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The City College of New York, CUNY *
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Course
10600
Subject
Geology
Date
Apr 3, 2024
Type
docx
Pages
6
Uploaded by CommodoreDoveMaster1079
Limnology is the study of lakes and paleolimnology
is the study of reconstructing past environments with data collected from inland waters (via sediment cores). Below are data from a lake sediment core that can be used to reconstruct past climate conditions for the Northeast. Table 1 shows the age estimate for three
layers in the lake sediment core and Figure 10 shows the depth to each new layer in the sediment core. Note that each individual layer cannot be age dated, so you can use Table 1
to estimate the age of layers in Figure 9
.
Depth
(cm)
Age (years
before present)
90
360 ± 30
193
1150 ± 50
285
2070 ± 140
Table 1. Echo Lake sediment age and thickness data adapted from Noren, et al. (2002)
4
.
0
10
20
30
40
50
60
0
50
100
150
200
250
300
350
400
450
500
Sediment layers in Echo Lake
Sample number
Depth to sediment layer (cm)
Figure 9. Sediment core data from Echo Lake, Vermont from Noren, et al.(2002).
1.
By visually interpreting the graph in Figure 10, how would you identify a potential flood event? How would you roughly estimate the range of years where each flood may have occurred? Please describe your approach in two to three sentences.
2.
Where do you see the first notable increase in depth to a sediment layer? At what depth did this nonlinear increase occur and approximately what year do you think this corresponds to? Three sentences.
3.
Make a table of the most
recent five flood events and estimate the age of each event.
Event Number
Year
Depth to flood layer
(cm)
1
2
Proxy 3: Charcoal data
Below is a lake sediment core dataset from Minnesota that was analyzed for charcoal particle concentrations (Figure 10). Charcoal particle concentration is a proxy for the occurrence of fires. The y-axis represents the count of charcoal particles greater than 125 nm in size that occurred at each layer of increasing
age across the sediment core. 0
200
400
600
800
1000
1200
1400
1600
0
5
10
15
20
Copper Falls Lake Charcoal Data
Years before present
Count of Charcoal Particles >125 nm
Figure 10. Charcoal sediment core data from Copper Falls Lake in Minnesota collected in 2011
5
.
1.
What about this chart suggests that wildfires may have occurred more frequently at one period compared to others over the past 1,600 years? Two to three sentences.
2.
What range of years do you think had an unusually large number of forest fires during the past 1,600 years? Please explain your reasoning in three to four sentence
3.
What happened in the political history of North America beginning about 450 years before the present? Two to three sentences.
4.
What types of local weather events do you think did the most to reduce the occurrence of wildfires between now and the period that you identified above? 5.Tabulate your findings:
Years
Period of increased wildfire
Proxy 4: Ice Core Data
0
2000
4000
6000
8000
10000
12000
-34.00
-33.00
-32.00
-31.00
-30.00
-29.00
-28.00
-27.00
-26.00
Greenland Oxygen Isotope Data
Ice Age (b2k)
d18O (%)
Figure 11. Oxygen isotope (18O) data plotted against age estimates from an ice core drilled on the Greenland ice sheet. Credit: Vinther, et al. (2009).
Ice age is measured in years before 2,000 A.D. (before 2000 or “b2k”).
1.
Why do you think 18
O (%) depletion is expressed as a negative number? Please explain in three to four sentences.
2.
What range of years do you think had the lowest global average temperatures? Please explain your reasoning in three to four sentences.
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3.
Now let’s zoom in on the last 1,200 years of data and look at a 100 -year moving average of 18
O depletion percent over time. Why do you think 18
O has become less depleted over the past 200 years?
0
200
400
600
800
1000
1200
-28.3
-28.2
-28.1
-28
-27.9
-27.8
-27.7
-27.6
-27.5
-27.4
-27.3
Greenland Oxygen Isotope Data
Ice Age (b2k)
100-year Average d18O (%)
4.
What 200-year period had the most 18
O depletion on average?
Years
Period of pronounced 18
O depletion
Part III: Final Questions
5.
Construct a timeline of data beginning from 1,600 years before present to show where you have different overlapping points of reference:
6.
Citing four lines of evidence present a hypothesis to explain why a roughly 400-year long period of increased charcoal frequency in Minnesota may have come to an end in the mid-1600s. Five to six sentences. 7.
Explain why you might be hesitant to draw definitive conclusions from the data presented today. What uncertainty do you have in your hypothesis above and what would you do to try and try to test your hypothesis?
Citations: 1. Wilhelm, B. et al.
Interpreting historical, botanical, and geological evidence to aid preparations for future floods. WIREs Water
6
, e1318 (2019).
2. Gajewski, K. Climatic Impacts on the Vegetation of Eastern North America during the Past 2000 Years. Vegetation
68
, 179–190 (1987).
3. Cook, E. R. & Krusic, P. J. NOAA/WDS Paleoclimatology - Cook - Mid Hudson Valley Region historical oak - QUSP - ITRDB NY041. (2013) doi:10.25921/4RTV-WD07.
4. Noren, A. J., Bierman, P. R., Steig, E. J., Lini, A. & Southon, J. Millennial-scale storminess variability in the northeastern United States during the Holocene epoch. Nature
419
, 821–824 (2002).
5. Pompeani, D. P., Cooke, C. A., Abbott, M. B. & Drevnick, P. E. NOAA/WDS Paleoclimatology - Pompeani fire data from Copper Falls Lake, Great Lakes region - IMPD USCFL001. doi:10.25921/ZRM0-RY90.
6. B.M. Vinther, S.L. Buchardt, H.B. Clausen, D. Dahl-Jensen, S.J. Johnsen, D.A. Fisher, R.M. Koerner, D. Raynaud, V. Lipenkov, K.K. Andersen, T. Blunier, S.O. Rasmussen, J.P. Steffensen, and A.M. Svensson. Holocene thinning of the Greenland ice sheet, Nature, 461, 385-388, 2009, doi:10.1038/nature08355.
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