Researchers find geologic evidence in deep sea linking a 2.4-million-year cycle called astronomical grand cycles
A new study has found evidence of erosion in the deep sea linking a 2.4-million-year cycle called “astronomical grand cycles” with the orbits of Earth and Mars, and global warming or cooling. Photo: iStock The Earth undergoes climate fluctuations in a newly discovered 2.4-million-year cycle. Geological sedimentary evidence in the deep sea has proved the existence of the cycle, which is linked with Mars’ orbit.
The new study published in journal Nature Communications has found evidence of erosion in the deep sea linking this 2.4-million-year cycle called “astronomical grand cycles” with the orbits of Earth and Mars, and global warming or cooling.
“We are now about 200,000 years into a warming cycle. In about 1 million years, we’ll reach the next peak,” Dietmar Muller from the University of Sydney told Down To Earth.
Adriana Dutkiewicz from the University of Sydney, and the lead author of the study, said the team was surprised to find these 2.4-million-year cycles in deep-sea sedimentary data. “There is only one way to explain them: They are linked to cycles in the interactions of Mars and Earth orbiting the Sun,” she explained in a statement.
There are other shorter astronomical cycles known previously. For example, a century ago, Serbian scientist Milutin Milankovitch hypothesised that the long-term, collective effects of changes in Earth’s position relative to the sun were a strong driver of the Blue Planet’s long-term climate.
Apart from the well-known astronomical cycles with periods of 19,000, 23,000, 41,000, 100,000 and 400,000 years that pace Earth’s climate, geological records also contain signals of much longer period “grand cycles”, which are predicted by astronomical theory.
These “grand cycles” that last millions and even tens of millions of years are similarly linked to changes in incoming solar radiation and paleoclimate, the researchers wrote in the study.
To discover evidence of the grand cycles, the team examined seafloor erosion resulting from the increased strength of deep ocean currents driven by orbital forces.
The gravity fields of the planets in the solar system, Muller explained, interfere with each other and this interaction, called a resonance, changes planetary eccentricity, which measures how close to circular their orbits are.
This interaction leads to periods of higher incoming solar radiation and warmer climates in cycles of 2.4 million years on Earth.
Further, warmer cycles are linked with warmer oceans, which, in turn, leads to vigorous deep ocean circulation.
The researchers speculate that the vigorous deep-sea circulation could potentially keep the ocean from becoming stagnant even if the system of ocean currents called Atlantic Meridional Overturning Circulation (AMOC) slows or stops functioning.
AMOC circulates water within the Atlantic Ocean, bringing warmer water to various parts of the globe while also carrying essential nutrients to sustain ocean life.
Research showed the AMOC has weakened over the past century. A recent 2024 paper published in journal Science showed the system is en route to tipping.
“Our deep-sea data spanning 65 million years suggests that warmer oceans have more vigorous eddy-driven circulation,” Muller said.
These deep ocean eddies, according to the researchers, are giant whirlpools and often reach the abyssal seafloor, which sits at depths of 3,000 to 6,500 metres and where sunlight doesn’t penetrate. These whirlpools lead to seafloor erosion and large sediment accumulations called contourites, similar to snowdrifts (deep piles of snow formed by the wind).
The ocean eddies, he added, would help provide oxygen to the deep ocean in a warmer world, while also drawing carbon dioxide from the atmosphere into the ocean.
Muller said the new results suggest that more intense deep-ocean eddies in a warmer world may counteract such ocean stagnation caused by AMOC. Going forward, the team plans to find more data that shows cycles driven by Earth-Mars interaction.
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