Non-marine biological evidence

Chapter 8

Non-marine biological evidence

• Plant Macrofossils• Diatoms• Insects• Ostracods

Plant Macrofossils

• Advantages: usually identifiable to the species level and easily dated.

• Disadvantages: fewer specimens relative to pollen, typically provides a discontinuous record.

• Used to assess fluctuations of tree-lines.• Unlike pollen, macrofossils are transported for

very short distances. Thus, they provide better information on tree-line movement.

Plant macrofossil-Artic

Plant macrofossil-Alpine tree-line

Diatom-based paleoclimatogical reconstructions

• Diatoms: Unicellular algae present in freshwater and marine systems.

• Found in polar, temperate, sub-tropical, and tropical regions.

Diatom-based paleoclimatogical reconstructions

• Based on the concept of ecological niche (a given population is adapted to survive and reproduce under a set of biotic and abiotic conditions).

• A niche can be devised as a multi-dimensional space in which the axes represent variables.

• In paleoclimatology, useful species are those with limited niches; whose abundance, distribution, and presence or absence are controlled by climatic factors.

• However, one needs to keep in mind that niches are dynamic and transient and that species can evolve and adapt.

• There are three main approaches to reconstruct paleo-climates:– Indicator species approach: relies on the

occurrence of species with known modern environmental tolerances.

– Assemblage approach– Transfer function approach

• Indicator species approach: relies on the occurrence of species with known modern environmental tolerances (benthic vs. planktonic).

• Assemblage approach: Based on modern analog techniques, where fossil and modern assemblages are statistically compared.

• Transfer function approach: modern taxa at different sites (Y) and environmental variables (X) are compared to obtain of a function of the form: Y= f(x) + variance.

f(x) is estimated by linear, non-linear, and/or multivariate regressions.

• Numerical techniques are employed to reconstruct temperature, pH, and salinity.

• Lakes are sampled for diatoms and measurements of temperature, pH, salinity, etc are performed simultaneously.

• Statistical methods (e.g., multi-component analysis) provide numerical relationships between diatoms and climatic parameters.

• Assumptions:– Modern taxa is related to the environment.– The measured environmental variables are ecologically

important.– Transfer functions adequately model the response of

modern taxa to the measured environmental variables.– Fossil taxa responded in a fashion predicted by the

transfer function.– Non-measured variables play a negligible role.

Larocque and Bigler (2004)

Detrended Canonical CorrespondenceAnalysis (DCCA).

Larocque and Bigler (2004)

Insects

• Midge flies (chironomid) are used to reconstruct temperature.

• They have a narrow ecological range, they are commonly present in aquatic systems, they are abundant, and they respond quickly to changes in temperature.

Insects

• Problems:Chironomids likely reflect water

temperature rather than surface temperature.

Because they can only be identified to the genus level, site-specific calibrations are needed.

Unknown effect of pH, salinity, lake/pond depth, nutrients.