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?

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

   • No; ice has no effect on salinity
   • 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
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; tides drive the deep water
   • No; Earth's spin by itself drives them
   • No; density differences from temperature and salinity drive them
   • Correct; wind pushes the water thousands of meters down to the floor
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 32 years
   • About 3,200 years
   • About 0.32 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 10.4 km
   • About 1,040 km
   • About 104 km
   • About 120 cm
7. 6.

   Example data: surface water moves 100 cm a second and deep water 2 cm a second. Over 1,000 km, how many more days does the deep water take, by Noah's math?

   • About 11.6 more days
   • About 98 more days
   • About 5,670 more days
   • About 567 more days
8. 7.

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

   • Fresh meltwater sinking fastest
   • Warm water near the equator sinking fast
   • Strong winds blowing at the surface
   • Cold, salty, dense water flowing south along the deep western Atlantic
9. 8.

   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 salinity drops as more ice forms
   • The saltier, colder water sinks
   • The water rises toward the ice
   • Nothing, since salt does not change density
10. 9.

    The global conveyor drawn on a world map. Which summary of thermohaline circulation fits NOAA, by Zee's reading?

    • Warm, fresh water sinks at the equator, then rises again near the poles
    • Sea ice freshens the water so it sinks
    • Cold, salty water sinks near the poles, flows deep and rises far away
    • Wind pushes the water to the bottom
11. 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
    • Deep flow is faster than surface currents
    • Deep flow loops in about 10 years
    • Both move about 1 cm a year