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Underwater Cypress Forest from Ice Age Reveals Its Secrets

Deep beneath the waves, miles from the coast of Alabama, lies a primeval underwater forest, a grove of giant cypress trees so fresh that their trunks still ooze sap when they're cut.

Most of the ancient giants, now covered with sea anemones and schooling fish, last grew roughly 50,000 years ago, making this underwater forest the oldest of its kind anywhere in the world.

Its location kept hidden by scuba divers who hoped to protect the ancient grove, the underwater forest is slowly giving up its secrets to scientists. Many of those secrets are being revealed in a new documentary, called "The Underwater Forest." The program, which is now available for viewing on YouTube, will air on July 23 and 24 on Alabama Public Television. [See Images of the Underwater Forest]

The dramatic changes that this forest underwent during a volatile period of climate change may also hold clues for Earth's climate future, experts said.

Amazing discovery

Several years ago, scuba-dive-shop owner Chas Broughton discovered the bald cypress forest more than a dozen miles (20 kilometers) from Mobile, Alabama, in the Gulf of Mexico, about 60 feet (18 meters) beneath the ocean's surface. In the middle of nowhere, surrounded by a sandy, barren seafloor, was a watery world blanketed with sea sponges, schooling fish, octopuses and crabs. When Broughton took a closer look, he found a grove of massive tree stumps overlooking a meandering, ancient riverbed carved into the seafloor. Like a coral reef, the ancient trees had become home for thousands of different sea creatures.

"It was quite magnificent," Broughton said in the documentary.  

In 2012, Broughton disclosed the existence of the site to Ben Raines, an environmental journalist for a local Alabama news site, but swore him to secrecy on the trees' precise location.

Mud and sand covered the forest for eons, creating an oxygen-free environment that protected the trees from the punishing environment of the ocean. But in 2004, Hurricane Ivan's powerful winds and waves uncovered some of the forest. Since then, scientists have slowly been revealing the site's hidden history.

The team is also working to make the forest a marine protected area, so salvage operations can't log the primeval grove and turn the ancient wood into high-end coffee tables.

Ancient grove

Tree scientists quickly identified the trees as the freshwater swamp-dwelling cypress species, notable for their craggy "knees," which anchor similar trees into the mud along the Gulf of Mexico today.

The team took cores from the trees to analyze the tree rings, then handed those samples on to Grant Harley, a dendrochronologist (a scientist who studies tree rings) at the University of Southern Mississippi. The growth rings, sap and wood fibers were still visible in the tree stumps.

"When we ran those samples through the band saw, you can smell the resin just like you were cutting into a fresh piece of wood today," Harley said.

The scientists said that though they originally thought, based on the depth of the site, that the trees were 10,000 years old, radiocarbon dating from nearby sediments suggests the forest dates to an ice age that prevailed more than 50,000 years ago.

Volatile period

Under a microscope, the growth rings are thinner than in modern-day bald cypress, the researchers said, suggesting that the trees faced higher levels of environmental stress (trees nowadays, with constant growing conditions, usually have fatter, more even tree rings). It may also have been drier and cooler than now.

Sea levels were 400 feet lower at the time than they are today, meaning the coastline extended far out into the sea.

At the time, the Gulf of Mexico was a volatile place, Raines said.

"The world was really rocking then, with sea level changing as much as 75 feet [23 m] in 1,000 years," Raines told Live Science.

Rising at a rate of about 8 feet (2 m) per 100 years, the changing sea levels exceed some of the worst-case scenarios currently predicted for modern-day climate change, Raines added.

Tree ring data revealed that all the trees lived and died in a 500-year period, with periods of stress and growth, and all the trees ultimately dying at the same time, Raines said. The team also managed to analyze pollen from sediments near the trees, and found a transition in the environment that occurred rather dramatically. At its height, the river delta was made up of grassland that then gave way to a vibrant cypress forest, the researchers said. As sea levels rose, the grassland gradually moved inland, with the grassy fringe closest to the water retreating, before rising waters swallowed up the whole forest.

The team said it is still learning more about the ancient climate during this ice age. But like everything in the ocean, the waterlogged cypress grove's time is limited. As storms and shifting tides continue to reveal more of the forest, it will gradually be devoured by shipworms and bacteria, like so much else in the sea, Raines said.

For now, however, thousands of tree stumps still stand, rooted in the mud where they first grew as seedlings.

Originally published on Live Science.

Tia Ghose