Tree-ring d13C records from living trees and Oligocene wood fossils from Nanning China, with seasonal paleoclimate proxy results

Two radial cores (QXS21A and QXS24A) from living Pinus massoniana trees growing at Qingxiushan Hill, Nanning, Guangxi, China (22°47'23.35” N, 108°23'4.26” E, elevation = 223 m) were collected in 2016 using an increment borer. Consecutive growth rings spanning the years 1990 to 2000 were selected from each core for analysis. Each ring was subdivided by hand using a razor blade parallel to the direction of growth. A total of 317 subsamples were collected from across the two cores. Fossil wood specimens were collected from the Santang Konservat Lagerstätte in the upper Yongning Formation in Nanning Basin, Guangxi, China (22°52'50” N, 108°25'2” E, elevation = 83 m). Three fossil wood samples (NNW010, NNW12B, and NNW021) were selected for intra-ring δ13C analysis. A total of 20 growth rings were subsampled (n = 518) following the same procedures as the modern wood. The wood fossils are stored and fully accessible in the Biological Museum of Sun Yat-sen University, Guangzhou, China. Bulk wood slices weighing between 80 and 150 µg were placed in pure tin capsules for stable isotope analysis. All δ13C values were determined using a Thermo Finnigan Elemental Analyzer (Flash EA 1112 Series, Bremen, Germany) coupled with a Delta V Advantage Isotope-ratio Mass Spectrometer (Thermo Fisher) at the University of Louisiana at Lafayette. Samples were analyzed with three internal laboratory reference materials (JGLY, δ13C = -43.51‰; JHIST, δ13C = -8.13‰; JGLUC, δ13C = -10.52‰). A quality assurance sample (JRICE, δ13C = -27.44‰) was analyzed as an unknown with each batch run, and yielded a <0.1‰ analytical uncertainty. Isotope values are reported in δ-notation (per mille, ‰) with respect to Vienna Pee Dee Belemnite (VPDB).