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Doctor of Philosophy




Fred Longstaffe


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 δ18Oprecipitation values at the time of sugar synthesis in the area, suggesting little to no isotopic enrichment. Grass species differ from δ18Oprecipitation 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 δ18Oleaf 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.

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