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Weather Lab 6-8 / Week 10 / Wednesday
3/6
Week 10 · Oceans, Currents and Climate Zones

Wednesday

Station Lab: Sinking water
// How moving water shapes the climate of a place
⏱ about 20 min

Wednesday: Station Lab: Sinking Water

Raven sets a tall clear jar of water on the Station Rooftop table. Next to it sit a cup of ice, a salt shaker and blue food coloring.

"Today we make a tiny North Atlantic," she says.

Rocket is already stirring. "Cold plus salt plus blue. Then I pour it in and it goes... where?"

"Predict first, then pour," Raven says. "What do you notice about how the blue moves?"

Nova hovers above the jar and lowers a thin beam of light into the water. "Watch the walls of the jar, not just the top," she hints.

Rocket tips the cup. A blue ribbon slides down the glass and pools at the bottom like a cold river.

"The conveyor belt," he whispers. "In a jar."

Your mission

You will test whether cold, salty water sinks below room-temperature water, the way NOAA describes near the poles.

Then you will test warm fresh water the same way and compare. Record what you see in the table.

  • A tall clear jar or glass, filled with room-temperature tap water
  • Two small cups
  • Ice cubes and a few spoonfuls of salt
  • Food coloring (two colors if you have them)
  • A spoon and a towel for spills
  • Your station log and a pencil
Safety first
A grown-up handles any warm water. Warm tap water is enough; never use hot water from a kettle or stove.
Nothing in this lab is tasted or drunk. Salt water and food coloring stay out of mouths.
Food coloring stains. Work on a towel or tray and wipe spills right away.
  1. Fill the jar with room-temperature water and let it sit still for five minutes.
  2. In the first cup, stir two spoonfuls of salt into a little ice water until most of the salt dissolves. Add a few drops of food coloring.
  3. Predict: will the cold, salty water sink, float on top or mix evenly? Write your prediction in the table.
  4. Tip the jar slightly. Pour one spoonful of the cold, salty water slowly down the inside wall.
  5. Watch for two minutes. Where does the color go? Draw what you see.
  6. Ask a grown-up to fill the second cup with warm tap water. Add a different color, with no salt.
  7. Pour one spoonful down the wall of the jar the same way. Watch for two minutes and record.
  8. Leave the jar for ten minutes. Then look again and record any change.
TestMy predictionWhat I saw at 2 minutesWhat I saw at 10 minutes
Cold, salty, colored water
Warm, fresh, colored water
PREDICT BEFORE YOU POUR
  • Read the question.
  • Tap your answer.
NOAA says saltier, colder water is denser. Where do you predict the cold, salty water will go?

What the jar shows

Near the poles, sea ice forms and leaves its salt behind. The water around it gets colder and saltier, so it sinks.

Your cold, salty water is a model of that polar water. The jar is a model of the ocean.

Warm water is less dense, so it tends to spread near the top instead of diving to the bottom.

A model is never the whole ocean. The real conveyor belt takes about 1,000 years, not two minutes.

What the lab showsTrue or false?
Cold, salty water is denser than room-temperature fresh water.?
Denser water tends to sink.?
The jar shows exactly how fast the real ocean moves.?
Near the poles, forming sea ice leaves salt behind in the water.?
WHY THIS EXERCISESinking dense water is the engine that starts the global conveyor belt.
When sea ice forms, the ____ is left behind in the water.
Cold, salty water is more ____ than warm fresh water. (Hint: it means heavier for its size.)

From the jar to the planet

In the real ocean, the sinking happens near the pole in the North Atlantic and in places off the coast of Antarctica.

Surface water flows in to replace the sinking water. That pull is part of what keeps the conveyor belt moving.

Scientists build models too, from jars like yours to huge computer programs. Models let them test how salt and heat change the currents.

THINK LIKE A MODELER
  • Read the question.
  • Tap your answer.
Your jar stands for the ocean. What does the cold, salty, colored water stand for?
What happens to surface water when dense water sinks below it?
On paper, draw your jar at the 2-minute mark and at the 10-minute mark. Label where each color ended up.
Try it
Save the jar for an hour, then look again. Has the color spread evenly? Think about why mixing takes time.

Great lab work. Tomorrow you read real climate numbers for four cities.

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