Ocean Circulation & Climate — Drills · Grade 9 Science

Chapter: Oceans, Carbon & Climate

What these drills covers

By the end of Ocean Circulation & Climate you should be able to:

8 questions, multiple choice and written answer, each with a worked explanation.

Vocabulary used: salinity, stratification, heat capacity.

Problem 1

At equal temperature and pressure, increasing salinity generally makes water…
  1. less dense
  2. more dense
  3. massless
  4. always freeze instantly
Answer and explanation

more dense

Dissolved salts generally increase seawater density.

Problem 2

State one limitation of a simple ocean conveyor diagram.
Answer and explanation

It hides variable pathways, mixing, regional differences, and changes over time.

Problem 3

Surface ocean currents are driven mainly by
  1. tides
  2. prevailing winds
  3. earthquakes
  4. the Moon's phases
Answer and explanation

prevailing winds

Wind dragging on the surface sets the large gyres in motion.

Problem 4

Deep ocean circulation is driven by differences in
  1. colour
  2. temperature and salinity, and therefore density
  3. wave height
  4. depth alone
Answer and explanation

temperature and salinity, and therefore density

Cold, salty water is denser and sinks, driving the deep overturning.

Problem 5

A warm current flowing toward a coast tends to make its climate
  1. colder
  2. milder
  3. drier always
  4. unchanged
Answer and explanation

milder

The current carries heat that moderates coastal temperatures.

Problem 6

Water becomes denser when it
  1. warms and freshens
  2. cools and becomes saltier
  3. warms and becomes saltier
  4. is stirred
Answer and explanation

cools and becomes saltier

Both lower temperature and higher salinity increase density.

Problem 7

Explain how sea ice formation contributes to deep ocean circulation.
Answer and explanation

When seawater freezes, most of the salt is excluded from the ice and left in the water below, raising its salinity. That water is also very cold, so it becomes dense enough to sink. The sinking drives the deep limb of the overturning circulation, which is why polar regions are where the deep ocean is renewed.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Why is ocean circulation described as a major part of Earth's climate system?
Answer and explanation

The ocean stores far more heat than the atmosphere and moves it over long distances, so currents redistribute energy from the tropics toward the poles and moderate the climates of coasts they pass. Changes in that circulation therefore change regional climate, which is why it is monitored as closely as the atmosphere.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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