Kasi Wilson - MEA100 Lab 8_ Paleoclimate [F23]
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North Carolina State University *
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Dec 6, 2023
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MEA100 Lab 8: Paleoclimatology
Instructions:
This file provided to you through the Google Assignment for this lab is your
personalized copy. You do NOT need to make copies, change sharing settings,
or create any other file - just edit this file directly and click submit in the Google
Assignment.
●
After reviewing the background material on Moodle and completing the pre-
lab questions, complete the lab below. Fill in your answers in the blue boxes
provided in this document.
●
You are encouraged to collaborate with your peers and to seek
help/feedback from your instructor as you work through the lab, but your
answers should be your own.
●
To submit your completed lab, open the Google Assignment in Moodle and
click the blue button that says “Open in Assignments.” Then click the blue
button labeled “Submit.” Again you do not need to create or add any
additional files.
●
Help us improve the lab by completing a few short questions at the end of
the lab.
Outcomes: In this lab you will…
●
Interpret proxy data from ice cores and ocean sediment cores to infer
how Earth’s climate has changed over the past 650,000 years.
Skills
This lab makes use of the following tools from our “Earth Scientist’s Toolbox”:
Change over time:
Time series
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Background
Paleoclimatology is the study of past climate. Paleoclimatology data are derived
from climate
proxies
, natural archives such as tree rings, ice cores, corals, and
ocean sediments, which preserve imprints of past climate. By studying various
proxies, paleoclimatologists can decipher information about temperatures,
precipitation, atmospheric composition, ocean chemistry, fire, and other aspects
of Earth’s climate over hundreds to millions of years in the past.
In your pre-lab preparation, you learned about stable isotopes and how
changing climate conditions can affect the ratios of stable isotopes in
precipitation, ice sheets, and the ocean. Now, you will apply those concepts to
interpret stable isotope data from
sediment cores and ice cores to understand
past glacial and interglacial episodes over the past 650,000 years.
Lab Exercise: Interpreting proxy data - ocean sediment cores and ice
cores
Part I. Ocean sediment cores
Ocean sediment cores can provide a wealth of information about past climate,
extending millions of years into the past. Layers of sediment deposited at the
bottom of the ocean include dust blown into the ocean by wind, sediment
eroded from the continents and transported by ocean currents, and fossils of
microscopic organisms (foraminifera, coccoliths, radiolarians, and diatoms) that
lived in the surface waters of the ocean or deep at the bottom of the ocean. The
shells of these microscopic organisms contain oxygen derived from seawater,
and thus provide a record of variations in
δ
18
O in the ocean.
The following plot shows variations in
δ
18
O measured in shells of deep-ocean
foraminifera preserved in ocean sediment
cores from around the globe. (The full
data-set stretches back millions of years, but we are just focusing on the past
650,000 years in this lab.)
Figure 1.
The stack of 57 globally distributed benthic δ18O marine sediment records (dark gray)
(Lisiecki and Raymo, 2005). Time in ka (thousands of years). Figure derived from Figure 6.3 of
the 2007 IPCC Report (AR4-WG1).
A copy of Figure 1 is provided below for you to annotate in response to
questions 1-3. (Note: The image may appear slightly blurry. Double-clicking on it
2
to open it with the Drawing tool will allow you to see a clearer image.)
1.
Annotate the copy of the plot from Figure 1 in the blue box above by
double-clicking on it to open it with the Drawing tool. Using the text-box
tool in the Drawing toolbar, add labels to indicate which end of the y-axis
represents a relatively higher proportion of the heavier oxygen isotope
and which represents a relatively higher proportion of the lighter oxygen
isotope, labeling them “Heavy” and “Light,” respectively.
Towards the top is heavy and towards the bottom is light.
2.
What information about past climate does this benthic δ18O data most
directly represent? Why? (You may want to review the video from the pre-
lab materials.)
δ18O changes directly with temperature. As the temperature fluctuates
so does the graph, the higher/heavier parts represent cooler water and
the lower/lighter represents warmer water.
3.
Again using the text-box tool in the Drawing toolbar to annotate the copy
of the Fig. 1 plot in the blue box above, label at least 3 sections of the
3
Figure 1.
The stack of 57 globally distributed benthic δ18O marine
sediment records (dark grey) (Lisiecki and Raymo, 2005). Time in ka
(thousands of years). Figure derived from Figure 6.3 of the 2007 IPCC
Report (AR4-WG1).
G
G
G
I
I
I
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plot that could represent colder,
glacial
intervals with a “G” and at least 3
sections that could represent warmer,
interglacial
intervals with an “I”.
Note: If unable to annotate the image above, you may describe your
answer by listing the peak years of glacial and interglacial intervals here:
●
Glacial intervals: …
●
Interglacial intervals: …
Part II. Ice cores
Ice cores drilled from ice sheets in Greenland and Antarctica can provide a
continuous, high-resolution record of snow accumulation, melting events, dust,
volcanic activity, wind patterns, temperature, and atmospheric composition over
the past 800,000 years.
Temperature record from ice cores
From the stable isotope ratio of a layer of an ice core, paleoclimatologists can
calculate how much warmer or colder local temperatures were when the snow
that makes up that layer was deposited. The plot below shows temperature
variations in Antarctica over the past 650,000 years, determined from ice core
data, compared with the oxygen isotope variations in ocean sediment cores that
you looked at in Part I.
Figure 2.
Variations in temperature in Antarctica (top, black line) over the past 650,000 years,
derived from stable isotope variations in ice cores. Compared to the same benthic (ocean
sediment core) δ18O values you looked at in Part I.
Time in ka (thousands of years). Figure
derived from Figure 6.3 of the 2007 IPCC Report (AR4-WG1).
4.
How do the patterns of variations in temperature in Antarctica compare to
the patterns of glacial vs. interglacial periods you identified in part I?
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As temperature goes down there is a glacial period and as temperature
goes up there is an interglacial period.
Gasses trapped in ice cores
The most unique feature of ice cores as a climate proxy is that they trap direct
samples of the ancient atmosphere as bubbles in the ice. This provides a
detailed record of the atmospheric concentrations of carbon dioxide, methane,
and other gases over time.
This is interesting from a climate perspective because carbon dioxide and
methane are
greenhouse gasses
- they absorb outgoing infrared radiation, and
cause warming at Earth’s surface. Additionally, we would expect the
concentrations of gasses in the atmosphere to be affected by changes in the
temperature of the oceans because the
solubility
of gas in water increases with
decreasing temperature. This means gasses may be absorbed into the ocean
when temperatures are colder and may be released from the ocean into the
atmosphere when temperatures are warmer.
The plot below shows the atmospheric concentrations of the greenhouse gasses
carbon dioxide (CO
2
; red, top line) and methane (CH
4
; blue, bottom line), derived
from air bubbles trapped within Antarctic ice cores.
5
Figure 3.
Variations of the atmospheric concentrations of the greenhouse gases
CO2 (red, top
line, with values marked on left axis
) and CH4 (blue, bottom line with values marked on right
axis
), derived from air trapped in ice cores from Antarctica. Time in ka (thousand years).
Figure
derived from Figure 6.3 of the 2007 IPCC Report (AR4-WG1).
5.
Describe the pattern of changes in atmospheric concentration of these
greenhouse gasses over the past 650,000 years.
As CO2 goes up so does CH4. When the gasses go up it means that the
temperature is warmer therefore the gasses are released from the ocean
into the atmosphere. When the temperature is cooler then the gasses
are absorbed into the ocean.
6.
Because of the time needed for air bubbles to be trapped as snow is
compressed to ice, the youngest gas bubbles from the ice core plotted
here are actually over 1,000 years old. Look up the most recent direct
measurements of atmospheric concentrations of CO
2
and CH
4
from
NOAA
:
https://www.esrl.noaa.gov/gmd/ccgg/trends/
Record the values of the most recent measurements below and plot them
on the copy of Figure 3 provided below by double clicking on the image
below to open it with the Drawing tool and dragging the stars to the
appropriate positions on the graph.
6
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Carbon dioxide: ____418.82 _____ppm
Methane: ____1915.25_____ppb
7.
Describe at least two ways the recent trends in greenhouse gas
concentration you found displayed on NOAA’s
Global Greenhouse Gas
Reference Network site
differ from changes observed in the ice core
record.
The recent trends we found on NOAA’s website displayed
concentrations that are far greater than what was previously graphed.
On the website the trend seems to be continuously going up instead of
fluctuating like the graph.
Part III. Putting it together
Now consider all of the paleoclimate proxy data we have looked at from the past
650,000 years. The following figure shows the same time series data for benthic
δ18O from ocean sediment cores, temperature change from Antarctic ice cores,
and greenhouse gas concentrations from Antarctic ice cores that you have
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Figure 3. Variations of the atmospheric concentrations of the greenhouse
gases CO2 (red, top line) and CH4 (blue, bottom line), derived from air trapped
in ice cores from Antarctica. Time in ka (thousand years). Figure derived from
Figure 6.3 of the 2007 IPCC Report (AR4-WG1).
→
Drag the stars for currentconcentrations of CO2 and CH4to the
appropriate location
Modern
CO2
Modern
CH4
already looked at plotted together on a single chart.
Figur
e 4.
Variations of the atmospheric concentrations of the greenhouse gasses
CO2 (red, top line) and
CH4 (blue, upper middle line), derived from air trapped within ice cores from Antarctica, and of
deuterium (δD; black, lower middle line) in Antarctic ice cores (Petit et al., 1999; Indermühle et al., 2000;
EPICA community members, 2004; Spahni et al., 2005; Siegenthaler et al., 2005a,b). The stack of 57
globally distributed benthic δ18O marine records (dark
gray, bottom line; Lisiecki and Raymo, 2005), is
displayed for comparison with the ice core data. Time in thousands of years. Figure derived from
Figure 6.3 of the 2007 IPCC Report (AR4-WG1).
8.
Describe ways in which the data examined in this lab exemplify elements
of “systems thinking” (e.g., interactions between subsystems, feedback
loops, cycles, etc.)
There’s a positive feedback loop between increasing greenhouse gas
concentrations and rising temperatures. The rise of δ18O is inversely
related to temperature,glaciation, and greenhouse gas concentration.
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