Earth’s interactions with Mars influence deep ocean circulation

Researchers have delved into the geological record of the deep sea to unveil a novel link between the orbital patterns of Earth and Mars, historical global warming episodes, and the intensification of deep ocean circulation. 

The investigation has revealed a surprising 2.4-million-year cycle in which deep currents fluctuate in strength, corresponding with periods of heightened solar energy and warmer global climates.

Climate change and ocean circulation 

The research was a collaboration between experts from the University of Sydney and Sorbonne University. The team examined the intricate relationship between climate change (on a geological timescale) and the dynamics of ocean circulation, aiming to enhance the predictive models for future climate scenarios. 

The study probes whether ocean-bottom currents grow stronger or weaker in warmer climates, distinct from the rapid global warming induced by human activities.

Decades of drilling data

Utilizing an extensive dataset from over fifty years of scientific drilling across numerous global sites, lead author Adriana Dutkiewicz from the University of Sydney’s EarthByte Group, along with Professor Dietmar Müller (University of Sydney) and Associate Professor Slah Boulila (Sorbonne), embarked on this exploratory journey.

The goal was to ascertain the relationship between sedimentary shifts and the Earth’s orbital changes, as well as their collective impact on deep ocean circulation.

Astronomical grand cycle 

Dutkiewicz and her team discovered that deep-sea currents exhibit shifts in a 2.4-million-year cycle, known as an “astronomical grand cycle,” that is influenced by the gravitational interactions between Earth and Mars. 

“We were surprised to find these 2.4-million-year cycles in our 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,” Dutkiewicz said.

“The gravity fields of the planets in the solar system interfere with each other and this interaction, called a resonance, changes planetary eccentricity, a measure of how close to circular their orbits are,” added Müller. 

Deep ocean circulation

This resonance effect leads to cycles of increased solar radiation and, consequently, warmer climates every 2.4 million years, which the study correlated with more active deep ocean circulation.

The research highlights the critical role of deep eddies during these warmer periods, suggesting they might help mitigate potential ocean stagnation scenarios feared to accompany a weakening of the Atlantic Meridional Overturning Circulation (AMOC). 

While AMOC facilitates water mass transport across different latitudes, deep ocean eddies are pivotal in ventilating the oceans during warm climates.

“We know there are at least two separate mechanisms that contribute to the vigor of deep-water mixing in the oceans. AMOC is one of them, but deep ocean eddies seem to play an important role in warm climates for keeping the ocean ventilated,” explained Müller. 

Warmer oceans have more vigorous deep circulation

“Our deep-sea data spanning 65 million years suggest that warmer oceans have more vigorous deep circulation. This will potentially keep the ocean from becoming stagnant even if Atlantic Meridional Overturning Circulation slows or stops altogether,” said Dutkiewicz.

This investigation not only challenges existing paradigms but also opens new pathways for understanding the interplay between ocean dynamics and marine life in future climates. 

The authors are optimistic that their findings will contribute to refining climate models, enhancing our ability to forecast and respond to climate change effectively.

The study is published in the journal Nature Communications.

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