Oceans could take thousands of years to recover from climate change, study says

It only took us an existential moment to damage them, but they won’t be fixed in our lifetime.

Researchers say ocean ecosystems have taken a hit from climate change – and that it could be thousands of years, not hundreds, before they recover. By analyzing layers of fossilized ocean fauna, scientists from UC Davis’ Bodega Marine Laboratory and Coastal and Marine Sciences Institute were able to make out correlations between abrupt climate change and disturbances in ocean biodiversity. Their study was published yesterday in the Proceedings of the National Academy of Sciences.

Biologically diverse seafloors can lose large amounts of dissolved oxygen as a result of climate change. The process – called deoxygenation – can disrupt the biodiversity of ocean ecosystems. But previous studies did not quantify these disturbances and recoveries in relation to sudden climate change. Led by Sarah Moffitt, a UC Davis research team began by extracting a huge fossil core from the ocean floor off Santa Barbara.

“After the initial sampling at sea, I took the entire core, which was about 30 feet long,” Dr. Moffitt said in a statement. “I cut it up like a cake, and I sampled the whole thing. Because of that, I had the whole record.”

The core contained fossil evidence from a period spanning 16,100 to 3,400 years ago. In that time, Moffitt noticed repeating patterns. Diverse seafloor ecosystems would experience deoxygenation coinciding with warming periods, and rapid loss of diversity would follow. In low-oxygen periods, fossil evidence was minimal. Even minor drops in oxygen levels appeared to curtail undersea life. And while the warming events seemed to last hundreds of years – possibly only decades – it took ecosystems thousands of years to bounce back. 

And it’s not all in the past – Moffitt says these deoxygenation events should viewed as analogues to the present.

“These past events show us how sensitive ecosystems are to changes in Earth’s climate – it commits us to thousands of years of recovery,” Moffitt said in a statement. “It shows us what we’re doing now is a long-term shift – there’s not a recovery we have to look forward to in my lifetime or my grandchildren's lifetime. It’s a gritty reality we need to face as scientists and people who care about the natural world and who make decisions about the natural world.”