Marine Life Can Take Millennia to Recover from Climate Change

It's no secret that climate change is wreaking havoc on our world's oceans, and now new research has shown that it can take marine life millennia to recover from climate change-related upheavals.

In the face of our rapidly changing climate, scientists had previously believed marine ecosystems to be pretty resilient, only taking hundreds of years to bounce back to normal. But after analyzing a 30-foot-long core sample of Pacific Ocean seafloor, researchers with the California Academy of Sciences are coming to a different conclusion. While it only takes decades to destroy ocean biomes, it may take these ecosystems thousands of years to recover from damage as a result of climate change and seawater deoxygenation.

Tens-of-thousands of years ago, heightened temperatures robbed our seas of oxygen (deoxygenation) as massive ice sheets started to melt. Now, with sea ice and glaciers fast retreating in the wake of climate change, scientists are worried that it could happen again.

Previously, studies that aimed to reconstruct Earth's climatic history relied heavily upon simple, single-celled organisms called Foraminifera. However, this new study, published in the journal PNAS, is the first to focus on multicellular life, which can paint a better picture of the health of ecosystems as a whole and the food webs within. The research team analyzed more than 5,400 invertebrate fossils, from sea urchins to clams, within a sediment core from offshore Santa Barbara, Calif.

"In this study, we used the past to forecast the future," researcher Peter Roopnarine, Academy curator of invertebrate zoology and geology, said in a press release. "Tracing changes in marine biodiversity during historical episodes of warming and cooling tells us what might happen in years to come. We don't want to hear that ecosystems need thousands of years to recover from disruption, but it's critical that we understand the global need to combat modern climate impacts."

The tube-like sediment core Roopnarine and his colleagues sampled provides a slice of ocean life as it existed between 3,400 and 16,100 years ago. It more or less depicts a before-and-after snapshot of what happened during the last major deglaciation on Earth - a time of abrupt climate warming when polar ice caps were melting and low oxygen zones in the ocean were expanding. (Scroll to read on...)

The findings revealed that after this dramatic shift in climate, seafloor ecosystems that were once diverse and full of oxygen became deoxygenated and also lost their incredible biodiversity. What's more is that invertebrate fossils are nearly non-existent during times of lower-than-average oxygen levels.

In periods of fewer than 100 years, oceanic oxygen levels decreased between 0.5 and 1.5 mL/L. Sediment samples during these periods show that relatively minor oxygen fluctuations can result in dramatic changes for seafloor communities.

The study results suggest that future periods of global climate change may result in similar ecosystem-level effects, with marine life recovery taking place on a millennial scale. As the planet warms (2014 was the hottest year on record), scientists expect to see much larger areas of low-oxygen "dead zones" in the world's oceans.

And this isn't just bad news for the various marine organisms that call the oceans home, but for those that depend on these delicate seafloor ecosystems as well.

"Folks in Oregon and along the Gulf of Mexico are all-too-familiar with the devastating impacts of low-oxygen ocean conditions on local ecosystems and economies," Roopnarine added. "We must explore how ocean floor communities respond to upheaval as we adapt to a 'new normal' of rapid climate change. We humans have to think carefully about the planet we are leaving for future generations."

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