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Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches.

Marine geology or geological oceanography is the study of the history and structure of the ocean floor. It involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal zone. Marine geology has strong ties to geophysics and to physical oceanography. [1]

Marine geological studies were of extreme importance in providing the critical evidence for sea floor spreading and plate tectonics in the years following World War II. The deep ocean floor is the last essentially unexplored frontier and detailed mapping in support of both military (submarine) objectives and economic ( petroleum and metal mining) objectives drives the research.–

Overview

A trench forms at the boundary where two tectonic plates meet

The Ring of Fire around the Pacific Ocean with its attendant intense volcanism and seismic activity poses a major threat for disastrous earthquakes, tsunamis and volcanic eruptions. [2] Any early warning systems for these disastrous events will require a more detailed understanding of marine geology of coastal and island arc environments.

The study of littoral and deep sea sedimentation and the precipitation and dissolution rates of calcium carbonate in various marine environments has important implications for global climate change. [3]

The discovery and continued study of mid-ocean rift zone volcanism and hydrothermal vents, first in the Red Sea and later along the East Pacific Rise and the Mid-Atlantic Ridge systems were and continue to be important areas of marine geological research. The extremophile organisms discovered living within and adjacent to those hydrothermal systems have had a pronounced impact on our understanding of life on Earth and potentially the origin of life within such an environment. [4]

Oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They also are the deepest parts of the ocean floor.

History

The study of marine geology dates back to the late 1800s during the 4-year HMS Challenger expedition. [5] [6] The HMS Challenger hosted nearly 250 people, including sailors, engineers, carpenters, marines, officers and a 6-person team of scientists, led by Charles Wyville Thomson. [5] [7] The scientists' goal was to prove that there was life in the deepest parts of the ocean. [7] Using a sounding rope, dropped over the edge of the ship, the team was able to capture ample amounts of data. Part of their discovery was that the deepest part of the ocean was not in the middle. [6] These were some of the first records of the mid-ocean ridge system.

Preceding World War II, marine geology was becoming more prevalent to the science community. During the early 20th-century, organizations such as the Scripps Institution of Oceanography and the Woods Hole Oceanographic Institution (WHOI) were created to support efforts in the field. [8] [9] With Scripps being located on the west coast of North America and WHOI on the east coast, the study of marine geology became much more accessible. [8] [9]

In the 1950s, marine geology had one of the most significant discoveries, the mid-ocean ridge system. After ships were equipped with sonar sensors, they travelled back and forth across the Atlantic Ocean collecting observations of the sea floor. [10] In 1953, a cartography Marie Tharp was able to generate the first three dimensional relief map of the ocean floor which defined the mountain range situated underwater in the middle of the Atlantic. The survey data was large step towards many more discoveries about the geology of the sea. [10]

A theoretical model of the formation of magnetic striping. New oceanic crust forming continuously at the crest of the mid-ocean ridge cools and becomes increasingly older as it moves away from the ridge crest with seafloor spreading.

Later, in 1960, an American geophysicist by the name of Harry H. Hess hypothesized that the seafloor was spreading from the mid ocean ridge system. [10] With support from the maps of the sea floor, and the recently developed theory of plate tectonics and continental drift, Hess was able to prove that the Earth's mantle continuous released molten rock from the mid-ocean ridge and solidified, causing the boundary between the two tectonic plates to diverge. [11] A geomagnetic survey was conducted that supported this theory. The survey was composed of scientists using magnetometers to measure the magnetism of the basalt rock protruding from the mid-ocean ridge. [10] [12] They discovered that on either side of the ridge, symmetrical "strips" were found as the polarity of the planet would change over time. [10] [12] This proved that seafloor spreading existed. In later years, newer technology was able to date the rocks and identified that rocks closest to the ridge were younger than the rocks near the coasts of the Western and Eastern Hemispheres land.

In the modern days, marine geology focuses on geological hazards, environmental conditions, habitats, natural resources, and energy and mining projects. [13]

Methods

There are multiple methods for collecting data from the sea floor without physically dispatching humans or machines to the bottom of the ocean.

Side-scan sonar

A common method of collecting imagery of the sea floor is Side-scan sonar. [14] [15] Developed in the late 1960s, the purpose of the survey method is to use active sonar systems on the sea floor to detect and develop images of objects. [14] The physical sensors of the sonar device are know as a transducer array and they are mounted onto the hull of a vessel which sends acoustic pulses that reflect off the seafloor and received by the sensors. The imaging can help determine the seafloors composition as harder objects generate a stronger reflectance and appear dark on the returned image. Softer materials such as sand and mud cannot reflect the arrays pulses as well so they appear lighter on the image. This information can be analyzed by specialist to determine outcrops of rock beneath the surface of the water. [15]

This method is less expensive than releasing a vehicle to take photographs of the sea floor, and requires much less time. [15] The side-scan sonar is useful for scientist as it is a quick and efficient way of collecting imagery of the sea floor, but it cannot measure other factors, such as depth. [14] [15] Therefore, other depth measuring sonar devices are typically accompanied with the side-scan sonar to generate a more detailed survey. [14]

Multibeam Bathymetry

Similarly to side-scan sonar, multibeam bathymetry uses a transducer array to send and receive soundwaves in order to detect objects located on the sea floor. [16] Unlike, side-scan sonar, scientists are able to determine multiple types of measurements from the recordings and make hypothesis' on the data collected. By understanding the speed at which sound will travel in the water, scientists can calculate the two way travel time from the ship's sensor to the seafloor and back to the ship. These calculations will determine to depth of the sea floor in that area. [16]

EM300 bathymetry of the three submarine volcanoes in the vicinity of Farallon de Pajaros Island. The data were collected using the EM300 multibeam system mounted on the hull of the R/V Thompson. The grid-cell size is 35 meters. The image is 2 times vertically exaggerated.

Furthermore, backscatter is another measurement used to determine the intensity of the sound that is returned to the sensor. [16] This information can provide insight on the geological makeup and objects of the sea floor as well as objects located within the water column. Objects in the water column can include structures from shipwrecks, dense biology, and bubble plumes. The importance of objects in the water column to marine geology is identifying specific features as bubble plumes can indicate the presence of hydrothermal vents and cold seeps. [16]

There are limitations to this technique. The distance between the sea floor and the sensor is related to the resolution of the map being created. [16] The closer the sensor is the sea floor, the higher the resolution will be and the farther away the sensor is to the sea floor, the lower the resolution will be. Therefore, it is common for remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) to be equipped with the multibeam sensor or for the sensor to be towed by the ship its self. This ensures that the resolution of the collected data will be great enough for proper analysis. [16]

Sub-bottom Profiler

A sub-bottom profiler is another sonar system used in geophysical surveys of the sea floor to not only map depth, but to map beneath the sea floor. [17] Mounted to the hull of a ship, the system releases low-frequency pulses which penetrate the surface of the sea floor and are reflected by sediments in the sub-surface. Some sensors can reach over 1000m below the surface of the sea floor giving hydrographers a detailed view of the marine geological environment. [18]

Many sub-bottom profilers can emit multiple frequencies of sound to record data on a multitude of sediments and objects on and below the sea floor. The returned data is collected by computers and with aid from hydrographers, can create cross-sections of the terrain below the sea floor. [17] The resolution of the data also allows scientists to identify geological features such as volcanic ridges, underwater landslides, ancient river beds, and other features. [17]

The benefit of the sub-bottom profiler is its capability to record information on the surface and below the seafloor. When accompanied with geophysical data from multibeam sonar and physical data from rock and core samples, the sub-bottom profiles delivers insights on the location and morphology of submarine landslide, identifies how oceanic gasses travel through the subsurface, discover artifacts from cultural heritages, understand sediment deposition, and more. [17]

Mariana Trench

The Mariana Trench (or Marianas Trench) is the deepest known submarine trench, and the deepest location in the Earth's crust itself. It is a subduction zone where the Pacific Plate is being subducted under the Mariana Plate. The bottom of the trench is further below sea level than Mount Everest is above sea level.

See also

References

  1. ^ Erickson, Jon (1996). Marine geology : undersea landforms and life forms. New York: Facts on File. ISBN  0-8160-3354-4. OCLC  32626212.
  2. ^ "What is the Ring of Fire? : Ocean Exploration Facts: NOAA Office of Ocean Exploration and Research". oceanexplorer.noaa.gov. Retrieved 2023-02-10.
  3. ^ Atwood, Trisha B.; Witt, Andrew; Mayorga, Juan; Hammill, Edd; Sala, Enric (2020). "Global Patterns in Marine Sediment Carbon Stocks". Frontiers in Marine Science. 7. doi: 10.3389/fmars.2020.00165. ISSN  2296-7745.
  4. ^ Merino, Nancy; Aronson, Heidi S.; Bojanova, Diana P.; Feyhl-Buska, Jayme; Wong, Michael L.; Zhang, Shu; Giovannelli, Donato (2019). "Living at the Extremes: Extremophiles and the Limits of Life in a Planetary Context". Frontiers in Microbiology. 10: 780. doi: 10.3389/fmicb.2019.00780. ISSN  1664-302X. PMC  6476344. PMID  31037068.
  5. ^ a b Heckel, Jodi; Bureau, Illinois News (2023-02-10). "Exploring the deep with the HMS Challenger | College of Liberal Arts & Sciences at Illinois". las.illinois.edu. Retrieved 2024-02-19.
  6. ^ a b Board, National Research Council (US) Ocean Studies (2000), "Achievements in Marine Geology and Geophysics", 50 Years of Ocean Discovery: National Science Foundation 1950—2000, National Academies Press (US), retrieved 2024-02-19
  7. ^ a b "HMS Challenger Expedition | History of a Scientific Trailblazer". www.rmg.co.uk. Retrieved 2024-02-19.
  8. ^ a b "Who We Are - Woods Hole Oceanographic Institution". www.whoi.edu/. Retrieved 2024-02-19.
  9. ^ a b "About Scripps Oceanography". scripps.ucsd.edu. Retrieved 2024-02-19.
  10. ^ a b c d e "Seafloor spreading | Evidence & Process | Britannica". www.britannica.com. Retrieved 2024-02-19.
  11. ^ "Plate Tectonics". education.nationalgeographic.org. Retrieved 2024-02-19.
  12. ^ a b "Seafloor Spreading". education.nationalgeographic.org. Retrieved 2024-02-19.
  13. ^ "marine geology research: Topics by Science.gov". www.science.gov. Retrieved 2024-02-19.
  14. ^ a b c d Johnson, Paul; Helferty. "The geological interpretation of side-scan sonar" (PDF). Reviews of Geophysics. 28.4: 357–380.
  15. ^ a b c d "Exploration Tools: Side-Scan Sonar: NOAA Office of Ocean Exploration and Research". oceanexplorer.noaa.gov. Retrieved 2024-02-19.
  16. ^ a b c d e f "Exploration Tools: Multibeam Sonar: NOAA Office of Ocean Exploration and Research". oceanexplorer.noaa.gov. Retrieved 2024-02-19.
  17. ^ a b c d "Exploration Tools: Sub-Bottom Profiler: NOAA Office of Ocean Exploration and Research". oceanexplorer.noaa.gov. Retrieved 2024-02-19.
  18. ^ Calvert, Mike (2022-05-27). "Guide to Sub-Bottom Profiling". aae technologies. Retrieved 2024-02-19.

Sources

  1. Erickson, Jon, 1996, Marine Geology: Undersea Landforms and Life Forms, Facts on File ISBN  0-8160-3354-4
  2. "What is the Ring of Fire? : Ocean Exploration Facts: NOAA Office of Ocean Exploration and Research". oceanexplorer.noaa.gov. Retrieved 2023-02-10.
  3. Atwood, Trisha B.; Witt, Andrew; Mayorga, Juan; Hammill, Edd; Sala, Enric (2020). "Global Patterns in Marine Sediment Carbon Stocks". Frontiers in Marine Science. 7. doi:10.3389/fmars.2020.00165/full. ISSN 2296-7745.
  4. Merino, Nancy; Aronson, Heidi S.; Bojanova, Diana P.; Feyhl-Buska, Jayme; Wong, Michael L.; Zhang, Shu; Giovannelli, Donato (2019). "Living at the Extremes: Extremophiles and the Limits of Life in a Planetary Context". Frontiers in Microbiology. 10. doi:10.3389/fmicb.2019.00780/full. ISSN 1664-302X.

External links