Breaks in ancient coral growth reveal Earth's climate past

Coral reefs are known for their vibrant colors and abundant marine life. They shelter countless fish and invertebrate species, stabilize coastlines, and supply vital resources for communities.

Scientists have speculated whether these important habitats underwent dramatic shifts in the distant past. A new investigation has unearthed a major interruption in coral growth in the Gulf of Eilat, raising new questions about coral resilience.

This region, at the northern tip of the Red Sea, is home to corals that tolerate warmer waters than many other reef systems. Their apparent resilience has made the area a favored spot for studying how reefs cope with changing conditions.

The latest findings come from a team led by Professor Adi Torfstein of The Hebrew University and Professor Oren Levy of Bar-Ilan University, in collaboration with several other international scientists.

The research opens a window into the historical factors that have shaped coral life.

Why coral reefs matter

Reefs are not just pretty landscapes. They play a role in the carbon balance of the oceans. Coral reefs are also biodiversity hotspots that support tourism and feed local fisheries.

Some species that thrive in reef environments form the basis of drug discovery. These organisms produce compounds that could one day lead to breakthroughs in treatments for human diseases.

Furthermore, coral skeletons serve as natural archives, preserving details about past water temperatures and nutrient levels.

By sampling these structures, researchers can piece together long-term climate shifts that might otherwise go unnoticed.

Pause in coral growth

The researchers found that there was a hiatus in coral growth between 4,400 and 1,000 years before 1950. The corals on certain reefs stopped growing for several thousand years.

The researchers suggest that a mix of tectonic (Earth’s crust movement) and glacio-eustatic (sea-level fluctuation due to ice changes) forces lowered the water level in this region.

Similar patterns were noted in other parts of the globe, hinting at a larger climate trend.

Corals in certain deeper zones survived and, when the sea rose again, they repopulated the reefs in shallower areas where other corals had died out. This rebound demonstrates how a single interruption might not eliminate a reef forever.

Most striking was the finding that this standstill persisted for nearly three millennia, which is a significant stretch in geological terms.

The researchers believe the pause in coral growth coincided with a period of global cooling, which reduced sea levels enough to disrupt reef expansion.

Future threats to coral reefs

Coral bleaching events have become more frequent in the past few decades, and have often been linked to the presence of warmer waters. Some reefs bounce back, but others suffer long-term harm, especially if pollution or destructive fishing adds stress to the situation.

Ocean acidification is another growing concern, as shifting pH levels can dissolve coral skeletons faster than they can regenerate. This chemical imbalance makes it tougher for new corals to build their stony foundations.

“Understanding how reefs have responded to past sea-level changes helps us predict their future resilience and informs conservation strategies,” noted Dr. Torfstein.

“While our research shows that coral communities can recover after major disruptions, today’s climate crisis presents unprecedented challenges that demand urgent action.”

Studying ancient corals

To investigate the environmental conditions in ancient times, the team drilled coral cores up to ten feet deep into the seafloor.

Each layer in these samples contains evidence about the salinity, temperature, and ecological conditions at the time the coral skeleton was formed.

By comparing layers from different time periods, the researchers identified distinct phases of coral growth.

One of the biggest revelations was a shift in carbon isotopes over recent centuries, suggesting increased human impact on local waters.

The approach of drilling and analyzing such extensive coral reef samples had been rarely applied in this region. It provided a way to see how these reefs evolved over the past 10,000 years, capturing both abrupt changes and gradual trends in the environmental indicators.

Learning from ancient corals

As scientists build on these findings, they understand more about the broader ocean changes that can happen over thousands of years.

This perspective is critical, considering that short-term surveys often miss the subtle shifts that accumulate over centuries.

Many marine ecosystems, from kelp forests to seagrass meadows, also face stress from temperature swings and habitat loss.

Learning from coral core records might help researchers anticipate shifts in other environments that share similar vulnerabilities.

Local communities in Eilat rely on healthy reefs for tourism and fishing, which raises the stakes for successful conservation.

Some groups are exploring restoration projects, including transplanting young corals and monitoring water quality, to help reefs survive tough conditions.

The study is published in Global Change Biology.

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