A chemical process on the ocean floor proved to be the critical element that prolonged one global ice age for 56 million years, whereas a subsequent cold snap concluded in merely 4 million years. This finding challenges the long-held belief that only volcanic carbon governed Earth’s most extreme climatic states.
Geological strata older than 600 million years show evidence of two global cooling events that lasted for vastly different durations.
By tracing the ebb and flow of carbon between the ocean and the atmosphere, Trent B. Thomas of the University of Washington (UW) demonstrated that heightened seafloor weathering could maintain greenhouse gases at levels low enough to extend deep-freeze conditions for scores of millions of years. The outcomes of this novel research were published in the journal Geology.
In his simulations, volcanic carbon emissions remained within the same bracket for both epochs, yet only the scenario featuring accelerated reactions at the ocean bottom replicated the protracted glaciation.
This imbalance was directed away from the sky toward the seabed, necessitating an understanding of how the ocean floor gained such a disproportionate command over Earth’s climatic clock. Geologists refer to these planetary deep-freeze episodes as “Snowball Earth” events—times when ice spread across nearly the entire globe, reaching close to the equator.
“There must be significant discrepancies within the carbon system between two ‘Snowball Earth’-like events,” stated Trent B. Thomas from the University of Washington.
Volcanoes release CO2, and a stabilizing feedback loop speeds up rock breakdown on warm, wet continents while slowing it down during cold spells. As ice starts to spread, bright surfaces reflect sunlight back to space, allowing glaciers to advance until the terrestrial thermostat fails.
With continents buried under ice, rock weathering minimized, but seawater continued to infiltrate cracks in the oceanic crust.
This process, known as seafloor weathering, involves seawater reacting with the underlying ocean rocks, sequestering carbon into mineral forms.
As a consequence of these reactions, dissolved ions were liberated while carbonate minerals precipitated, enabling the ocean to retain more carbon as atmospheric CO2 levels dropped.
Although this mechanism plays a minor part today, Thomas’s model suggests it could become the primary carbon sink during an ice cover lasting millions of years.
To test this concept, the University of Washington team ran 10,000 simulations encompassing the oceans, air, and bedrock during a global deep freeze.
This investigation found that carbon input from Earth’s interior remained constant, while the reactions occurring on the seabed either intensified or diminished.
The extended cooling period was attributed to a single factor: seafloor weathering rates were approximately 25 to 53 times faster than present-day levels, substantially surpassing those during the short cold phase.
Since carbon emission rates stayed within modern margin of error across the studies, the findings implied that the majority of the time elapsed was governed by processes on the seafloor.
Elevated CO2 acidified seawater during the ice ages, causing deep-sea rocks to dissolve more rapidly wherever water could reach them.
Because rivers were choked with ice, far less sediment reached the deep ocean, leaving older seafloor crust exposed to ongoing seawater circulation. This reduced sediment load resulted in fewer sealing layers within the seabed fractures, likely allowing more water to flow through and react.
Under such conditions, with continents frozen and quiescent, the ocean floor might become the chief carbon removal agent.
The texture of the bedrock mattered because seawater could only react where it could penetrate and travel through the crust. Scientists call this openness “porosity”—the fraction of rock constituted by interconnected empty spaces.
Near hot hydrothermal vents on the seafloor, specific minerals can solidify within fissures, blocking water flow and slowing reactions. More open crust maintains reactivity for longer, so changes in porosity could dictate whether Earth remains frozen for extended periods.
It is possible that ocean chemistry regulated crustal porosity through the amount of sulfate—a dissolved sulfur compound in seawater—available near the vents.
With high sulfate levels, minerals are more readily formed in the hot crust, sealing fissures and limiting water-rock contact.
Geochemical evidence presented in the paper suggests sulfates were virtually absent during the prolonged glaciation, only to reappear before the shorter ice age.
If these timings hold true, minor shifts in ocean chemistry might determine whether a “snowball” event ends quickly or lingers.
Low sulfates and open pores could establish a feedback loop that sustains high rates of seafloor weathering and delays thawing.
Fewer cementing minerals keep the crustal pores open, permitting greater seawater circulation through the rock and sustaining the reaction.
Prolonged ice cover might also drive down ocean oxygen levels, which, in turn, could keep sulfate concentrations low.
“This is just an attempt to initiate a discussion,” Thomas noted, outlining how ocean chemistry could influence seafloor reactions.
The planet’s climate may depend more heavily on the chemistry of the ocean floor than previously thought, particularly when surface conditions become unfavorable for typical rock weathering.
On an ice-covered world, greenhouse gas concentrations might creep up slowly over centuries, yet the chemical makeup of the ocean bottom could still dictate when the ice begins to recede.
Even without the full “snowball” effect, colder oceans or fractures remaining open on the seafloor could regulate the speed at which carbon is scrubbed from the atmosphere.
Contemporary climate challenges involve much faster changes and living ecosystems, so this work mainly reframes our perspective on the very long term, rather than offering short-term forecasts.
The new explanation links the duration of ancient global freezes to chemical reactions on the ocean floor that continuously draw down atmospheric carbon.
Further research will necessitate geological mapping and geochemical data to ascertain if seafloor porosity truly varied as the model predicts.
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