Geography of the Oceans

Geography of the Oceans Oceans cover ~ % of Earth’s surface Divided into 4 basins Pacific Atlantic Indian Arctic Shallow Seas Mediterranean, Gulf of Mexico and S. China Sea connect main oceans Basins connect at . Exchange of seawater, materials, & some migration paths 71 South Pole

Geology Basics

Structure of the Earth Thought to have formed 4.6 B years ago Dust & particles left from the Big Bang As Earth cooled Particles settled by . Divided into 4 layers density

Inner Core Mostly composed of iron alloys Solid Thickness 1221 km Temp. ~ 6000 °C (10,832 °F)

Outer Core Composed of iron and nickel Liquid Thickness 2259 km Temp. Produces Earth’s magnetic field Thickness 2259 km Temp. ~ 4500-5500°C (8132 - 9932 °F)

Mantle “Plastic” Boundaries Thickness 2891 km Hot temps make it flow like a liquid Crust “floats” on top Causes plate movement Boundaries Moho Discontinuity (Crust boundary) Gutenberg Discontinuity (Core boundary) Thickness 2891 km Upper Lower

Crust Outermost layer of Earth Extremely thin 46.6% oxygen! 2 types ranges 7-70 km 46.6% oxygen!

Cont. vs. Oceanic Crusts Cont. Oceanic Granite Basalt Density = 2.7 g/cm3 Thickness is 7-70 km Oldest rocks > 3.8 billion years old Oceanic Basalt Density = 3.0 g/cm3 Thickness 10 km or less Oldest rocks < 200 million years old

Plate Tectonics – “To Build”

Earth’s Lithospheric Crust Divided into “plates” Major & Minor Makes up Crust and upper mantle Covers up Lower mantle, outer core and inner core Plates move in different directions Cracking of the crust

Plate Boundaries

Plate Boundaries & Seismic Activity Plate boundaries can be identified Studying seismic activity

Major Lithospheric Plates North American South American Pacific Eurasian African Nazca Indo-Australian Antarctic

Types of Plate Boundaries CONVERGENT BOUNDARY

Ocean vs. Ocean Boundary Di = “two” Divergent Moving apart Composed of basalt, iron, and silicon High density rocks Mid-Ocean Ridge and seafloor spreading

Cont. vs. Cont. Boundary Con = “with” Convergent collision Move together Granite, silicon, and aluminum Lower density rocks Mountain building Ex: Himalayas, Atlas Mountains Con = “with”

Ocean vs. Cont. Boundary Subduction zone Plate edges override or slide past others Less dense cont. plate overrides the denser oceanic plate Oceanic plates subduct down into the mantle & are remelted Results in trenches and volcanoes Ex. Peru/Chile Trench

Peru/Chile Trench

Pangaea/Seafloor Spreading

Background Proposed by Alfred Wegener Why? Widely unaccepted 1912 Thought all continents were one huge land mass that later broke apart Why? Continent’s shapes roughly fit together like a puzzle The rocks and fossils on different continents matched Widely unaccepted Convection cells - magma He was a meteorologist, not a geologist

Break-up of Pangaea

Background (cont.) H. Hess and J. Wilson 1960’s Proposed mechanism for continental drift Named “Geo-poetry” to avoid criticism

Background (cont.) Glomar Challenger Drilled series of holes in Mid-Atlantic Ridge (Deep Sea Drilling Project) Findings Continental rocks date the Earth to about 4.5 billion years old Law of Superposition Oldest rocks at bottom & younger rocks above Found no rock older than 3 billion years old with many being much younger

Background (cont.) Core samples from Mid-Ocean Ridges (MOR) Matching magnetic striping in rocks on both sides Project FAMOUS 1977 Alvin photographed magma squeezing out of MOR Creation of new sea floor

New Theory – Sea Floor Spreading Vine and Matthews Scientists/Geologists used all data for new theory on plate tectonics Theory of Sea Floor Spreading Explained continental drift Wegener was correct

Ocean Floor Bathymetry (Intro) Depth Metry = Measure Ocean Floor Bathymetry (Intro) Oceanic bathymetry is similar to continental topography except continent features are smaller due to erosion M.O.R.

S.O.N.A.R. Structures on ocean floor mapped by SOund Navigation And Ranging Echo sounding Equation Depth = time * 1484 m/s 2 (round trip) [1484 m/s = speed of sound in water]

Division of the Ocean Floor Basins – deep ocean Abyssal plain Abyssal hill Seamount Island Guyot Trenches Mid-Ocean Ridge (MOR) Rift valley Margins – shallow Continental shelf Continental slope Submarine Canyons Turbidity currents Continental rise

Transition from continent to deep ocean basins Bathymetry Margins Transition from continent to deep ocean basins

Continental Shelf Underwater extension of the continent Most biologically productive area Why? High light availability

Continental Slope Very steep cliff into basin Usually 1-2 mile drop-off Materials tumble down slope Form turbidity currents Cut canyons into slope

Turbidity currents on slope

Continental Rise Sediment “speed bump” Accumulation of sediment at base of continental slope Found b/w cont. slope & abyssal plain

Parts of the Basins

Abyssal Plain Flat, featureless region Common Rare Similar to a desert Atlantic and Indian Oceans Rare Pacific Ocean

Abyssal Hill Domes of sediment deposition that shift Similar to sand dunes on land 10 – 300m small

Seamount Underwater volcanoes Summits do not break the surface! Must raise at least 1000m off of seafloor Forced up by magma

Island Seamounts extending up & out of the water Yellow (hot spots) Seamounts extending up & out of the water Differ from continents because they have no margins Usually associated with “hot spots” Active volcanoes Ex: Hawaiian Islands

Guyot Islands shortened by weathering and erosion Start out as islands Reclassified as W & E occur and re-submerge feature Similar to land plateaus

Trench Subduction zones Form boundary around Pacific plate Basalt is re-melted into asthenosphere Top portion of mantle Form boundary around Pacific plate Ring of Fire Seismic & volcanic activity

Mid-Ocean Ridge (MOR)

Mid-Ocean Ridge (MOR) Longest mtn. range in the world 40,000 miles long Covers % of Earth’s surface Divergent plate boundary New seafloor is being formed Iceland Large section of MOR extending above the water Due to sitting on a “hot spot” 23

Rift Valley Vent resulting from divergent plate boundaries Allow magma to recreate new ocean floor