Mars lies around 140 million miles from our Pale Blue Dot. Yet despite the vast distance, it turns out the red planet has a greater impact on ours than we originally thought. Mars’ gravitational pull significantly affects the ocean depths. Surprising recent geological studies reveal a hidden effect of this interplanetary interaction, manifesting as cyclic changes in deep ocean currents. This discovery, published in Nature Communications and led by the University of Sydney, provides a new perspective on Earth’s past and future climate.

At the heart of this research lies the concept of an astronomical “grand cycle,” a pattern emerging from the alignment of Earth and Mars’ orbits. This newly discovered 2.4 million-year rhythm, though subtle, influences our planet’s climate by modulating solar radiation and temperature. Unlike the anthropogenic climate changes of recent history, these cycles belong to a natural order, shaped by the gravitational dance of celestial bodies.

“We were surprised to find these 2.4-million-year cycles in our deep-sea sedimentary data,” lead author Adriana Dutkiewicz said. “There is only one way to explain them: they are linked to cycles in the interactions of Mars and Earth orbiting the Sun.”

The solution to this mystery was hidden deep in the sea. Through an analysis of sedimentary data from 293 deep-sea drill holes, Dutkiewicz and her colleagues unearthed evidence of 387 sediment breaks over the past 70 million years, indicative of fluctuating ocean currents. These breaks, clustering around the 2.4 million-year mark, aligned with known warm periods in Earth’s history, such as the Paleocene-Eocene Thermal Maximum. This alignment indicates a potential connection between the gravitational impact of Mars and changes in Earth’s climate.

The study questions common beliefs about how the ocean behaves as the world warms, pointing to a more dynamic scenario. Warmer climates, it seems, stir the deep ocean into greater activity, countering the feared stagnation that might follow a slowdown in the Atlantic Meridional Overturning Circulation (AMOC). The AMOC circulates water from north to south and back in a long cycle within the Atlantic Ocean.

“We know there are at least two separate mechanisms that contribute to the vigor of deep-water mixing in the oceans,” said co-author Dietmar Müller, also from the University of Sydney. “AMOC is one of them, but deep ocean eddies seem to play an important role in warm climates for keeping the ocean ventilated. Of course, this would not have the same effect as AMOC in terms of transporting water masses from low to high latitudes and vice-versa.”

Despite its distant orbit and modest size, this study shows that Mars is surprisingly influential on Earth’s climate, potentially driving “giant whirlpools” — at least every couple of millions of years or so.

“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.