- Our existence is governed by natural cycles, from the daily rhythms of sleeping and eating, to longer patterns such as the turn of the seasons and the quadrennial round of leap years.
- Our research is published in Nature Communications.
Milankovitch cycles and ice ages
- Most of the natural cycles we know are determined one way or another by Earth’s movement around the Sun.
- And over time, the gravitational jostling of the planets changes the shape of these orbits in a predictable pattern.
- These alterations affect our long-term climate, influencing the coming and going of ice ages.
Earth and Mars
There are also slower rhythms, called astronomical “grand cycles”, which cause fluctuations over millions of years. One such cycle, related to the slow rotation of the orbits of Earth and Mars, recurs every 2.4 million years.
The cycle is predicted by astronomical models, but is rarely detected in geological records. The easiest way to find it would be in sediment samples that continuously cover a period of many millions of years, but these are rare. Much like the shorter Milankovitch cycles, this grand cycle affects the amount of sunlight Earth receives and has an impact on climate.
Gaps in the record
- When we went hunting for signs of these multimillion-year climate cycles in the rock record, we used a “big data” approach.
- Scientific ocean drilling data collected since the 1960s have generated a treasure trove of information on deep-sea sediments through time across the global ocean.
- Instead, we concentrated on the parts of the sedimentary record that are missing — breaks in sedimentation called hiatuses.
- Analysing the timing of hiatus periods across the global ocean, we identified hiatus cycles over the past 65 million years.
Warming and deep currents
- Some of these suggest that ocean mixing has become more intense over the last decades of global warming.
- Deep-ocean eddies are predicted to intensify in a warming, more energetic climate system, particularly at high latitudes, as major storms become more frequent.
Can Mars keep the oceans alive?
- Our deep-sea data spanning 65 million years suggest that warmer oceans have more vigorous eddy-driven circulation.
- This process may play an important role in a warmer future.
- Our results and analyses of deep ocean mixing suggest that more intense deep-ocean eddies may counteract such ocean stagnation.
Adriana Dutkiewicz receives funding from the Australian Research Council. Dietmar Müller and Slah Boulila do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
