A Stable Isotope Investigation Of Pollen From Pinery Provincial Park, Southwestern Ontario, Canada

Author

Deana M. Schwarz, The University of Western OntarioFollow

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Fred Longstaffe

Abstract

Pollen is a useful proxy for reconstructing paleoclimate; however, the relationship between its stable isotopic composition and the environment in which it forms is still poorly understood. We examine the stable oxygen, carbon, and nitrogen isotope compositions of pollen from tree (coniferous and deciduous), grass (C₃ and C₄), and marsh species from Pinery Provincial Park, Ontario, and its environs, and maple and oak tree species from eight localities across the United States of America, to (i) determine the major environmental influences on pollen δ¹⁸O, δ¹³C, and δ¹⁵N values, (ii) examine the causes of stable isotopic variability of pollen from different plant species from the same location, and (iii) assess whether the isotopic composition of pollen corresponds to that of plant cellulose.

Assuming a cellulose-water fractionation factor of +27‰, δ¹⁸O values of T. latifolia (cattails) closely match δ¹⁸O_{precipitation} values at the time of sugar synthesis in the area, suggesting little to no isotopic enrichment. Grass species differ from δ¹⁸O_{precipitation} values at the time of sugar synthesis by +3.5 to +5.8‰, and tree species by +10.2 to +13.2‰, indicating increased levels of transpiration, and its attendant effects on δ¹⁸O_{leaf water} values, prior to pollen synthesis. Bulk leaf cellulose δ¹⁸O values differ by +0.6 to +2.1‰ relative to pollen in tree species versus up to +5.2‰ in grass species. These results suggest that the biochemical pathway used by sugars during translocation in grass species results in mixing of ¹⁸O-poor source water with leaf water. The δ¹³C value of pollen is likely controlled by a combination of factors such as photosynthetic pathway, and relative humidity (water stress) at the time of the formation of sugars used in pollen formation. The nitrogen isotope composition of pollen reflects a complex array of parameters, which were not resolved in this study, but likely reflects site-specific conditions affecting the more open versus more closed nature of the nitrogen cycle.

Recommended Citation

Schwarz, Deana M., "A Stable Isotope Investigation Of Pollen From Pinery Provincial Park, Southwestern Ontario, Canada" (2016). Electronic Thesis and Dissertation Repository. 4254.
https://ir.lib.uwo.ca/etd/4254