The effect of diagenesis on carbon isotope values of fossil wood

Abstract

The carbon isotope (δ13C) value of modern and fossil wood is widely used as a proxy for environmental and climatic change. Many researchers who study stable carbon isotopes in modern and recently deceased trees chemically extract cellulose (δ13Ccell) rather than analyzing whole wood (δ13Cwood) due to concerns that molecular variability across tree rings could influence δ13Cwood values, and that diagenesis may preferentially degrade cellulose over lignin. However, the majority of deep-time researchers analyze δ13Cwood without correcting for possible diagenetic effects due to cellulose loss. We measured δ13Ccell, δ13Cwood, and cellulose content of 38 wood fossils that span ∼50 m.y. in age from early Eocene to late Miocene, using variability across such a large range of geologic ages and settings as a natural laboratory in diagenesis. For comparison with our measurements, we produced a literature compilation of 1210 paired δ13Ccell and δ13Cwood values made on fossil and modern trees. We report that, on average, the apparent enrichment factor (ε) between δ13Ccell and δ13Cwood (ε = δ13Ccell – δ13Cwood) is 1.4‰ ± 0.4‰ larger in deep-time samples than Holocene wood, and this can be explained by loss of cellulose during degradation, independent of atmospheric chemistry or climate conditions during growth. A strong linear correlation exists between δ13Cwood and δ13Ccell in both deep-time (r2 = 0.92) and Holocene (r2 = 0.87) samples, suggesting that either substrate can provide a reliable record of environmental conditions during growth. However, diagenetic effects must be corrected if δ13Cwood values are compared to extant trees or across long time scales, where cellulose content may vary.

Late Oligocene Precipitation Seasonality in East Asia Based on δ13C Profiles in Fossil Wood

“…However, normalized δ 13 C records of the modern wood showed the relative changes in δ 13 C value to be consistent across individuals (Figure 2c). On average, the late Oligocene wood fossils had significantly lower δ 13 C values than the modern wood (Kruskall-Wallis rank sum test, p < 0.001) (Figures 2d-2f), consistent with preferential preservation of lignin relative to cellulose (Lukens et al, 2019a) and/or higher atmospheric CO 2 levels in the Oligocene relative to today (Foster et al, 2017;. Notably, the fossil wood showed a similar quasi-periodic intra-ring δ 13 C pattern to the modern wood, consistent with the evergreen habit inferred for the specimens based on previous work (Huang et al, 2018;Schubert & Jahren, 2011).…”

“…For modern and fossil samples, bulk wood slices weighing between 80 and 150 µg were wrapped in tin capsules for δ 13 C analysis. Cellulose was not extracted for these data; previous work has shown a robust linear correlation between the δ 13 C value recorded in bulk wood tissue and α‐cellulose (Lukens et al., 2019a), and the goal of the current study was to analyze relative changes in δ 13 C value rather than exact values (after Schubert & Jahren, 2011). All δ 13 C values were determined using a Thermo Finnigan Elemental Analyzer (Flash EA 1112 Series) coupled with a Delta V Advantage isotope‐ratio mass spectrometer (Thermo Fisher) at the University of Louisiana at Lafayette.…”

An annual-resolution stable isotope record from Swiss subfossil pine trees growing in the late Glacial

“…This differential decay is a crucial consideration, as various wood components have divergent isotopic signatures, which can significantly impact the resultant wholewood stable isotopic signature. For example, a consistent enrichment of δ 13 C (Loader et al 2003;Lukens et al 2019) and inconsistent δ 18 O contained in lignin compared to cellulose (Park & Epstein 1961, Wilson & Grinsted 1977, Barbour 2002, McCarroll & Loader 2004, Borella et al 1999. During burial and preservation of subfossil wood, infiltration of sediment-laden water leads to the reduction of specific acidic groups (native carboxyls and salt-derived carboxylates), and production of others (e.g.…”

Mineralogical and paleobotanical investigations of Oligo-Miocene petrified wood from the southwest of Thrace Basin (NW Turkey)

“…In many parts of the world (such as Indonesia, America, Germany, Egypt, Iran, etc.) there are petrified wood forests formed at different times by volcanic activities (Voudouris et al, 2007;Dietrich et al, 2013;Mustoe, 2017;Mustoe and Viney, 2017;Hassan, 2019;Lukens et al, 2019;Mustoe et al, 2019;Pe-Piper et al, 2019). Various fossil forest locations were identified in Turkey, mainly in central Anatolia (Ankara-Çamlıdere-Kızılcahamam, Bolu-Seben, Tokat-Zile etc.)…”