Deep ocean currents: cold, salty water sinks

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   A classmate says warm water sinks because it is heavier. Which reply fits NOAA, by Esme's reading?

   • Correct; warm water sinks at the poles and then spreads out
   • Correct; warmth adds weight
   • No; warm water is less dense and stays near the surface
   • No; warm, fresh water sinks fastest
2. 2.

   Sea ice forming above saltier, sinking water. A student says freezing sea ice makes nearby water fresher. Which reply fits NOAA, by Jun's reading?

   • Correct; the ice takes up the salt
   • No; the salt is left behind, so nearby water gets saltier
   • Correct; the ice melts as it forms
   • No; ice has no effect on salinity
3. 3.

   Wind arrows above, density arrows far below. A student says deep ocean currents are driven by wind, like surface ones. Which reply fits NOAA, by Kira's reading?

   • Correct; wind pushes the water thousands of meters down to the floor
   • No; Earth's spin by itself drives them
   • Correct; tides drive the deep water
   • No; density differences from temperature and salinity drive them
5. 4.

   Water moves 2 cm a second (example data). About how many years does it take to travel 20,000 km, by Luz's math?

   • About 3,200 years
   • About 0.32 years
   • About 32 years
   • About 10,000 years
6. 5.

   A deep current moves 4 cm a second (example data). How far does it go in 30 days, by Milo's math?

   Use the picture in question 4.

   • About 104 km
   • About 120 cm
   • About 1,040 km
   • About 10.4 km
7. 6.

   Four evidence cards, labeled A to D. Which evidence best shows deep water sinks near the poles, by Pia's reading (NOAA)?

   • Cold, salty, dense water flowing south along the deep western Atlantic
   • Warm water near the equator sinking fast
   • Fresh meltwater sinking fastest
   • Strong winds blowing at the surface
8. 7.

   Sea ice forming above saltier, sinking water. Model data: sea ice forms over a basin, and the salinity beneath it climbs from 34 to 35 g/kg. What should happen next, by Ren's reading?

   • The saltier, colder water sinks
   • The water rises toward the ice
   • The salinity drops as more ice forms
   • Nothing, since salt does not change density

9. Read this first

   Use this

   The global conveyor drawn on a world map.

10. 8.

    Which claim about the conveyor do NOAA's figures support, by Tala's reading?

    • It moves a small volume quickly, looping in about a single year
    • It starts near the equator
    • It is driven by surface wind by itself
    • It moves a huge volume slowly, about 1,000 years a loop
11. 9.

    Which summary of the conveyor's route fits NOAA, by Ari's reading?

    • Runs one small loop in a single ocean
    • Sinks at Antarctica and rises in the North Atlantic, by itself
    • Sinks in the North Atlantic, flows to Antarctica, then rises in other oceans
    • Sinks at the equator, flows north, and rises in the Arctic
12. 10.

    Which summary of the speeds fits NOAA, by Bo's reading?

    • Deep flow is a few cm a second; surface currents are tens to hundreds
    • Both move about 1 cm a year
    • Deep flow loops in about 10 years
    • Deep flow is faster than surface currents