🌊Oceanography Unit 3 – Marine Provinces and Sediments

Key Concepts and Definitions

• Marine provinces distinct regions of the ocean floor characterized by specific geomorphological features and sediment types
• Ocean basins large depressions in the Earth's crust that hold the world's oceans
• Continental margins transition zones between the continents and the deep ocean basins
  • Includes the continental shelf, continental slope, and continental rise
• Abyssal plains vast, flat areas of the deep ocean floor covered by fine-grained sediments
• Seafloor spreading process by which new oceanic crust is formed at mid-ocean ridges and spreads outward
• Sediments solid particles that settle at the bottom of a body of water
  • Can be classified based on their origin (terrigenous, biogenous, hydrogenous, or cosmogenous)
• Sediment distribution patterns influenced by factors such as ocean currents, water depth, and proximity to land

Ocean Basin Structure

• Ocean basins formed by plate tectonic processes over millions of years
• Major components include the continental margins, abyssal plains, mid-ocean ridges, and oceanic trenches
• Continental margins consist of the continental shelf (shallow, flat area adjacent to continents), continental slope (steep drop-off), and continental rise (gentle slope at the base of the continental slope)
• Abyssal plains cover vast areas of the deep ocean floor and are characterized by flat, featureless topography
• Mid-ocean ridges extensive underwater mountain ranges formed by seafloor spreading
  • Divergent plate boundaries where new oceanic crust is created
• Oceanic trenches deep, narrow depressions in the seafloor associated with subduction zones (convergent plate boundaries)
• Seamounts and guyots isolated underwater mountains that rise from the seafloor
  • Guyots are flat-topped seamounts that have been eroded by wave action

Types of Marine Provinces

• Continental shelf shallow, flat area adjacent to continents with water depths typically less than 200 meters
  • Characterized by thick layers of sediment and high biological productivity
• Continental slope steep drop-off between the continental shelf and the deep ocean basin
  • Inclined at angles between 3° and 6° and extends to depths of about 2,000 meters
• Continental rise gentle slope at the base of the continental slope formed by the accumulation of sediments
• Abyssal plains vast, flat areas of the deep ocean floor with water depths ranging from 3,000 to 6,000 meters
  • Covered by fine-grained sediments (clay and silt) and have low biological productivity
• Mid-ocean ridges extensive underwater mountain ranges formed by seafloor spreading
  • Characterized by high heat flow, volcanic activity, and hydrothermal vents
• Oceanic trenches deep, narrow depressions in the seafloor associated with subduction zones
  • Can reach depths of over 10,000 meters (Mariana Trench)

Continental Margins

• Continental margins transition zones between the continents and the deep ocean basins
• Passive margins form along the edges of continents that are not associated with plate boundaries
  • Characterized by wide continental shelves, thick sediment layers, and lack of volcanic activity (eastern coast of North America)
• Active margins form along the edges of continents that are associated with plate boundaries
  • Characterized by narrow continental shelves, thin sediment layers, and frequent volcanic and seismic activity (western coast of South America)
• Continental shelf shallow, flat area adjacent to continents with water depths typically less than 200 meters
  • Width varies from a few kilometers to over 1,500 kilometers (Siberian Shelf in the Arctic Ocean)
  • Thick layers of sediment accumulate on the continental shelf due to input from rivers and coastal erosion
• Continental slope steep drop-off between the continental shelf and the deep ocean basin
  • Inclined at angles between 3° and 6° and extends to depths of about 2,000 meters
  • Submarine canyons and landslides are common features on the continental slope
• Continental rise gentle slope at the base of the continental slope formed by the accumulation of sediments
  • Sediments are transported down the continental slope by turbidity currents and other mass-wasting processes

Deep Ocean Basins

• Deep ocean basins vast areas of the ocean floor with water depths greater than 3,000 meters
• Abyssal plains cover approximately 40% of the deep ocean floor
  • Flat, featureless topography with gradients less than 1:1000
  • Covered by fine-grained sediments (clay and silt) that accumulate at slow rates (1-10 mm per 1,000 years)
• Mid-ocean ridges extensive underwater mountain ranges formed by seafloor spreading
  • Divergent plate boundaries where new oceanic crust is created
  • Characterized by high heat flow, volcanic activity, and hydrothermal vents
• Oceanic trenches deep, narrow depressions in the seafloor associated with subduction zones
  • Form at convergent plate boundaries where oceanic crust is subducted beneath another plate
  • Can reach depths of over 10,000 meters (Mariana Trench)
• Seamounts and guyots isolated underwater mountains that rise from the seafloor
  • Formed by volcanic activity and can reach heights of several thousand meters above the surrounding seafloor
  • Guyots are flat-topped seamounts that have been eroded by wave action when they were at or near sea level

Seafloor Sediments and Their Origins

• Seafloor sediments solid particles that settle at the bottom of the ocean
• Terrigenous sediments derived from land and transported to the ocean by rivers, wind, or ice
  • Composed of rock and mineral fragments (quartz, feldspar, clay minerals)
  • Dominant type of sediment on continental margins and near the mouths of large rivers (Amazon River, Mississippi River)
• Biogenous sediments formed from the remains of marine organisms
  • Composed of calcium carbonate (shells, tests) or silica (diatom frustules, radiolarian skeletons)
  • Dominant type of sediment in the deep ocean basins away from continental margins
• Hydrogenous sediments formed by chemical precipitation from seawater
  • Includes manganese nodules, phosphorites, and evaporites
  • Manganese nodules slow-growing concretions of iron and manganese oxides that form on the seafloor
• Cosmogenous sediments derived from extraterrestrial sources (meteorites, cosmic dust)
  • Make up a minor component of seafloor sediments
• Sediment grain size and composition vary depending on the source and transport mechanisms
  • Coarser sediments (sand and gravel) are typically found on the continental shelf and near the mouths of rivers
  • Finer sediments (clay and silt) are found in the deep ocean basins and on the continental rise

Sediment Distribution Patterns

• Sediment distribution patterns influenced by factors such as ocean currents, water depth, and proximity to land
• Terrigenous sediments dominant on continental margins and near the mouths of large rivers
  • Accumulate in thick layers on the continental shelf and slope
  • Grain size decreases with increasing distance from the shoreline
• Biogenous sediments dominant in the deep ocean basins away from continental margins
  • Accumulate at slower rates compared to terrigenous sediments
  • Distribution influenced by factors such as water depth, ocean circulation patterns, and biological productivity
• Abyssal plains characterized by fine-grained sediments (clay and silt) that accumulate at slow rates
  • Sediment thickness increases with increasing distance from the mid-ocean ridges
• Mid-ocean ridges have thin sediment cover due to the young age of the oceanic crust and the high heat flow
  • Sediments are primarily composed of biogenous material (calcareous and siliceous oozes)
• Oceanic trenches act as sediment traps, accumulating thick layers of terrigenous and biogenous sediments
  • Sediments are transported into the trenches by turbidity currents and other mass-wasting processes
• Seamounts and guyots often have thin sediment cover due to their isolated location and the action of bottom currents
  • Sediments are primarily composed of biogenous material (calcareous and siliceous oozes)

Environmental and Economic Significance

• Continental shelves are important fishing grounds and sources of mineral resources (oil, gas, sand, and gravel)
  • Shallow water depths and high biological productivity support diverse marine ecosystems
  • Coastal development and pollution can negatively impact the health of continental shelf environments
• Deep ocean basins are important reservoirs of biodiversity and play a crucial role in global climate regulation
  • Abyssal plains cover vast areas of the seafloor and are home to unique benthic communities
  • Deep ocean circulation patterns influence the distribution of heat and nutrients throughout the world's oceans
• Mid-ocean ridges are important sites of hydrothermal activity and mineral formation
  • Hydrothermal vents support unique chemosynthetic communities and are potential sources of valuable mineral resources (copper, zinc, gold)
  • Seafloor massive sulfide deposits are forming at active hydrothermal vent sites
• Manganese nodules and cobalt-rich crusts are potential sources of valuable metals (manganese, cobalt, nickel, copper)
  • Found on the seafloor of the deep ocean basins and on the flanks of seamounts and guyots
  • Extraction of these resources is currently limited by technological and economic challenges
• Methane hydrates are a potential source of energy found in continental margin sediments
  • Estimated to contain more carbon than all other fossil fuel reserves combined
  • Extraction of methane hydrates poses significant environmental and technological challenges
• Marine sediments provide valuable records of Earth's climate and oceanographic history
  • Changes in sediment composition and accumulation rates can reflect variations in ocean circulation patterns, biological productivity, and continental weathering rates over geologic time scales