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, and provide new knowledge about the forces that shape the Earth’s surface.
Earthquakes and volcanoes are among Earth’s most spectacular and terrifying geological events. The Mount St. Helens eruption of 19 and the Haiti earthquake of 2010 are recent and memorable examples of the extreme power that often accompanies these events. The Indian Ocean tsunami of 2004 was caused by an underwater earthquake that is estimated to have released the energy of 23,000 Hiroshima-type atomic bombs, and caused the deaths of more than 150,000 people.
Volcanoes and earthquakes are both linked to movements of tectonic plates, which are portions of the Earth’s outer crust (the lithosphere) about 5 km thick, as well as the upper 60 - 75 km of the underlying mantle. These plates move on a hot flowing mantle layer called the asthenosphere, which is several hundred kilometers thick. Heat within the asthenosphere creates convection currents (similar to the currents that can be seen if food coloring is added to a heated container of water). Movement of convection currents causes tectonic plates to move several centimeters per year relative to each other.
Where tectonic plates slide horizontally past each other, the boundary between the plates is known as a transform plate boundary. As the plates rub against each other, huge stresses are set up that can cause portions of the rock to break, resulting in earthquakes. Places where these breaks occur are called faults. A well-known example of a transform plate boundary is the San Andreas fault in California. View animations of different types of plate boundaries at:http://www.seed.slb.com
A convergent plate boundary is formed when tectonic plates collide more or less head-on. When two continental plates collide, they may cause rock to be thrust upward at the point of collision, resulting in mountain-building (the Himalayas were formed by the collision of the Indo-Australian Plate with the Eurasian Plate). When an oceanic plate and a continental plate collide, the oceanic plate moves beneath the continental plate in a process known as subduction. Deep trenches are often formed where tectonic plates are being subducted, and earthquakes are common. As the sinking plate moves deeper into the mantle, fluids are released from the rock causing the overlying mantle to partially melt. The new magma (molten rock) rises and may erupt violently to form volcanoes, often forming arcs of islands along the convergent boundary. These island arcs are always landward of the neighboring trenches. View the 3-dimensional structure of a subduction zone at: https://oceanexplorer.noaa.gov/explorations/03fire/logs/subduction.html.
Where tectonic plates are moving apart, they form a divergent plate boundary. At divergent plate boundaries, magma rises from deep within the Earth and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater (Iceland is an exception), and form submarine mountain ranges called oceanic spreading ridges. While the process is volcanic, volcanoes and earthquakes along oceanic spreading ridges are not as violent as they are at convergent plate boundaries. View the 3-dimensional structure of a mid-ocean ridge at: https://oceanexplorer.noaa.gov/explorations/03fire/logs/ridge.html.
Along the western coast of Chile, three of Earth’s tectonic plates intersect in a way that does not occur anywhere else on the planet (see Figure 1). Chile, and the other countries of South America, lie on top of the South American tectonic plate. To the west of Chile, the Nazca plate extends beneath the Pacific Ocean and meets the Pacific Plate along a divergent plate boundary called the East Pacific Rise. The southern edge of the Nazca plate adjoins the Antarctic Plate along another divergent plate boundary called the Chile Rise. The eastern edge of the Chile Rise is being subducted beneath the South American plate at the Chile Triple Junction (CTJ), which is unique because it consists of a mid-oceanic ridge being subducted under a continental tectonic plate. The eastern portion of the Nazca Plate is also being subducted along the Peru-Chile Trench, and the Andes mountains are one consequence of this process.Not surprisingly, complex movements of three tectonic plates at the CTJ result in numerous earthquakes. In fact, the largest earthquake ever recorded occurred along the Peru- Chile Trench in 1960. While earthquakes and volcanoes are often associated with massive destruction and loss of human life, the same processes that cause these events are also responsible for producing unique habitats for very different life forms.
One of the most exciting and significant scientific discoveries in the history of ocean science was made in 1977 at a divergent plate boundary near the Galapagos Islands. Here, researchers found large numbers of animals that had never been seen before clustered around underwater hot springs flowing from cracks in the lava seafloor. Similar hot springs, known as hydrothermal vents, have since been found in many other locations where underwater volcanic processes are active. Hydrothermal vents are formed when the movement of tectonic plates causes deep cracks to form in the ocean floor. Seawater flows into these cracks, is heated by magma, and then rises back to the surface of the seafloor. The water does not boil because of the high pressure in the deep ocean, but may reach temperatures higher than 350° C. This superheated water dissolves minerals in Earth’s crust. Hydrothermal vents are locations where the superheated water erupts through the seafloor. The temperature of the surrounding water is near-freezing, which causes some of the dissolved minerals precipitate from the solution. This makes the hot water plume look like black smoke, and in some cases the precipitated minerals form chimneys or towers.
The presence of thriving biological communities in the deep ocean was a complete surprise, because it was assumed that food energy resources would be scarce in an environment without sunlight to support photosynthesis. Researchers soon discovered that the organisms responsible for this biological abundance do not need photosynthesis, but instead are able to obtain energy from chemical reactions through processes known as chemosynthesis. Photosynthesis and chemosynthesis both require a source of energy that is transferred through a series of chemical reactions into organic molecules that living organisms may use as food. In photosynthesis, light provides this energy. In chemosynthesis, the energy comes from other chemical reactions. Energy for hemosynthesis in the vicinity of hydrothermal vents often comes from hydrogen sulfide. For additional discussion about the source of energy in chemosynthesis, see “More About Chemosynthesis and Reducing Habitats,” below.
In chemosynthetic communities where hydrogen sulfide is present, large tubeworms (phylum Pogonophora) known as vestimentiferans are often found, sometimes growing in clusters of millions of individuals. Vestimentifera have been regarded previously as a distinct phylum or a group within the phylum Pogonophora. Recent molecular evidence suggests that Vestimentifera and Pogonophora should be considered part of the polychaete family Siboglinidae within the phylum Annelida. 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, sea stars, crabs, lobsters, isopods, sea cucumbers, and fishes. Specific relationships among these organisms have not been wellstudied.
Ocean explorers have also discovered chemosynthetic communities that use other forms of chemical energy. Cold seeps are areas where hydrocarbon gases (such as methane) or oil seep out of sediments and commonly found along continental margins. Like hydrothermal vents, cold seeps are home to many species of organisms that have not been found anywhere else on Earth. Typical features of cold seep communities 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 hydrates may be of considerable benefit as a new energy resource, but may also pose substantial risks. See”More About Methane and Methane Hydrates,” below.
Chemosynthetic communities also are found in other deep ocean habitats. In some parts of the ocean, dissolved oxygen concentration is very low, usually because oxygen has been depleted by large amounts of decaying organic matter. Under these conditions, hydrogen sulfide builds up and can support communities of organisms similar to those found near hydrothermal vents and cold seeps. These communities are also found around dead whales (called whale falls) and large masses of dead kelp or trees. Although there are similarities between the chemosynthetic communities in these different habitats, hydrothermal vents, cold seeps, and large organic falls each have hundreds of endemic species (endemic means that these species aren’t found anywhere else). Even along the global ridge crest, which is almost almost continuous along its entire length, at least six different groups of endemic fauna have been recognized (Van Dover et al., 2002).
The reasons for the diversity are not clear. One hypothesis is that these systems are usually separated by large areas in which conditions are not suitable for chemosynthetic communities, and this isolation contributes to differences between communities. The vicinity of the CTJ is particularly interesting in regard to this question, because it is the only known location on Earth where all types of these ecosystems can co-exist. Scientists want to know whether hydrothermal vents, cold seeps, oxygen minimum zones, and falls of organic material still show a high degree of endemism when these habitats are close together, or whether there are more similarities or even “hybrid habitats” that have intermediate characteristics?
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.
The INSPIRE: Chile Margin 2010 expedition is directed toward three key questions:
To answer key questions, the INSPIRE: Chile Margin 2010 expedition is directed toward:
Hydrothermal vents and cold-seeps cause changes to the chemistry and physical characteristics of the surrounding seawater. As this altered seawater diffuses away from vent and coldseep sites, it produces plumes that are distinctly different from normal seawater. Scientists search for these plumes, since they provide clues about the location of hydrothermal vents and cold-seeps.
To locate hydrothermal vent and cold-seep ecosystems, expedition scientists will use deeptow sidescan sonar and data recorders that can detect chemical and physical water characteristics that signal the presence of hydrothermal vents and cold-seeps. Once plumes have been located, the depth and size of selected plumes will be investigated in more detail using instruments that measure conductivity, temperature, and depth (CTD) so that the source of the plume can be located within an area of about 1 km. High resolution maps of this area will be prepared using an autonomous underwater vehicle (AUV). Finally, the AUV will collect overlapping photographs of the vent or cold-seep site.
Major technologies involved with these activities include:
Sonar (which is short for SOund NAvigation and Ranging) systems are used to determine water depth, as well as to locate and identify underwater objects. In use, an acoustic signal or pulse of sound is transmitted into the water by a sort of underwater speaker known as a transducer. The transducer may be mounted on the hull of a ship, or may be towed in a container called a towfish. If the seafloor or other object is in the path of the sound pulse, the sound bounces off the object and returns an “echo” to the sonar transducer. The time elapsed between the emission of the sound pulse and the reception of the echo is used to calculate the distance of the object. Some sonar systems also measure the strength of the echo, and this information can be used to make inferences about some of the reflecting object’s characteristics. Hard objects, for example, produce stronger echoes that softer objects. This is a general description of “active sonar”. “Passive sonar” systems do not transmit sound pulses. Instead, they “listen” to sounds emitted from marine animals, ships, and other sources.
Side-scan sonar systems use transducers housed in a towfish, usually towed near the sea floor, to transmit sound pulses directed sideways, rather than straight down. Return echoes are continuously recorded and analyzed by a processing computer. These data are used to construct images of the sea floor made up of dark and light areas. These images can be used to locate seafloor features and possible obstructions to navigators, including shipwrecks (for more information visit: https://oceanexplorer.noaa.gov/technology/tools/sonar/sonar.html.)
The INSPIRE: Chile Margin 2010 expedition will use sidescan sonar systems mounted on a Towed Ocean Bottom Instrument (TOBI), which is a platform that can be towed at depths ranging from 200 m to 6000 m. TOBI systems provide a scale of seafloor mapping that is intermediate between surface sidescan systems and seafloor photography. To detect the chemical and physical clues that signal the presence of plumes, six Miniature utonomous Plume Recorders (MAPR) will also be attached along the tow wire that connects the TOBI with the ship at the surface. MAPRs are described below.
Side-scan sonar systems do not provide bathymetric data. When this information is needed, multibeam sonar systems are used. A multibeam system uses multiple transducers pointing at different angles on either side of a ship to create a swath of signals. The time interval between signal transmission and return echo arrival is used to estimate depth over the area of the swath. In some systems, the intensity of the return echo is also used to infer bottom characteristics that can be used for habitat mapping. The INSPIRE: Chile Margin 2010 expedition will use a Simrad SM2000 multibeam sonar system to obtain high quality maps of survey areas that have not been mapped previously. For more information about the SM2000, see http://www.whoi.edu . For more information about sonar systems, visit our sonar web page: https://oceanexplorer.noaa.gov/technology/tools/sonar/sonar.html.
Salinity is the concentration of salt and other inorganic compounds in seawater, and is one of the most basic measurements used by ocean scientists. Often, salinity is measured with an instrument called a CTD (conductivity, temperature, and depth) which measures how conductivity and temperature in the water column changes relative to depth. Conductivity is a measure of how well a solution conducts electricity and is directly related to salinity. CTD data can also be used to determine seawater density which is a primary driving force for major ocean currents.
Modern CTDs are fairly small and may be launched from a ship by itself or may be attached to an underwater vehicles. Often, CTDs are attached to a much larger metal frame called a rosette, which also holds several water sampling bottles that are used to collect water at different depths.Water samples collected during the INSPIRE: Chile Margin 2010 expedition will be analyzed to determine the presence of methane and other substances that indicate the presence of hydrothermal vents or cold-seeps. Because scientists often repeatedly raise and lower a CTD rosette while studying an area of interest, the motion of the CTD may resemble the movement of a yo-yo; and the resemblance has led to the nickname “tow-yo” for this type of CTD sampling. See https://oceanexplorer.noaa.gov/technology/tools/sonde_ctd/sondectd.html for more information.
In addition to CTDs, the INSPIRE: Chile Margin 2010 expedition will also use Miniature Autonomous Plume Recorders (MAPRs) which are attached to the wire used to tow the TOBI sidescan sonar.
MAPRs are inexpensive, simple, and rugged instruments that provide an easy-to-use way to collect chemical and physical data in conjunction with other ocean exploration activities. The MAPRs used to explore the CTJ will include sensors to measure temperature, pressure, optical backscatter, and redox potential. Optical backscatter is important because the oxidation of methane from cold-seeps causes precipitates of carbonate material to form. These precipitates cause the normally clear deep-ocean water to become cloudy so that light shining through the water is scattered and reflected back toward the light source.
Redox potential is a measure of the tendency of a substance to gain or lose electrons. Redox potential is measured in volts, and increases directly with the tendency of a substance to gain electrons and become reduced (see More About Chemosynthesis and Reducing Habitats, below). Because chemosynthetic communities are based on chemical substances that can donate electrons, these chemical substances have a tendency to lose electrons. So a drop in redox potential may signal the presence of chemosynthetic communities nearby.
For more information about MAPRs, see http://www.pmel.noaa.gov/vents/PlumeStudies/MAPRposter.html.
Autonomous Underwater Vehicles (AUVs) are underwater robots that operate without a pilot or cable to a ship or submersible. This independence allows AUVs to cover large areas of the ocean floor, as well as to monitor a specific underwater area over a long period of time. Typical AUVs can follow the contours of underwater mountain ranges, fly around sheer pinnacles, dive into narrow trenches, take photographs, and collect data and samples.
Until recently, once an AUV was launched it was completely isolated from its human operators until it returned from its mission. Because there was no effective means for communicating with a submerged AUV, everything depended upon instructions programmed into the AUV’s onboard computer. Today, it is possible for AUV operators to send instructions and receive data with acoustic communication systems that use sound waves with frequencies ranging roughly between 50 hz and 50 khz. These systems allow greater interaction between AUVs and their operators, but basic functions are still controlled by the computer and software onboard the AUV.
Basic systems found on most AUVs include: propulsion, usually propellers or thrusters (water jets); power sources such as batteries or fuel cells; environmental sensors such as video and devices for measuring water chemistry; computer to control the robot’s movement and data gathering functions; and a navigation system.
Navigation has been one of the biggest challenges for AUV engineers. Today, everyone from backpackers to ocean freighters use global positioning systems (GPS) to find their location on Earth’s surface. But GPS signals do not penetrate into the ocean. One way to overcome this problem is to estimate an AUV’s position from its compass course, speed through the water, and depth. This method of navigation is called ‘dead reckoning,’ and was used for centuries before GPS was available. Dead reckoning positions are only estimates however, and are subject to a variety of errors that can become serious over long distances and extended time periods.
If an AUV is operating in a confined area, its position can be determined using acoustic transmitters that are set around the perimeter of the operating area. These transmitters may be moored to the seafloor, or installed in buoys. Some buoy systems also include GPS receivers, so the buoys’ positions are constantly updated. Signals from at least three appropriately positioned transmitters can be used to accurately calculate the AUV’s position. Although this approach can be very accurate, AUV operators must install the transmitters, and the AUV must remain within a rather small area.
A more sophisticated approach uses Inertial Navigation Systems (INS) that measure the AUV’s acceleration in all directions. These systems provide highly accurate position estimates, but require periodic position data from another source for greatest accuracy. On surface vessels and aircraft equipped with INS, additional position data are often obtained from GPS. On underwater vessels, the accuracy of INS position estimates is greatly improved by using a Doppler Velocity Logger (DVL) to measure velocity of the vessel’s speed. On some AUVs, several of these systems are combined to improve the overall accuracy of onboard navigation. For more information about INS and DVL systems, visit https://www.oceanexplorer.noaa.gov/explorations/08auvfest.
The INSPIRE: Chile Margin 2010 expedition will use an AUV named ABE, which stands for Autonomous Benthic Explorer. ABE is capable of collecting bathymetric and magnetic data, and is navigated by a combination of acoustic transponders, DVL, and a magnetic compass. Onboard equipment includes multibeam mapping sonar and probes for measuring conductivity, temperature, optical backscatter and redox potential. Since it was launched in 1994, ABE has completed more than 200 deep-ocean dives.
In addition to the techniques and instruments described above, the INSPIRE: Chile Margin 2010 expedition will also use seismometers to monitor earthquake activity in the vicinity of the CTJ, and will collect samples in ABE dive areas for studies of rock formation at spreading ridges and subduction zones.
Photosynthesis and chemosynthesis are similar in that they are both processes that provide energy needed to form molecules that can serve as energy sources (food) for living organisms. This energy is captured and stored in other molecules, and is moved from one molecule to another molecule when electrons are transferred between the molecules. These transfers take place in a series of reactions called an electron transport chain.
Photosynthesis begins when a photon of radiant energy from the sun strikes a molecule of chlorophyll or other photosynthetic pigment. This energy causes the photosynthetic pigment molecule to release an electron that is captured by another organic molecule. This molecule releases an electron to a third organic molecule, and the process continues through several other molecules. Each time an electron is transferred, the molecule that gains the electron also gains energy; and the molecule that loses the electron loses energy. The last molecule in the chain keeps the electron, and has a higher energy content than before it received the electron. Some energy is lost each time an electron moves from one molecule to another, so the last molecule in the chain contains less energy than the energy of the photon that started the process. The photosynthetic pigment regains its lost electron from a water molecule through a series of reactions called photolysis that release oxygen gas as a by-product. The energy produced by the series of electron transfers is used by photosynthetic organisms to convert carbon dioxide into organic molecules (such as sugars) that can serve as energy sources (food) needed by living organisms.
In chemosynthesis, the electron transport chain begins with the loss of an electron from a substance such as hydrogen sulfide or methane. As in photosynthesis, the electron is passed along an electron transport chain, and the energy produced by a series of electron transfers is used by chemosynthetic organisms to convert carbon dioxide into molecules that can serve as energy sources (food) for living organisms. Known chemosynthetic organisms from deep-sea environments are bacteria or Archaea, and these microbes often are the basis of complex food webs.
When an atom or molecule loses an electron it is said to be oxidized, and when an atom or molecule gains an electron it is said to be reduced. A reducing substance is a substance that reduces; in other words, it donates electrons. Similarly, an oxidizing substance is a substance that oxidizes; that is, it receives electrons. A reaction in which one or more electrons are transferred between two molecules is called a redox reaction. Note that the terms oxidation, reduction, and redox may also be used in slightly different ways for some types of chemistry, but these distinctions are not important for this discussion.
Here is an example of a simple redox reaction:z
H2 + F2 > 2 HF
A molecule of hydrogen gas reacts with a molecule of fluorine gas to form hydrogen fluoride.
The reaction may also be written as an oxidation reaction and a reduction reaction:
H2 > 2 H+ + 2 e-
(the oxidation reaction)
and
F2 + 2 e-> 2 F-
(the reduction reaction)
where e- stands for an electron
Chemosynthesis depends upon the availability of reducing substances such as hydrogen sulfide or methane that can donate electrons. Habitats in which these substances occur are called reducing habitats.
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. 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.
Scientists are interested in methane hydrates for several reasons. A major interest is the possibility of methane hydrates as an energy source. 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. In addition to their potential importance as an energy source, scientists have found that methane hydrates are associated with unusual and possibly unique biological communities that may be sources of beneficial pharmaceutical materials.
While such potential benefits are exciting, methane hydrates may also cause big problems. Although methane hydrates remain stable in deep-sea sediments for long periods of time, as the sediments become deeper and deeper they are heated by the Earth’s core. Eventually, temperature within the sediments rises to a point at which the clathrates are no longer stable and free methane gas is released (at a water depth of 2 km, this point is reached at a sediment depth of about 500 m). The pressurized gas remains trapped beneath hundreds of meters of sediments that are cemented together by still-frozen methane hydrates. If the overlying sediments are disrupted by an earthquake or underwater landslide, the pressurized methane can escape suddenly, producing a violent underwater explosion that may result in disastrous tsunamis (“tidal waves”).
The release of large quantities of methane gas can have other consequences as well. Methane is one of a group of the so-called “greenhouse gases.” In the atmosphere, these gases allow solar radiation to pass through to the surface of the Earth, but absorb heat radiation that is reflected back from the Earth’s surface, thus warming the atmosphere. Many scientists have suggested that increased carbon dioxide in the atmosphere produced by burning fossil fuels is causing a “greenhouse effect” that is gradually warming the atmosphere and the Earth’s surface. A sudden release of methane from deep-sea sediments could have a similar effect, since methane has more than 30 times the heat-trapping ability of carbon dioxide. In 1995, Australian paleoceanographer Gerald Dickens suggested that a sudden release of methane from submarine sediments during the Paleocene epoch (at the end of the Tertiary Period, about 55 million years ago) caused a greenhouse effect that raised the temperatures in the deep ocean by about 6° C. The result was the extinction of many deep-sea organisms known as the Paleocene extinction event. More recently, other scientists have suggested that similar events could have contributed to mass extinctions during the Jurassic period (183 million years ago), as well as to the sudden appearance of many new animal phyla during the Cambrian period (the “Cambrian explosion, about 520 million years ago).
