Pollen
Modified with permission from Global Climates - Past, Present, and Future, S. Henderson, S. Holman, and L. Mortensen (Eds.). EPA
Report No. EPA/600/R-93/126, U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC. 25 - 38.
Background
Evidence found in the fossil record indicates that in the distant past, the earth's climate was very different than it is
today. There have also been substantial climatic fluctuations within the last several centuries, too recently for the
changes to be reflected in the fossil record. Since these changes are important to understanding potential future climate
change, scientists have developed methods to study the climate of the recent past.
Although human-recorded weather records cover only the last few hundred years or so, paleoclimatologists and
paleobotanists have found ways of identifying the kinds of plants that grew in a given area, from which they can infer
the kind of climate that must have prevailed. Because plants are generally distributed across the landscape based on
temperature and precipitation patterns, plant communities change as these climatic factors change. By knowing the
conditions that plants preferred, scientists can make general conclusions about the past climate.
How do paleobotanists map plant distribution over time? One way is to study the pollen left in lake sediments
by wind-pollinated plants that once grew in the lake's vicinity. Sediment in the bottom of lakes is ideal for determining
pollen changes over time because it tends to be laid down in annual layers (much like trees grow annual rings). Each
layer traps the pollen that sank into the lake or was carried into it by stream flow that year.
To look at the "pollen history" of a lake, scientists collect long cores of lake sediment, using tubes approximately
5 centimeters (cm) in diameter. The cores can be 10 m long or longer, depending upon the age of the lake and amount
of sediment that's been deposited. The removed core is sampled every 10 to 20 cm and washed in solutions of very
strong, corrosive chemicals, such as potassium hydroxide, hydrochloric acid, and hydrogen fluoride. This harsh process
removes the organic and mineral particles in the sample
except for the pollen, which is composed of some of the most
chemically resistant organic compounds in nature. Microscope
slides are made of the remaining pollen and examined to
count and identify the pollen grains.
Because every plant species has a distinctive pollen
shape, botanists can identify from which plant the pollen
came. Through pollen analysis, botanists can estimate the
composition of a lake area by comparing the relative amount
of pollen each species contributes to the whole pollen sample.
Carbon dating of the lake sediment cores gives an approximate
age of the sample.
Scientists can infer the climate of the layer being studied by relating it to the current climatic preferences of the
same plants. For example, they can infer that a sediment layer with large amounts of western red cedar pollen was
deposited during a cool, wet climatic period, because those are the current conditions most conducive to the growth of
that species.
Why are scientists who study climate change interested in past climates? First, by examining the pattern of plant
changes over time, they can determine how long it took for plant species to migrate into or out of a given area due to
natural processes of climate change. This information makes it easier to predict the speed with which plant communities
might change in response to future climate change. Second, by determining the kinds of plants that existed in an area
when the climate was warmer than at present, scientists can more accurately predict which plants will be most likely to
thrive if the climate warms again.
Data:
July Avg.
Temperature
(C)
July
Normalized
Temp Celcius
Annual
Precipitation
(cm)
13.97
11.03
93.09
31.9064
263
7
0.974
14.11
10.89
91.70
33.3036
130
16
0.890
14.30
10.70
89.75
35.2497
223
9
0.961
14.85
10.15
84.26
40.7387
152
30
0.835
15.34
9.66
92.77
32.2277
151
38
0.799
15.43
9.57
92.26
32.7443
254
10
0.962
17.56
7.44
112.18
12.81635
266
24
0.917
17.62
7.38
100.91
24.09472
172
26
0.869
17.62
7.38
100.91
24.09472
235
15
0.940
15.64
9.36
76.33
48.6728
107
6
0.947
14.29
10.71
97.83
27.16534
356
3
0.992
15.82
9.18
107.57
17.4253
229
32
0.877
16.40
8.60
66.27
58.72716577
256
8
0.970
15.44
9.56
91.91
33.09454
287
3
0.990
16.98
8.02
83.33
41.67
189
18
0.913
16.98
8.02
83.33
41.67
199
15
0.930
19.38
5.62
123.56
1.444990088
92
37
0.713
16.76
8.24
85.17
39.82564
261
6
0.978
16.76
8.24
85.17
39.82564
234
10
0.959
16.77
8.23
85.10
39.89854
158
4
0.975
20.10
4.90
73.31
51.695
4
42
0.087
19.60
5.40
76.80
48.2015
111
103
0.519
19.41
5.59
69.32
55.6756
50
153
0.246
20.53
4.47
95.88
29.1210478
67
62
0.519
20.59
4.41
69.79
55.214
173
74
0.700
20.97
4.03
86.96
38.03667472
25
200
0.111
20.98
4.02
86.75
38.24513645
10
291
0.033
21.01
3.99
86.13
38.86752816
122
25
0.830
22.37
2.63
70.28
54.72408535
56
123
0.313
22.72
2.28
68.09
56.90659
10
54
0.156
21.01
3.99
86.13
38.86752816
30
44
0.405
21.03
3.97
85.79
39.21136991
35
73
0.324
21.21
3.79
82.42
42.57519021
21
65
0.244
22.12
2.88
59.03
65.975
16
9
0.640
22.15
2.85
58.85
66.1535
158
31
0.836
Normalized
Precp (cm)
Sum Pine
Sum Oak
Ratio P:O
22.78
2.22
64.58
60.42049
9
159
0.054
22.33
2.67
57.52
67.4795
2
214
0.009
22.27
2.73
65.20
59.79823877
6
90
0.063
22.38
2.62
57.21
67.7855
2
41
0.047
23.26
1.74
52.37
72.63248369
6
24
0.200
22.49
2.51
27.94
97.06
9
4
0.692
** Pine: Oak ratio is more like a gradient, where 0 represents Pine and 1 represents Oak**
Questions:
1. Graph the Pine : Oak ratios against normalized temperature and in a separate graph against normalized
precipitation.
***Be sure to include a trend line and r2 value for each variable***
2. Determine the ratio of trees at various temperature and precipitations. Decipher trends and record
observations.
3. What conclusions can be made about the environments of the two tree species? (hint: think temperature and
precipitation). Use 3 pieces of evidences from your research to support your ideas.
4. How can present day data such as this be use by paleoclimatologists to reconstruct past climates? (see below
diagram)
5. What are the limitations of this source of information?
This may be a helpful tool for predicting where certain trees grow based on climate.
Resources:
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http://www.ncdc.noaa.gov/paleo/pollen/viewer/webviewer.html
Budburst
http://www.ncdc.noaa.gov/paleo/pollen.html
http://www.esd.ornl.gov/projects/qen/nerc.html
http://www.esd.ornl.gov/projects/qen/adams3.html
http://www.ucar.edu/learn/1_2_2_10t.htm