New Interpretations of An Old Data Source: Fossil Pollen and the Reconstruction of Neotropical Quaternary Paleoclimate

Fossil pollen has been used for decades in the reconstruction of Quaternary paleoclimate. Multiple numerical techniques have been developed to identify temperature and precipitation changes from pollen counts in the context of temperate plant communities. However, quantitative estimates of climatic change have been difficult to obtain for the lowland Neotropics, where sister species are often found in very different habitats and comparative information on the taxonomic composition of plant communities is limited.

Approaching the ecophysiological diversity of plant clades above the rank of species as a probability distribution rather than minimum and maximum thresholds provides greater resolution in the identification of small fluctuations in climate. Using multiple lacustrine pollen records from lowland Bolivia, I demonstrate how a likelihood analysis of family-level fossil pollen counts can be used to reconstruct Neotropical paleoclimate and provide information on historic patterns of climatic change.

Family-based climatological proxies have several advantages over biome-based reconstructions. Climatic estimates can be derived even when novel combinations of taxa are observed in the fossil record, extending the utility of the model to deep-time data. The model is also dynamic. Plant communities do not need to be in equilibrium and individualistic dynamics can be incorporated into estimates.

This regional analysis suggests that northeastern Bolivia experienced cooling (1–3 °C) and drying (400 mm/yr), relative to present, during the late Pleistocene (50,000–12,000 cal yr B.P.). Immediately prior to the Last Glacial Maximum (~21,000 cal yr B.P.), there is a distinct transition from cooler temperatures and variable precipitation to a period of warmer temperatures and relative dryness that extends to the mid-Holocene (5000–3000 cal yr B.P.). This prolonged reduction in precipitation occurs against the backdrop of increasing atmospheric CO₂ concentrations, indicating that the presence of mixed savanna and dry forest communities in northeastern Bolivia was not solely the result of low CO₂ levels.