Download Pollen paper reading project

Science 119
Name:
Final project on pollen interpretation: reading a scientific paper
Due: Tuesday, June 10
Objective: Throughout the quarter, you’ve read and used references in the scientific
literature. Generally, these readings have been selections. In this exercise, you’ll closeread a scientific paper (a publication in a peer-reviewed journal) and answer some
questions from the reading. In doing this, you will gain some insight as to how scientists
read scientific papers.
Reading: Grigg, L.D., and Whitlock, C., Late-Glacial Vegetation and Climate Change in
Western Oregon, Quaternary Research 49, 287 – 298 (1998)
For the purposes of this assignment, you need not cite any sources (since we assume
you’re reading the paper) and you may use Wikipedia or other trusted encyclopedic
sources as necessary.
Title and author
1. There are two code words here related to time: Quaternary and Late-Glacial.
Numerically, how many years ago were they?
2. Why do the authors include their address and institutional affiliation?
Abstract
3. More code: What does “cal yr B.P.” stand for?
Every abstract should allow you to tell what the main result of the research was. This
abstract contains roughly 230 words – not easy to tell what’s the most important. So
break it down:
4. What was the main material used to determine their results? Hint: First word in the
abstract.
5. What was this material used for? Hint: second line.
6. Was only one type of this material used, or were several different kinds used? If
several, exactly how many?
7. How many, and what type of localities were sampled for this material?
8. So what did this material allow the authors to infer? We don’t want a word-for-word
copy of the abstract; paraphrase the middle twenty lines of the abstract.
Introduction
9. More code: What is the “Younger Dryas” event? Why is it called that?
10. Is the Younger Dryas event considered to be worldwide, or is there some
controversy about that? Specifically, does the Younger Dryas event show up in the
Pacific Northwest, according to earlier studies?
11. Write the full citation of one of these earlier studies about the Younger Dryas in the
Pacific Northwest.
12. In which mountain range is each of the two study sites located? At what
elevation is each? Most importantly, in which vegetation zone is each site?
13. Make two lists, one for each zone above. Populate each list with the genus/species
of what the authors believe are the major plants.
Methods
14. Why did the authors core the lake bottom sediments? What is the underlying
assumption about cores, pollen and timing?
15. How were the species present in each core identified? Write the full citation of
one reference the authors used for identification.
16. What constitutes a “sample” of the core, according to the authors? How many
pollen grains were counted within each sample?
17. Write one “work-around” the authors had to make in identifying species from pollen.
18. Even the charcoal in each sample was quantified! How big did a charcoal grain
need to be, in order to be counted?
Lithology and chronology
19. More code: What’s “gyttja”? Is this typical for lakes?
20. Further code: What’s “U/Th” and “14C”? What general topic do these refer to?
21. According to Table 1, as the authors got deeper in the core (first column), what
happened to the age of that material? Is this consistent or inconsistent with your
answer to question 14?
22. How did the authors convert “uncalibrated ages” to “calibrated ages”, and how
was this calibration done? Warning: there are two different ways, depending on the age
of the material.
23. In Figure 2, is the age/depth relationship linear? Why would you expect that both
graphs “flatten out” towards the bottom of each core?
Late-Glacial Pollen Records
24. From Table 2, list the species and percentage breakdown of pollen found in
Pollen Zone LL-4a.
25. Is Pollen Zone LL-4a contained in one sample (see question 16), or does it contain
many samples? Hint: compare the depths in Table 1 versus depths in Table 2.
26. So subzone LL-4 is similar to the pollen distribution where and when?
Figure 3 is a typical pollen frequency diagram. Note that each column represents a
different species, and the width of each species’ curve at a given age is the percent
abundance of that species pollen in that age’s sample. For instance, Picea (first column)
is 20% of all pollen in the 14500 cal yr B.P. sample but is virtually gone at 14000 cal yr
B.P. (at Little Lake)
27. What seems to be the relationship between the presence of Pseudotsuga-type
pollen and Tsuga mertensiana pollen?
28. What’s “arboreal” versus “nonarboreal”? Why are the authors concerned about
the nonarboreal species?
29. In Figure 4, at Gordon Lake, is there the same relationship between the presence
of Pseudotsuga-type pollen and Tsuga mertensiana pollen as you saw at Little Lake
(question 27)? Did the transition between the two genera at Gordon Lake happen at
the same time as the transition at Little Lake?
Discussion
30. In the first line of the discussion section, the authors infer that there is a “shift from
open subalpine to closed montane forest at Little Lake between 15,700 and 14,850
cal yr B.P.” What species change allows them to make such an inference?
31. What do they infer about the climate change when the shift from open subalpine
to closed montane forest occurs?
32. To what do they attribute the prominent charcoal peak at 14,900 to 14,850 cal yr
B.P.? What species’ pollen support their hypothesis?
33. Is a similar shift from open subalpine to closed montane forest seen at Gordon Lake?
When does this shift occur? What sort of climate change there accomplished the shift?
34. Why might the warming from 14,850 to 14,500 cal yr B.P. have been seen at Little
Lake but not at Gordon Lake?
35. In Figure 5, the far right column shows that, globally, both sea level and the
amount of solar insolation were rising. What affect should both of those have on
global temperatures? Is this change reflected obviously in the Little Lake and Gordon
Lake temperature reconstruction (second column from right)?
36. Why is the period from 12,400 – 11,000 cal yr B.P. called the “Pinus Period” by the
authors? What kind of climate is implied by this? Is this period consistent at both lakes?
37. BIG QUESTION: Do these lake core pollen records show evidence for the Younger
Dryas event? Why or why not? Hint: The answer need not be the same for each of the
studied lakes!
38. OTHER BIG QUESTION: If these changes in pollen distribution in the period from
12,400 – 11,000 cal yr B.P were not due to the Younger Dryas event, to what do the
authors attribute this inferred climate change?
39. In the last paragraph of the Discussion section, the authors suggest yet another
reason why the Younger Dryas event may not have been seen in the pollen record of
these lakes. What is this reason?
Conclusions
40. As an author, you should not introduce any new information in the Conclusions
section. Is there anything the authors mention here that wasn’t mentioned earlier in the
paper?