Tree-Ring Anatomy Improves the Reliability of Temperature Reconstructions Using Relict Wood

Abstract Tree rings are crucial for reconstructing past climates, with maximum latewood density (MXD) as a key metric. However, wood integrity is critical for accurate MXD-based reconstructions, raising concerns when using potentially degraded relict wood. Quantitative wood anatomy (QWA) provides a morphometric alternative. We compared X-ray and QWA-derived density measurements from recent and five-millennia-old relict wood from Siberia's Yamal region. We measured bulk density and holo-cellulose-to-wood ratio and employed spectroscopic analyses to identify chemical factors affecting density loss. The findings indicate likely abiotic degradation in relict wood, evidenced by significantly lower bulk density, holo-cellulose content, and MXD than recent samples, while anatomical density and maximum radial cell wall thickness appeared unchanged. MXD-based estimates suggested 1.7°C colder June-August (JJA) temperatures 4,700 years ago, while QWA-based estimates indicated 0.4°C warmer JJA temperatures than the 20th-century mean. For relict wood with potential mass loss due to degradation, QWA is recommended over traditional MXD methods.