CaCO 3 is very important chemically

HYDROGENEOUS SEDIMENTS: precipitation of dissolved elements in water 1.Evaporites Evaporation in isolated basins E.g., Mediterranean Sea 6 M.Y. agoE.g., Mediterranean Sea 6 M.Y. ago Precipitation of "salts"Precipitation of "salts" NaCl (halite)NaCl (halite) CaSO 4 2H 2 O (gypsum)CaSO 4 2H 2 O (gypsum)

Salt Mine under Detroit: Shallow sea over 400 m.y. ago

2. Manganese nodules and crusts Mn + Fe oxides (+ Cu, Co, Ni)Mn + Fe oxides (+ Cu, Co, Ni) In deep ocean basins and along mid-ocean ridgesIn deep ocean basins and along mid-ocean ridges Origin: -- chemical reaction between oxygen in water and dissolved Mn +FeOrigin: -- chemical reaction between oxygen in water and dissolved Mn +Fe Mn + Fe come mostly from sediments and hydrothermal ventsMn + Fe come mostly from sediments and hydrothermal vents

3) Phosphate minerals P released when organic matter degrades- Minerals precipitatedP released when organic matter degrades- Minerals precipitated On Cont. shelvesOn Cont. shelves 4) Metal sulfides from hydrothermal vents Collect on ocean floorCollect on ocean floor Metal-rich (gold, copper)Metal-rich (gold, copper)

Fig. 4.18

Class The Oceans ECONOMIC RESOURCES ON OR UNDER THE SEA FLOOR ON OR UNDER THE SEA FLOOR

Economic Decision: Are extra costs of offshore production offset by profits? SEA FLOOR vs. LAND

Building materials- inexpensive, HUGE TONNAGESBuilding materials- inexpensive, HUGE TONNAGES – Sand + Gravel- aggregate for concrete, etc. – Shell deposits- aggregate or cement PhosphatePhosphate –Needed for fertilizers –Cont. Shelf deposits- future? Hydrocarbons (fossil fuels)Hydrocarbons (fossil fuels) Important Resources: Continental margins

Present operationsPresent operations 30% of world oil output, some natural gas 30% of world oil output, some natural gas Increasing - e.g., Indonesia Increasing - e.g., Indonesia Origin of petroleum and natural gas:Origin of petroleum and natural gas: Accumulation of organic matterAccumulation of organic matter Need high sedimentation rate, or else bacteria consume the organic matterNeed high sedimentation rate, or else bacteria consume the organic matter Changed to oil during burial (>100˚C)Changed to oil during burial (>100˚C) Hotter/longer cooking converts it to natural gasHotter/longer cooking converts it to natural gas Later migration of oil/gas upward into “traps”Later migration of oil/gas upward into “traps” Hydrocarbons (fossil fuels)

Continental margins -- target for all offshore productionContinental margins -- target for all offshore production Poor preservation of organic matter in deep sea and higher costPoor preservation of organic matter in deep sea and higher cost Hydrocarbons (cont’d)

Offshore Oil Rigs

How much petroleum is left?

Gas Hydrates:Gas Hydrates: Water and gas combine to form a dense materialWater and gas combine to form a dense material Layers of this found in ocean sedimentsLayers of this found in ocean sediments Possible HUGE energy sourcePossible HUGE energy source Possible HUGE source of greenhouse gas if some gets released (e.g., slumping)Possible HUGE source of greenhouse gas if some gets released (e.g., slumping) Hydrocarbons (cont’d)

Can I put this down now?

Manganese nodules Metals, scattered on the ocean floor Limitations now: –High costs vs. on-shore mines –Ownership of sea floor (?)

Types of fossils observed tells us about temperatures, ecosystems, etc.Types of fossils observed tells us about temperatures, ecosystems, etc. Chemical analysis tells us about temperature and chemistry of the waterChemical analysis tells us about temperature and chemistry of the water –Isotope ratio measurements…. Ocean Sediments as Recorders of Earth History

16 O = oxygen with 8 neutrons (most common) 18 O = oxygen with 10 neutrons As CaCO 3 is formed from dissolved ions, the 18 O/ 16 O ratio depends on temperature

18 O/ 16 O Warmer Colder

Paleoclimate Research Why does the earth have ice ages?Why does the earth have ice ages? How does the earth’s climate system work?How does the earth’s climate system work? How will it respond to increased greenhouse gases?How will it respond to increased greenhouse gases? Does it tend to resist change?Does it tend to resist change? Does it tend to amplify the effects of changes (e.g., added greenhouse gases)?Does it tend to amplify the effects of changes (e.g., added greenhouse gases)? Are there “thresholds” we should avoid?Are there “thresholds” we should avoid?