Hydrogen isotope ratios as a Larix detector in archaeological wood samples

Identifying wood species in archaeological specimens is important for the evaluation of timber structures and the conservation of historic buildings. Microscopic wood anatomy is the most commonly used technique for species identification. However, its application is problematic for the analysis of deteriorated wood. In addition, a particular challenge is the distinction of Picea from Larix due to their similar microscopic features. Recently, an analysis of stable isotopes of cellulose has shown that Larix is characterized by significantly more depleted deuterium values compared to Picea as well as other conifers from the Alpine region. To verify if this fact can be used in archaeological studies, we obtained 36 specimens, most of which were not clearly identified as larch or spruce. The cellulose could be extracted from 20 of them. We identified Larix and non-Larix species (Picea) without ambiguity from the deuterium content, except for one sample with an intermediate value. In conclusion, the evaluation of deuterium content is a valuable tool for the study of archaeologic wood

Larch Cellulose Shows Significantly Depleted Hydrogen Isotope Values With Respect to Evergreen Conifers in Contrast to Oxygen and Carbon Isotopes

The analysis of the stable isotope of the tree-ring cellulose is an important tool for paleo climatic investigations. Long tree-ring chronologies consist predominantly of oaks and conifers in Europe, including larch trees (Larix decidua) and cembran pines (Pinus cembra) that form very long tree ring chronologies in the Alps and grow at the treeline, where tree growth is mainly determined by temperature variations. We analyzed δ13C, δ18O and δ2H isotopes in the cellulose extracted from tree-rings of wood samples collected at high altitude in the Swiss and Tyrol Alps, covering the whole Holocene period. We found that larch cellulose was remarkably more depleted in deuterium than that of cembran pine, with mean δ2H values of −113.4 ± 9.7‰ for larch and of −65.4 ± 11.3‰ for cembran pine. To verify if these depleted values were specific to larch or a property of the deciduous conifers, we extended the analysis to samples from various living conifer species collected at the Bern Botanical Garden. The results showed that not only the larch, but also all the samples of the deciduous larch family had a cellulose composition that was highly depleted in δ2H with regard to the other evergreen conifers including cembran pine, a difference that we attribute to a faster metabolism of the deciduous conifers. The δ18O values were not statistically different among the species, in agreement with the hypothesis that they are primary signals of the source water. While the δ13C values were slightly more depleted for larch than for cembran pine, likely due to metabolic differences of the two species. We conclude that the deciduous larch conifers have specific metabolic hydrogen fractionations and that the larch unique signature of δ2H is useful to recognize it from other conifers in subfossil wood samples collected for paleoclimatic studies. For climate information the absolute δ2H values of larch should be considered carefully and separate from other species

Assessing earlywood-latewood proportion influence on tree-ring stable isotopes

Tree-ring stable isotopes are typically measured in latewood cellulose to mitigate potential carry-over effects from previous year storage pools. The isotopic composition of individual tree-ring segments is thought to include considerable intra-annual variability. This sampling strategy may be complicated by steep intra-annual isotope gradients that can rival the inter-annual variability, however. Consistent sampling of latewood material may not always be possible due to low sample availability or high prevalence of narrow rings or low amounts of latewood because of species-specific changes in ring width. Therefore, years that contain samples with higher portions of non-latewood (earlywood) material may influence the final chronology of isotopic variability. Here, we analyze the potential influence that changing earlywood and latewood components of individual tree rings can have on stable carbon and oxygen records from Quercus spp. and Pinus heldreichii chronologies. Analysis of stable isotopes in oak tree rings with varying amounts of latewood show no statistically significant differences in the range of isotopic composition, nor any major differences when considering the same calendric year. Similar results were found for the pine data, when comparing stable isotope measurements with earlywood-to-latewood ratio and maximum density. We argue that this simple approach should be applied to any long-term tree-ring stable isotope record in order to provide a better understanding of the potential biases that could arise from previously recorded intra-annual variability in the wood

Recent summer warming over the western Mediterranean region is unprecedented since medieval times

© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)Contextualising anthropogenic warming and investigating linkages between past climate variability and human history require high-resolution temperature reconstructions that extend before the period of instrumental measurements. Here, we present maximum latewood density (MXD) measurements of 534 living and relict Pinus uncinata trees from undisturbed upper treeline ecotones in the Spanish central Pyrenees. Spanning the period 1119–2020 CE continuously, our new MXD composite chronology correlates significantly with gridded May–September mean temperatures over the western Mediterranean region (r = 0.76; p ≤ 0.001; 1950–2020 CE). Based on an integrative ensemble approach, our reconstruction reveals unprecedented summer warming since 2003 CE. The coldest and warmest reconstructed temperature anomalies are −3.4 (±1.4) °C in 1258 and 2.6 (±2.2) °C in 2017 (relative to 1961–90). Abrupt summer cooling of −1.5 (±1.0) °C was found after 20 large volcanic eruptions since medieval times. Comparison of our summer temperature reconstruction with newly compiled historical evidence from the Iberian Peninsula suggests a lack of military conflict during or following exceptionally hot or cold summers, as well as a general tendency towards less warfare and more stable wheat prices during warmer periods. Our study demonstrates the importance of updating and refining annually resolved and absolutely dated climate reconstructions to place recent trends and extremes of anthropogenic warming in a long-term context of natural temperature variability, and to better understand how past climate and environmental changes affected ecological and societal systems.The National Park “Aigüestortes i Estany de Sant Maurici” provided sampling permissions, and Meteo France temperature measurements from Pic du Midi. U.B. and J.E. were supported by the Czech Science Foundation grant HYDRO8 (23-08049S), and the ERC Advanced grant MONOSTAR (AdG 882727).Peer reviewe

Measurements of stable isotopes of cellulose from tree rings on Holocene samples – influence of plant species and cambial age and their impact on the interpretation of palaeoclimate

Tree rings are one of the most commonly used proxies for palaeoclimatic studies of the Holocene, in particular the width of the rings (TRW) has been found to be valuable for climate reconstructions. However, it has been shown that other tree-ring parameters can also serve as climate proxies providing additional climate information, such as the chemical composition of the wood, in particular the stable cellulose isotopes of the tree rings, which consist of the stable isotopes δ18O, δ13C and δD (or δ2H). The first objective of this work was to complete the measurements of the Eastern Alpine Conifer Chronology (EACC), which consists of more than 7000 samples from about 200 trees of two conifer species collected in the Swiss and Tyrolean Alps at high altitudes at the tree line. In this way, a continuous record of cellulose and isotope content was established, covering the last 9000 years. This large database was designed for palaeoclimate studies as well as for physiological studies. In the initial analysis of the database, we found that one of the two species, the larch, had uniquely low δD values compared to the other species in the database, the cembran pine. We then extended the analysis to several conifer species from the Bern Botanical Garden and confirmed the uniquely low value of the deciduous Larix genus. This new finding was published in the journal Frontiers in Earth Science. This unique signature of larch could be useful in archaeology, as it is important to determine the wood species and it is not always possible to distinguish the sample from spruce and larch using standard wood anatomy analysis. To test whether deuterium measurements can solve the plant genus assignment problem; we analysed about 20 archaeological wood samples that were uncertainly determined. The isotope data allowed us to clearly distinguish the genus in all but one of the samples, although they came from very different sites. The results are included in a manuscript that we submitted to the Journal of Archeological Science. Before using the database for palaeoclimatic studies, it was important to check how the different cambial ages and the different absolute ages of the trees that make up the EACC database affect the isotope records. These two features offer the possibility of investigating the influence of cambial age on tree rings’ isotopic composition to separate it from climatic influences. We found no age-related trend for the three isotopes in samples with a cambial age of more than 100 years. This suggests that the values of the tree isotopes after the 100 cambial years are suitable for palaeoclimatic purposes without detrending. In contrast, trends in the juvenile phase are consistent, with differences between species. We published these results in the Biogeoscience Journal. In a further step, we continued the analysis by investigating whether and how the relationships between isotopes and TRW change with the age of the cambium by examining the correlations at different ages and how different detrending methods affect these relationships. The results showed a changing relationship between carbon and hydrogen across cambial age, which could indicate differential use of reserves in the juvenile phase. We submitted the results of this study to the journal Forests. The EACC isotope database was designed for climate studies throughout the Holocene. Volcanic eruptions are known to produce short thermal climate trends. Studying short climate trends avoids the problem of varying absolute values between sample origins by examining climatic effects within the life span of trees. We use the last 2000 years of the database to examine the effects of volcanic eruptions and which separate the Icelandic eruptions from the tropical eruptions. In addition, we have also studied two eruptions, Tambora 1815 CE and Katla 750 – 764 CE, with an annual resolution of cellulose isotopes. We found that oxygen records the tropical eruption with negative values, in contrast, the hydrogen and carbon isotopes show no obvious variations. In conclusion, we show that the complete EACC isotope database has potential for future analysis or comparison with other databases. Therefore, we plan to make all data publicly available in a suitable archive

Alpine Holocene tree-ring dataset: age-related trends in the stable isotopes of cellulose show species-specific patterns

Stable isotopes in tree-ring cellulose are important tools for climatic reconstructions even though their interpretation could be challenging due to nonclimate signals, primarily those related to tree aging. Previous studies on the presence of tree-age-related trends during juvenile as well as adult growth phases in δD, δ18O, and δ13C time series yielded variable results that are not coherent among different plant species. We analyzed possible trends in the extracted cellulose of tree rings of 85 larch trees and 119 cembran pine trees, i.e., in samples of one deciduous and one evergreen conifer species collected at the tree line in the Alps, covering nearly the whole Holocene. The age trend analyses of all tree-ring variables were conducted on the basis of mean curves established by averaging the cambial-age-aligned tree series. For cambial ages over 100 years, our results prove the absence of any age-related effect in the δD, δ18O, and δ13C time series for both the evergreen and the deciduous conifer species, with the only exception being larch δD. However, for lower cambial ages, we found trends that differ for each isotope and species; i.e., mean δ13C values in larch do not vary with aging and can be used without detrending, whereas those in cembran pine show a juvenile effect, and the data should be detrended. Mean δ18O values present two distinct aging phases for both species, complicating detrending. Similarly, mean δD values in larch change in the first 50 years, whereas cembran pine changes between 50 and 100 years. Values for these two periods of cambial age for δD and δ18O should be used with caution for climatic reconstructions, ideally complemented by additional information regarding mechanisms for these trends

Investigating Masking Effects of Age Trends on the Correlations among Tree Ring Proxies

Age-related trends are present in tree-ring widths (TRW), but their presence in tree rings isotope is debated. It is unclear how cambial age influences the relationships between TRW and isotopes. Tree-ring isotopes of alpine larch and cembran-pine trees showed only trends in the juvenile period (>100 years), which might mask the inter-relations between tree-ring proxies during cambial age. This work tries to unmask the age-trend influences by examining the correlations in TRW—stable isotopes with and without age-trend correction. The non-detrended and linear-detrended values of TRW, of δD and δ18O showed significant correlations for ages up to 100 years, but not afterward. However, the correlation values, after spline or first-difference time-series detrending, were not age-related. Thus, detrending methods affect the correlations in the juvenile phase and may affect climate-related interpretations. The correlations between TRW and δ13C were not age-related, while those among the isotopes were significant throughout the ages. The correlation between δ13C and δD was the exception, as it became significant only after age > 100 years, suggesting a different use of reserves in the juvenile phase. In conclusion, the relationships among the tree-ring parameters are stable in all the different detrend scenarios after the juvenile phase, and they can be used together in multi-proxy paleoclimatic studies. The data of the juvenile phase can be used after spline-detrending or first-difference time-series calculation, depending on the purpose of the analysis to remove age-related trends. The work also provides clues on the possible causes of juvenile age trends

Alpine Holocene Triple Tree Ring Isotope Record

Stable isotope ratios from tree rings are important proxies of past climate variations. We have access to a calendar-dated wood material from wood collected at glacier forefields and peat bog sites located in the Alps. They are of two species, larch (Larix decidua) and cembran pine (Pinus cembra). All the wood samples were collected at high altitudes in the Swiss and Tyrol Alps, they cover the whole Holocene period and belong to the Eastern Alpine Conifer Chronology Dataset (Nicolussi et al., 2009; doi:10.1177/0959683609336565). We analysed the δ13C, δ18O and δ2H isotope ratios of alpha cellulose obtained from blocks of 5 annual rings from 203 trees. Cellulose was extracted following the modified Jayme-Wise method (Boettger et al., 2007; doi:10.1021/ac0700023). The isotopes values were determined using conventional Isotope Ratio Mass Spectrometry (Isoprime 100) coupled to a pyrolysis unit (HEKAtech GmbH, Germany), which is similar to the previously used TC/EA (for technical details see (Leuenberger 2007). This approach was extended to measurements of non-exchangeable hydrogen of alpha-cellulose using the on-line equilibration method (Filot et al., 2006 (doi:10.1002/rcm.2743); Loader et al., 2015(doi:10.1021/ac502557x)). The results are reported in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB) for carbon and to Vienna Standard Mean Ocean Water (VSMOW) for hydrogen and oxygen (Coplen 1994; doi:10.1351/pac199466020273). For all the δ13C values after 1000 CE we applied the factor described in Leuenberger (2007; doi:10.1016/S1936-7961(07)01014-7) to correct for the δ13C depletion of CO2 caused by the Industrial Revolution from about 1850 onwards (Leuenberger, 2007)