.<\/p>\n
In their study, University of Southampton\u2019s Professor Thomas Gernon and his colleagues examined 2,600 individual layers within the Sturtian Port Askaig Formation, each recording a single year of deposition.<\/p>\n
\u201cThese rocks preserve the full suite of climate rhythms we know from today \u2014 annual seasons, solar cycles, and interannual oscillations \u2014 all operating during a Snowball Earth. That\u2019s jaw dropping,\u201d Professor Gernon said.<\/p>\n
\u201cIt tells us the climate system has an innate tendency to oscillate, even under extreme conditions, if given the slightest opportunity.\u201d<\/p>\n
\u201cThese rocks are extraordinary,\u201d added Dr. Chloe Griffin, also from the University of Southampton.<\/p>\n
\u201cThey act like a natural data logger, recording year-by-year changes in climate during one of the coldest periods in Earth\u2019s history.\u201d<\/p>\n
\u201cUntil now, we didn\u2019t know whether climate variability at these timescales could exist during Snowball Earth, because no one had found a record like this from within the glaciation itself.\u201d<\/p>\n
The microscopic analysis showed that the layers likely formed through seasonal freeze-thaw cycles in a calm, deep-water setting beneath ice.<\/p>\n
When the researchers used statistics to analyze variations in layer thickness, a surprising signal emerged.<\/p>\n
\u201cWe found clear evidence for repeating climate cycles operating every few years to decades,\u201d Dr. Griffin said.<\/p>\n
\u201cSome of these closely resemble modern climate patterns, such as El Ni\u00f1o-like oscillations and solar cycles.\u201d<\/p>\n
These climate cycles, however, were unlikely to have been the norm for Snowball Earth.<\/p>\n
\u201cOur results suggest that this kind of climate variability was the exception, rather than the rule,\u201d Professor Gernon said.<\/p>\n
\u201cThe background state of Snowball Earth was extremely cold and stable.\u201d<\/p>\n
\u201cWhat we\u2019re seeing here is probably a short-lived disturbance, lasting thousands of years, against the backdrop of an otherwise deeply frozen planet.\u201d<\/p>\n
The team ran climate simulations for Snowball Earth, which showed that a completely ice-sealed ocean would suppress most climate oscillations.<\/p>\n
However, if a small fraction, around 15%, of the ocean surface remained ice-free, familiar atmosphere-ocean interactions could resume.<\/p>\n
\u201cOur models showed that you don\u2019t need vast open oceans,\u201d said University of Southampton\u2019s Dr. Minmin Fu.<\/p>\n
\u201cEven limited areas of open water in the tropics can allow climate modes similar to those we see today to operate, producing the kinds of signals recorded in the rocks.\u201d<\/p>\n
\u201cThis finding supports a scenario in which Snowball Earth was generally frozen solid but punctuated by intervals, sometimes dubbed \u2018slushball\u2019 or more extensive \u2018waterbelt\u2019 states, when small patches of open ocean emerged.\u201d<\/p>\n