GEOSCI 106 Lab 9_ Carbon cycle- MARCH
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Dec 6, 2023
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GEOSCI/ENVIR ST 106: Environmental Geology
Lab 9: Carbon cycle
Assignment overview:
The carbon cycle is responsible for the movement of carbon between various
reservoirs in the Earth: the ocean, atmosphere, soil, rocks, and life. Because Earth’s temperature is
sensitive to the amount of carbon-bearing molecules in the atmosphere (carbon dioxide, methane, and
more), understanding how Earth’s carbon cycle works is critical for understanding how Earth’s climate is
going to change in the future. In this lab, you will explore the processes that influence carbon
concentrations in the atmosphere.
Instructions:
Fill out each red highlighted field (_________) according to each question’s instructions.
Submission:
To submit the assignment on Canvas, use the following steps:
1.
In Google Docs, generate a PDF: File → Download as → PDF Document
2.
In Google Docs, use Share → Get Shareable Link, and copy the link address
3.
In Canvas, upload your PDF to the assignment.
4.
In Canvas, paste the link address to your Google Doc in the assignment comments.
Potentially useful things:
This lab will require doing some calculations involving multiplication and
division. To arrive at the right answers, it will be helpful to carefully keep track of the units in your
calculations. To help with this, you may find the following numerical conversions useful. It will also be
useful to review the information on these topics that was covered in lecture.
1 part per million = 0.000001
1 ton = 1000 kg
1 Gigaton = 10
9
kg
1
Figure 1.
Net Primary Productivity (NPP) on land in units of grams of carbon (g C) per m
2
of the
Earth’s surface per year. Figure from Haberl et al. (2007).
Figure 2.
Net Primary Productivity (NPP) in the ocean in units of grams of carbon per m
2
of the
Earth’s surface per year. Figure from NASA Goddard Agency.
2
1. In lecture, we saw that Net Primary Productivity (NPP) is a quantity that describes how quickly
organic material is generated through the growth of plants and animals. NPP has units of the mass of
carbon (g of C) per square meter (m
2
) of the Earth’s surface per year. In other words, it’s a proxy for
the rate at which new life is growing. For example, if the only thing growing in a 1 m
2
garden were a
cantaloupe, and if that cantaloupe grew and gained 1000 g of carbon over one year, then that little
garden patch would have a NPP of 1000 g of carbon per m
2
per year. These are the units of NPP in
Figures 1 and 2, which show global maps of NPP on land and in the oceans, respectively.
(a) Examine Figure 1. In what region on land does the highest NPP tend to be found? What is the
maximum value NPP reaches on land? Based on the material discussed in lecture, why does NPP
tend to be highest there? (3 points)
Location: _Northern South America________
Maximum value: _1200-1500________
Reason: _Lots of tropical rainforrests________
(b) Examine Figure 2. In what region in the oceans does the highest NPP tend to be found? What is
the maximum value NPP reaches in the oceans? Based on the material discussed in lecture, why does
NPP tend to be highest there? (3 points)
Location: _Western Coast of South America________
Maximum value: _800+________
Reason: _Coastal Upwelling zone________
(c) Where is NPP higher on average: On land or in the ocean? (1 point)
Land_________
3
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Figure 3.
Measurements at Mauna Loa in Hawaii show a steady increase in atmospheric carbon
dioxide (CO
2
) concentrations since the mid-20
th
century. The red line shows the concentration
each month, and the black line shows a smoothed moving average through the data.
2. (a) The red line in Figure 3 shows measurements of atmospheric carbon dioxide (CO
2
) concentrations
measured at Mauna Loa, Hawaii, from 1958 to the present. Based on the data in this figure, what is the
current atmospheric CO
2
concentration? Be sure to report the most recent value in this figure and to
include the units in your answer. (1 point)
Approximately 411 parts per million_________
(b) What is the current mass of carbon dioxide in the atmosphere? To calculate this, multiply the mass of
the atmosphere (~5.1·10
18
kg) by the atmospheric CO
2
concentration that you measured in the previous
question and the fraction of a CO
2
molecule’s mass that is carbon (i.e., the molar mass of carbon (12
g/mol) and the molar mass of CO
2
(44 g/mol)). In this equation, be sure to represent the concentration as
a fraction. For example, if half of the atmosphere were made of CO
2
, the value to use for atmospheric
CO
2
concentration in this equation would be 0.5. (1 point)
4
ass
of
carbon
Mass
of
atmosphere
)(
CO
concentration
)
M
= (
2
Molar
mass
of
C
Molar
mass
of
CO
2
_(5.1x10^18)(.000411)(12/44)=5.72x10^14kg________
(c) How much have atmospheric CO
2
concentrations
increased since this monitoring program began in
1958? (1 point)
Approximately 95 parts per million_________
(d) What was the mass of the carbon in the atmosphere in 1958? Use the same formula you used in part
(b) above, but with the peak 1958 concentration. How much CO
2
has been added to the atmosphere since
1958? As in part (a), be sure to include the units. (2 points)
Mass of atmospheric CO
2
in 1958: _4.44x10^14_kg_______
Extra mass of CO
2
added between 1958 and the present: _1.28x10^14 kg________
Figure 4.
Carbon fluxes to and from the atmosphere (image from Figure 18.1 in the textbook,
Montgomery (2019),
Environmental Geology
, 11th edition). Numbers in this figure represent the
rate at which carbon is transferred between reservoirs in units of billions of tons of carbon per
year.
5
3. As discussed in lecture earlier this semester, the residence time is defined as the length of time a given
object stays in a given reservoir before leaving it. For example, the average residence time of a water
molecule in the ocean is about 1000 years. The average residence time is calculated as the mass of the
reservoir divided by the rate at which new mass comes into the reservoir.
esidence
time
(
years
)
R
=
Mass
of
reservoir
(
kg
)
Rate
at
which
mass
is
added
to
reservoir
(
kg
/
year
)
(a) Examine Figure 4 closely. Pay special attention to how the figure shows carbon being added to and
removed from the atmosphere. How much more carbon is added to the atmosphere each year than is
removed from it? (1 points)
_52 billion tons per year________
(b) Given your answers to the preceding questions and the information in Figure 4, what is the average
residence time of carbon in the atmospheric reservoir? (2 points)
_5.1x10^18/4.17x10^13 kg/year = 122302 years________
6
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Figure 5.
Zooming in on a few years of the same measurements in Figure 1 show annual
fluctuations in atmospheric carbon dioxide (CO
2
). On the x-axis, the numbers are aligned with
large ticks marks that indicate the beginning of each year. For instance, the label “2018” lies
under a large tick that indicates January 2018.
4. (a) Figure 5 shows that atmospheric CO
2
concentrations fluctuate up and down in a regular pattern
every year. At what time of year (i.e., which month) are CO
2
concentrations highest? In which month are
they lowest? (1 points)
_They are highest in May and lowest in September.________
(b) How much do CO
2
concentrations fluctuate each year? In other words, how much do the fluctuations
deviate from the smoothed average concentrations (the black line in Figure 5)? (1 points)
_About 4 parts per million in both directions________
7
(c) Why do these annual CO
2
fluctuations happen? In your answer, describe the processes that are
responsible for making CO
2
concentrations go up and down each year, and describe why CO
2
concentrations reach maximum and minimum values at the same time every year. (4 points)
_The plant cycle is the reason that the CO2 fluctuations happen because in the months where the values
are highest, the plants are most active and where they are the lowest the are the least active.________
Figure 6.
Earth’s tectonic plate configuration 900 million years ago (Bogdanova et al., 2009).
Light gray colors indicate continents, and dark gray colors indicate oceans.
(d) Figure 6 shows a reconstruction of Earth’s continents 900 million years ago, which reveals that the
continents used to be in very different places than they are today. (For reference, you can see the present
locations of the continents in the same reference frame in Figure 7.) Given this plate configuration, how
would the annual cycles in atmospheric CO
2
at 900 million years ago have differed from those observed
today (e.g., in Figure 5)? Explain why they would have differed in this way. (3 points)
_There would be no carbon activity in west africa and Amazonia because they are in the location where
antarctica is and there is no carbon activity there. I think there would also be a lot more activity in the
ocean as it is the majority.________
8
Figure 7.
Earth’s present continental configuration. Image from Wikipedia.
References
Bogdanova, S. V., Pisarevsky, S. A., & Li, Z. X. (2009). Assembly and breakup of Rodinia (some
results of IGCP Project 440).
Stratigraphy and Geological Correlation
,
17
(3), 259.
Haberl, H., Erb, K. H., Krausmann, F., Gaube, V., Bondeau, A., Plutzar, C., ... & Fischer-Kowalski,
M. (2007). Quantifying and mapping the human appropriation of net primary production in
earth's terrestrial ecosystems.
Proceedings of the National Academy of Sciences
, 104(31),
12942-12947.
9
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