Interrogating trees for isotopic archives of atmospheric sulphur deposition and comparison to speleothem records

Palaeorecords which depict changes in sulphur dynamics form an invaluable resource for recording atmospheric pollution. Tree rings constitute an archive that are ubiquitously available and can be absolutely dated, providing the potential to explore local- to regional-scale trends in sulphur availability. Rapid isotopic analysis by a novel “on-line” method using elemental analyser isotope ratio mass spectrometry (EA-IRMS) is developed, achieving sample precision of <0.4‰ using sample sizes of 40 mg wood powder. Tree cores from NE Italy show trends in pollution, evidenced through increasing concentrations of sulphur towards the youngest growth, and inverse trends in sulphur isotopes differentiating modern growth with light sulphur isotopes (+0.7‰) from pre-industrial growth (+7.5‰) influenced by bedrock composition. Comparison with speleothem records from the same location demonstrate replication, albeit offset in isotopic value due to groundwater storage. Using EA-IRMS, tree ring archives form a valuable resource for understanding local- to regional-scale sulphur pollution dynamics

Izostanek juvenilnega efekta potrjen v stabilnih izotopih ogljika in kisika v branikah evropskega macesna

Članek obravnava razmerja ogljikovih in kisikovih izotopov v branikah blizu stržena na prsni višini (cca 1,2 m) treh evropskih macesnov (Larix decidua Mill.), rastočih v mešanem gozdu s predraslimi hrasti in nasajenimi evropskimi macesni v zahodnem Walesu, Velika Britanija. Neklimatskega naraščajočega trenda v razmerjih ogljikovih izotopov, ki ga je sicer opaziti pri drugih vrstah v letih juvenilne rasti, ni, in tudi razmerje stabilnih izotopov ne kaže pomembnih trendov med odraščanjem drevesa. Rezultati iz prvih desetih branik ob strženu se bistveno ne razlikujejo od naslednjih dveh nizov desetih branik. O izostanku juvenilnega efekta v ogljikovih izotopih evropskega macesna so že poročali v zvezi z macesni, rastočimi v nesklenjenih sestojih v Franciji in to pripisali nezastrtosti krošenj in posledične neuporabe ogljikovega dioksida, ki ga pri dihanju oddajajo drevesa. Analizirana drevesa v zahodnem Walesu so rasla v nasadu s predraslimi hrasti, ki so bili starejši od podraslih macesnov. Macesni, kot svetloljubne drevesne vrste, so morali tekmovati za prostor in svetlobo, zato domnevamo, da je morebiten pojav juvenilnega efekta pri stabilnih izotopih prej posledica sprememb v hidravlični prevodnosti lesa, kot pa česa drugega. Ker današnja praksa izogibanja juvenilnega lesa omejuje potencial stabilnih izotopov drevesnih branik za dendroklimatološke in fiziološke raziskave, bi bile potrebnih dodatne raziskave o učinkih juvenilne rasti na pojav juvenilnega efekta v meritvah stabilnih izotopov.We report carbon and oxygen isotope ratios measured from the pith at breast height (ca. 1.2m) of three European larch (Larix decidua Mill.) trees growing in a mixed wood in West Wales, UK. The non-climatic rising trend of carbon isotope ratios reported for other species during early (juvenile) growth is not present and neither isotope shows significant trends as the tree matures. Results from the first ten rings are not significantly different from the next two sets of ten rings. Absence of a juvenile effect in carbon isotopes of European larch has been reported from trees growing in a low density stand in France and attributed to an absence of shading and no use of respired carbon dioxide. This site, in contrast, is densely wooded and the dominant oaks predate the larch trees, suggesting that juvenile effects, when present, may instead be caused by changes in hydraulic conductivity. More research is needed on juvenile effects as the current practice of avoiding juvenile wood is restricting the potential of stable isotope analysis of tree rings for dendroclimatology and plant physiology

A 1000-year carbon isotope rainfall proxy record from South African baobab trees (Adansonia digitata L.)

A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab ( Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone

Intra-annual variability of wood formation and δ13C in tree-rings at Hyytiälä, Finland

Investigation of the relationship between tree-ring stable carbon isotope composition (δ13C) and environmental variables at the intra-seasonal scale can inform on the understanding of the environmental forcing affecting trees during the active period of radial growth. Recent progress in the measurement techniques for assessing the δ13C signature of tree rings at high spatial resolution provides an opportunity to derive tree physiological information at fine temporal scale, within a given year. Three δ13C time series of resin-extracted wholewood from tree-rings of Scots pine trees (Pinus sylvestris L.) sampled at Hyytiälä (Finland) have been produced by using laser-ablation stable isotope mass spectrometry. These intra-seasonal stable isotope series exhibit a strong common signal (EPS = 0.96) demonstrating the capacity of trees within a stand to preserve a common intra-seasonal response to external controls in a similar manner as found with annual measurements. To estimate when wood cells are active and responsive to environmental information, a Gompertz approach, assessed against microcore data, was adopted to model the timing of wood formation. The addition of a cell lifetime function into environment-growth models may evaluate more completely, the environmental effect on intra-annual tree-ring δ13C values and that during the growing season. Statistical analysis of the resulting tree-ring δ13C intra-annual signal implies a shift in importance from the influence of the environmental variables through out the growing season

Climatic controls on the survival and loss of ancient types of barley on North Atlantic Islands

This study was partly funded by a Scottish Government Rural and Environment Science and Analytical Service award (PM, JW and TSG). The Scottish Northern Cairngorms reconstruction was finalised through the project NERC project ‘SCOT2K: Reconstructing 2000 years of Scottish climate from tree rings (NE/ K003097/1)’ while the new central and northwest Scottish data were developed as part of a NERC Iapetus PhD project.For ancient types of barley at sites in the Scottish Isles, Faroes, and Iceland, we calculated minimum temperature requirements for grain production (grain production threshold, GPT) as accumulated degree days over the cropping season. Site suitability for barley from AD 1200 to 2000 was investigated by comparing these thresholds with reconstructions of annual cropping season degree days (CSDD) using temperature and tree-ring data. In Iceland, between AD 1200 and 1500, reconstructed CSDD were more favorable in the southwest (Reykjavik), with fewer years below the GPT, than in the North, East and West, but there were two periods (1340–1389 and 1426–1475) with low average CSDD and several years below the GPT which possibly influenced the abandonment of barley cultivation around this time. Reconstructed CSDD for the Faroes (Tórshavn) had only one year below the GPT, but 15 periods of four or more consecutive years with low CSDD which would have challenged barley cultivation, especially in the thirteenth century. Reconstructed CSDD were highest for the Scottish Isles, allowing a more prominent role of barley in the farming system and economy. Nevertheless, years with poor harvests or famines were common and about half were associated with low CSDD, resulting in a significant temperature link but also demonstrating the important contribution of other factors. Despite frequent unfavorable years in both the Faroes and Scottish Isles, resilient production systems, well-adapted barley strains and socio-economic factors allowed barley cultivation to continue, and some ancient types to survive to the present day.Publisher PDFPeer reviewe

Inter-genus Oxygen Isotope Dendrochronology of the Newport Medieval Ship Keel

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Oxygen isotope dendrochronology of Llwyn Celyn; One of the oldest houses in Wales

We report the application of oxygen isotope dendrochronology to date a high-status and remarkably unaltered late medieval hall house on the eastern border of South Wales. The oak timbers have either short and complacent ring series, or very strong growth disturbance, and none were suitable for ring-width dendrochronology. By using stable oxygen isotopes from the latewood cellulose, rather than ring widths, it was possible to cross-match and date all 14 timber samples and to provide felling dates related to several phases of building. The hall and solar cross-wing were constructed shortly after 1420CE, which is remarkably early. The house was upgraded using timbers felled in the winter of 1695/6CE by ceiling over of the hall and inserting a chimney. A separate small domestic building was added at the same time and the addition of the kitchen is likely to be contemporaneous. A substantial beast house was added a few years before the house was refurbished, emphasising the importance of cattle as the main source of wealth. A small barn with timbers felled in spring 1843 CE was added later. Llwyn Celyn is one of the most important domestic buildings in Wales, but without the new approach none of the phases of its evolution could have been dated precisely. Oxygen isotope dendrochronology has enormous potential for dating timbers that have small numbers of rings and/or show severe growth disturbance and it works well in regions where tree growth is not strongly constrained by climate. The research was generously supported by the Leverhulme Trust, Natural Environment Research Council, Landmark Trust and the UK National Lottery Heritage Fund

Are there enormous age-trends in stable carbon isotope ratios of oak tree rings?

We test a recent prediction that stable carbon isotope ratios from UK oaks will display age-trends of more than 4‰ per century by measuring >5400 carbon isotope ratios from the late-wood alpha-cellulose of individual rings from 18 modern oak trees and 50 building timbers spanning the 9th to 21st centuries. After a very short (c.5 years) juvenile phase with slightly elevated values, the number of series that show rising and falling trends is almost equal (33:35) and the average trend is almost zero. These results are based upon measuring and averaging the trends in individual time-series; the ‘mean of the slopes’ approach. We demonstrate that the more conventional ‘slope of the mean’ approach can produce strong but spurious ‘age-trends’ even when the constituent series are flat, with zero slope and zero variance. We conclude that it is safe to compile stable carbon isotope chronologies from UK oaks without de-trending. The isotope chronologies produced in this way are not subject to the ‘segment length curse’, which applies to growth measurements, such as ring width or density, and have the potential to retain very long-term climate signals