Introduction to Oceanography & Ocean History

What are the 5 major oceans of Earth?

Atlantic, Indian, Pacific, Arctic, and Southern.

What were the primary motivators for early human ocean travel?

Finding land, curiosity, resource depletion, faster travel, and trade.

What is the significance of the Pesse canoe?

Oldest surviving boat (Netherlands, ~10,000 yrs ago), used for rivers, not oceans.

Aristotle's view of the ocean

Believed the ocean occupied the deepest parts of Earth. 384-322 BC.

Eratosthenes' achievement

Calculated Earth's circumference within 1% using shadows cast by sticks in two cities. 276-195 BC

Ptolemy's contribution to navigation

Developed an early map utilizing latitude and longitude.

Viking navigation milestone

Theoretically the first to use the North Star (Polaris) for navigation around 900 AD.

Zheng He

Led 7 major maritime voyages for China between 1405 and 1433.

James Cook's scientific expeditions

Measured ocean depth using a weight attached to a wax-covered rope. 1768-1779.

What does SCUBA stand for?

Self-Contained Underwater Breathing Apparatus.

HMS Challenger Expedition

First global scientific voyage dedicated to ocean science; sampled deep ocean and Mariana Trench.

What theory did the HMS Challenger expedition dispel?

The Azoics Theory (the belief that no life existed below 550 meters).

Early navigational cues used by mariners

Cloud reflections of islands, bird flight patterns, stars, ocean swells, stick charts, and water smell.

What 6 elements (CHONPS) make up 95% of the biosphere?

Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur.

Stellar Nucleosynthesis

The process by which heavier elements are formed inside stars.

Solar Nebular Disk Model

Model explaining solar system formation via gravitational attraction of heavy elements into protoplanets.

Giant Impact Hypothesis evidence

Moon rocks are younger, less dense than Earth, but share a similar chemical composition.

Origin of Earth's atmosphere and oceans

Volcanic outgassing released water vapor and gases, which condensed into rain to form oceans ~4 bya.

Earth's water distribution (highest to lowest volume)

Oceans/Seas (97%), Lakes/Rivers (2%), Snow/Ice (1%), Atmospheric (0.00057%).

Cation vs. Anion

Cation is a positively charged ion; Anion is a negatively charged ion.

Water molecule polarity

Dipole structure with a partial negative charge near oxygen and positive near hydrogen.

Cohesion vs. Adhesion in water

Cohesion is water sticking to water; adhesion is water sticking to other substances.

Heat vs. Temperature

Heat is energy from molecular vibrations; temperature measures the object's response to heat change.

High Heat Capacity of water

Water can absorb or lose large amounts of heat with only a small temperature change.

Latent Heat

Heat gained or lost per unit mass when a substance changes state (e.g., evaporation/sweat).

First submarine

Operated at depths of 12-15 feet. 1600 AD.

Egyptian sea exploration

4000-3000 BC

Greek and Phoenician sea exploration

900-700 BC

Who led the HMS Challenger expedition?

Charles Wyville Thomson.

How far did the HMS Challenger travel?

68,890 nautical miles circumnavigating the globe.

What parameters did the HMS Challenger measure at each station?

Ocean depth, bottom temperature, and bottom samples for chemical/physical analysis.

Big Bang

Occurred approximately 13.77 billion years ago (bya).

Big Bang Nucleosynthesis

Occurred 100-300 seconds after the Big Bang.

When did our solar system start to form relative to the Big Bang?

8.7 billion years after the Big Bang.

Stellar Nucleosynthesis (simple definition)

The formation of the heavier elements.

What is salinity?

Total amount of solid material dissolved in water.

What is excluded from the definition of salinity?

Dissolved organic substances and fine particles in suspension.

Operational definition of dissolved vs. particulate

Dissolved passes through a 0.02 filter; particulate does not.

Average salinity in the ocean

35 parts per thousand (35‰).

Units used to measure ocean salinity

Parts per thousand (‰).

What does 35‰ salinity mean?

35 grams of salt per 1,000 grams of seawater.

Principle of Constant Proportion

The relative proportions of major dissolved ions remain constant everywhere.

Formula relating salinity to chlorinity

Salinity = 1.80655 × chlorinity (‰)

Fit of continents evidence for Pangea

The shorelines of separate continents fit together like puzzle pieces.

Mountain evidence for Pangea

Appalachian Mountains extend to connected ranges in Greenland, the UK, and Norway.

Glacier evidence for Pangea

Glacial deposits across separate continents share similar materials and chemical signatures.

Fossil evidence for Pangea

Matching plant fossils are found in separated areas that align when continents are joined.

Who is Alfred Wegener?

Proposed the Continental Drift Hypothesis and named Pangea. 1912.

Density Stratification

The division of Earth into distinct layers based on density.

Density gradient of Earth's layers

Each deeper layer is heavier (denser) than the layer above it.

Density (definition)

An expression of heaviness; the amount of mass contained in a given volume.

Core (Compositional Layer)

Iron, Nickel, Sulfur

Mantle (Compositional Layer)

Silicate Minerals (84% of Earth's volume)

Oceanic Crust

Basalt

Continental Crust

Granite

Inner Core (Mechanical Layer)

Rigid/Solid

Outer Core (Mechanical Layer)

Liquid/Melts

Mesosphere (Mechanical Layer)

Plastic

Asthenosphere (Mechanical Layer)

Plastic

Lithosphere (Mechanical Layer)

Rigid

Effect of increased pressure on melting point

Increasing pressure leads to a higher melting point.

Continental Crust (thickness and density)

Thick and light (low density).

Continental Crust (texture and color)

Coarse-grained and light-colored.

Oceanic Crust (thickness and density)

Thin and dense.

Oceanic Crust (texture and color)

Fine to coarse-grained and dark-colored.

Isostatic Adjustment

The vertical movement of Earth's crust.

Cause of Isostatic Adjustment

Buoyancy of Earth's lithosphere floating on the denser, plastic-like asthenosphere.

Isostatic Rebound

The rising of Earth's crust after heavy material on it is removed.

Glacial example of Isostatic Rebound

Land rising back up after heavy glaciers melted about 10,000 years ago.

How do warmer temperatures cause sea level rise?

Warmer temperatures cause water molecules to expand, increasing total ocean volume.

How does ice melt contribute to sea level rise?

Melting glaciers and ice sheets add large volumes of fresh water to the ocean.

Who was Harry Hess?

US Navy Captain who kept his sonar depth recorder running continuously during WWII.

Harry Hess's observation of ocean basin centers

Found extensive mountain ridges in the centers of ocean basins.

Harry Hess's observation of continental margins

Found extremely deep ocean trenches at the edges of ocean basins and continental margins.

Harry Hess's observation of undersea volcanoes

Observed that undersea volcanoes had flattened tops.

Harry Hess's observation of sediment thickness

Found less sediment accumulation at mid-ocean ridges.

World Distribution of Mid Oceanic Ridges

World's longest mountain chain

Where is new ocean crust formed according to seafloor spreading?

At mid-ocean ridges.

Why are ridge volcanoes eroded flat on top?

They originally form near the ocean surface where erosion occurs before sinking.

What occurs at deep ocean trenches in seafloor spreading?

The ocean floor descends back into the mantle.

Why does ocean sediment thin toward mid-ocean ridges?

The seafloor near ridges is younger and has had less time to accumulate sediment.

Relationship between rock age, temperature, and density

As oceanic rocks age and cool, they become more dense.

Why does older ocean crust sink deeper into the upper mantle?

Cooling increases its density, causing it to sink deeper due to isostasy.

How does seafloor depth change with distance from mid-ocean ridges?

The seafloor gets progressively deeper with distance from the ridge.

Oldest Seafloor rock

180 million years old

Oldest Continental Rock

4 billion years old

New Crust is...

swallow in depth, ridges

Old Crust is...

deep in depth, trenches

Subduction Zone

A convergent boundary where old, cold, dense oceanic plates sink back into the mantle.

What tectonic feature forms at a subduction zone?

An oceanic trench, where sinking plate material returns to the mantle.

Magnetic Anomalies

Stripes of magnetism on the ocean floor that serve as a historical record of new sea floor.

What are Magnetic Polarity Reversals?

Events where Earth's magnetic poles switch.

How frequently do Earth's magnetic polarity reversals occur?

At irregular intervals between 25,000 to 30 million years.