Seasonal hydroclimate recorded in high resolution δ18O profiles across Pinus palustrus growth rings

The trees sampled in this study are growing at the Persimmon Gully Nature Preserve (30º 19' N, 93º 32' W, 15 masl) in southwestern Louisiana. Four cores (2A, 3B, 15A, 15B; all Pinus palustris) were extracted from three longleaf pine trees using an increment borer. One tree was sampled in duplicate from opposite sides of the trunk to produce two replicate cores (15A and 15B) to study intra-tree replication of oxygen isotope profiles. The four cores were mounted on wooden bases and sanded with 600-grit sandpaper to aid in identification of annual growth rings. Tree rings corresponding to the years 2001-2008 were manually sampled at 0.1 to 0.3 mm resolution under a binocular microscope using a razor blade, resulting in an average of 14 slices per growth ring. Cellulose was extracted from a total of 421 bulk wood slices using the modified Brendel method (Brendel et al. (2000, doi:10.1002/(SICI)1099-1565(200001/02)11:1<7::AID-PCA488>3.0.CO;2-U); Gaudinski et al. (2005, doi:10.1021/ac050548u)). Purified α-cellulose samples ranging in mass from approximately 50-100 μg were wrapped in silver capsules and analyzed for δ18Ocell values using a High-Temperature Conversion Elemental Analyzer coupled with a DELTA V Advantage Isotope Ratio Mass Spectrometry (IRMS) instrument (Thermo Fisher Scientific, Inc., USA) located at the University of Louisiana at Lafayette. The resulting values were expressed in delta notation (δ18O) in units per mil (‰) with respect to reference Vienna standard mean ocean water (VSMOW). Two internal laboratory standards (ACELL = 32.33 ± 0.06‰, JCELL01 = 17.64 ± 0.09‰) and a quality control sample (JCELL02 = 20.44‰) were analyzed with the cellulose samples. Standard deviation of the quality control samples was 0.11‰ (n = 9).