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.