Deep Ocean Discoveries
*The first in a series exploring the process of scientific discovery
By Paige Brown
It is earth’s last frontier: the ocean floor. Researchers currently have more detailed maps of the surface of Mars than they do of our own deep ocean. But thanks to several LSU coastal science researchers, that is beginning to change.
Harry Roberts, LSU Boyd Professor and former director of the Coastal Studies Institute in the Department of Oceanography and Coastal Sciences, is collaborating with researchers from the Bureau of Ocean Energy Management, or BOEM; the National Oceanic and Atmospheric Administration, or NOAA, and other universities to investigate newly discovered and unusual deep-water coral mounds in the Gulf of Mexico. These mounds are the strange, cold and dark water relatives of the tropical coral reefs we’ve seen in pictures of prime vacationing spots. As a part of a multi-institutional project, Roberts and his colleagues located and are now investigating these deep-water mounds and their coral communities on the continental slope of the northern Gulf of Mexico. This research is an outgrowth of previous projects designed to study unusual seafloor communities called chemosynthetic communities, which are organisms that live on the chemical products produced at sites of natural oil and gas seepage in the deep ocean. Chemosynthetic communities as well as deep water coral communities are protected by BOEM.
“In the larger context, as part of the deep water coral project, we are discovering new things on the ocean floor of the Gulf,” Roberts said. “The ocean floor is the last major frontier on earth. There are many important things yet to be discovered. That is the fun for me.”
The Gulf of Mexico has been known as a province rich in oil and gas since early explorers provided accounts of the region. Today, the investment of oil industry capital in the Gulf’s deep-water offshore province has produced high resolution technologies for mapping the ocean floor and the geology below the seabed. One particular technology, called 3-dimensional, or 3-D, seismic, is used in the exploration for oil and gas. This technology uses sound waves to produce a volume of data that can be “sliced” to create profiles of the geology below the ocean bottom, or plan-view maps of any depth horizon, including the seafloor. When sound waves, or acoustic signals, are sent to the ocean floor from ships such as NOAA’s Ronald H. Brown, the reflected signals that come back can give information about hard, soft, low and high features, for example.
The northern Gulf of Mexico continental slope from Texas to Florida is almost totally covered by 3-D seismic data.
“There is no other deep water province on earth with as much 3-D seismic coverage as the northern Gulf,” Roberts said.
Because the deep water coral project is funded by BOEM, Roberts and geoscientists at BOEM can access and use the 3-D seismic dataset archived in BOEM in New Orleans to meet project goals. The database is very important to the project because 3-D seismic seafloor maps can identify “hard bottom areas” necessary as substrates for coral attachment and growth.
As Roberts wrote in a 2010 issue of Deep-Sea Research, 3-D seismic mapping revealed a much more complex seafloor than was previously imagined. Roberts and his scientific colleagues were initially puzzled by several areas in the Gulf that appeared as bright spots in their ocean floor maps.
“Over the years, we learned what these highly reflective areas on the ocean floor mean,” Roberts said. His group found that bright spots on the 3-D seismic maps of the ocean floor correlated to areas where oil and gas are seeping up from underground.
“Microbial communities are feasting on the hydrocarbons,” Roberts said, referring to the oil and gas seeping from the ocean floor in these areas. “At those sites where oil and gas are leaking to the ocean floor from deep underground, it is like an oasis for marine organisms. This is an important food source, for not only microbial communities but also for larger animals like tubeworms that live on hydrogen sulfide and methane-feeding mussels. There are all kinds of unusual animals living in these areas.”
The underwater microbe and animal communities that feed on cold oil and gas seeping in the Gulf of Mexico have become the most intensively studied and best understood of any cold seep communities in the world. As the microbes feed on oil and gas, they produce calcium carbonate, a common substance found in rocks and the main component of shells of marine organisms. These calcium carbonate byproducts form materials as hard as concrete. Such hard surfaces can in turn serve as substrates for the growth of unique coral communities, for example.
“These sea floor areas are hard,” Roberts said. “Within these areas are really magnificent bottom feeders that live on natural gas and other seep-related chemical products. This is really a weird community. This line of research started because people brought these animals to the surface and had no idea what they were.”
Today, BOEM recognizes both the significance of chemosynthetic communities and the importance of protecting them from activities of the oil and gas industry as well as other human activities. Charged with protecting deep-water communities, the BOEM has funded well studies focusing on locating and understanding the unique plants and animals that live on the products of natural deep ocean oil and gas leaks in the Gulf.
“These communities are protected by the federal government,” Roberts said. “But the other side of that coin is the research, discovering where these communities are located and how they function. Mapping the locations of these chemosynthetic communities so that pipelines and production platforms are not damaging them is important.”
Roberts has been studying seafloor geology and the unique chemosynthetic communities in the Gulf of Mexico since the 1980s. He has been responsible, along with colleague Bill Shedd at BOEM in New Orleans, for selecting ocean floor sites on 3-D seismic maps that are most likely to contain hard, hydrocarbon feeding communities. Roberts started using 3-D seismic data for finding hard bottoms associated with hydrocarbon seeps as far back as the early 1990s. The same, but upgraded, methodologies are now being used to find probable sites for deep water corals.
“Looking for and studying these chemosynthetic sites was an objective in itself,” Roberts said. “But over the years, that objective morphed into another project to investigate deep-water coral communities in the Gulf of Mexico.”
As part of the deep water coral project, using 3-D seismic data, Roberts and colleagues discovered a group of unusual mounds on the upper continental slope southeast of the modern Mississippi River Delta. The mounds appear transparent on seismic maps, but are sitting on a highly reflective surface. They are nearly 1,500 feet underwater, with the largest rising nearly 140 feet above the surrounding seafloor.
In 2009, Roberts and his fellow researchers used a high tech remotely operated underwater vehicle named “Jason” from Woods Hole Oceanographic Institution to map, photograph and acquire samples from one of the mounds they had found.
“We found living thickets of coral covering these mounds,” Roberts said. “I got really excited about this. It was the first deep water coral mound of this type found in the Gulf of Mexico. It was a very exciting find.”
What Roberts and his fellow researchers had found was a rare coral habitat for the Gulf of Mexico. The coral turned out to be Lophelia pertusa, a coral known from the deep water Gulf of Mexico but not usually known to form such large mounds.
The mound top and upper flanks were completely covered with living thickets of Lophelia. Normally, corals need a hard surface on which to settle and grow. The seismic data suggest a hard surface beneath the mounds on which the original coral colonies grew. The tall mounds, however, appear to have formed by corals growing on top of corals. The mystery lies in how the mounds got started and how long it took for the mounds to grow to their present sizes.
With additional support to the original deep water coral project funded by BOEM and NOAA, Roberts is now concentrating on determining the characteristics of these mounds inside and out. These mounds of deep ocean coral are significant because they represent huge accumulations of slow-growing deep-water coral skeletal material, probably representing tens of thousands of years of growth.
The problem is that finding a coral mound in the Gulf would be rather like finding a “needle in a haystack” without access to the 3-D seismic database.
“How you find these coral sites is very important to understand,” Roberts said. “You have to use some sort of dataset that will allow you to prioritize sites that have a high probability of having chemosynthetic communities and overlying corals mounds.”
Once they solved the problem of finding these rare coral mounds on 3-D seismic maps and profiles, Roberts and his colleagues could begin investigating the living corals on the mounds as well as the material below the surface that makes up the mounds. In order to access the interior of the largest mound, BOEM had a contractor take long cores, called jumbo piston cores, from the mound. The longest core was more than 50 feet long. Core samples from the mound will help Roberts determine how old the mound is and how fast it has been growing.
The coral mounds also contain valuable historical oceanographic information about the Gulf of Mexico, which is housed in the coral skeletal material as well as the sediments that have accumulated around this material.
“We are trying to figure out exactly how these coral mounds got started, how long the mounds have existed and how fast they have grown,” Roberts said. “Our cores may be able to provide valuable historical information about the unique conditions that caused these features to develop. If the mounds represent a long enough time span, they may contain a record of Gulf conditions during the last ice age, including abnormal discharge events from the Mississippi River.”
Roberts is now sending additional coral samples from throughout the mound core to be radiocarbon dated. Dating will provide a basic framework for interpreting historical data contained in the core.
“We are just now starting the process of trying to figure out how this mound got started and why it grew where it did,” Roberts said. “There is a record of oceanographic conditions and geologic conditions housed in this mound that may not be as easy to access anywhere else in the Gulf. It’s like a library. We just have to figure out what the card catalog is telling us.”
Corals can serve as beacons for the effects of biological disturbances such as oil spills on the ocean floor. By investigating the corals, researchers can build a history of disturbances in the Gulf not readily available anywhere else.
“Our research is part of the discovery process in the oceans,” Roberts said. “It is pure exploration, similar to what the USA is doing on Mars with the Rover. This is the part of science that drives most scientific people: the thrill of discovery. Regardless of what it is – a new frog, a cure for cancer or a new feature on the ocean floor – it’s all fun when you discover it.”
For more information on the Coastal Studies Institute, visit http://www.csi.lsu.edu/.
For more information on BOEM, visit http://www.boem.gov/.