BAESI
Name _______________________________
Modeling the Formation of Deep Ocean Water
Supplies for each group
Shoebox
Tap water
Paper cups (4)
Plastic cup with blue, salty, icy water
Plastic cup with red, fresh, icy water
Clips (2)
Extras: cups of salt, tap water, ice; food coloring, 2 one-liter beakers, 2 60-ml cups,
coffee stirrers
A. Effects of salinity and temperature.
1. Fill a shoebox about halfway with tap water. This will represent fresh water.
2. Use a pencil to poke a hole in the bottom of two paper cups and clip the cups to
the shoebox so that the bottoms of the cups are just above the level of the water in
the box.
Paper cups
wy
Water
3. Pour a small amount of the blue, salty, icy water into one of the paper cups.
Describe your observations:
4. Now pour a small amount of the red, fresh, icy water into the other paper cup.
Describe your observations:
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5. Place the waters in order of increasing density: cold/salty; warm/fresh; cold/fresh
Lowest density: _________________________________________________
Intermediate density: ____________________________________________
Highest density: _________________________________________________
6. How does salinity affect density?
7. How does temperature affect density?
B. Oceans and Climate: How Could Warming Cause Cooling?
Refer to article below to answer the questions.
1. What is the Great Ocean Conveyor Belt and what drives it?
2. What keeps Europe's winters relatively mild?
3. Where on Earth is the coldest and saltiest water found?
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4. How long does dense water remain on the ocean floor?
5. How might global warming shut down the Conveyor?
6. How could the collapse of the Great Ocean Conveyor Belt due to global warming
lead to cooler temperatures in Europe?
The Great Ocean Conveyor Belt
Source: http://www.pbs.org/wnet/savageseas/weather-article.html
El Niño has strong effects on weather and climate measured on a scale of months. But
broad circulation patterns in the world's oceans also control climate patterns on a scale of
decades to centuries. In fact, Europeans may owe their very existence to heat transported
to the North Atlantic by a global system of currents known as the Great Ocean
Conveyor Belt.
NASA
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Unlike most ocean currents, which are driven by surface winds, the flow of the Conveyor
Belt is driven by differences in the temperature and salinity of seawater. Cold, salty water
sinks; warm, less salty water stays on the surface. This sets up a system of interconnected
deep and shallow currents that transport heat from the tropics to higher latitudes. The
Gulf Stream, for instance, is part of the Conveyor Belt. It helps to ferry heat to the North
Atlantic that keeps Europe's winters relatively mild. Without the Conveyor Belt, the city
of Dublin would have an Arctic climate and much of the rest of Europe would be too
frigid for trees to grow.
The Conveyor Belt begins in the North Atlantic. There the water grows colder and saltier
and sinks. This feeds a sluggish mass called the North Atlantic Deep Water.
With a flow 20 times that of all the world's rivers combined, the deep water flows
southward over the ocean floor. The flow is vast, but not swift: Once deep water forms, it
may not touch the open air again for 1000 years.
The flow surfaces again around Antarctica, where it is chilled
again. Ultimately, it surfaces in the Indian and Pacific Oceans
and then flows back north into the South Atlantic and
eventually into the North Atlantic. The heat it carries warms
the frigid, eastward moving air masses from Canada,
Greenland, and Iceland. This flow of ocean-warmed air helps
keep the winter climate of Europe balmier than at equivalent
latitudes in North America.
The Great Conveyor Crash?
Some scientists are concerned that polar
ice will melt, with potentially disastrous
effects across the globe.
The Great Ocean Conveyor Belt is mighty, but it is not invincible. Some scientists
believe that it may be vulnerable to the effects of global climate change, whether natural
or manmade. Computer simulations suggest that if the North Atlantic warmed just
slightly, or were diluted by freshwater from increased rainfall or melting continental
glaciers, the formation of deep water might decrease enough to shut down the conveyor.
Both effects -- warming or dilution -- are possible consequences of global warming.
Global average temperatures are now on the rise. Scientists are still struggling to figure
out how much of the rise is natural -- part of the ceaseless cycles of climate on Earth -and how much is the result of the burning of fossil fuels and other human activities.
Either way, scientists are closely watching the polar regions for signs of trouble. The
trouble could show up as a decline in the amount of sea ice in the Arctic or crumbling ice
sheets in the Antarctic -- both could prove to be the early warning signs of harmful global
warming, like the proverbial canary in a coal mine.
-- By Daniel Pendick
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C. Introducing more inquiry
Using the “extra” materials provided, design an experiment to satisfy a question and/or
curiosity that has arisen during parts A & B.
1. Describe your question / curiosity.
2. Design your experiment.
3. Describe your observations.
4. What is the result of your experiment? In other words, how does it answer (or not)
your original question?
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D. Extension: All kinds of salinity.
Source: http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/ocean_basics/hot_cold_lesson.html
Note: Ocean salinity is measured in parts per thousand (‰, “per mil”) or g/L.
A per mil is defined as:
1‰ = 10−3= 1⁄1000 = 0.001 = 0.1%
1% = 10‰
8.75 ‰ salinity
35 ‰ salinity
120 ‰ salinity
8.75 g salt / L water
35 g salt / L water
120 g salt / L water
0.31 oz salt / L water
1.23 oz salt / L water
4.23 oz salt / L water
1. Make a liter of “regular” (35‰) seawater. Use the 60 ml (2 oz) cup, the 1 L (1000 ml)
beaker, and the conversion table to create your mixture and pour it into the shoebox.
2. If you are a “not-so-salty” group, make a liter of seawater that is ¼ as salty as
“normal” sea water (8.75 ‰). Color this solution red.
3. If you are a “super salty” group, make a liter of seawater that is about 4 times as salty
as “normal” sea water (120 ‰). Color this solution blue.
4. Share half of your solution with a group that has made the other solution: Pour half of
your solution into their empty 1L beaker. Pour half of their solution into your empty 1L
beaker.
5. Record your predictions about what will happen when you mix the hypertonic (more
saline than seawater) and the hypotonic (less saline than seawater) solutions into your
shoebox.
6. Take your two paper cups (with small holes poked in the bottom) and clip them to the
side of the shoebox, so the bottom of each cup is just above the water level. Pour the red
and blue solutions separately into each cup.
7. Record your observations.
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8. Were the salinity differences between your solutions enough to create “density
stratification” (or “density layering”) in your shoebox ocean? If so, how many layers did
you observe?
9. Look at the map of sea-surface salinity from the World Ocean Atlas 2005.
What is the range of salinity?
How does this compare to the range of salinity you used in the experiment?
Do you think the salinity differences shown on the map are enough to create density
layers in the ocean? If not, what other variable would help?
How could you, in your shoebox model, test what is the smallest salinity difference
needed to create density layers?
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10. After analyzing a map of sea surface salinity, you may be curious what the salinity
range is for the deep ocean. Here is a map that shows a vertical slice through the Atlantic
Ocean, all the way from the Arctic Ocean to Antarctica. These are typical salinity values
for the deep ocean.
The arrows mark the flow of deep currents (not surface currents). How many deep
currents do you see? What is their density difference?
11. Below is a diagram (Siedler, 2001) that shows the complexity of deep-ocean currents
around the Antarctic continent. The “Great Ocean Conveyer Belt” is more complicated
than a simple “one-deep, one-shallow” model. As observed in your experiments, you can
create more than two density layers in your shoebox, through a range of temperature and
salinity differences. The same is true for the real ocean.
How many density layers are shown in the diagram?
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