Non-marine biological evidence

1. Non-marine biological evidence Chapter 8

2. Non-marine biological evidence • Plant Macrofossils • Diatoms • Insects • Ostracods

3. 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.

5. Plant macrofossil-Artic

6. Plant macrofossil-Alpine tree-line

7. Diatom-based paleoclimatogical reconstructions • Diatoms: Unicellular algae present in freshwater and marine systems. • Found in polar, temperate, sub-tropical, and tropical regions.

8. 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.

9. 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.

10. 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

11. 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.

12. 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.

13. 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.

14. 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.

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

16. Larocque and Bigler (2004)

17. 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.

18. 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.