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Light and water availability are likely to vary over the lifespan of closed-canopy forest trees, with understory trees experiencing greater limitations to growth by light and canopy trees greater limitation due to drought. As drought and shade have opposing effects on isotope discrimination (Δ13C), paired measurement of ring width and Δ13C can potentially be used to differentiate between water and light limitations on tree growth. We tested this approach for Cedrela trees from three tropical forests in Bolivia and Mexico that differ in rainfall and canopy structure. Using lifetime ring width and Δ13C data for trees of up to and over 200 years old, we assessed how controls on tree growth changed from understory to the canopy. Growth and Δ13C are mostly anti-correlated in the understory, but this anti-correlation disappeared or weakened when trees reached the canopy, especially at the wettest site. This indicates that understory growth variation is controlled by photosynthetic carbon assimilation due to variation in light levels. Once trees reached the canopy, inter-annual variation in growth and Δ13C at one of the dry sites showed positive correlations, indicating that inter-annual variation in growth is driven by variation in water stress affecting stomatal conductance. Paired analysis of ring widths and carbon isotopes provides significant insight in what environmental factors control growth over a tree's life; strong light limitations for understory trees in closed-canopy moist forests switched to drought stress for (sub)canopy trees in dry forests. We show that combined isotope and ring width measurements can significantly improve our insights in tree functioning and be used to disentangle limitations due to shade from those due to drought. [ABSTRACT FROM AUTHOR]

As the worldwide standard for radiocarbon (14C) dating over the past ca. 50,000 years, the International Calibration Curve (IntCal) is continuously improving towards higher resolution and replication. Tree-ring-based 14C measurements provide absolute dating throughout most of the Holocene, although high-precision data are limited for the Younger Dryas interval and farther back in time. Here, we describe the dendrochronological characteristics of 1448 new 14C dates, between ~11,950 and 13,160 cal BP, from 13 pines that were growing in Switzerland. Significantly enhancing the ongoing IntCal update (IntCal20), this Late Glacial (LG) compilation contains more annually precise 14C dates than any other contribution during any other period of time. Thus, our results now provide unique geochronological dating into the Younger Dryas, a pivotal period of climate and environmental change at the transition from LG into Early Holocene conditions. [ABSTRACT FROM AUTHOR]

The African baobab, Adansonia digitata, has great paleoclimatological potential because of its wide distributional range and millennial lifespan. However, dendroclimatological approaches are hampered by dating uncertainties due to its parenchyma-dominated wood anatomy. Here, securely-dated time series of annual wood increment growth and intra-ring stable isotopes of carbon and oxygen of cellulose for a baobab tree from Oman covering 1941 to 2005 were established. Precise dating with the bomb peak by highly resolved 14C measurements proved the annual character of the baobab's growth rings. But, F14C values of tree-ring cellulose were found up to 8.8 % lower than in the corresponding atmospheric CO2 for the period around the bomb peak. In conjunction with a considerable autocorrelation of the δ13C series this points to the incorporation of previous years' carbon significantly affecting the average age of derived wood. Terminal parenchyma bands, marking the tree-ring boundaries, were found to be significantly younger than their corresponding tree ring indicating that parenchyma tissue is alive for many years undergoing cell division, reorganization and potential growth. No autocorrelation was found in the δ18O series of tree-ring cellulose despite the huge water-storage potential of this stem-succulent tree species. Tree-ring width and stable isotope ratios have revealed significant climate sensitivity. δ18O was found to be a good climate proxy followed by tree-ring width and δ13C. Tree-ring width and intra-ring δ18Omin correlated well with each other and with precipitation amount for the period from pre-monsoon May to the end of the monsoon season in September/October. Intra-annual stable isotope courses were found rather similar for both δ13C and δ18O. Years with particularly low monsoon rain were reflected by increased stable isotope values in the mid-section of intra-annual courses. Distinct patterns with low subseasonal isotope values seem indicative for years with heavy rainfall events from pre-monsoonal cyclones. Rain events from post-monsoonal cyclones may also be recorded, however, only two years of observation prevent from a conclusive evaluation. [ABSTRACT FROM AUTHOR]

The comprehensive procedure of wood sample preparation, including tree-ring dissection, cellulose extraction, homogenization and packing for stable isotope analysis, is labour intensive and time consuming. Based on a brief compilation of existing methods, we present a methodological approach from pre-analyses considerations to wood sample preparation, semi-automated chemical extraction of cellulose from tree-ring cross-sections, and tree-ring dissection for stable isotope ratio mass spectrometry: the Cross-Section Extraction and Dissection (CSED) guideline. Following the CSED guideline can considerably increase efficiency of tree-ring stable isotope measurement compared to classical methods We introduce a user-friendly device for cellulose extraction, allowing simultaneous treatment of wood cross-sections of a total length of 180 cm (equivalent to 6 increment cores of 30 cm length) and thickness of 0.6–2.0 mm. After cellulose extraction, tree-ring structures of 10 tree species (coniferous and angiosperm wood) with different wood growth rates and tree-ring boundaries, largely remained well identifiable. Further, we demonstrate that tree rings from cellulose cross-sections can be dissected at annual to intra-seasonal resolution, utilizing simple manual devices as well as sophisticated UV-laser microdissection microscopes in a way that sample homogenization is no longer necessary in most cases. We investigate seasonal precipitation signals in high-resolution intra-annual δ 18 O cellulose values from African baobab, performed by using UV-laser microdissection microscopes. [ABSTRACT FROM AUTHOR]

According to the Intergovernmental Panel on Climate Change (IPCC), all of Africa is very likely to warm up more than the global average during this century. Especially (semi-)arid regions are expected to experience particularly high warming and possibly catastrophic droughts. However, assessments of the impacts of climate change on these regions are currently impeded by a lack of transregional high temporal resolution proxy data for the African continent. Baobab trees are widely distributed in (semi-)arid Africa and can reach ages of up to 2000 years. This pilot study was aimed at investigating African baobabs, Adansonia spp., from a site in Botswana using multiple dendroclimatological methods. Increment cores from 16 individual baobabs growing on Kubu Island (20°53' S, 25°49' E), a granite pluton located in the Kalahari, were collected in June 2011 to test for annual growth and the species' utility for palaeoclimatic studies. Due to the particular wood fabric and relatively high water content, baobab increment cores were packed in air-tight opaque tubes and stored in a freezer to prevent drying and mould formation. The complicated wood anatomical structure was found to be analysed best using a microscope with incident UV light, allowing tree-ring boundaries to be distinguished. Nonetheless, potential differences in individual site conditions, as well as diverse tree ages, caused conventional dendrochronological crossdating to fail. Missing and false tree rings could be identified due to the strong relationship between tree-ring width and annual precipitation amount allowing the development of a preliminary 50 year-long baobab chronology (1960–2009). Subsequently, stable carbon and oxygen isotope analyses revealed significant correlations of Δ13C and δ18O of tree rings with climate data. Year-to-year isotope variability and trends were found to be in good agreement with established models of fractionation. Intrinsic water-use efficiency has mainly increased over the study period (2–30 %). Despite the demonstrated high potential of African baobabs as a valuable high-resolution climatearchive, we conclude that more dendrochronological calibration studiesare required at various sites in southern Africa. Furthermore, ecophysiological monitoring of climate and stable isotope signal transfer from the atmosphere, through soil and leaves into the tree rings is necessary to fully understand tree-ring formation and climate response of the African baobab. [ABSTRACT FROM AUTHOR]

The Last Glacial–Interglacial Transition (LGIT; 15,000–11,000 cal BP) was characterized by complex spatiotemporal patterns of climate change, with numerous studies requiring accurate chronological control to decipher leads from lags in global paleoclimatic, paleoenvironmental, and archaeological records. However, close scrutiny of the few available tree-ring chronologies and radiocarbon-dated sequences composing the IntCal13 14C calibration curve indicates significant weakness in 14C calibration across key periods of the LGIT. Here, we present a decadally resolved atmospheric 14C record derived from New Zealand kauri spanning the Lateglacial from ~13,100–11,365 cal BP. Two floating kauri 14C time series, curve-matched to IntCal13, serve as a 14C backbone through the Younger Dryas. The floating Northern Hemisphere (NH) 14C data sets derived from the YD-B and Central European Lateglacial Master tree-ring series are matched against the new kauri data, forming a robust NH 14C time series to ~14,200 cal BP. Our results show that IntCal13 is questionable from ~12,200–11,900 cal BP and the ~10,400 BP 14C plateau is approximately 5 decades too short. The new kauri record and repositioned NH pine 14C series offer a refinement of the international 14C calibration curves IntCal13 and SHCal13, providing increased confidence in the correlation of global paleorecords. [ABSTRACT FROM AUTHOR]

Abstract: A novel procedure has been developed to conduct cell structure measurements on increment core samples of conifers. The procedure combines readily available hardware and software equipment. The essential part of the procedure is the application of a confocal laser scanning microscope (CLSM) which captures images directly from increment cores surfaced with the advanced WSL core-microtome. Cell wall and lumen are displayed with a strong contrast due to the monochrome black and green nature of the images. Consecutive images are merged into long images representing entire increment cores which are then analysed for cell structures in suitable software. [Copyright &y& Elsevier]

The sensitivity of European lowlands to the hydrological impacts of climate change has manifested in flood and drought events of increasing severity over recent decades. Reconstructing the long-term history of hydroclimatic fluctuations in this region is critical to our understanding of its current and future ecosystem dynamics. This is especially important considering that this region is widely susceptible to anthropogenic influences (e.g. large monoculture farms and forests, vast drained peatlands), and it also contains unique, near-natural habitats, including registered UNESCO World Heritage sites (e.g. Müritz National Park). In this study, we use annually resolved multi-centennial records of stable carbon and oxygen isotope chronologies from tree ring cellulose in lowland (50-90m asl.) pine and oak trees (P. sylvestris, Q. petraea) in NE-Germany to reconstruct hydroclimatic variability. Using a calibration and verification approach, we have evaluated the response to instrumental climate data and trends in variables such as local temperature, precipitation, drought indices (PDSI, SPEI), soil moisture, evapotranspiration potential (ETP) and vapor pressure. While ring widths correlate strongly to winter temperature in the study region, strong correlations with summer hydroclimatic conditions were found for both tree-ring 13C and 18O. The strongest relationships occur with ETP, soil moisture, and SPEI. From 1979 to 2010, current-year ETP (JJA) and soil moisture (JJA) show no significant relationships to 13C, but they are strongly correlated to 18O (r=0.66, ETP; r=-0.65, soil moisture). Slightly weaker correlations exist with SPEI (JJA) (r=-0.53, 18O; r=-0.42, 13C). In general, climate relationships with 13C are consistently weaker than those with 18O, but all correlations are significant at the 99% level. Based on a detailed assessment of stable isotope-climate relationships and resulting reconstruction of hydroclimatic baseline variability, we will attempt to assess the sensitivity of tree ring stable isotopes to summer drought. Special attention will be paid to the most recent droughts of 2003 and 2018, the latter of which is considered unprecedented in view of instrumental weather records. Wood anatomical analyses of tree rings from 2018 have revealed that most pine trees formed relatively few latewood cells this year. In contrast, oak tree rings showed normal latewood to earlywood proportions in 2018. Investigation of this discrepancy by additional intra-annual isotope analyses will inform the discussion of the possible limitations of using stable isotope records to reconstruct severe droughts. [ABSTRACT FROM AUTHOR]

Stable oxygen isotopes records (δ18O) in tree-rings are commonly used to assess the response of trees to environmental variability being a valuable tool for studying past climate at different temporal and spatial scales. This is particularly relevant in semi-arid regions like the southern Tropical Andes, where ongoing environmental changes coincide with a rapidly increasing demand for hydrological resources, presenting a challenge for ecosystem dynamics and water resource management. In this study, we aim to determine the main spatio-temporal variability of a new network of δ18O Polylepis tarapacana chronologies during the last century, and their relationships with hydroclimate and tropical circulation at local to subcontinental scales throughout the Tropical Andes. For this purpose, we develop six δ18O P. tarapacana tree-ring chronologies across a 450 km latitudinal moisture gradient in the southern Tropical Andes adjacent to the Atacama Desert, covering the period 1900–2007. Results show a clear latitudinal gradient in the δ18O values across the network and significant relationships are observed with other δ18O tree-ring chronologies in Tropical South America, demonstrating clear regional climate influences at a subcontinental scale. A principal component analysis of the δ18O tree-ring chronologies demonstrate a strong regional environmental signal contained in the network, exhibiting a main temporal pattern (PC1 δ18O) that explains 63% of the total variance during the period 1900–2007. Comparisons between PC1 δ18O and environmental variables showed significant negative relationships with precipitation and soil moisture, and positive relationships with temperature and vapor pressure deficit (VPD) during summer when the South American monsoon occurs. The main δ18O tree-ring network signal clearly records tropical atmospheric and circulation patterns across South America. The easterly wind flux conditions from the Amazon basin favor lower δ18O values, and the PC1 δ18O exhibit significant positive correlations with VPD across the entire Tropical Andes and the northern portion of the Amazon basin, and as well as outgoing longwave radiation across the southern Tropical Andes and part of the Amazon basin. The close relationships between the regional signals from our δ18O tree-ring network with the previously mentioned parameters, highlight the potential to develop future hydroclimatic-related reconstructions with these δ18O records to assess climate variability and change across the Tropical Andes. • A δ18O Polylepis tarapacana tree-ring network is developed in the Southern Tropical Andes. • The δ18O chronologies highlight a strong common signal. • Hydroclimate variability controls δ18O P. tarapacana content across our network. • Tropical atmospheric and circulation patterns show a close relation with δ18O tree-rings. [ABSTRACT FROM AUTHOR]

Abstract: δ 13C and δ 18O of tree rings contain time integrated information about the environmental conditions weighted by seasonal growth dynamics and are well established as sources of palaeoclimatic and ecophysiological data. Annually resolved isotope chronologies are frequently produced by pooling dated growth rings from several trees prior to the isotopic analyses. This procedure has the advantage of saving time and resources, but precludes from defining the isotopic error or statistical uncertainty related to the inter-tree variability. Up to now only a few studies have compared isotope series from pooled tree rings with isotopic measurements from individual trees. We tested whether or not the δ 13C and the δ 18O chronologies derived from pooled and from individual tree rings display significant differences at two locations from the Iberian Peninsula to assess advantages and constraints of both methodologies. The comparisons along the period 1900–2003 reveal a good agreement between pooled chronologies and the two mean master series which were created by averaging raw individual values (Mean) or by generating a mass calibrated mean (MassC). In most of the cases, pooled chronologies show high synchronicity with averaged individual samples at interannual scale but some differences also show up especially when comparing δ 18O decadal to multi-decadal variations. Moreover, differences in the first order autocorrelation among individuals may be obscured by pooling strategies. The lack of replication of pooled chronologies prevents detection of a bias due to a higher mass contribution of one sample but uncertainties associated with the analytical process itself, as sample inhomogeneity, seems to account for the observed differences. [Copyright &y& Elsevier]

The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri ( Agathis australis ) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Niño – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions. [ABSTRACT FROM AUTHOR]