Nonmarine biological evidence Chapter 8 Nonmarine biological evidence

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, p. H, and salinity. • Lakes are sampled for diatoms and measurements of temperature, p. H, 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.

Detrended Canonical Correspondence Analysis (DCCA). Larocque and Bigler (2004)

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 p. H, salinity, lake/pond depth, nutrients.