Mounds of coral could provide history of Gulf

While looking for research sites in deep water southeast of the Mississippi River delta, scientists found something they hadn’t seen before, but the discovery could give a glimpse into the history of the Gulf of Mexico.

“We found these funny looking mounds,” said Harry Roberts, Boyd professor of marine geology and geophysics/sedimentology at LSU. “We had never seen mounds like this on the continental slope.”

These were round mounds but there was no indication that they were mud volcanoes, he said.

“So we dived on them and found they were just covered with corals,” Roberts said. “We assumed (the mounds) were built, throughout their history, of coral upon coral.”

So, Roberts and a team of researchers, drilled 50- to 60-foot cores through and around one of the mounds and took the material to the surface for more study.

“The object was to get at what’s inside that mound,” he said. “The corals are all the way through.”

Although corals are found spread throughout the northern Gulf of Mexico, this was the first time the corals were found to have built up over time into the mound formation.

Tests are being done on the layers of soil to look at how long this coral mound has been building and what organisms are found in the different layers.

The tests could help explain why the coral didn’t grow for long periods of time, but started growing again.

Roberts said that about 13 feet down the core, there’s a lapse in the coral growth that lasts tens of thousands of years, but then the coral grows again.

“It houses information of the Gulf of Mexico,” Roberts said. “It’s a really complicated history.”

There’s a lot of history to look at. The material just below the live coral is more than 40,000 years old.

At the bottom of the core sample, the material is 100,000 to 120,000 years old, he said.

A biologist on the team is looking at genetic testing of corals to see if these corals evolved. Another researcher is studying tiny bugs found in layers in an attempt to learn more, such as the history of salinity in the area.

“We’re just right at the beginning,” Roberts said. “The questions are now why did this series of mounds form where they did and we don’t see them anywhere else.”

The discovery is an outgrowth of work Roberts and others have been doing in the waters of the northern Gulf of Mexico since the late 1970s.

At that time, Roberts said, oil companies started moving their operations from the very shallow areas off shore to deeper waters.

He and another researcher started work on finding a good site for a deepwater rig just south of the Mississippi River delta in 1,027 feet of water.

In that investigation, the researchers came up with a lot of information about the continental shelf.

“I got really interested in the continental slope deepwater,” Roberts said.

Off the Louisiana coast, the researchers found strange ecosystems that evolved to live off these areas where oil and gas naturally seep to the surface.

Eventually, Roberts said, 3-D seismic images of the sea floor were used to see if these seeps could be identified.

The team also used a number of submarine and remotely operated underwater vehicles to see what was actually on the sea floor.

“We’ve gotten pretty good at picking sites and knowing what’s there,” Roberts said.

The study of these underwater seep ecosystems led to exploration of deepwater corals through the use of readily available 3-D seismic maps of the sea floor.

It was during a project that started in 2005, when Roberts and others looked for suitable research sites, when they came across the strange-looking mounds southeast of the Mississippi River delta and their current work began.

“It’s just exciting to discover something new,” Roberts said.