Why Are Scientists Exploring Deep Bottom Communities in the Gulf of Mexico?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on earth, cures for human diseases, answers on how to achieve sustainable use of resources, links to our maritime history, and information to protect endangered species.
The Gulf of Mexico produces more petroleum than any other region in the United States, even though its proven reserves are less than those in Alaska and Texas. Since the 2005 disruption in Gulf of Mexico oil production caused by Hurricane Katrina, efforts have intensified to find more crude oil and drill more wells. Despite the threat of more hurricanes, the Gulf of Mexico has advantages: oil workers are not in danger of being kidnapped by armed insurgents as is the case in Nigeria; no foreign president threatens to raise oil companies' taxes, as has happened in Venezuela; and OPEC doesn't control oil production in the Gulf of Mexico.
Responsibility for managing exploration and development of mineral resources on the Nation’s outer continental shelf is a central mission of the U.S. Department of the Interior’s Minerals Management Service (MMS). In addition to managing the revenues from mineral resources, an integral part of this mission is to protect unique and sensitive environments where these resources are found. To fulfill its mission, MMS has conducted a series of seismic surveys to map areas between the edge of the continental shelf and the deepest portions of the Gulf of Mexico. These maps provide information about the depth of the water as well as seismic amplitude, which is affected by the type of material that is found on the seafloor. In areas where the seafloor is covered with soft mud, seismic amplitude is low, while hard surfaces such as rocks or shellfish beds produce a high seismic amplitude.
MMS scientists are particularly interested in finding deep-sea chemosynthetic communities in the Gulf of Mexico, because these are unique communities that often include species that are new to science and whose potential importance is presently unknown. In addition, the presence of these communities often indicates the presence of hydrocarbons at the surface of the seafloor. To locate these communities, scientists have used manned submersibles to study areas of high seismic amplitude in the Gulf of Mexico.
The 2006 Expedition to the Deep Slope was focused on discovering and studying the sea floor communities found near seeping hydrocarbons on hard bottom in the deep Gulf of Mexico. The sites visited by the Expedition were in areas where energy companies will soon begin to drill for oil and gas. A key objective was to provide information on the ecology and biodiversity of these communities to regulatory agencies and energy companies. Based on seismic surveys, 20 sites were selected where chemosynthetic communities were likely to be found. These sites were photographed using an unmanned camera system, and ten sites were selected for follow-up dives by scientists aboard the research submersible ALVIN. These dives revealed that hydrocarbons seepage and chemosynthetic communities were present at all ten sites. The most abundant chemosynthetic organisms seen were mussels and vestimentiferan tubeworms. Expedition to the Deep Slope 2007 is focused on detailed sampling and mapping of four key sites visited in 2006, as well as exploring new sites identified from seismic survey data.
The primary objectives of the Deep Slope expeditions are:
• To explore and describe known, or newly-discovered chemosynthetic communities at depths below 1,000-meters in the central and western Gulf of Mexico;
• To explore and describe all other hard bottom biological communities in the central and western Gulf of Mexico, regardless of whether or not they are associated with active hydrocarbon seepage or chemosynthetic communities;
• To estimate how sensitive these communities are to impacts from human activities, and to understand how deep communities are similar or different from similar communities in shallower waters;
• To develop ways to use remote sensing information (such as bathymetry or seismic surveys) to predict the presence of hard-bottom biological communities at depths below 1,000 meters; and
• To describe and explain the diversity distribution and abundance of marine species at depths below 1,000 m in the central and western Gulf of Mexico, as well as to improve understanding of the ecology of marine species in areas of active hydrocarbon seep activity and in chemosynthetic communities.
Meeting these objectives will provide information that is needed to protect sensitive and unique deep-sea ecosystems, as well as to ensure safe and environmentally sound exploration and production of U.S. natural gas, oil, and other mineral resources.
During the 2006 Expedition to the Deep Slope, scientists used the submersible Alvin to dive on hydrocarbon seep communities that had never before been visited by humans. Scientists participating in the Expedition to the Deep Slope 2007 will return to these communities and visit others as well - but without leaving the deck of their ship!
The key to this kind of expedition is a remotely operated vehicle (ROV) system named Jason II/Medea. This is a two-part system: Jason II is a mobile platform that carries sonar and video imaging equipment as well as manipulator arms for collecting samples. Jason II gives scientists a ‘virtual presence’ in deep ocean waters at depths up to 6,500 meters. A 35-meter cable connects Jason II to a second ROV named Medea, which is connected to the surface ship by a 10-kilometer fiber optic cable. This arrangement allows Medea to buffer Jason II from movements of the ship, and provides a second platform that allows scientists to observe Jason II during seafloor operations.
The Jason II/Medea system is operated from a control van that is loaded aboard the host ship along with the ROV. Additional equipment and supplies are carried in tool and rigging vans.
The advantage of the Jason II/Medea system is that it allows much longer observation periods than are possible with manned submersibles; the average Jason dive is 21 hours (compared to Alvin dives which are six to ten hours), though dives as long as 71 hours have been made on some occasions. The system is designed, built, and operated by the Deep Submergence Laboratory of Woods Hole Oceanographic Institution.
Chemical Mapping with Mass Spectrometry
To learn more about how deep-sea chemosynthetic communities work, it is essential for scientists to know what kinds and quantities of gases and liquids are seeping from the ocean floor. The traditional way to obtain this information is to collect water and sediment samples that are later analyzed in a laboratory. This approach requires a large number of samples to obtain a good picture of how chemicals are distributed in a given community, and some chemicals may degrade between the time samples are collected and analyzed.
A newer approach is to use chemical sensors that can be mounted on an ROV. Data from these sensors can be integrated with navigation data (such as data provided by a GPS system) to produce detailed maps of how chemicals are distributed over a study site. A particularly useful sensor for this purpose is the mass spectrometer, which is a device that measures the atomic mass of ions (or more accurately, the mass-to-charge ratio of these ions). Mass spectrometers used on ROVs for chemical mapping can make the necessary measurements almost as soon as water samples are collected, in about 10 seconds. A big advantage of rapid in-situ measurements is that these measurements can warn of dangerous geologic activity (such as volcanic eruptions). Another advantage is that real-time measurements can provide the basis for dynamic re-tasking, which means that an ROV can alter from its sampling program if certain chemicals are detected. This means that an autonomous underwater vehicle (which is a robot that operates independently of a surface ship) could be instructed to automatically seek the source of chemicals that might be emitted from underwater volcanoes, cold seeps, hydrothermal vents, and other interesting features.
More About Chemosynthetic Communities
The first chemosynthetic communities were discovered in 1977 near the Galapagos Islands in the vicinity of underwater volcanic hot springs called hydrothermal vents, which usually occur along ridges separating the Earth’s tectonic plates. Hydrogen sulfide is abundant in the water erupting from hydrothermal vents, and is used by chemosynthetic bacteria that are the base of the vent community food chain. These bacteria obtain energy by oxidizing hydrogen sulfide to sulfur:
CO2 + 4H2S + O2 > CH2O + 4S +3H2O
(carbon dioxide plus sulfur dioxide plus oxygen yields organic matter, sulfur, and water).
Visit http://www.pmel.noaa.gov/vents/ for more information and activities on hydrothermal vent communities.
Chemosynthetic communities in the Gulf of Mexico were found by accident in 1984. These communities are similar in that they are based upon energy produced by chemosynthesis; but while energy for the Galapagos communities is derived from underwater hot springs, deep sea chemosynthetic communities in the Gulf of Mexico are found in areas where gases (such as methane and hydrogen sulfide) and oil seep out of sediments. These areas, known as cold seeps, are commonly found along continental margins, and (like hydrothermal vents) are home to many species of organisms that have not been found anywhere else on Earth. Typical features of communities that have been studied so far include mounds of frozen crystals of methane and water called methane hydrate ice, that are home to polychaete worms. Brine pools, containing water four times saltier than normal seawater, have also been found. Researchers often find dead fish floating in the brine pool, apparently killed by the high salinity.
Methane hydrate is a type of clathrate, a chemical substance in which the molecules of one material (water, in this case) form an open lattice that encloses molecules of another material (methane) without actually forming chemical bonds between the two materials. Methane is produced in many environments by a group of Archaea known as the methanogenic Archaeobacteria. These Archaeobacteria obtain energy by anaerobic metabolism through which they break down the organic material contained in once-living plants and animals. When this process takes place in deep ocean sediments, methane molecules are surrounded by water molecules, and conditions of low temperature and high pressure allow stable ice-like methane hydrates to form. These deposits are significant for several reasons:• The U. S. Geological Survey has estimated that on a global scale, methane hydrates may contain roughly twice the carbon contained in all reserves of coal, oil, and conventional natural gas combined.
• Methane hydrates can decompose to release large amounts of methane which is a greenhouse gas that could have (and may already have had) major consequences to the Earth’s climate.
• Sudden release of pressurized methane gas may cause submarine landslides which in turn can trigger can trigger catastrophic tsunamis.
• Methane hydrates are associated with unusual and possibly unique biological communities containing previously unknown species that may be sources of beneficial pharmaceutical materials.
Where hydrogen sulfide is present, large tubeworms known as vestimentiferans are often found, sometimes growing in clusters of millions of individuals. At present, vestimentiferans are generally considered to be part of the phylum Annelida, but they are sometimes grouped as a separate phylum (Pogonophora). These unusual animals do not have a mouth, stomach, or gut. Instead, they have a large organ called a trophosome that contains chemosynthetic bacteria. Vestimentiferans have tentacles that extend into the water. The tentacles are bright red due to the presence of hemoglobin which can absorb hydrogen sulfide and oxygen which are transported to the bacteria in the trophosome. The bacteria produce organic molecules that provide nutrition to the tube worm. A similar symbiotic relationship is found in clams and mussels that have chemosynthetic bacteria living in their gills. Bacteria are also found living independently from other organisms in large bacterial mats A variety of other organisms are also found in cold seep communities, and probably use tubeworms, mussels, and bacterial mats as sources of food. These include snails, eels, starfish, crabs, lobsters, isopods, sea cucumbers, and fishes. Specific relationships between these organisms have not been well-studied.
Deepwater chemosynthetic communities are fundamentally different from other biological systems, and there are many unanswered questions about the individual species and interactions between species found in these communities. These species include some of the most primitive living organisms (Archaea) that some scientists believe may have been the first life forms on Earth. Many species are new to science, and may prove to be important sources of unique drugs for the treatment of human diseases. Because their potential importance is not yet known, it is critical to protect these systems from adverse impacts caused by human activities.