MAR 110: Introductory Oceanography

1. MAR 110: Introductory Oceanography Marine sediments

2. Pollutants and the sea, part 1 • Waste water enters rivers and streams through overland flow, groundwater flow, and drainage pipes. • Coastal installations may discharge wastes directly into the ocean. • Eventually, all water-borne wastes enter the ocean, either dissolved or suspended in the water. • Rain and snow wash particles from the atmosphere into the ocean. Properties of ocean water

3. Pollutants and the sea, part 2 • Some wastes rapidly decompose. • Some resist decomposition. • Many minerals are in elemental form, thus cannot be broken down. • These include metals that we regard as pollutants. • Persistent pollutants can cause serious problems to aquatic life as they are subject to bioconcentration. • Oftentimes the best way to remove such pollutants is by dredging and removal or by capping of contaminated sediments. Properties of ocean water

4. Pollutants and the sea, part 3 • 1956: Minamata, Japan • A 5-year-old girl lapsed into a convulsive delirium; An examination showed permanent brain damage. • The girl was the tip of the iceberg of a major health crisis. • People in the coastal village had eaten fish and shellfish from the bay as a staple part of their diet. • For many years, the Chisso Chemical Plant had discharged industrial wastes containing mercury into the bay. • Elemental mercury is insoluble in water, so they thought it would sink to the bottom and become buried in sediments, thus pose little health hazard. Properties of ocean water

5. Pollutants and the sea, part 4 • Minamata, Japan (continued): • In 1959, scientists demonstrated that bacteria in the bottom sediments converted elemental mercury into methylmercury, a soluble and highly mobile form of mercury that could enter the food chain. • Methylmercury attacks the central nervous system as elemental mercury does. • More than 3,500 people were severely affected; of those, about 50 died from what is now called Minamata Disease. • After decades of cleanup, the bay is safe for human use. • The bay, its sediments, and resident organisms are still monitored. Properties of ocean water

6. Sediments • Sediments are particles that settle on the ocean floor. • Sediments blanket most of the ocean floor. • Most of the particles that make up those sediments form at the interface between the environmental spheres: atmosphere, biosphere, geosphere, and hydrosphere. • They are transported by rivers, wind, ice, and gravity to the oceans. • Marine sediments consist of excreta and secretions of organisms; shells, bones, and teeth; rock fragments; soil particles; and material from outer space. Properties of ocean water

7. Sediment characteristics, part 1 • Sediments differ in source, composition, size, and accumulation rate. • Size refers to the diameter of particles. • Sediments include gravels, sands, and muds. • Mud: Muds include clays (particles less than 0.0039 mm) and silts (between 0.0039 mm and 0.0625 mm). • Sand: Sands range from very fine (0.0625 mm) to very coarse (2 mm). • Gravel: Gravels include granules (between 2 mm and 4 mm), pebbles (between 4 mm and 64 mm), cobbles (between 64 mm and 256 mm); and boulders (greater than 256 mm). Properties of ocean water

8. Sediment characteristics, part 2 • Size (continued): • Sediment accumulations (deposits) vary in the range of grain size; this is known as sorting. • Well-sorted sediments have a narrow range of grain sizes, where as poorly sorted sediments have a diverse mixture of grain sizes. • Fine-grained sediments are transported farther; Coarse-grained sediments settle out of the transport medium sooner. • Example: Sediments along continental margins are poorly sorted, with larger grain sizes; Sediments on the deep ocean floor are well sorted, with smaller grain sizes. Properties of ocean water

9. Properties of ocean water

10. Sediment characteristics, part 3 • Sediment deposits are thickest along continental margins and near islands; they become thinner with increasing distance from land. • Source media, such as rivers, lose energy as they reach the ocean; the decrease in velocity diminishes the ability to transport particles; the larger particle settle first. Properties of ocean water

11. Sediment characteristics, part 4 • Sediments can accumulate at the rate of as much as 8,000 m in 1,000 years. • In the deep ocean, sediments accumulation rates range from 0.5 to 1 cm in 1,000 years. • Sediments are generally thickest where the ocean floor is oldest and thinnest where it it youngest. • Particle size determines the rate at which it sinks. • Sands may sink to the ocean floor in a matter of days, whereas clays may take more than a century. • Particles may also dissolve in ocean water. Properties of ocean water

12. Terminal velocity • Terminal velocity is the constant speed attained by a particle falling through a motionless fluid. • The terminal velocity is a function of gravity and the fluid resistance. • Falling particles accelerate because of gravity until the fluid resistance equals gravity; the particle falls at a constant velocity (the terminal velocity) thereafter. • Terminal velocity increases with increasing particle size, all else being equal. • Terminal velocity decreases with increasing density of the fluid, all else being equal. Properties of ocean water

13. Properties of ocean water

14. Sediment classification, part 1 • Marine sediments are classified on the basis of their source: • Lithogenous (from rock) • Biogenous (from organisms) • Hydrogenous (precipitated from seawater) • Cosmogenous (from outer space) • Lithogenous sediments account for 75 percent of all marine sediments. • Most come from weathering and erosion of pre-existing rock. Properties of ocean water

15. Sediment classification, part 2 • Lithogenous sediments (continued): • Most come from weathering and erosion of pre-existing rock. • Weathering: The physical and chemical decomposition of rocks exposed to the atmosphere. • Weathering removes carbon dioxide from the atmosphere. • Erosion: The transport of weathering products, usually by water, wind, glaciers, and gravity. • Some lithogenous material comes from explosive volcanic activity. • Tephra refers to igneous particles that fall through the air and accumulate in the ocean. Properties of ocean water

16. Sediment classification, part 3 • Lithogenous sediments (continued): • The chemical composition of lithogenous sediments depends on the chemical composition of source rock. • Oxygen is the most abundant element in the crust, followed by silica, aluminum, iron, and calcium. • The silicone-oxygen tetrahedrom (SiO4) is the primary building block of silicate minerals. • The ratio of silicon to oxygen varies; For example, quartz is made primarily of SiO2) . Properties of ocean water

17. Properties of ocean water

18. Properties of ocean water

19. Sediment classification, part 3 • Lithogenous sediments (continued): • Silicate minerals: • Ferromagnesium silicates contain iron and magnesium, are dark in color and are relatively dense • These are the primary components of oceanic crust (what geologists used to call sima). • Rocks rich in ferromagnesium silicates usually weather more quickly. • Nonferromagnesium silicates contain aluminum, calcium, sodium, or potassium; are relative light in appearance and are less dense thatn ferromagnesium silicates. • These are the primary components of continental crust (what geologists used to call sial). Properties of ocean water

20. Sediment classification, part 4 • Lithogenous sediments (continued): • Tropical and subtropical rivers account for the bulk of river-borne marine sediments. • This in part results from the higher weathering and erosion rates caused by the higher temperatures and precipitation amounts characteristics of tropical and subtropical regions. • Rivers transport the products of weathering in suspension, solution, or as part of what is called the bed load (stuff on the bottom). • Once the river hits the ocean, the heavier particles settle out first, while finer sediments can be carried far beyond the river’s mouth. Properties of ocean water

21. Properties of ocean water

22. Sediment classification, part 5 • Lithogenous sediments (continued): • All parts of the ocean receive windborne dust. • This is the primary way that lithogenous material from regions far from the ocean reach the sea. • Windborne (aeolian) material makes up much of the red and brown clays of the mid-ocean basins, especially at about 30 degrees North latitude and 30 degrees South latitude – these are where the Earth’s two great desert belts are located. • Dust from one region, such as the Sahara, can be blown across entire ocean basins. • Saharan dust may provide nutrients that trigger red tides in the Gulf of Mexico; it may also harbor a fungus that attacks coral reefs. Properties of ocean water

23. Properties of ocean water

24. Sediment classification, part 6 • Lithogenous sediments (continued): • Glaciers erode bedrock and transport rock fragments, even very large ones, to the ocean. • Glaciers, when the reach the sea, float on the surface of the water, and can break off (calve) to form icebergs. • Icebergs, driven by wind and water currents, can transport sediments from polar regions a long distance. • As icebergs melt, the sediments sink to the bottom; such poorly sorted materials are called glaciomarine sediments. • Glaciomarine sediments cover 20 percent of the ocean floor. • Sudden releases of icebergs during ice age events are called Heinrich Events. Properties of ocean water

25. Sediment classification, part 7 • Biogenous sediments include excretions, secretions, and remains of organisms – including shells, corals, and skeletal parts. • Most biogenous material is made of calcium carbonate (CaCO3) or silica (SiO2), materials that many marine organisms to form their shells. • Biogenous sediments are the dominant component of 30 to 70 percent of sediments in the mid-depths. • Skeletal remains account for 25 to 50 percent of all particles suspended in seawater. Properties of ocean water

26. Properties of ocean water

27. Sediment classification, part 8 • Biogenous sediments (continued): • Calcareous sediments are the most abundant of all biogenous sediments. • They originate in the calcium carbonate shells of organisms such as foraminifera, pteropods, and coccolithophores. • The carbonate (and other) materials often dissolve in seawater as the shells sink; but if they reach the ocean floor and are covered by other sediments, they will be preserved. • In waters less than about 4,500 m deep, calcareous muds cover half the sea floor. • They accumulate at rates of between 1 and 4 cm per 1,000 years. Properties of ocean water

28. Properties of ocean water

29. Properties of ocean water

30. Sediment classification, part 9 • Biogenous sediments (continued): • Fecal pellets make up most of the larger biogenous particles. • Fecal pellets are often large, with high terminal velocities, thus can sink to the bottom in a matter of days. • Fecal pellets transport organic material to the ocean floors, thus serve as a nutrient source for bottom-dwelling organisms. • Marine snow is a combination of fecal pellets and remains of organisms that fall to the bottom. • Siliceous materials are second in abundance among biogenous sediments. • They are made of the tests (shells) of diatoms, and radiolaria. Properties of ocean water

31. Properties of ocean water

32. Properties of ocean water

33. Sediment classification, part 10 • Biogenous sediments (continued): • Phosphate materials are rare in marine sediment deposits. • Hydrogenous sediments originate from materials that are chemically precipitated (come out of solution) from seawater. • They may form coatings on the sea floor. • Some hydrogenous sediments are created in chemical reactions in hot seawater from deep-sea vents. • Examples include some carbonates, halite (NaCl), gypsum (CaSO4·2H2O), and manganese nodules. Properties of ocean water

34. Sediment classification, part 11 • Hydrogenous sediments (continued): • In shallow waters, an increase in temperature may cause dissolved carbonates to precipitate out. • Where evaporation rates are high, salts precipitate out in the following order: carbonate salts, sulfate salts, and halite. • Manganese nodules are irregularly shaped, black or brown nodules on the sea floor. • They are about 18 percent manganese, 17 percent iron, and maller amounts of copper, cobalt, and nickel. • While ranging to slabs with a mass of hundreds of kilograms, most are the size of potatoes. Properties of ocean water

35. Sediment classification, part 12 • Hydrogenous sediments (continued): • Manganese nodules (continued): • Manganese nodules occur on the floors of all oceans except the Arctic; they are most abundant in a 5,000-km belt on the floor of the tropical Pacific from southeast of Hawai’i to north of 10 degrees North latitude. • The nodules begin as coatings on hard objects, such as shark’s teeth or whale ear bones; marine organisms that burrow into the benthos turn the nodules over, exposing all sides to seawater (and to the source of precipitated material). • Growth rates range from 1 to 10 mm per million years. • During that time, the nodules must remain unburied, thus they indicate slow sedimentation rates. Properties of ocean water

36. Properties of ocean water

37. Sediment classification, part 13 • Cosmogenous sediments come from outer space, usually as meteorite or comet fragments. • Most extraterrestrial objects burn up in the atmosphere; and those that survive the fall typically dissolve in seawater before reaching the bottom; nevertheless, cosmogenous sediments are found mixed with other sediments. • Some cosmogenous sediments are remnants from the formation of the planets; their chemical composition typically mirrors that of the Earth’s core and mantle. • Others are silicate rocks blasted from the surface of other planets. Properties of ocean water

38. Sediment classification, part 14 • Cosmogenous sediments (continued): • Tektites are indirectly cosmogenous in origin, made from solidified rocks that melted when meteorites struck the Earth. • They have a teardrop or dumbbell shape, and are usually 2.5 to 5 cm in diameter. • Great numbers of tektites are found in the Gulf of Mexico near the site of the meteorite impact at the Chicxulub Crater in the Yucatan Peninsula. Properties of ocean water

39. Coastal-margin deposits, part 1 • Neritic deposits are those that are along continental margins. • Most (about 95 percent) of the largest river-borne sediments are trapped and deposited in bays, wetlands, estuaries, beaches, or deltas. • About 5 percent of river-borne sediments reaches the continental shelf or slope. • Little terrestrial sediment is transported beyond the continental margin, except where such sediment is carried by major sediment-exporting rivers, such as the Mississippi, Ganges, or Yangtse. Properties of ocean water

40. Coastal-margin deposits, part 2 • As a river enters the ocean, the velocity of the water slows so that the heaviest particles settle out first. • Except where high velocities carry the sediments off as quickly as they are deposited, the sediments form deposits known as deltas. • Distributaries are branching series of channels that cut through deltas. • Unless artificially confined, rivers may switch their primary channels abruptly, as has happened with the Mississippi. • Deltas are often highly modified by humans. • The building of the Aswan High Dam on the Nile has led to increasing erosion and subsidence. Properties of ocean water

41. Properties of ocean water

42. Coastal-margin deposits, part 3 • Wetlands are low-lying areas either covered with water or with soils that are saturated for at least part of the year. • Wetlands are common in coastal and delta regions, such as along the Atlantic and Gulf coasts. • Wetlands accumulate large amounts of organic matter and help control flooding by taking up excessive water during high water episodes. Properties of ocean water

43. Coastal-margin deposits, part 4 • Turbidity currents are intermittent avalanches of dense, sediment-rich waters that flow down submarine canyons, carrying sediments to the ocean floor. • Bruce Heezen was the first to rigorously document the existence of turbidity currents following analysis of Transatlantic telegraph cable breaks that followed the 1929 Grand Banks earthquake. • Deposits formed by turbidity currents are called turbidites. • Because they are denser than seawater, turbidity currents flow downslope, eroding channels as they go. Properties of ocean water

44. Properties of ocean water

45. Coastal-margin deposits, part 5 • Marine sediments accumulate rapidly in coastal areas. • Accumulation rates are as high as several meters per thousand years. • The sediments are often buried to quickly to be modified by reactions with seawater or with dissolved oxygen in the seawater. • Bottom-dwelling organisms cannot consume all the nutrients. • The sediments are often multicolored, the colors depending on the oxidation state of iron in the sediments. Properties of ocean water

46. Deep-ocean deposits, part 1 • Fine-grained deposits gradually accumulate on the ocean floor in pelagic deposits. • Accumulation rates average about 1 mm per 1,000 years. • The average thickness of pelagic deposits is between 500 and 600 m. • Because of the small size and resulting slow terminal velocity of the particles that make up pelagic sediments, they are transported over vast distance by ocean currents. • The long times given them ample time to react chemically with or be dissolved by seawater. • Iron in these particles becomes oxidized, leading to the formation of red clays and brown muds. Properties of ocean water

47. Deep-ocean deposits, part 2 • Some pelagic deposits are more than 30 percent biogenous in origin. • Those made largely of the calcium carbonate shells (tests) of coccolithophores, pteropods, and foraminifera are called calcareous oozes. • Calcareous oozes are typically found in deposits in waters shallower than the carbonate compensation depth (CCD) – the depth at which calcium carbonate dissolves. • The CCD averages about 4,500 m. • The rate at which calcium carbonate dissolves is a function of temperature, with the solution rate slower at lower temperatures. • Calcareous oozes are light in color. Properties of ocean water

48. Deep-ocean deposits, part 3 • Biogenous sediments (continued): • Siliceous oozes are formed from the tests of diatoms and radiolaria. • Seawater is undersaturated with silica such that it dissolves at all depths, thus are found only below surface waters where the organisms that form such deposits are very abundant. • Calcareous and siliceous oozes consist primarily of clay-size particles. • Sand-sized particles make up less than 10 percent of deep-ocean deposits. • The coarsest particles are volcanic in origin. Properties of ocean water

49. Properties of ocean water

50. Marine sedimentary rock, part 1 • Marine sediments are produced at the interfaces between the environmental spheres:, biosphere, geosphere, and hydrosphere. • The first step is weathering and erosion of bedrock, followed by transport by rivers, wind, ice, and gravity to the oceans. • Some of the transported material is in solution in water. • Lithification is the formation of rock from sediments. • It involves both compaction and cementation of sediment particles at relatively low temperatures. • Precipitated minerals fill pores spaces between particles. Properties of ocean water