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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.