4: Ocean Sediments: Sources, Sinks, and Distribution

4: Ocean Sediments: Sources, Sinks, and Distribution

1. Lithogenic Sediments

   • fragments of rocks (grains) eroded off land and transported to ocean
     • via wind, water (river runoff), ice (glacial debris)
       • ice sediment not limited to where its cold
         • volcanic material: ash plume (dust rock fragments)
           • blown as far as stratosphere then into ocean
     • plus material produced by terrestrial and oceanic volcanic activity

2. biogenic sediments

   • result of what organisms make
     • skeletons: out of silica, calcium carbonate, or phosphatic material
       • occurs in larger scale on shoreline. ex: corals
         • fragments of invertebrates (shore)
     • algae (near shore)
       • some algae have floats: bulbs with gas
         • inside of algae: skeleton of calcium carbonate; covered with photosynthetic cells
           • becomes ultimately limestone
     • plankton
       • microscopic organisms photosynthesizing and being eaten by zooplankton in ocean
         • pull minerals out of seawater into skeleton
           • some dissolve, some cover ocean floor
             • known as "oozes"
               • siliceous ooze
                 • diatoms: phytoplankton
                 • radiolarians: zooplankton
                 • accumulating this material; becomes compressed: lithofied materials: becomes chert
                   • microcrystals and quartz
               • calcareous ooze
                 • build out of calcium carbonate/limestone
                 • coccolithophores: phytoplankton
                   • accumulates into chalk
                 • foraminifera: zooplankton
                   • accumulates into micrite
             • can be deposited anywhere in ocean, far from land
               • just need sun at surface of ocean
     • organic detritus: from fish (far in ocean)
       • "marine snow"
         • non-mineralized detritus -- fecal matter/carcasses
       • organisms in ocean feed on this as it rains down on ocean floor

3. hydrogenic sediments

   • precipiate out in oceans from inorganic chemical processes
     • water is super satruated by something like salt
   • evaporites
   • carbonates
     • layers of limestone at the bottom of ocean
   • hydrothermal
     • limited to areas of volcanic activity
       • hydrothermal vents
         • hot sea water out from crusts
           • disolved minerals: very hot, shock treated in cold sea water
             • looks like smoke to us: will sink down and cover the area: deposits of mineral metals
           • minerals from magma
   • manganese nodules
     • places on ocean floor littered with little balls: nodules
       • as far as we know: inorganic process
   • phosphate nodules
     • same as manganese, can form crusts

4. cosmogenic sediments

   • particles and fragments of meteorites
     • sediment is distributed across surface of the planet
       • see these anywhere all across the ocean: deep ocean sediments
         • they don't make their own layers

5. Anthropogenic sediment

   • particles of human-produced products, esp glass and plastic
   • microplastics
   • glass/garbage/concrete/asphalt
     • made of silica, difficult to erode
     • humans make a large amount of glass
       • hardness of 5.5-6

6. sinks

   • means by which sediments can be permanently/semi-permanently removed from the oceans
     • sealevel change can shift deposition into the interior of continents where oceanic sediments are trapped following sealevel drop
       • epeiric seas
       • some sediments are subducted and recycled back into the mantle
         • some ocean sediments are accreted onto the continent by means of the accretionary wedge
           • accretion
             • ex: olympic mountains
             • ex: golden gate bridge: paleo-feature last active ~80 mil ya
         • subduction

7. william smith

   • macroinvertibrates first appear around 600-700 years ago
     • each rock that has these specimen is that age
   • trilobytes in cambrian period
   • fossil order not random, sucession based on evolutionary existence
     • using human garbage to date

8. distribution

   • passive margin sedimentation
     • lithogenic sediment generally becomes finergrained as the distance from the shore increases
       • from sand to silt to clay
     • storm transportation
       • coarse lithogenic material can be moved into deeper water (outer shelf or shelf slope) by storm scour
         • these deposits are called tempestites
       • turbidite
         • underwater mass sediment gravity flow. turbidites often form abyssal fans at the base of submarine canyons
           • underwater debris slide
           • can travel over and beyond fan
         • sealevel change
           • seafloor spreading rates: high
           • icebergs melting

9. hydrothermal vents

   • underwater volcanos/hot spots
     • unique ecosystems: completely cut off from sunlight
       • entire food chain based off of chemistry
   • dominated by chimney smokers
     • name depends on color of "smoke"
       • actually little percipitated particles of sediment
         • water perculates down through crust
           • sea water gets hotter as it soaks through crust
             • never reaches magma
             • does not flash into steam because of pressure
               • water heats up and convects through same cracks
                 • acts as super solvent, dissolving minerals in rocks
                   • when it gets to the top, reaching water thats 2 celcius
                     • all minerals percipitate out as solid: the smoke
                       • pools out several hundred meters up
   • the original chimney consists of a wall of anhydrite (CaSO4)
     • forms as Ca2+ ions disolved in hot fluid react with seawater sulfate SO4 -2
       • interstices of porous anhydrite act as nucleation sites for cu, zn, fe sulfide compounds dissolved in superheated fluids
         • turns white chimney black
         • inner walls become coated with chalcopyrite CuFeS2
           • build quickly, collapse, rebuild
         • when ions of Fe Zn Cu and S exit the anoxic environment of chimney, they react with oxygen and other ions to form metal sufides and oxides
           • turns smoke black
           • these precipitates settle out and cover surrounding seafloor---create hydrothermally derived lithogenic sediments

10. dissolution of biogenic particles

    • as you go down toward ocean floor: more pressure, colder temp
      • Radiolaria (SiO2)
        • ocean toward surface requires constant rebuilding because dissolution rate is high
          • sinking into deep ocean: dissolution decreases dramatically
      • Foraminifera (CaCO3)
        • toward surface, little dissolution
          • down toward floor: large dissolution due to higher acidity
            • will be dissolved by reaching ~ 5km
        • spikes so they "drag" going down
      • organic fecal matter protects skeletons on their way to the ocean floor
    • Robustness (surface area/volume)and mineralogy of skeletons also influences dissolution rates
      • calcite: fairly robust against dissolution. vs aragonite (material dissolves readily)
      • low surface area, high volume: more robust
      • ex: pancake high surface area, low volume; less robust
    • carbonate compensation depth (CCD)
      • the solubility of CaCO3 depends largely on presence of dissolved CO2
        • higher dissolution rate in deeper water
          • as pressure rises, CO2 rises
          • as temperature rises, CO2 lowers
          • age of water up, CO2 up
          • >4000m in atlantic
            • >2500 in s.pacific
              • >1000 in n.pacific
      • CO2 + H2O <-> H2CO3
        • CO2 + H2O <-> HCO3- + H+

11. sediment distribution factors

    • distance to land/source
    • water chemistry
      • depth
      • temperature
      • pressure
      • age
    • currents
    • accumulation rates

12. locations of sediments

    • siliceous oozes: around equator
    • calcareous oozes will not hit ocean floor (dissolve)
    • deep sea clay (mud and muck)
      • made of windblown clay particles into the deepest parts of the ocean
      • enriched in organic tissue/muck

13. sampling ocean sediments

    • grab sampler
      • claws grab ocean floor surface
      • bulk sample/layering destroyed
    • gravity corer
      • pipe filled with sediment layers
        • uses vacuum mechanism to keep core in pipe
    • slide-hammer corer
      • seals off valve like vacuum
        • samples layers in pipe