Water that evaporates from the sea rises as vapor, condenses into clouds as it cools, and falls back as rain or snow; water that lands on the ground flows back to the sea through rivers and groundwater.
Sunlight is what keeps this cycle turning, so the Earth's water is neither lost nor gained but simply keeps changing form.
Within the sea, water also moves in great streams called ocean currents: warm currents carry warm water from low to high latitudes, and cold currents carry cold water from high to low latitudes.
As the second diagram shows, in a large Northern Hemisphere ocean a warm current runs along the western edge and a cold current along the eastern edge, so the water turns clockwise.
The Water Cycle
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The water cycle: evaporation from the sea, clouds moving, rain and snow, rivers and groundwater
💧 Water Moves in a Loop, Changing Form
①Water in the sea and on land absorbs the sun's heat and evaporates into vapor
②The vapor rises, cools and condenses into clouds
③When droplets in the clouds grow large enough, they fall as rain or snow
④The water flows back to the sea through rivers and groundwater, and the cycle repeats
Ocean Currents
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The loop formed in a large Northern Hemisphere ocean by a warm current on the western edge and a cold current on the eastern edge
🌊 Great Streams in the Sea
①An ocean current is a large stream of seawater flowing steadily in one direction
②A warm current flows from low latitudes to high latitudes
③A cold current flows from high latitudes to low latitudes
④Currents are driven mainly by steady winds pushing on the sea, and they carry heat that changes the climate of nearby coasts
③Warm currents are warm and flow from low to high latitudes
④Cold currents are cold and flow from high to low latitudes
⑤Examples: the Gulf Stream and the Kuroshio are warm currents; the California Current and the Oyashio are cold currents
Examples and Unit Review
Example 1
List in order the stages water passes through from leaving the sea to returning to it, and name the energy source that drives this cycle.
1
Seawater evaporates into vapor, the vapor condenses into clouds, and rain or snow falls from the clouds.
2
The water flows back to the sea through rivers and groundwater. What evaporates the water and drives the cycle is energy from the sun.
▸ Evaporation → condensation (clouds) → precipitation (rain, snow) → rivers and groundwater → sea; the energy source is the sun
During the cycle water only changes between liquid, gas and solid; the total amount on Earth stays the same.
Example 2
How do warm and cold currents differ in direction and temperature, and what do ocean currents affect?
1
A warm current is a warm stream flowing from low to high latitudes; a cold current is a cold stream flowing from high to low latitudes.
2
Currents carry heat that changes the climate of nearby regions, and where warm and cold currents meet, nutrients gather and rich fishing grounds form.
▸ Warm currents flow from low to high latitudes and are warm; cold currents flow from high to low latitudes and are cold. Currents affect climate and fishing grounds
At the same latitude, a coast with a warm current has milder winters, and a coast with a cold current has cooler summers.
Unit Test
Which statement about the water cycle and ocean currents is correct?
①The energy that drives the water cycle comes from heat inside the Earth
②A warm current flows from high latitudes to low latitudes and is cold
③Water circulates by changing state through evaporation and condensation
④Precipitation is the process where water turns into water vapor
⑤Ocean currents have no effect on climate
▸ ③ Water circulates by changing state through evaporation and condensation
1
The driving force of the water cycle is solar energy (① wrong), and a warm current flows from low to high latitudes and is warm (② wrong).
2
Precipitation is rain or snow falling from clouds (④ wrong), and ocean currents strongly affect climate and fishing grounds (⑤ wrong); water circulates by changing state through evaporation and condensation (③ correct).