Chapter 3 Part 2: The World Ocean

Water Column

• Stratification: Water layers with different densities; densest water sinks to the bottom, least dense remains at the surface.

• Water Column: A vertical section of water extending from the surface down.

• Temperature Distribution:

  • Deep water: Cold and dense.

  • Surface water: Usually warm and less dense.

• Profile: Graph depicting temperature, salinity, or other characteristics at various depths.

Ocean Density Profiles

• Pycnocline: Zone of quick density increase with depth (Graph A).

• Thermocline: Zone of rapid temperature drop with depth (Graph B).

• Halocline: Zone of rapid salinity increase with depth (Graph C).

Stability of the Water Column

• Stability Factors:

  • Low Stability: More dense water over less dense water leads to easier mixing.

  • High Stability: Increased density with depth limits mixing.

Downwelling

• Occurs when surface water becomes denser than deep water; happens typically in winter when cooling increases density.

• Process: Surface water sinks, displacing less dense water below.

• Importance: Brings dissolved oxygen down to deeper waters.

Upwelling

• Mechanism: Winds blow across the ocean, pushing surface water away, causing deeper nutrient-rich water to rise.

• Resulting water is colder and rich in nutrients.

Thermohaline Circulation

• Known as "The Great Ocean Conveyor Belt".

• Definition: Movement patterns of water masses influenced by temperature (thermo) and salinity (haline).

• Functions:

  • Regulates Earth’s climate by distributing heat.

  • Mixes ocean chemically.

  • Affects marine life abundance.

The Great Ocean Conveyor Belt

• Key Characteristics: Distinction between warm and cold water is crucial for understanding ocean dynamics.

Three-Layered Ocean Structure

• Layers:

  • Surface Layer: Mixed layer from surface down to 200 meters, influenced by wind, waves, and currents.

  • Intermediate Layer: From 200 to 1,500 meters, characterized by thermocline with rapid temperature drop.

  • Deep/Bottom Layers: Below 1,500 meters, uniformly cold.

Ocean Motion

• Constant motion through waves, currents, and tides.

• Most intense at surface where surface currents and waves are driven by wind (which is powered by the sun).

• Coriolis Effect: Influences wind and currents.

Coriolis Effect

• Explanation: Earth's rotation causes moving objects to bend rather than travel in a straight line.

The Coriolis Effect in Action

• Deflects winds and currents: Right (clockwise) in the northern hemisphere, Left (counterclockwise) in the southern hemisphere.

Trade Winds

• Characteristics: Winds bent 45º towards the equator due to the Coriolis effect.

• Description: Known for being the steadiest winds on Earth, moving from east to west in the tropics.

Westerlies and Polar Easterlies

• Westerlies: Found at middle latitudes, moving from west to east.

• Polar Easterlies: At high latitudes, these winds are variable and move from east to west.

Ekman Spiral

• Process: Surface winds initiate surface current at a 45º angle due to the Coriolis effect; this movement propagates to layers below, creating an angled flow.

Equatorial Currents and Gyres

• Equatorial Currents: Wind-driven surface currents moving parallel to the equator under trade winds' influence.

• Gyres: Large, circular systems formed by the combination of equatorial currents, influenced by the Coriolis effect.

Wave Measurement

• Definitions:

  • Crest: Highest part of a wave.

  • Trough: Lowest part of a wave.

  • Wave Height: Vertical distance from trough to crest.

  • Wavelength: Distance between crests.

  • Period: Time taken for two successive crests to pass a fixed point (in seconds).

Characteristics of Waves

• Water particles do not progress with the wave; they move in circular motions. Waves transmit energy but do not transport water per se.

Wave Formation

• Generative Forces: Created primarily by wind; stronger and longer winds produce larger waves.

• Fetch: Distance over which the wind blows; longer fetch results in bigger waves.

From Seas to Swells

• Seas: Formed during storms, sharp crests and flat troughs.

• Swells: After the storm, waves smooth out into rounded crests and troughs, exhibiting ideal circular motion.

Surf Formation

• Process: Waves slow in shallow waters, growing higher and steeper until they break, creating surf.

Tides

• Rhythmic rise and fall of sea levels, heavily impacting nearshore sea life.

• Influenced by the gravitational forces of the moon and sun along with Earth's rotation.

Centrifugal vs. Gravitational Forces

• Centrifugal Force: Causes water to bulge outward on the side away from the moon.

• Gravitational Force: Pulls water toward the moon, creating tidal bulges.

Earth's Rotation and Tides

• Approximately 24-hour day cycle, location moves in and out of tidal bulges leading to two alternating high and low tides daily.

• The moon's orbit adds approximately 50 minutes to the tidal cycle (total 24 hours and 50 minutes).

Effect of the Sun on Tides

• The sun creates tidal bulges but with half the gravitational pull compared to the moon due to its distance.

Spring Tides

• Occurs when the earth, moon, and sun align (full and new moons); leads to highest high tides and lowest low tides (twice monthly).

Neap Tides

• Result when the sun and moon are at right angles (quarter moons); leads to lower high tides and higher low tides (also twice monthly).

Variability of Tides

• Tides differ by location, basin shape, and depth.

  • Semidiurnal Tides: Two high and two low tides daily.

  • Mixed Semidiurnal Tides: Successive high tides at different heights.

  • Diurnal Tides: Rare, characterized by one high and one low tide daily.

Tide Table Example

• Functional Purpose: Provides predicted times and heights for high and low tides in coastal areas.