HR: 0800h
AN: PP11A-1424    [Abstracts]
TI: Limits on the Natural Oxygen-18 Abundance of Cellulose: Intra-molecular Patterns
AU: * Sternberg, L
EM: l.sternberg@miami.edu
AF: Department of Biology, University of Miami, Coral Gables, FL 33124 United States
AU: Jahren, H
EM: jahren@jhu.edu
AF: Department of Earth and Planetary Science, John Hopkins University, Baltimore, MD 21218 United States
AU: Anderson, W
EM: andersow@fiu.edu
AF: Earth Sciences Department, Florida International University, Miami, FL 33199 United States
AU: Pinzon, M C
EM: pinzon@bio.miami.edu
AF: Department of Biology, University of Miami, Coral Gables, FL 33124 United States
AB: The oxygen isotope composition of tree-ring cellulose is an often-invoked quantitative proxy for multiple environmental factors, including paleotemperature, paleohumidity and paleoprecipitation patterns. A broad survey of aerial and aquatic plants reveals an upper limit to the ¹⁸O enrichment of cellulose relative to water at the site of cellulose synthesis, which we explain via the comparison of individual oxygen atoms within the cellulose molecule. We collected stems from various geographical regions, extracted stem water and cellulose and determined the oxygen isotope ratios of these two components. The cellulose was hydrolyzed to its glucose moieties and derivatized to determine the oxygen isotope ratios of the oxygens attached to carbon 3, 4, 5, 6 of the glucose moieties, which allowed us to calculate the oxygen isotope ratios of the oxygen attached to the carbon 2 of the glucose moieties. A compilation of results from our collection and from previous publications shows that δ¹⁸O values of cellulose increase with δ¹⁸O values of stem water only for samples having stem water with δ¹⁸O values below -10‰ (SMOW). However, the δ¹⁸O values of stem cellulose levels off and remains constant for stems having water with δ¹⁸O values greater than -10‰. This pattern suggests a limit on the enrichment of stem (and by inference tree ring) cellulose. This limitation had previously been ascribed to environmental factors affecting leaf water (e.g., humidity, stomatal conductance, solute potential). A compilation of the δ¹⁸O values of cellulose from aquatic plants versus that of their ambient water, however, shows the same general pattern which has been previously explained on the basis of evaporation rates and heterogeneities of lake water. We disprove the previous explanations by demonstrating differential isotopic effects on the oxygen atoms of the cellulose molecule. Our observation on the δ¹⁸O values of oxygen attached to carbon 2 versus those attached to carbon 3, 4, 5, 6 indicates that the more isotopically enriched are the oxygens attached to carbon 3, 4, 5, 6 -- the more isotopically depleted is the oxygen attached to carbon 2. From these patterns we suggest a biochemical basis for the observed limit in ¹⁸O enrichment of cellulose, in contrast to the previously posited environmental influences.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1620 Climate dynamics (0429, 3309)
DE: 1851 Plant ecology (0476)
DE: 4870 Stable isotopes (0454, 1041)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005