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SAMPLE PAPER
3
Level 3 Earth and Space Science
3.4: Demonstrate understanding of processes in the
ocean system
Credits: Four
Check that you have completed ALL parts of the box at the top of this page.
You should answer ALL parts of ALL questions in this booklet.
If you need more room for any answer, use the space provided at the back of this booklet.
Check that this booklet has pages 2–9 in the correct order and that none of these pages is blank.
YOU MUST HAND THIS BOOKLET TO YOUR TEACHER AT THE END OF THE ALLOTTED TIME.
EXEMPLAR FOR EXCELLENCE
NOTE: These exemplars do not fully show Grade Score Marking (GSM) because
of the small sample of student scripts involved, and the absence of a cut score
OF PERFORMANCE
meeting toOVERALL
determine LEVEL
grade boundaries.
GSM can be seen in the level 1 and level 2
exemplars from the 2012 examinations, which will be published on the NZQA website
when the assessment schedules are published.
© New Zealand Qualifications Authority, 2012
All rights reserved. No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.
2
You are advised to spend 60 minutes answering the questions in this booklet.
QUESTION ONE: THERMOHALINE CIRCULATION
Thermohaline circulation is the large-scale movement of water due to temperature and
salinity gradients.
http://www.shorstmeyer.com/msj/geo130/conveyor/conveyor.html
Discuss the transport of heat and water in the thermohaline circulation.
Your answer should include:
• how temperature affects the density of water
• how salinity affects the density of water
• effects of temperature and salinity differences on the circulation of water around the oceans.
Thermohaline circulation is global movement of water due to differences in temperature and
salinity of different parts of the oceans. Both temperature and salinity affect the density of
water.
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Warmer water is less dense than cold water and will rise as a result. Warm water is less
dense because the water particles are further apart therefore there are fewer particles in a
set volume.
The effect of salinity on the oceans is that the higher the salinity the denser, therefore the
dense salty water will sink. A high salinity is when there is a high concentration of salt
particles.
Both temperature and salinity are factors in the movement of the oceans in the thermohaline
circulation. Nearest the equator there is greater heat energy from the sun, which heats the
ocean, making it less dense. This results in the warm shallow currents. The water then flows
to the North Atlantic where surface cooling occurs because heat is lost to the atmosphere.
This results in the water becoming denser and therefore sinking. The water then flows
towards the Antarctic region where the salinity increases due to the freezing of water.
When water freezes the salt does not freeze and remains in the surrounding solution,
therefore increasing the salinity of the liquid water. This makes the water very dense as it is
both cold and has a high salinity, resulting in a very deep current. This deep current then
moves towards the tropical regions because the water in the tropical region has moved
because it has become less dense due to the heating from the sun. Also important is the
mixing of the deep salty current with the fresh waters from the melting ice.
The interaction of both temperature and salinity result in the global circulation of water in
the oceans.
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QUESTION TWO: CARBON CYCLE
The carbon cycle involves the atmosphere and the oceans. The oceans contain 50 times
more CO2 than the atmosphere.
Discuss how physical (solubility) and biological pumps work to cycle the CO2 in the oceans:
• explanation of physical and biological pumps
• how physical and biological pumps contribute to the movement of carbon in the oceans.
You may draw a labelled diagram in the box provided to support your answer.
The biological pump results in both organic and inorganic carbon in the oceans. All the living
organisms in the ocean contain organic carbon in their tissues. When they die they sink to the
ocean floor, removing carbon from the cycle. Some living organisms take up carbon dioxide,
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which they use to make carbonate shells and structure (inorganic carbon). This removes the
carbon dioxide from the surface waters and takes it to the deep water layers where it is
locked up for an extended time. Some of the locked up carbon can be reintroduced into the
physical pump by microorganisms.
The physical pump relies on the solubility of CO2 in different temperatures of water. At the
poles the water temperature is less so more CO2 from the atmosphere is dissolved in the
surface water. This sinks to the ocean floor in a type of vertical circulation. The water that
replaces the sinking CO2-rich water will now be at the surface where it can dissolve further
CO2 from the atmosphere. When the cold water moves towards the equator it will rise and
become warmer, releasing CO2 back into the atmosphere. The physical mixing of the oceans is
also important to the carbon cycle in the ocean. This occurs when warm water in surface
ocean currents travels to higher latitudes where it cools, causing the water to sink. This
results in the global movement of CO2 in the oceans. This global movement of CO2 is driven by
Thermohaline circulation.
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QUESTION THREE: LAYERING IN THE OCEAN
The oceans have three major layers. They are the mixed layer, the pycnocline (barrier
layer) and the deep layer.
http://oceanmotion.org/html/background/ocean-vertical-structure.htm
Discuss the key processes affecting each layer and how they interact with each other.
Your answer should include:
• the properties of each layer
• the transport of energy and matter
• the interaction of the three layers.
You may draw a labelled diagram in the box provided to support your answer.
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The mixed layer at the surface is where wind driven surface currents occur. These surface currents
are changeable: they are influenced by changes in the wind, precipitation and temperature
changes. These processes cause dynamic change. This layer is not very deep, generally not greater
than 100 m. The wind stirs the surface waters resulting in a well mixed layer of uniform density.
The pycnocline is the middle layer between the mixed and deep layers. It typically extends from 500
m to 1 000 m and is very stable. Water density changes rapidly through the pycnocline with depth.
This density change is a result of temperature and/or salinity. If the density change is a result of a
rapid change in temperature it is referred to as a thermocline, whereas if the density change is a
result of a rapid change in salinity it is referred to as a halocline. A thermocline is when the
temperature decreases rapidly with depth, whereas the halocline increases salinity with depth.
The deep layer is below the pycnocline and is cold, dark and stable. Most of the ocean is deep
layer. In this layer density increase gradually increases with depth and water only moves slowly in
this layer. There are not many currents in this layer.
The three layers exist due to gravitational separation in which the density of a layer is less than the
density of the layer below.
As the pycnocline is very stable it acts as a barrier, supressing mixing between the mixed and deep
layers. There is no interaction between the deep layer and the other two layers because the
pycnocline prevents vertical motion within the ocean. Very strong winds can cause temporary
mixing of the top two layers. But the original layered structure will rapidly re-establish when the
winds drop.
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