Ocean Currents 16.1 assessment

Ocean currents are classified based on which of the following factors?

• Temperature and salinity

• Wind patterns

• Earth's rotation

• All of the above

Answer explanation

Ocean currents are influenced by temperature, salinity, wind patterns, and Earth's rotation. Therefore, the correct classification is 'All of the above' as each factor plays a significant role in their movement.

Which of the following is an example of a surface current that affects coastal climates?

• Gulf Stream

• Amazon River

• Himalayan Glacier

• Sahara Desert

Answer explanation

The Gulf Stream is a warm ocean current that influences coastal climates, particularly in North America and Europe, by moderating temperatures. The other options are not surface currents.

Gyres are large systems of circular ocean currents formed by global wind patterns and forces created by Earth's rotation. Why do they rotate in different directions in the Northern and Southern Hemispheres?

• Due to the Coriolis effect

• Because of the Earth's magnetic field

• As a result of ocean salinity

• Because of the gravitational pull of the moon

Answer explanation

Gyres rotate in different directions in the Northern and Southern Hemispheres due to the Coriolis effect, which is caused by Earth's rotation. This effect deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

What is upwelling, and why is it important for marine ecosystems?

• Upwelling is the process where deep, cold, and nutrient-rich water rises to the surface, supporting marine life.

• Upwelling is the movement of warm surface water to the ocean depths, reducing marine biodiversity.

• Upwelling is the horizontal movement of water across the ocean surface, unrelated to nutrient distribution.

• Upwelling is the process of water evaporation from the ocean surface, affecting weather patterns.

Answer explanation

Upwelling is crucial as it brings nutrient-rich water to the surface, fostering marine life. This process supports diverse ecosystems, making the correct choice the one that highlights its role in enhancing marine biodiversity.

Density currents are formed due to differences in:

• temperature and salinity

• pressure and volume

• wind and humidity

• altitude and latitude

Answer explanation

Density currents are primarily influenced by differences in temperature and salinity. Variations in these factors lead to changes in water density, causing currents to form as denser water sinks and less dense water rises.

How do surface currents differ from density currents?

• Surface currents are primarily driven by wind, while density currents are driven by differences in water density.

• Surface currents occur deep in the ocean, while density currents occur at the surface.

• Surface currents are slower than density currents.

• Surface currents are found only in the Atlantic Ocean, while density currents are found in all oceans.

Answer explanation

Surface currents are primarily driven by wind, causing them to flow along the ocean's surface. In contrast, density currents are influenced by variations in water density, which can occur at different depths.

The role of wind in generating surface currents is:

• to create waves that move water

• to directly push water across the surface

• to have no effect on water movement

• to cool the water surface

Answer explanation

The correct answer is 'to directly push water across the surface' because wind exerts force on the water, causing it to move and generate surface currents, which are essential for ocean circulation.

Temperature and salinity affect density currents by:

• Increasing temperature decreases density, while increasing salinity increases density.

• Increasing temperature increases density, while increasing salinity decreases density.

• Both temperature and salinity increase density.

• Both temperature and salinity decrease density.

Answer explanation

Increasing temperature decreases density because warmer water is less dense. Conversely, increasing salinity increases density as saltwater is denser than freshwater. Thus, the correct choice is that increasing temperature decreases density, while increasing salinity increases density.

The Gulf Stream is a _______.

• river

• ocean current

• mountain range

• desert

Answer explanation

The Gulf Stream is a powerful ocean current in the Atlantic Ocean, known for its warm waters that influence climate. It is not a river, mountain range, or desert, making 'ocean current' the correct choice.

Compare upwelling and downwelling. How are they different?

• Upwelling brings nutrient-rich water to the surface, while downwelling pushes surface water down.

• Upwelling occurs in the deep ocean, while downwelling occurs near the shore.

• Upwelling and downwelling both bring warm water to the surface.

• Upwelling and downwelling are processes that occur only in freshwater bodies.

Answer explanation

Upwelling and downwelling are distinct processes. Upwelling brings nutrient-rich water from the depths to the surface, enhancing productivity, while downwelling involves the sinking of surface water, often leading to nutrient depletion.