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Cross-dating is considered one of the most important principles of dendrochronology. The first known cross-dating attempts, conducted between the years 1737 and 1783 by independent researchers in France, Germany, and Sweden, were related to the identification of growth rings believed to have formed during the harsh winter of 1708-1709. In this paper, we present a novel perspective on the birth of dendrochronology and cross-dating in the 1700s. We focus on the ideas and experimental studies of one of the lesser known pioneers, Johan Leche (1704-1764), the Professor of Medicine at the Royal Academy (Turku, Finland). Instead of winter harshness, Leche was fascinated by the drought that killed and damaged several trees and tree species in the summer of 1757. Leche conducted several dendrochronological and field experiments described only in his unpublished manuscript filed in the National Archives in Sweden. Reviewing Leche's measurements of ring-width series of multiple radii and his comparisons between the radii, it seems only fair to include him in the long list of natural historians who made important contributions to the field ofdendrochronology. His manuscript was never published, which is why Leche's dendrochronological experiments and recommendations never reached a wider audience. Key words: tree-ring research, dendrochronology, dendroclimatology, cross-dating, history of science. La datation croisee est consideree comme un des plus importants principes de la dendrochronologie. Les premieres tentatives connues de datation croisee, effectuees entre les annees 1737 et 1783 par des chercheurs independants en France, en Allemagne et en Suede, etaient reliees a l'identification de cernes de croissance qu'on croyait avoir ete formes durant le rude hiver de 1708-1709. Dans cet article, nous presentons une nouvelle perspective sur la naissance de la dendrochronologie et la datation croisee au cours des annees 1700. Nous mettons l'accent sur les idees et les etudes experimentales menees par un des pionniers moins connus, Johan Leche (1704-1764), le professeur de medecine a l'Academie royale (Turku, Finlande). Au lieu de la severite de l'hiver, Leche etait fascine par la secheresse qui avait tue et endommage plusieurs arbres et especes d'arbres a l'ete de 1757. Leche realisa plusieurs etudes dendrochronologiques et experiences sur le terrain decrites seulement dans son manuscrit non publie depose dans les Archives nationales en Suede. Lorsqu'on examine les mesures de Leche qui portent sur les series dendrochronologiques de multiples rayons, il semble seulement juste de l'inclure dans la longue liste d'historiens de la nature qui ont apporte d'importantes contributions au domaine de la dendrochronologie. Son manuscrit n'a jamais ete publie, ce qui explique pourquoi les travaux de Leche en dendrochronologie et ses recommandations n'ont jamais rejoint une plus large audience. [Traduit par la Redaction] Mots-cles : recherche sur les cernes des arbres, dendrochronologie, dendroclimatologie, datation croisee, histoire des sciences., Introduction Climatic change has over recent decades led to a growing need to better understand historical climate variability. For this purpose, local and national archives are continuously and systematically scrutinized [...]

In recent years, much evidence has been presented on the 4.2 ka event. A review of 317 palaeoclimate papers shows that dry conditions were common during the event, especially from Eastern Mediterranean to India. The 4.2 ka event was not, however, a global drought event. Wet conditions were reported especially for central/northern Europe and sub-Saharan Africa. The 4.2 ka event is typically characterized either as short (4.2–4.0 ka) or long (4.4–3.8 ka) episode, possibly developing over an extended interval of time, in keeping with the North Atlantic forcing and correlating with the Bond 3 event of ice-rafted debris. This forcing is understood to drive a southward migration of the Inter-Tropical Convergence Zone (ITCZ), resulting in decreased rainfall over most of the Asian monsoon region, with possibility that an interplay of El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) has modulated the global circulation. Cold conditions were also reported but less frequently, in comparison to other Bond events such as the 8.2 ka event, Dark Ages Cold Period and Little Ice Age. Some high-resolution records show a double peak structure of which two anomalies are tree-ring dated to 4.14–4.05 ka and 3.97 ka. Accurately and precisely dated high-resolution records indicative of various climatic variables, especially outside of the traditional study region (Mediterranean–Middle East–India–China), including reconstructions of the ENSO and NAO histories and ITCZ migrations, are crucially needed for rigorous examination of the global scale characteristics of the 4.2 ka event and its forcings. Such research seems to be just beginning. [ABSTRACT FROM AUTHOR]

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The Carrington event of 1859 has been the strongest solar flare in the observational history. It plays a crucial role in shedding light on the frequency and impacts of the past and future Solar Energetic Particle (SEP) events on human societies. We address the impact of the Carrington event by measuring tree‐ring 14C with multiple replications from high‐latitude locations around the event and by comparing them with mid‐latitude measurements. A transient offset in 14C following the event is observed with high statistical significance. Our state‐of‐the‐art 14C production and transport model does not reproduce the observational finding, suggesting features beyond present understanding. Particularly, our observation would require partially fast transport of 14C between the stratosphere and troposphere at high latitudes. The observation is consistent with the previous findings with the SEP events of 774 and 993 CE for which faster integration of 14C into tree rings is observed at high latitudes. Plain Language Summary: Strong Earth‐directed solar eruptions can cause 14C concentration spikes in the atmosphere. Large enough events may leave a signal in the annually grown tree‐rings as they capture the isotopic carbon fingerprint through photosynthesis. Such rapid 14C increases have been detected, for instance, starting in years 774 and 993 CE. However, no increase has been observed following the Carrington event of 1859, despite it being the largest solar eruption of the modern era. Notably, all prior 14C measurements covering the Carrington event come from mid‐latitude trees. To achieve a broader geographical coverage, we have measured the event from several high‐latitude locations. After comparing the high‐ and mid‐latitude measurements, we have found a statistically significant difference lasting for several years post‐Carrington. To better understand the difference, we have adopted a 14C production and atmospheric transport model capable of simulating regional differences. Despite the improved model, we found it unable to reproduce the observational results, which suggests features beyond current understanding. Ultimately, the observation emphasizes the role of subtle 14C differences in tree‐ring 14C studies, potentially opening new ways to study past solar phenomena and atmospheric dynamics. Key Points: A transient offset in 14C from high‐latitude Finnish Lapland tree rings was observed between years 1861 and 1863The Carrington event and the stratosphere‐troposphere dynamics are discussed as potential explanations for the disparityThe discovery underscores the importance of transient offsets, high‐latitude tree rings in spotting anomalous solar/geomagnetic phenomena [ABSTRACT FROM AUTHOR]

Tree-ring data is commonly used in forest science and dendrochronology. As the collected datasets represent restricted populations of theoretical infinite sample size, an interesting question deals with the sample selection that is carried out during the fieldwork and through the data analyses. This paper considers the latter issue, by statistically examining a recently completed Scots pine dataset of timberline tree-rings from Lapland (northern Finland). Following the detrending of individual ring-width series, the composition of the data was restricted using a pre-determined criteria of linear correlativity between the individual sample series and the master chronology (Rmaster). This procedure reduced both the number of sites and the sample size (i.e. the number of individual tree-ring series) and altered the tree-ring statistics of the remaining subset of the data in a systematic fashion. It was seen that the first-order autocorrelation, mean sensitivity and standard deviation all ascended with the uplifted Rmaster criterion. Conspicuously, such filtering also reduced the correlation between the resulting tree-ring chronology and climate parameter. The results indicated that the screening of the data will alter the chronology statistics in a way that may be artificially generated, irrelative to the predetermined sample selection criteria. We remain to assume that the most fundamental selection of data is attained through the cross-dating process.