Earth’s recovery from the last glacial period was more brutal than previously thought. Researchers deciphered that plotline from a 30-foot core of sea sediments drilled from the Santa Barbara Basin containing more than 5,000 fossils spanning nearly 13,000 years.
"The recovery does not happen on a century scale; it’s a commitment to a millennial-scale recovery," said Sarah Moffitt, a marine ecologist at UC Davis’ Bodega Marine Laboratory and lead author of the study. "If we see dramatic oxygen loss in the deep sea in my lifetime, we will not see a recovery of that for many hundreds of years, if not thousands or more."
Studies already have chronicled declines in dissolved oxygen in some areas of Earth’s oceans. Such hypoxic conditions can expand when ocean temperatures rise and cycles that carry oxygen to deeper areas are interrupted.
As North American glaciers retreated during a warming period 14,700 years ago, an oxygen-sensitive community of seafloor invertebrates that included sea stars, urchins, clams and snails nearly vanished from the fossil record within about 130 years, the researchers found.
We found incredible sensitivity across all of these taxonomic groups, across organisms that you would recognize, that you could hold in your hand, organisms that build and create ecosystems that are really fundamental to the way ecosystems function," Moffitt said. "They were just dramatically wiped out by the abrupt loss of oxygen.”
That highly diverse community soon was replaced with a relatively narrow suite of bizarre and extreme organisms similar to those found near deep-ocean vents and methane seeps in modern oceans, Moffitt said. Evidence of that transition was confined to such a narrow band of sediments that the turnover could have been "nearly instantaneous," the study concluded.