Image: WikiMedia Commons

Image: WikiMedia Commons

It seems counterintuitive that something so vast and fertile as the sea could be endangered by invisible greenhouse gases, but the fossil record proves otherwise.

Today, the ocean is being threatened on multiple fronts. It’s absorbing so much carbon that it is acidifying faster than anytime in the last 300 million years; it’s stuffed with plastic and killing wildlife; it’s warming so quickly it’s breaking scientists’ charts; and if the warming continues, the planet will become a very different place.   

Aside from the plastic, changes like these are not unprecedented. The planet has gone through many cycles of natural climate variation in the last four billion years. The problem is, man-made greenhouse gases are accelerating these changes about 10 times faster than normal.

What happens to the ocean when global warming pushes it past its limits? Scientists have a pretty good idea.

In a study published Monday in the Proceedings of the National Academy of Sciences, researchers analyzed a 30-foot core of sea sediment obtained from the Santa Barbara Basin. The core dates back almost 13,000 years and contains over 5,000 fossils, essentially giving scientists a series of snapshots into the ancient sea.

When ocean temperatures rise, the amount of dissolved oxygen can decline, much as it does in ocean dead zones. This occurred over 14,000 years ago as glaciers melted across North America. Over a relatively short amount of time (about 130 years), starfish, clams, snails and urchins just about disappeared from the fossil record.

“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,” Sarah Moffitt, a marine ecologist at UC Davis and the lead author of the study, told The LA Times. “They were just dramatically wiped out by the abrupt loss of oxygen.”

Fire coral. (Image Credit: WikiMedia Commons)

Fire coral. (Image Credit: WikiMedia Commons)

The animals were replaced by a narrower range of extremophiles: creatures that could survive in the de-oxygenated conditions. It took about 1,000 years for the ocean floor to regain the rich biodiversity that it once had.

How the marine community was decimated and then adapted gives us a chilling but informative glimpse at how our own oceans will respond to higher temperatures and less oxygen.

As Moffitt explained, her team’s research illustrates which biomes and animals “are on the chopping block for a future of abrupt climate warming and unchecked greenhouse gas emissions.”

Which leads humanity to an interesting crossroads, for those who are paying attention. Moffitt sums it up eloquently: “We as a society and civilization have to come to terms with the things that we are going to sacrifice if we do not reduce our greenhouse gas footprint.”

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