Sixty feet beneath the green waves of the Gulf of Mexico, ten miles from the nearest land, stands an ancient forest of giant trees.
Covered in dense carpets of sea anemones, crawling with spidery arrow crabs and toadfish, the sprawling stumps of massive cypress trees spread across the seafloor.
Unmistakable to eyes that have seen the cypress growing today in the swamps of the Gulf Coast, the trunks bear the jagged, craggy outline that is the hallmark of the species. Away from each stump lies another clue, a telltale ring of cypress knees, the knobby wood outgrowths believed to help the trees survive in the soupy mud of the south’s river deltas.
The trees run along a small drop off along the Gulf’s bottom south of the Fort Morgan peninsula. For hundreds of yards, the stumps follow the lazy meanders of what appears to be an ancient river channel that runs to the north, toward the modern day Mobile-Tensaw Delta, which drains Alabama and portions of Tennessee, Georgia and Mississippi.
Drifting along the river channel, floating over the edge of a sunken forest rendered in the blues and greens of the deep sea is enchanting.
The way the story goes, a fisherman happened onto the drop off shortly after Hurricane Katrina and started catching red snapper along it. After a few successful trips, he asked a scuba diving buddy to take a look and tell him what was on the bottom. The diver came up and reported seeing dozens of tree stumps in every direction.It is believed the forest was uncovered by the towering waves generated by Hurricane Katrina. Big hurricanes can move sand around at depths of 100 feet or more. It is possible the next big storm could cover the entire forest up again. The location is a closely guarded secret. Only a small handful of people know where the forest lies, and few of them are willing to disclose the GPS coordinates needed to anchor a boat above it.
The stumps along the edge of the old river channel are the most exposed, in some cases rising as much as five feet off the bottom, usually beginning with a tangle of roots and ending in a stump about five feet in diameter. Looking down on a stump from above, dozens of fish can be seen swimming among the roots. Fallen trees are also visible, logs too large to wrap arms around lying here and there on the bottom.
Fish typically associated with natural and artificial reefs in the northern Gulf swim above and around the stumps in dense clouds. Hi hats sporting black and silver stripes and distinctively tall dorsal fins school together along with beaugregories, ruby red lips, grouper and various snapper species. Soapfish nestle in the nooks and crannies of the stumps.
Moving east, away from the edge of the river channel, more stumps dot the seafloor, but seldom rise more than a few inches above the surrounding sand. Swarming with sea life, even the low stumps are large, often several feet in diameter. The outer layer of wood is soft and easily broken with bare hands.
Nick Tew, a geologist with the Geological Survey of Alabama, said that the stumps had likely been preserved for millenia by virtue of being buried beneath a few feet of sand, which prevented oxygen from reaching them. The same phenomenon is responsible for bones and remnants preserved in peat bogs and other oxygen-deprived locations.
“It certainly makes sense that these were preserved under anaerobic conditions and, unfortunately, now that they are exposed, they will deteriorate,” Tew said. “How neat to find those stumps exposed out there!”
Based on historic sea level depths, Mimi Fearn, head of the Earth Sciences Department at the University of South Alabama, said the forest was likely 10,000 to 12,000 years old. Research conducted for a scientific paper titled “Sea-level history of the Gulf of Mexico since the Last Glacial Maximum“ suggests a slightly broader range of 8,000 to 14,000 years old, due to the confounding influence of sediments from the Mississippi River.
“If you look back, current stands of sea level weren’t reached until 4,000 years ago. Before that, your absolute low stands would have been during the last glacial maximum about 18,000 years ago. After that, you have a gradual rise over the next period of time,“ Fearn said, discussing the geologic history of coastal Alabama.
“We know its pretty old. We have some stumps on the Fort Morgan peninsula, on the Gulf beach side. We had those dated and they are about 2,000 years old. Those are exposed on the beach today.”
Cypress trees cannot live along salty coastal beaches. The trees exist only in brackish or freshwater swamps and cannot tolerate high levels of salt. The presence of the 2,000 year old stumps on today’s Gulf beach means that area was once part of the swampy Mobile-Tensaw Delta.
Likewise, the far more ancient stumps 10 miles offshore also required a freshwater swamp to live in.
“What you found will represent an old shoreline. Its really fascinating,” Fearn said. Scientists have done some work reconstructing the ancient shorelines, she said, based on sediment cores and depth measurements taken offshore.
“It shows the Mobile River extending much farther out, much like what we have in the delta today, just much farther offshore. Imagine that delta being there offshore if you dropped sea level down. Same vegetation we have in the Delta today. We’re not talking so old that trees would have changed. It would look much like it looks today, a big swamp.”
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When the Gulf was at its shallowest, 18,000 years ago, the river delta would have been even farther offshore, Fearn said. The Gulf would have been about 120 feet shallower than it is today. That means the shoreline would have been between 20 and 30 miles offshore of the present day shoreline.
“During the sea level low associated with continental glaciation, what is now our shallow marine shelf was exposed and characterized by terrestrial environments, such as rivers and swamps,” Tew said. “Most evidence of this is usually covered with sand, but the old river channels and associated features can be seen on some geophysical profiles that have been collected across the area.”
Tew and Fearn said it was a rare treat to uncover a relic forest deep beneath the ocean. Both suggested that radiocarbon dating of wood samples could provide a more precise date for the age of the trees, and yield new clues about the history of the Gulf and its river deltas.
“The contours of the Gulf of Mexico have changed considerably since the last glacial period,” Fearn said. “I think it is really exciting to see something like this. It’s fun to imagine what it would have been like.”