Deep Ocean Currents
Dana Desonie, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2013 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including
CK-12 Curriculum Material) is made available to Users
in accordance with the Creative Commons Attribution/NonCommercial/Share Alike 3.0 Unported (CC BY-NC-SA) License
(http://creativecommons.org/licenses/by-nc-sa/3.0/), as amended
and updated by Creative Commons from time to time (the “CC
License”), which is incorporated herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: May 13, 2013
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C ONCEPT
Concept 1. Deep Ocean Currents
1
Deep Ocean Currents
• Describe the processes that drive deep ocean currents.
Why do small fish live in upwelling zones?
Seawater is always on the move. Water that comes up to the surface from deep is rich with nutrients. Plankton gather
where nutrients are plentiful. Small fish come to eat the plankton. Of course, larger fish and birds come to eat the
smaller fish. So upwelling is responsible for an abundance of life.
Deep Currents
Currents also flow deep below the surface of the ocean. Deep currents are caused by differences in density at the
top and bottom. More dense water takes up less space than less dense water. It has the same mass but less volume.
Water that is more dense sinks. Less dense water rises. What can make water more dense?
Downwelling
Water becomes more dense when it is colder and when it has more salt. In the North Atlantic Ocean, cold winds chill
the water at the surface. Sea ice grows in this cold water, but ice is created from fresh water. The salt is left behind
in the seawater. This cold, salty water is very dense, so it sinks to the bottom of the North Atlantic. Downwelling
can take place in other places where surface water becomes very dense (Figure 1.1).
When water sinks it pushes deep water along at the bottom of the ocean. This water circulates through all of the
ocean basins in deep currents.
Upwelling
Sometimes deep ocean water rises to the surface. This is called upwelling. The figure below shows why it happens
(Figure 1.2). Strong winds blow surface water away from shore. This allows deeper water to flow to the surface and
1
www.ck12.org
FIGURE 1.1
Deep currents flow because of differences
in density of ocean water.
take its place.
FIGURE 1.2
An upwelling occurs when deep ocean
water rises to the surface.
When water comes up from the deep, it brings a lot of nutrients with it. Why is deep water so full of nutrients? Over
time, dead organisms and other organic matter settle to the bottom water and collect. The nutrient-rich water that
comes to the surface by upwelling supports many living things.
An animation of upwelling is seen here: http://oceanservice.noaa.gov/education/kits/currents/03coastal4.html.
Upwelling also takes place along the equator. Winds blow the surface water north and south. This leaves a void that
deep water can upwell into. The nutrients rise to the surface and support a great deal of life in the equatorial oceans.
2
www.ck12.org
Concept 1. Deep Ocean Currents
Vocabulary
• deep currents: Ocean currents that travel vertically up and down; this water also travels deeper in the ocean.
• downwelling: Ocean water that sinks due to higher density.
• upwelling: Cold, nutrient-rich water that rises from oceanic depths.
Summary
• Cooling or evaporation of fresh water from the sea surface makes surface water dense. This causes the surface
water to undergo downwelling.
• Downwelling of cold, dense water pushes deep water along. This drives thermohaline circulation.
• Upwelling takes place at some coastlines or along the equator. Upwelling brings cool, nutrient-rich water to
the surface.
Practice
Use the resource below to answer the questions that follow.
• Ocean Odyessey-Density Current at http://www.youtube.com/watch?v=FuOX23yXhZ8 (2:39)
MEDIA
Click image to the left for more content.
1.
2.
3.
4.
5.
6.
7.
How does temperature affect the density of water?
How does salinity affect density?
What does the density difference create?
Where is the NADW?
Where is the AABW?
How long does it take a water molecule to complete the circuit of the global conveyor belt?
What is an upwelling? What does it do?
Review
1. Why is upwelling important?
2. What causes downwelling?
3. How are deep currents created?
References
1. CK-12 Foundation - Christopher Auyeung. . CC-BY-NC-SA 3.0
2. CK-12 Foundation - Hana Zavadska. . CC-BY-NC-SA 3.0
3