The world’s oceans soak up about a quarter of the carbon dioxide that humans pump into the air each year—a powerful brake on the greenhouse effect. In addition to purely physical and chemical processes, a large part of this is taken up by photosynthetic plankton as they incorporate carbon into their bodies. When plankton die, they sink, taking the carbon with them. Some part of this organic rain will end up locked into the deep ocean, insulated from the atmosphere for centuries or more. But what the ocean takes, the ocean also gives back. Before many of the remains get very far, they are consumed by aerobic bacteria. And, just like us, those bacteria respire by taking in oxygen and expelling carbon dioxide. Much of that regenerated CO2 thus ends up back in the air.

A new study suggests that CO2 regeneration may become faster in many regions of the world as the oceans warm with changing climate. This, in turn, may reduce the deep oceans’ ability to keep carbon locked up. The study shows that in many cases, bacteria are consuming more plankton at shallower depths than previously believed, and that the conditions under which they do this will spread as water temperatures rise. The study was published this week in the journal Proceedings of the National Academy of Sciences.

“The results are telling us that warming will cause faster recycling of carbon in many areas, and that means less carbon will reach the deep ocean and get stored there,” said study coauthor Robert Anderson, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory.

Two years ago a team of scientists visited Costa Rica’s subduction zone, where the ocean floor sinks beneath the continent and volcanoes tower above the surface. They wanted to find out if microbes can affect the cycle of carbon moving from Earth’s surface into the deep interior. According to their new study in Nature, the answer is affirmatively—yes they can.

This groundbreaking study shows that microbes consume and—crucially—help trap a small amount of sinking carbon in this zone. This finding has important implications for understanding Earth’s fundamental processes and for revealing how nature can potentially help mitigate climate change.

At a subduction zone there is communication between Earth’s surface and interior. Two plates collide and the denser plate sinks, transporting material from the surface into Earth’s interior. Showing that the microbes at the near-surface are playing a fundamental role in how carbon and other elements are being locked up into the crust provides a profound new understanding of Earth processes and helps researchers model how Earth’s interior may develop over time.