Marine Science I Honors - Air-Sea Interactions: Wind and Ocean Currents

Air-Sea Interactions: Wind and Ocean Currents

Learning Intentions & Success Criteria

• Learning about the relationship between sunlight, the atmosphere, and the ocean, and what causes currents and where they flow.
• Appreciating how heat, sediment, nutrients, and organisms move within the seas.
• Describing how the Coriolis effect creates circular airflow and current patterns.
• Identifying and naming the currents of the world and how currents create gyres.
• Listing the three major factors that drive ocean currents.

The Importance of Sunlight

• Life gets almost all of its energy from the sun.
• Solar energy drives the wind and ocean currents.
• Earth's temperature relies on sunlight.
• The sun provides life and the conditions for life.

Air and the Sun

• Air is a mixture of gases.
• The Four Layers of the atmosphere include:
  • Troposphere: The lowest layer, up to 15,000m or 49,200ft.
  • Stratosphere: 50,000m to 164,200ft.
  • Mesosphere: 90,000m to 295,200 ft.
  • Thermosphere: The top layer, extending into space, 110,000m or 360,800 ft.

Breakdown of Air (on average)

• Gases that make up the air:
  • Nitrogen: 78.08\%
  • Oxygen: 20.95\%
  • Argon: 0.93\%
  • Carbon Dioxide: 0.03\%
  • All Other Gases: 0.01\%

Temperature

• The amount of water vapor in the air relates to temperature, density, and pressure.
• As temperature rises, air pressure increases, and density decreases.
• Adding water vapor decreases the density even more.
• Warm air is less dense than cool air.
• When saturated air cools, water vapor condenses, forming rain (above freezing) or snow (below freezing).
• Understanding air masses and the weather they create is important because:
  1. These movements redistribute heat around Earth.
  2. Precipitation is the primary source of fresh water.

The Earth’s Heat Balance

• About 50% of sunlight reaches the Earth's surface.
• All absorbed energy reradiates back into space as infrared radiation to maintain balance.
• Imbalance would cause Earth to grow hotter, making life unsustainable.

Uneven Heating

• Factors causing uneven heating:
  • Earth is round.
  • The axis is tilted.
  • The orbit is elliptical.
• Uneven heating causes weather due to convection.
• Convection: Vertical circular currents caused by temperature differences in a fluid, such as air.
• Warm air rises, cooler air replaces it, creating a circular airflow pattern that drives wind patterns and ocean currents.

Deflection to the Right or Left

• Wind drives major ocean currents due to the rising and falling of warm and cool air.
• Water flows in the same direction as the wind.
• The Coriolis Effect causes moving objects to deflect to the RIGHT in the NORTHERN Hemisphere and to the LEFT in the SOUTHERN Hemisphere.

Coriolis Effect

• If the Earth did not rotate, air would circulate between the poles (high pressure) and the equator (low pressure) in a simple pattern.
• Due to Earth's rotation, circulating air deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• This deflection is called the Coriolis effect.
• The Coriolis effect is caused by the Earth's rotation relative to an object in motion over its surface
• Motion is relative to the observer. Standing on the equator, you're motionless relative to anyone on Earth but moving relative to someone in space.

The Coriolis Effect and the Wind

• The Coriolis effect deflects air to the right in the Northern Hemisphere, creating a circular flow pattern.
• Atmospheric circulation cells are six distinct air masses (three in each hemisphere) with individual airflow patterns.
• Hadley Cells: Between the equator and approximately 30 degrees north or south.
• Trade winds: Air rising at the equator and moving northward.
• Ferrel Cells: Between 30 and 60 degrees latitude. Wind descends from Hadley cells and doesn’t turn towards the equator.

Wind Patterns

• Trade Winds (Easterlies): Permanent east-to-west winds in the Earth's equatorial region.
• Westerlies: Prevailing winds from the west toward the east in the middle latitudes (30-60 degrees latitude), originating from high-pressure areas.
• Polar Easterlies: Dry, cold winds blowing from the east, emanating from the polar highs around the North and South Poles.

Atmospheric Wind Patterns

• Hadley Cell: Tropical atmospheric circulation of air rising near the equator, flowing poleward at 12–15 km, cooling and descending in the subtropics (around 25 degrees latitude), and returning equatorward near the surface.
• Ferrel Cell: Circulation of air in the mid-latitudes (between 30 and 60 degrees N and S). Air flows poleward and eastward near the surface and westward at higher altitudes, opposite of the Hadley cell. Plays a major part in heat transport.
• Polar Cell: Smallest and weakest cells, extending from 60-70 degrees north and south to the poles. Air sinks over the highest latitudes and flows out towards lower latitudes at the surface.

Doldrums

• The doldrums are an area where the northern hemisphere's trade winds collide with the southern hemisphere's trade winds.
• Intense solar heating near the equator forces warm, moist air up into the atmosphere.
• As the air rises, it cools, causing showers and storms.
• The rising air mass subsides in the horse latitudes, where air moves downward.
• Little surface wind in this area, causing calm conditions for sailing ships.

Intertropical Convergence Zones (ITCZ)

• The geographic equator is at 0° latitude, but the meteorological equator (ITCZ) marks the temperature equilibrium, shifting north and south with seasonal changes.
• Atmospheric and ocean circulation are approximately symmetrical on either side of the ITCZ.
• Major deserts are found at 30 latitude, where downward airflow brings dry air, leading to little rainfall and significant evaporation.
• Ocean/seas alongside deserts have higher salinity due to high evaporation and low rainfall.

Ocean Currents

• Ocean currents are continuous, predictable, directional movements of seawater driven by gravity, wind (Coriolis Effect), and water density.
• Ocean water moves horizontally (currents) and vertically (upwellings or downwellings).
• This abiotic system transfers heat, influences biodiversity, and affects Earth’s climate system.

3 Causes of Currents

1. Wind:
   • Wind blowing long enough in one direction causes a water current to develop.
   • The current flows until internal friction or friction with the sea floor dissipates its energy.
2. Changes in sea level:
   • Sea level is the average height of the sea’s surface.
   • Ocean circulation causes slopes to develop, creating pressure gradient force.
3. Variations in water density:
   • Differences in water density cause horizontal differences in water pressure.
   • Higher density initiates a current that flows below the surface.

Winds Drive Currents

• Wind drives major ocean currents due to the rising and falling of warm and cool air.
• Water flows in the same direction as the wind.

Gyres

• The combination of westerlies, trade winds, and the Coriolis effect results in circular flow in each ocean basin, called a gyre.
• Five major gyres:
  1. North Atlantic Gyre
  2. South Atlantic Gyre
  3. North Pacific Gyre
  4. South Pacific Gyre
  5. Indian Ocean Gyre
• The flow of currents is a balance of pressure gradient force, friction, and the Coriolis effect.

Subtropical Gyres

• Large rotating currents starting near the equator.
• Play an important role in moderating climate by transferring heat from the equator towards the poles.
• Responsible for concentrating plastic trash in certain areas of the ocean.

The Ekman Transport

• Discovered by Fridtjof Nansen.
• The wind and the Coriolis effect influence water below the surface.
• Upper water currents push the deep water below it, creating a spiral motion.
• Each water layer flows to the right of the layer above (to the left in the Southern Hemisphere).
• Ekman spiral: Spiraling effect of water layers.
• Ekman transport: Net motion imparted to the water column down to friction depth.
• The net effect is to move water 90° to the right of the wind in the Northern Hemisphere or to the left in the Southern Hemisphere.

Western and Eastern Boundary Currents

• Satellite images show the oceans are