Non-marine paleoclimate records

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Non-marine paleoclimate records

• Pollen Data

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Basis for Pollen Studies

• Pollen grains can directly identify plant
  species.
• Pollen is widely present and abundantly produced.
• Pollen grains are resistant to decay.

Alnus
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Pollen Studies

• Palynology is the study of pollen
• Pollen grains can be found in caves, lake
  sediments, soils, peat deposits, marine
  sediments, glacial deposits.
• Pollen data provides information of changes in
  vegetation, climate, and human disturbance of
  terrestrial ecosystems.

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Pollen Production

• Pollen production is inversely proportional to
  the probability of fertilization.
• Authogamous plants lt Entomophilous lt
  Anemophilous
• (self-fertilizing)
  (insect-fertilizing) (wind-dispersed)
• Pollen can be produced during different seasons
  by different plants.
• How representative are pollen grains of species
  distribution and abundance?

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Genus Pollen Production Grain/flower Rate of Fall (cm/sec)
Pinus gt15 million 2
Picea 200,000 9
Abies 100 40
Poacea 90,000 10
Betula 10,000 1
Quercus 9,000 5
Fagus 15 8
Acer 8,000 4
Tilia 20,000 18
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Pollen Production

• Pollen production is species-specific. Whereas
  some plants can produce 70,000 grains per anther,
  others produce up to 100 grains per anther.
• The pollen record is biased towards
  wind-pollinated plants (all gymnosperms and most
  angiosperms) because these plants need to produce
  vast quantities of pollen.

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Pollen Production

• Anemophilous plants (wind-pollinated) produce
  light, aerodynamically shaped pollen.
• Pollen deposition depends on grain shape and
  weight, wind velocity, wind direction, canopy
  cover

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Pollen dispersal

• Travel distance is inversely proportional to
  pollen-grain size.
• Pollen grains are filtered as they move through
  the canopy.
• Some light pollen grains can be transported
  long-distances in the upper atmosphere.
• In general, pollen from low-standing plants have
  low probability of dispersal.

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Pollen dispersal

• Meteorological conditions control pollen
  dispersal.

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Pollen and vegetation
Lakes regional vegetation
Ponds local vegetation
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Pollen percentages in surface samples from
eastern Canada.
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Pollen and Vegetation

• Surface pollen composition is different than
  vegetation composition and abundance.
• Pollen composition at a given point within an
  ecosystem is fairly consistent.
• But, pollen compositions at different sites
  within the same ecosystem are slightly different.
• However, the difference between pollen
  composition among sites in different ecosystems
  is far greater than the difference between sites
  within a single ecosystem.

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Pollen Analysis

• Sediments are collected
• Pollen grains are isolated from the sediment
  matrix via chemical treatments.
• Isolated pollen grains are mounted onto a glass
  slide, and they are identified and quantified
  under a microscope.

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Pollen Analysis

• Pollen counts in each slide are reported in
  percentages of the total pollen count (excluding
  wetland or rare species).
• Changes in the of one species are interpreted
  to reflect a similar change in the composition of
  vegetation.

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Pollen Analysis

• Problem of pollen counts could give
  unrealistic information of vegetation composition
  if, for instance, a plant species is replaced by
  an abundantly pollen-producing plant.

Y-axis Time
X-axis pollen grains
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Pollen Analysis

• To circumvent biases associated with pollen
  production, one could use pollen flux density
  values (pollen grain/yr-cm2).
• However, accurate and numerous dates are needed.
  Because this is rare, pollen fluxes are not used
  very often.

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Pollen Interpretation

• Pollen diagrams are usually divided into zones to
  facilitate interpretations.
• Changes in pollen composition are interpreted to
  indicate changes in climate or human disturbance.

St. Paul, MN (Matsch, 1976).
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Pollen Interpretation

• Two general interpretative approaches exist
• Individualistic Approach Past environmental
  conditions are reconstructed on the basis of
  present-day ecology and environmental tolerance
  and optima of a plant species.
• Assemblage Approach Past environmental
  conditions are reconstructed on the basis modern
  plant associations in climate/ biogeographical
  regions.

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Pollen Interpretation

• Individualistic approach (Midwest)
• Decline in hardwood species (beech, maple, oak,
  hickory) and/or increase in conifer species
  (spruce, fir, pine) indicates cooling.
• Increase in ash and/or elm indicates wet
  environments.
• Decline in trees and increase in grasses
  indicates drier conditions.

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Pollen record for Money Creek and Pine Creek in
southeastern Minnesota (Baker et al., 2002).
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Pollen Interpretation

• Assemblage Approach
• Modern Analog Technique (MAT) Central
  assumption If two assemblages contain a similar
  mixture of pollen grains, then the communities
  that produced those assemblages must also have
  been similar.
• Another assumption Plant composition in an
  ecosystem is at equilibrium with the environment.

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Pollen Interpretation

• MAT relies on the dissimilarities of modern and
  fossil assemblages.
• To determine if they are the same, the threshold
  of relatedness is based on statistical
  comparisons between paired populations within and
  between ecosystems.

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Pollen Interpretation

• Hierarchical Analog Approach Based on functional
  analogs rather than on plant associations.
• First level of analyses similar to MAT
• Second level based on plant functional types.
• Third level based on plant life forms.

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Williams, 2003.
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Williams, 2003.
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Pollen Interpretation

• Transfer Functions A polynomial equation is
  fitted to observed pollen data.
• Not often used because these functions assume
  that only one parameter controls the distribution
  of vegetation (pollen).
• Particularly problematic for ecosystems with no
  modern analog.

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Macrofossils

• Plant remains (leaves, fruits, flowers, roots,
  etc) are preserved in some particular
  environments (e.g., swamps).
• Advantage species can readily be identified,
  provides good radiocarbon dates.
• Disadvantage Few locations are available and
  modern analogs are difficult to established.

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Tree-line (Ecotone)

• Gradual transition from mature dense forest
  through open, discontinuous woodland, to isolated
  trees or grasslands.
• Artic Ecotone Boreal forest/tundra
• Plant macrofossils are collected from soils.
• Soil type changes as vegetation changes.
• Tree line coincides with July temperature
• Tree line also coincides with mean summer
  position of the Arctic front.

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• Caveats of the record
• Trees invades grasslands at a faster pace than
  grasses colonize forests.
• Trees live longer than grasses, but grasses grow
  faster than trees.
• Fire frequency affects tree line.
• Invasion of new species.
• Records are usually incomplete.
• Are modern tree lines at equilibrium?
• What is the lag time?

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