Deep ocean currents: cold, salty water sinks

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Water samples (model data)

   Sample	Temperature	Salinity
   A	2 °C	35 g/kg
   B	2 °C	33 g/kg
   C	20 °C	35 g/kg
   D	20 °C	33 g/kg

2. 1.

   Using the sample table, which water would sink below the others, by Bo's reading?

   • D, the warmest and freshest
   • B, cold and fresher
   • A, the coldest and saltiest
   • C, warm and salty
3. 2.

   Using the sample table, which water would stay at the surface, by Esme's reading?

   • C, warm and salty
   • B, cold and fresher
   • D, warm and fresher
   • A, cold and salty

4. Use this

   The global conveyor drawn on a world map.

5. 3.

   After sinking in the North Atlantic, which way does the deep water flow, by Kira's reading (NOAA)?

   • Straight up to the surface
   • North, toward the Arctic
   • South, past the equator, toward Antarctica
   • East, across the Atlantic into a closed inland sea
6. 4.

   Where do branches of the conveyor rise back toward the surface, by Luz's reading (NOAA)?

   • Near the poles, where they cool
   • In the Indian and Pacific Oceans, as they warm
   • They stay deep for good
   • At the conveyor's North Atlantic start, where they cool
7. 5.

   NOAA: cold bottom water returns to the surface through mixing and wind-driven upwelling. Why must it come back up, by Milo's reading?

   • Deep water evaporates
   • Surface water keeps sinking, so deep water rises to close the loop
   • Deep water stays below for good
   • Deep water warms at the bottom and boils
9. 6.

   A deep current moves 3 cm a second (example data). How far does it go in one day, by Noah's math?

   • About 260 m
   • About 72 cm
   • About 26 km
   • About 2.6 km
10. 7.

    At about 2.6 km a day, about how far does that current go in a year, by Pia's math?

    Use the picture in question 6.

    • About 95 km
    • About 950 km
    • About 2.6 km
    • About 9,500 km
12. 8.

    NOAA: a loop takes about 1,000 years. If a parcel covers 60,000 km in that time (example), what is its average speed, by Ren's math?

    • About 60 km a year
    • About 60,000,000 km a year
    • About 6 km a year
    • About 60 km a day
13. 9.

    NOAA: wind and tidal currents move tens to hundreds of cm a second. How does a 3 cm/s deep current compare with a 100 cm/s surface current, by Tala's math?

    Use the picture in question 8.

    • The deep current is about 33 times faster
    • The surface current is 97 times faster
    • The surface current is about 33 times faster
    • They are about equal
14. 10.

    The global conveyor drawn on a world map. NOAA: warm surface waters are low in nutrients, and deep water in the conveyor is enriched again. Why are upwelling zones rich in algae, by Ari's reading?

    • Sinking water carries algae down
    • Sea ice adds nutrients as it forms
    • Warm surface water holds the most nutrients
    • Rising deep water brings nutrients back to the sunlit surface