Pollen Stratigraphy

I. Pollen Stratigraphy and Vegetation Interpretation

• Pollen has been used for more than a century to interpret changes in vegetation since the last glacial maximum
• Terrestrial pollen records are best when obtained from lake or peat sediment records are obtained by cores

A. Standard pollen record methods


1. count and identify 200 pollen grains/sample
2. divide census into three parts

• arboreal pollen (AP)
• nonaboreal polle (NAP)
• spores
3. express results as percentages of total pollen or total AP at that particular depth
4. sometimes results expressed as grains/cubic centimeter
5. the plant assemblage at a particular horizon is known as the pollen spectrum
6. histograms of succesive spectra comprise a pollen curve
7. curves from a series of stratigraphic positions in a core form a pollen diagram
8. age dates are determined by carbon-14 dating
9. history of vegetation change through time linked to climate, glacial, and the influencesof man

B. Pollen record data

1. particlar species may be over- or underrepresented

some trees shed much more pollen than others

some propagate the pollen more effectively

2. vegetation changes best noted near a ecotone (a boundary) such as
between tudra and subarctic forest or between prairie and
temperate forest.

C. Pollen records of Europe and North America

Europe
1. the post-glacial pollen record of Europe is divided into IX zones
2. detailed records of vegetation changes throughout Europe and Russia
3. vegetation record of Europe western)

30 species of trees

6 species of deciduous trees in northern Europe

easier record to deal with

more palynologists studying the record

North America

+ 130 species of trees

+ as many a 30 species of a single genus

+ some species of particular genera hard to differentiate (e.g. 13 species of Pinus)

II. Toward a unified picture of glacial-oceanographic-vegetation at the last glacial maximum (18,000 yr. B.P.)

• Studies now present a clear picture of ocean sea surface temperatures, the extent of glacial sea ice/terrestrial ice sheets, and the general patterns of continental vegetation in the northern hemisphere.
• Terrestrial Ice Exent
• based of the distribution of glacial erosional and
• depositional landforms
• Sea Ice
• based on the distribution of marine lithofacies and biofacies
• Vegetation
• based on hundreds of pollen curves from North America-Europe and Asia
• Sea Surface Temperature
• modeled by the CLIMAP project
• identified 18,000 yr. B.P. level in cores throughout the oceans
• studied modern plankton and related abundance to sea surface
• temperature
• wrote equations linking taxa to temperature
• employed equations to determine 18,000 yr. sea surface temperatures
• mapping of 18,000 yr. isotherms and anomalies
• Results
• shown and discussed in class

Interpretation of elevation by Paleobotanical evidence

• Sierra Nevadas
• Rocky Mts.

Critera (physiognomic) often used:

1. Leaf length to width ratio <1:1 - % highest in dry, mixed coniferous forest
2. small size- % highest in short, tropical deciduous forest and scrub & dry, mixed coniferous forest
3. lobed- % highest in mixed northern hardwood and dry, mixed coniferous forest
4. teeth regular- % highest in mixed northern hardwood and dry, mixed coniferous forest
5. attenuate apex (drip tip)- humid habitat
6. large size- tropical
7. length to width ratio 2-4:1 - % lowest in mixed northern hardwood and dry, mixed coniferous forest
8. no teeth- % lowest in mixed northern hardwood and dry, mixed coniferous forest
9. incised margin (e.g. adler)- cool climate
10. smooth margin- high mean annual precipation and temperature, entire margin % increases with mean annual temperature