Ocean Basins Structure of the Oceans From Continental Shelf to Abyssal Depths

2 Measuring Depth  85 BC Posidonius ~2km  Hemp line and greased lead weight  tension  Fathoms (6 feet)  Piano wire and cannonball w/ winch  By 1895 only 7000 measurements to 2000m and 550 to >9000m  Echo sounder (depth recorder) 1920s  Meteor- mid-Atlantic ridge  1950s detailed mapping of ridges and trenches  Heezen and Tharp

Echo Sounder

4 Bathymetry  LADS (shallow water)  Laser airborne depth sounder  Fixed winged aircraft/ GPS  Operating depth of m  Gravity measurements  Changes in sea surface elevation  Seamounts +5m and ridges +10m  Trenches m  Satellite altimetry  Side-scan sonar

Marine Gravity Anomalies by Satellite Altimetry

8 Bathymetry of the Sea Floor  Continental Margin- Passive and Active  Continental shelf (Flat km, 65km; m deep)  Continental shelf break  Continental slope (Steep)  Submarine canyons  Turbidity currents and turbidites  Continental rise  Ocean Floor  Ridges, Rises and Trenches

Shelf Break Slope Rise Computer Drawn Topographic Profiles Mid- Atlantic ridge

Continental Shelves

Formation of Shelves by trapping of land derived sediments

Turbidity Currents- 90km/hr, 300kg of sed in suspension

Submarine Canyon

Ancient Turbidite Sequence Bouma Sequence Top- (E)Pelagic Seds (D)Parallel Laminated Sands (C)Rippled, wavy or convoluted laminae (B)Plane Parallel Laminae Bottom-(A)Massive Graded D C A

17 Bathymetry of the Sea Floor  Ocean Floor  Deep seafloor ( m cover 30% of Earth’s surface)  Abyssal Plain (Flat)  Pelagic sediments and turbidites  Abyssal hills and seamounts & Guyots  <1000m high; steep sided volcanoes  Found on 50% Atlantic and 80% Pacific seafloor  Some become atolls  Ridges, Rises and Trenches  65,000km mountain range  Challenger Deep (Mariana Trench 11,020m)

Major Ocean Basins

24 Sediments  Continental margins and ocean basins receive continuous supply  Organic  plankton  Terrigenous (Land)  Rivers, beaches  Atmospheric  wind  Space  tektites (meteorites)

26 Continental Margin  Thick Sequence of sediments (1000’s m)  Passive margin  Gravels, sands, muds  Rates of deposition vary 8m/yr in estuaries  5m/1000yr quiet bays  Shelf and slope 10-40cm/1000yrs  Carbonates  Salts  Potential for resources  Oil  Gas  Methane Hydrates

27 Sand and Gravel  1.2 billion tons/yr  Reserves of 800 billion tons  US 450 billion tons  UK & Japan take 20% from seafloor  Other materials found within such as Fe, U, Pt, Au & Diamond  The Tin Belt of SE Asia  Carbonate sands

Oil and Gas account for 95% of material exploited from the sea 24.8% of oil and 20.7% gas in US came from offshore production (1997)

Gas Hydrates and other Gases Geopressurized zones Methane Hydrates, crystalline solids of gas and water abundant in arctic regions and marine sediments 1 ft 3 releases 160 ft 3 gas Offshore east coast area of potentially 1300 trillion ft 3 gas Reserves 4x10 20 ft 3

32 Atmosphere-Wind  Winds from deserts transfer terrigenous sediment 1000’s kms into ocean basin  Annual supply to oceans 100x10 6 metric tons  Sahara-Caribbean connection  Reefs  Soils

Sorting Poorly Well

44 Biogenous Sediment  Planktonic- Siliceous and Carbonate Oozes  Phytoplankton  Diatoms (silica)  Coccolithosphorids (carbonate)  Zooplankton  Radiolarians (silica)  Foraminefera (carbonate)  Lysocline (dissolution)  CCD (carbonate compensation depth) <20% preservation CO3 ~4500m  Atlantic (5000m)  Pacific ( m); Equatorial Pacific (5000m)

DiatomsCoccolithosphorids

Radiolarians

Foraminifera

48 Hydrogenous Sediment  Slow formation in water column  Chemically precipitated  Carbonates (ooids, calcareous muds)  Phosphorites (fertilizers)  Continental shelf and slope  Reserve ~ 50 billion tons  Nodules or crusts  Due to high nutrients-upwelling  Salts (Mediterranean)  Manganese nodules  Concentric layering  High in Fe, Cu also  1-10cm diameter  Hydrothermal vents (smokers)-ores (sulfides)

49 Upwelling  When wind blow offshore, they push the warm surface waters away from the coastline  This creates a region of low pressure and may result in upwelling of deep water to replace surface water.  The deep waters contain dissolved nutrients which can support abundant life at the surface  Many fishing grounds exist in these areas, notably the west coast of N. & S. America and w coast of Africa

55 Laws and Treaties  200-mile EEZ  Law of the Sea (1982)  All wealth is shared by humanity  Regulated by UN  Profits shared  US did not sign treaty  Provisional Understanding Regarding Deep Seabed Matters (1984)- Western countries (US, UK, Germany, Japan…)  4 consortia awarded exploration licenses

56 Sediments as Records  Paleoceanography  Isotopic studies  Oxygen isotope ratios in skeletal material to infer past climate ( 18 O: 16 O)  Dependant on ratio in seawater  During glaciations is 16 O removed, so 18 O: 16 O ratio increases in seawater  Marine plankton distribution  Circulation models