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Changing World Oceans
Lab Report
Introduction
We investigated the phenomenon of ocean acidification. Ocean acidification is a
process by which the pH of the ocean decreases. Ocean acidification is an important topic to
study because not only does it affect marine organisms1,2, it also affects human populations by
reducing food resources. Recent studies have come to light indicating that the rate of ocean
acidification is ten times more than previously thought3.
Ocean acidification occurs when elevated carbon dioxide concentrations appear in the
atmosphere. This
high concentration
of atmospheric CO2
increases the
diffusion of CO2 into
the world oceans.
Once in the ocean,
several steps occur,
creating conditions
which have been
shown to
negatively affect
marine organisms
like pteropods3. The steps are outlined in Figure 1. First, carbonic acid is formed, then the
hydrogen ions dissociate (break free from the carbonic acid molecule). The excess hydrogen
ions then bind to free carbonate ions. These carbonate ions are used by shellfish and other
organisms like coccolithophorids, which is a phytoplankter. When the carbonate ions become
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scarce, the organisms may not be able to effectively build their shells, rendering them adapted
to their environment.
In the first part of our experiment we modeled the interaction of the atmosphere (with
an increased concentration of CO2) and the hydrosphere into where the CO2 dissolved. We
monitored pH changes in buffered and unbuffered water samples. In the second part we
tested the effect of acid on sea shells, using vinegar, and in the third part we tested the effect
of acid on proteins using qualitative comparisons by placing fish muscle tissue in lemon juice.
Our hypotheses for these experimental parts were as follows in Table 1.
Table 1. The statistical hypotheses we tested for the 3 parts of the lab activity.
1 If the carbon dioxide content increases in the air then it will diffuse into the water
2 If acids are added to buffered and unbuffered solutions then the solution with the buffer
will change (decrease) a smaller amount than the unbuffered solution.
3 If the shells are affected by acidic environments then the shells will lose mass when placed
in acid
4 If proteins are affected by acidic environments then fish filets placed in acid will change
their appearance
Materials and Methods
We used the following materials for the 3 parts of the lab in Table 2.
Table 2. The materials used in the ocean acidification lab activities.
Vinegar
Baking soda
Scoopula
1-L container
Fish tank air hose tubing
Duct tape
Clear plastic bin or 5L fish tank pH strips or pH probes (2)
CO2 probe
Masking tape / marker
15cm (6in) pie tins (4)
Deionized water (1L)
Deionized water wash bottle
500ml beaker (waste water)
Graduated cylinder
Balance
Waxed paper
Forceps
Sea shells (various sizes) (3)
Raw fish filet (1X2X1 cm)
Lemon juice
Paper towels
Styrofoam cups
We constructed a tank modeling the atmosphere / hydrosphere interface as shown in Figures 2
and 3. We mixed baking soda and vinegar to create a source of carbon dioxide and fed the gas
into the tank using the aquarium tubing. The pie tins and pH probes were secured using tape
and cut styrofoam cups. The carbon dioxide probe rested on the lab table. A data recorder was
connected to the probe sensors. Baking soda and vinegar were added periodically to maintain
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a high concentration of carbon dioxide in the enclosed area. Duct tape was used to seal the gap
between the tank and the table created by the tubes going into the tank.
Carbon dioxide concentration and pH
data were collected continuously for 30
minutes. During the waiting period, sea shells were massed and put into vinegar. Observations
were made and then the samples soaked overnight. Ending mass was recorded the next day. A
1x2x1 cm block of fish filet was cut, qualitative observations were made and the fish massed
then placed in another pie tin. Lemon juice was added to completely submerge the fish and the
sample was set aside for overnight soaking. Ending observations were made the next day.
Graphs were constructed from pooled classroom data in an Excel spreadsheet and
before and after mean mass statistical comparisons made using t-tests which the teacher
performed. Pooling the data allowed for multiple measurements and statistical testing.
Results
Part 1: Atmosphere / hydrosphere interactions
The experimental setup successfully raised the CO2 concentration in the tank from 250
to 8417 ppm with the last 10 minutes ranging from 4000 to 6000ppm (Figure 4). The pulsed
increases in CO2 were a result of adding more baking soda and vinegar to the 1L bottle.
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The pH of the
buffered and
unbuffered water
samples showed
different responses to
the high atmospheric
carbon dioxide. The
pH from the
unbuffered water
sample dropped from
7.9 to 7.4 while the
pH from the buffered
solution stayed
relatively steady
maintaining a pH of
8.2 throughout most of the trial period (Figure 5).
In using classroom
data and comparing the
beginning and ending pH
readings of buffered and
unbuffered water, there
was a difference in the two
water samples. Paired ttests revealed a significant
change for the buffered
water (t(4) = 18.99, p <
.001), however there was
no significant change for
the unbuffered water
(t(4)=1.00,p=0.37) (Table 3).
When shells were exposed to an acidic environment they lost mass (Table 4).
The acid of the lemon juice changed the consistency of the raw fish. Initially the fish
was flexible and translucent. After soaking the fish overnight in the acid it became more firm
and opaque.
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Table 3. Comparison of the change in pH of buffered and unbuffered conditions.
Group
Unbuffered
Beg.
1
2
3
4
5
6
Average
SD
95% Confidence
7.9
7.8
7.7
7.9
7.7
7.6
7.77
End
7.4
7.5
7.3
7.5
7.3
7.2
7.37
Buffered
Diff.
-0.5
-0.3
-0.4
-0.4
-0.4
-0.4
-0.40
0.06
0.05
Beg.
8.2
8.1
8.3
8.2
8.1
8.2
8.18
End
8.2
8.2
8.2
8.1
8.0
8.2
8.15
Diff.
0.0
0.1
-0.1
-0.1
-0.1
0.0
-0.03
0.08
0.07
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Discussion
We set out to investigate the carbon dioxide interactions between the atmosphere and
hydrosphere and to see the chemical and biological effects of such interactions. We
successfully created a high concentration of carbon dioxide in our model atmosphere. This high
concentration of CO2 diffused into the water samples and decreased the pH of the unbuffered
water sample, which mimicked the process of ocean acidification and supported our first
hypothesis. Our second hypothesis was also supported. The buffered water sample showed no
change in pH, indicating the importance of having buffers in a solution to protect from pH
changes. This is in contrast to the unbuffered water sample which significantly decreased in
pH. Our third hypothesis was also supported by the data. Even though we used a variety of
shell species, they all lost mass to a greater or lesser extent when exposed to acidic conditions.
Finally for our fourth hypothesis we provided supporting evidence of a qualitative change in the
protein of the fish filet.
Although we attempted to have strict controls of our experiment, we did have some
conditions that may have added to the variability of our data. We did not always put in the
same amount of vinegar and baking soda in the feeder bottle (some spilled) and that may be
why we had such a big spike in the carbon dioxide in the atmosphere at the 15 minute mark of
our sampling.
Our setup was meant to model what is happening in the real world, but some important
differences need to be mentioned. In nature the highest natural carbon dioxide concentrations
are in the 300-400ppm range, we created concentrations much higher than that to ensure we
could see results in a short amount of time. The same could be said for the shells in the
vinegar. The pH of vinegar is ~3 whereas the ocean pH is ~8.0. This exaggerated increase in
acidity allowed us to see the effects on a short time scale. Similarly, the lemon juice pH is 3 and
the effect on proteins was also exaggerated because of the higher ocean pH. This process of
putting fish in lemon juice is known as making ceviche, a Hispanic dish where the fish are
“cooked” in acid instead of cooking with heat. Both processes do the same thing by denaturing
(changing the shape) of the proteins.
Our experimental setup allowed us to see the physical, chemical, and biological effects
of ocean acidification. The acidification of the oceans has already affected marine organisms
like pteropods, which are vital to the food web of the eastern Pacific Ocean where they live.
These marine pelagic mollusk shells get degraded from the low pH conditions found there.
Other studies have shown that conchs cannot escape predators because of neurotransmitter
deficiencies due to conditions of high carbon dioxide2. If similar afflictions affect organisms
lower in the food web, it could severely change the ecosystem stability because each of the
organisms in the next trophic level would also be affected.
This study is inspiration for further studies. We could investigate the effects of different
water temperatures and how the uptake of carbon dioxide in the water changes with different
water temperatures. We could also test different shell species and different proteins like fish
slime so see how that reacts to changing pH.
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We could improve our experiment by adding a control to the shell experiment, using
deionized water to compare loss of mass of shells. We should test all the same species of shell
and determine the type of crystal structure it has (calcite, high magnesium calcite, or aragonite)
to further refine our knowledge of which organisms would most be affected by ocean
acidification.
To conclude, we learned that ocean acidification is a process we must educate ourselves
on and work on ways to reduce this process. The only way we see this changing is if we reduce
the concentrations of carbon dioxide in the atmosphere. In order to reduce carbon dioxide in
the atmosphere, we need to burn fewer fossil fuels. We need to assess our own lifestyles to
see how we can be more energy efficient in all that we do. We can start with simple things like
turning off lights, use energy efficient cars, closing the door when we go outside to conserve air
conditioning, and many other little things. We need to be good stewards of our planet to
ensure we have a good quality of life.
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Literature Cited
National Oceanic and Atmospheric Administration. (2014, April 30). Ocean acidity is dissolving
shells of tiny snails off U.S. West Coast. ScienceDaily. Retrieved June 26, 2014 from
www.sciencedaily.com/releases/2014/04/140430101914.htm
Society for Experimental Biology. (2013, July 5). Jumping snails leap over global warming.
ScienceDaily. Retrieved June 26, 2014 from
www.sciencedaily.com/releases/2013/07/130705101824.htm
The Earth Institute at Columbia University. (2014, June 2). Modern ocean acidification is
outpacing ancient upheaval: Rate may be ten times faster. ScienceDaily. Retrieved June
26, 2014 from www.sciencedaily.com/releases/2014/06/140602170341.htm