L10 – The dynamic nature of oceans and shorelines, Part II

Dynamic Nature of Oceans and Shorelines

  • Introduction to Part Two of the hydrosphere discussion focusing on oceans, rivers, streams, ice, and the atmosphere.

Importance of Water

  • Presented image of Chopu, a surf spot illustrating the immense power and size of ocean waves.

  • Water is heavy; example of a cubic meter of water weighing 2,000 pounds, comparable to a car.

  • Discussion on the impact of hurricanes on coastal communities, emphasizing water movement and risks associated.

Surface Currents in Oceans

  • Northern Hemisphere Surface Currents: Large rotating masses of water move clockwise; includes cold currents along the California coast.

  • Southern Hemisphere Surface Currents: Rotating counterclockwise, impacting ocean dynamics differently between hemispheres.

  • Relationship between wind regimes and water currents established.

Upwelling vs. Downwelling

Upwelling

  • Example from California: offshore winds blow surface waters away, allowing deeper nutrient-rich waters to rise.

  • Summary of upwelling:

    • 1. Winds blow surface waters offshore.

    • 2. Upwelling of nutrient-rich deep waters replaces displaced surface waters.

    • 3. Phytoplankton thrive in nutrient-rich waters, leading to a chain of larger marine organisms.

    • Conclusion: Upwelling supports rich marine biodiversity along the California coast.

Downwelling

  • Example from East Coast (Florida): Warm equatorial waters move northward and become saltier and denser, sinking to depth.

  • Summary of downwelling:

    • 1. Warm water evaporates, increasing salinity.

    • 2. Increased salinity leads to increased density, causing sinking.

Understanding Tides and Waves

Tides

  • Highest and lowest tides occur when the Earth, Moon, and Sun are in alignment (new/full moons).

  • During alignment, gravitational pull creates tidal bulges, leading to extreme tides.

  • Weak tides occur when the moon is at a 90° angle relative to the Earth and Sun (first/third quarter moons).

Waves

  • Waves are primarily generated by wind, not gravity.

  • Key variables for wave formation are: wind speed, consistency, duration, and surface area over which wind blows.

  • Ocean waves are generally larger than lake waves due to greater surface area.

Coastal Interactions

Erosional vs. Depositional Environments

  • Headlands: Areas of high wave energy that erode land.

  • Coves: Areas of reduced wave energy where sediment is deposited.

  • Result: Coastlines tend to straighten over time as headlands erode and coves accumulate sediment.

Hurricanes and Climate Change

  • Storm surge is a significant outcome of hurricanes, often leading to flooding in coastal areas.

  • Increasing global temperatures correlate with increased intensity and frequency of hurricanes.

  • Summary of hurricane dynamics:

    • 1. Increased frequency of intense hurricanes; the 100-year storm becomes more common.

    • 2. Emergence of new, more intense storms as global climate changes.

    • 3. Sea level rise exacerbates hurricane impacts.

Conclusion

  • Understanding these dynamics is essential as we continue discussing the hydrosphere, focusing on freshwater systems and the cryosphere in future sessions.

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