Ocean currents

Based on the students’ water sample data, which factor most likely caused the deeper water sample to have a higher density?

• It was collected earlier in the day

• It had a higher salinity

• It was exposed to more sunlight

• It had less dissolved oxygen

During the tray experiment, warm water rose and moved across the surface. Which change would most reduce this convection pattern?

• Make the warm side only slightly warmer — the smaller temperature gap weakens density differences.

• Add food coloring only to the warm side — color changes but density does not.

• Stir the tray once — mixing resets, but temperature differences return quickly.

• Use a deeper tray — depth changes shape, not the temperature difference.

Use Table 1. If the shore sample cooled to 20°C but salinity stayed the same, what change in density would you expect?

• Density increases

• Density decreases

• Density stays exactly the same

• Density first increases then decreases

Which observations from the passage support the idea that temperature affects water movement? (select all options that apply)

• Warm-colored drop spread across the surface

• Cold-colored drop sank and moved along the bottom

• Shallow shore water had lower salinity

• Deeper water sample felt heavier when poured

A student models the poles by placing ice cubes on one end of the tray. Which outcomes would you expect? (select all options that apply)

• Faster sinking of water near the ice

• Slower movement of warm water on the opposite side

• Warmer water rising more quickly

• No density differences remaining in the tray

True or false- In the passage, salinity and temperature both influence water density.

• True

• False

True or false- If the students heated both sides of the tray equally, warm water would still rise on one side and sink on the other.

• True

• False

Using both tables, explain why currents at the equator tend to move along the surface while currents near the poles tend to move deeper.

Imagine a coastline where freshwater from a river mixes with cold, salty ocean water. Predict how the currents near the river mouth might form and justify your reasoning.

Match the following-

• Greater salinity increases density

• Deeper sample showed higher density

• Temperature difference drives convection

• Cold water sinks quickly

• Colder water is heavier

• Warm surface water moves away from heat source