Oceanography Study Notes - Tides and Currents

Unit 1: Oceanography

Topic D: Tides & Currents

AICE Marine Science AS Part 1 - Tides: Cause, Effect, & Calculated
Section 1: Introduction to Tides

  • Tides: Twice each day, the level of the seas and oceans rises and falls.

  • Determining Factors: This pattern is influenced by the alignment of Earth, Moon, and Sun, as well as environmental factors such as winds.

Section 2: Gravity and Orbits

  • Earth and Moon:

    • Earth orbits the Sun as a planet.

    • The Moon is a natural satellite that orbits the Earth.

    • Gravity's Role:

    • Gravity keeps the Earth in orbit around the Sun.

    • Gravity keeps the Moon in orbit around the Earth.

Section 3: High Tides and Low Tides

  • Gravitational Effects:

    • High and low tides are produced primarily by the gravitational effects of both the Moon and the Sun on Earth's water bodies.

Section 4: Types of Tides
4.1 Spring Tides

  • Definition: The largest tidal range.

  • Occurrence: Happens twice a month.

  • Factors:

    • Greatest Gravitational Pull: Occurs when the Earth, Moon, and Sun are aligned (straight line).

    • Moon Phases: Noticed during New Moon and Full Moon.

4.2 Neap Tides

  • Definition: The smallest tidal range.

  • Occurrence: Happens twice a month.

  • Factors:

    • Weakest Gravitational Pull: Occurs when the Earth, Moon, and Sun form a right angle.

    • Moon Phases: Noticed during the 1st and 3rd Quarter Moon.

Section 5: Formation of Tides

  • Spring vs. Neap Tides Animation:

    • An animation depicting Moon phases and their influence on tides (not graphically represented in transcript).

Section 6: Tidal Pattern and Measurements
6.1 Tidal Range

  • Definition: The vertical movement of water on the coast; the change in water height on the coastline due to gravitational forces.

  • Tidal Range: The distance between high and low tides, which changes daily.

  • Factors Influencing Tidal Range:

    • Alignment of the Earth, Moon, & Sun:

    • When in a straight line = greater gravitational pull = larger tidal range (Spring Tides).

    • When at right angles = less gravitational pull = smaller tidal range (Neap Tides).

    • Coastal Geomorphology:

    • Narrow coastal areas increase tidal range.

    • Wind:

    • Increased wind speed pushes more water on and off the coast, increasing tidal range.

    • Air Pressure:

    • Low air pressure = increased tidal range.

    • Size of the Water Body:

    • Larger bodies of water (oceans, seas) have greater tidal ranges compared to smaller bodies.

Section 7: Case Study - Bay of Fundy

  • Location: Eastern Canada, between New Brunswick and Nova Scotia.

  • Tidal Range: Features a maximum tidal range of up to 17 m (56 ft).

  • Details:

    • The maximum spring tidal range at the mouth of the Bay of Fundy is around 2 m (6.6 ft).

    • Amplification of tidal energy at the northern end of the Minas Basin causes the larger 17-meter tidal range, often stranding ships.

Section 8: Tidal Boars

  • Definition: A tidal bore is a wall of water that moves upstream in certain coastal areas where the tide rushes into a river, developing a steep slope due to river flow resistance.

  • Characteristics:

    • A true tidal wave caused by incoming tides.

    • Can reach heights of 5 m (16.4 ft) or more.

    • Can travel at speeds of up to 24 km/h (15 mph).

  • Conditions for Formation:

    1. Large spring tidal range of at least 6 meters (20 feet).

    2. Rapid rise of flood tide phase with a longer ebb tide phase.

    3. Low-lying rivers with persistent seaward currents at high tide.

    4. Shallowing sea floor disposition extending inland.

    5. Progressive narrowing of the basin towards upper reaches.

  • Examples of Regions:

    • Approximately 60 places in the world experience tidal bores.

    • Notable examples include the Amazon River (up to 5 m), Qiantang River (largest in the world at up to 8 m), Petitcodiac River, and others.

Section 9: Conclusion

  • Key Takeaways:

    • Tides are a complex interplay of gravitational forces and environmental factors.

    • Understanding tides and currents is vital for marine science and coastal geography.