Significant Climate Research Articles

A new large-volume equilibration method for high-precision measurements of dissolved noble gas stable isotopes.

Noble gases are widely used as physically based climate proxies, notably in dissolved water samples as tracers of past recharge temperature in groundwater and air-sea gas exchange processes in seawater. Recent advances in measuring large-volume samples of dissolved noble gas isotopic ratios at high precision have expanded the range of climate parameters that can be interpreted. We build on prior methods for measuring noble gas stable isotopes at high precision with a new large-volume equilibration (LVE) method wherein sample gases are equilibrated in the sample flask between the dissolved phase and the headspace. The original dissolved gas composition is determined by measuring the headspace gases and correcting for the equilibrium dissolved gas content of the discarded water using known solubilities and fractionation factors. We evaluate the accuracy and precision of this method with air-equilibrated water standards of known noble gas composition. Replicate air-equilibrated water standards and field measurements demonstrate that the LVE method achieves comparable precision to prior methods, with major advantages of measuring the Ne content as a constraint on excess air and allowing for long-term sample storage. Isotope ratios measured with the LVE method in replicate samples were consistent between two laboratories, and LVE elemental noble gas abundances agreed closely with replicate samples measured using established copper-tube methods and static noble gas mass spectrometry. The new LVE method enables reconstruction of past water table depths at ±1m precision along with excess air, recharge temperature, and age and hydrogeochemical indicators. It has wide application to investigating climate signals and physical gas exchange processes in groundwater and seawater.

Hydroclimate and vegetation variability of high Andean ecosystems.

Mountain ecosystems are sensitive to climate fluctuations; however, the scarcity of instrumental data makes necessary the use of complementary information to study the effect of climate change on these systems. Remote sensing permits studying the dynamics of vegetation productivity and wetlands in response to climate variability at different scales. In this study we identified the main climate variables that control vegetation dynamics and water balance in Cumbres Calchaquíes, NW Argentina. For this, we built annual time series from 1986 to 2019 of Soil Adjusted Vegetation Index (SAVI, to quantify spare vegetation productivity), lake area, and snow-ice cover of peatlands, as indicators of mountain productivity and hydrology. We used a decompose function to explore trend, seasonality and random signal of the three-time series, and explored for significant changes in the mean value of consecutive periods. We used correlational analysis to explore their associations with climate records at local, regional, and global scales. The results showed that, SAVI and hydrological indicators presented different fluctuation patterns more pronounced since 2012, when they showed divergent trends with increasing SAVI and decreasing lake area and snow-ice cover. The three indicators responded differently to climate; SAVI increased in warmer years and lake area reflected the water balance of previous years. Snow-ice cover of peatlands was highly correlated with lake area. La Niña had a positive effect on lake area and snow-ice cover and a negative on SAVI, while El Niño had a negative effect on SAVI. Fluctuations of lake areas were synchronized with lake area in the nearby Argentinian puna, suggesting that climate signals have regional extent. The information provided by the three hydroclimate indicators is complementary and reflects different climate components and processes; biological processes (SAVI), physical processes (snow ice cover) and their combination (lake area). This study provides a systematic accessible replicable tool for mountain eco-hydrology long-term monitoring.

Seawater signatures of Ordovician climate and environment

Abstract Tracking climatic changes throughout the Ordovician is crucial to a better understanding of the coevolution of life and environment on Earth. Ordovician climate fluctuations have been the subject of a vigorous and productive body of work over the past two decades. Here we present a synthesis of studies that have focused on reconstructing Ordovician climate and environment via direct geochemical proxy datasets and/or numerical modelling approaches. Many new insights have been gained on potential causes of events: the timing and potential causes of the major radiation of Ordovician marine life, changes in weathering and the transition from a greenhouse-to-icehouse state, and cooling and (de)oxygenation during the end-Ordovician Glaciation. Marked improvements in sample resolution/distribution of traditional palaeotemperature (oxygen isotopes), palaeoredox (sulfur isotopes) and weathering proxy records (strontium and neodymium isotopes), as well as the development of new palaeoenvironmental proxies (e.g. clumped, uranium, molybdenum and thallium isotopes; iodine, iron, trace metal geochemistry), have led to better constraints on Ordovician climate and environment. These recent works have led to a more nuanced understanding of the Ordovician Earth System, which allows the global community to focus future efforts on answering remaining questions regarding palaeoclimate and environment, as well as embark upon new investigations.

Orbital‐Insolation Controlled Porites Coral δ13C Seasonality Variations Since the Mid‐Holocene in the Northern South China Sea

AbstractCoral skeleton δ13C is a routinely measured indicator in modern insolation change research, but the knowledge of environmental and climatic signals recorded in its seasonality during geological time is sparse. In this study, we present eight Porites coral δ13C records from the mid‐late Holocene to the present from the northern South China Sea (NSCS). Compared with the main control factors for modern δ13C changes, coral δ13C seasonality in the NSCS since the mid‐Holocene shows a long‐term decreasing trend, which is consistent with the change trend as orbital‐induced (precession) insolation seasonal amplitude. By excluding other influencing factors, we speculate that the stronger coral δ13C seasonality (18.8%) over the mid‐Holocene than modern period is attributable to the metabolic effect, which predicts the stronger coral δ13C seasonality under stronger insolation seasonality. Our study has implications for coral δ13C seasonality as a potential indicator to record past insolation information under different climatic backgrounds.

Climate–Growth Relationships in Laurus azorica—A Dominant Tree in the Azorean Laurel Forest

Forests on oceanic islands, such as the Azores archipelago, enable interesting dendroclimatic research, given their pronounced climatic gradients over short geographical distances, despite the less pronounced seasonality. The Lauraceae play an essential ecological role in Macaronesian natural forests. An example is Laurus azorica (Seub.) Franco, a relevant species given its high frequency and physiognomic dominance in Azorean laurel forests. This study aims to quantify climate–growth relationships in L. azorica using a dendroecological approach. We sampled four stands at São Miguel and two stands at Terceira islands, for a total of 206 trees. Following standard dendrochronological methods and rigorous sample selection procedures, we obtained relatively low rbar values and high temporal autocorrelation. Using a stepwise Random Forest analysis followed by Generalized Linear Models calculation, we found prominent effects of present and previous year temperature, but a low precipitation signal on growth rings, with some model variation between stands. Our results agreed with previous observations for broad-leaved species with diffuse porous wood, contributing to increase the baseline dendroecological knowledge about Azorean forests. Due to the high levels of within- and between-stand variation, and to refine the climatic signal analysis, complementary approaches should be explored in the future.

The patchwork loess of Central Asia: Implications for interpreting aeolian dynamics and past climate circulation in piedmont regions

ABSTRACTReconstruction of mass accumulation rates (MARs) in loess deposits are widely used for interpreting long‐term aeolian transport and climate dynamics in terrestrial environments. However, these interpretations are often driven by a preponderance of reconstructions from individual or selected sites, which can bias our understanding of past climate, especially in the absence of other proxy information. Recent studies on MARs from multiple loess sites in Arid Central Asia (ACA) reveal disparities in the timing of peaks in accumulation between sites, as well as asynchronies with loess flux in the Chinese Loess Plateau (CLP). We investigate this issue by (1) dating five new sites from the western Ili Basin, therefore extending the spatial cover of loess chronologies across ACA and (2) combining that with MARs from >30 sites across ACA and the CLP over the last 60 ka. Our results indicate spatio‐temporal inhomogeneity in the timing and rate of loess deposition across the ACA, and highlight the importance of interrogating local and regional influences on dust supply and transport. Our synthesis of MARs from ACA and the CLP suggests that the timing of peak dust flux as an indicator of large‐scale climate dynamics is best derived from an aggregate of sites; this removes site‐specific bias where local processes or topographic settings outweigh the climate signature.

Influence of lake-basin morphology on climate-sediment transfer functions: Early Eocene Wilkins Peak Member, Green River Formation, Wyoming

Lacustrine strata are often among the highest-resolution terrestrial paleoclimate archives available. The manner in which climate signals are registered into lacustrine deposits varies, however, as a function of complex sedimentologic and diagenetic processes. The retrieval of reliable records of climatic forcing therefore requires a means of evaluating the potential influence of changing sedimentary transfer functions. Here, we use high-resolution X-ray fluorescence core scanning of the Wilkins Peak Member of the Green River Formation to characterize the long-term evolution of transfer functions in an ancient lacustrine record. Our analysis identifies a shift in the frequency distribution of Milankovitch-band variance between the lower and middle Wilkins Peak Member across a range of temporally calibrated elemental intensity records. Spectral analysis of the lower Wilkins Peak Member shows strong short eccentricity, obliquity, precession, and sub-Milankovitch−scale variability, while the middle Wilkins Peak Member shows strong eccentricity variability and reduced power at higher frequencies. This transition coincides with a dramatic decline in the number and volume of evaporite beds. We attribute this shift to a change in the Wilkins Peak Member depositional transfer function caused by evolving basin morphology, which directly influenced the preservation of bedded evaporite as the paleolake developed from a deeper, meromictic lake to a shallower, holomictic lake. The loss of bedded evaporite, combined with secondary evaporite growth, results in reduced obliquity- and precession-band power and enhanced eccentricity-band power in the stratigraphic record. These results underscore the need for careful integration of basin and depositional system history with cyclostratigraphic interpretation of the dominant astronomical signals preserved in the stratigraphic archive.

Disentangling Holocene Climate Change and Human Impact from Palaeoenvironmental Records from the Scottish West Coast

Phases of rapid climate change throughout the early to mid Holocene coincide with regional human population expansion in Scotland and North-West Europe. Palaeoenvironmental signals of climate and anthropogenically driven vegetation changes can therefore be difficult to separate. To identify whether it is possible to distinguish potential signatures of anthropogenic clearance and agricultural activities from climatic drivers of landscape change in the early to mid Holocene in the region, two topographically contrasting sites on the Isle of Skye and the Isle of Bute were investigated. A multiproxy approach including pollen, spore, microcharcoal, loss on ignition and particle size analyses was adopted to investigate changes in vegetation and climate. There are subtle indications that the 8200 cal BP climate event had an effect on the vegetation composition at both sites. Signals of anthropogenic woodland clearance are apparent early in the sequence at Peat Hill (Bute), indicated by a peak in Poaceae (grass) cereal-type (7–14%) at 8592–8793 cal BP, alongside a decrease in arboreal pollen, which could not be associated with a regional episode of climate change. Early to mid Holocene vegetation changes at Lyndale House (Skye) occur alongside regional changes in precipitation and sea level and therefore cannot be readily separated. Continuous declines in arboreal pollen from ca. 5000 cal BP at Lyndale House indicates the onset of widespread clearance on Skye via felling and sustained grazing pressures.

Two-stage multivariate dynamic linear models to extract environmental and climate signals in coastal ecosystem data

Two-stage multivariate dynamic linear models to extract environmental and climate signals in coastal ecosystem data

КЛИМАТИЧЕСКИЙ СИГНАЛ В РАДИАЛЬНОМ ПРИРОСТЕ МОЛОДНЯКА И ДЕРЕВЬЕВ СОСНЫ ОБЫКНОВЕННОЙ

The article describes the results of a radial growth (2005–2019) analysis among the trees and undergrowth of Scots pine, which grows under extreme ecological conditions of the Uchalinsky Mining and Processing Plant (the Republic of Bashkortostan). Comparatively large variation of the trait was revealed among the trees in intra- and interannual levels. Multidirectional signals of the climatic factors influence on plant growth were found in the two alternative age groups. Monthly temperatures turned out to be more critical in this process for trees, precipitation was more important for the undergrowth. The fact of a statistically significant correlation of the radial increase with the amount of precipitation in October of previous years was revealed in the first age group. Monthly temperatures in January and July had a significant positive effect on the annual growth of trees, but April temperatures negatively correlated with this indicator. A negative correlation between the high temperatures of June and July and the increase in plant diameter was found in the undergrowth. To ensure a high radial increase in this age group, more precipitation in September of previous years and July of current years is important. It was shown that the occurrence of these patterns in the younger generation of Scots pine depends on forest growing conditions. The results obtained allow to quantify the climatic signals in the growth of the plant and can be useful in predicting the impact of climate change on this species.

Multiscale characteristics of the early spring temperature and response to climate indices over the past 179 years in the Qinling Mountains

Examination of the periodic differences in temperature in the Qinling Mountains at different time scales is highly important in research on the long-term evolution of the regional climate system and ecological environment. Based on February-April temperature data from 1835 to 2013 obtained at 27 weather stations in the Qinling Mountains reconstructed through tree rings, the multiscale characteristics of the early spring temperature time series on the southern and northern slopes of the Qinling Mountains and the response to climate signals were analyzed. The results indicate that the early spring temperature in the Qinling Mountains exhibits significant periodic characteristics on multiple time scales. Reconstruction at the different time scales reveals that the interannual scale change in the temperature variation on the northern slope of the Qinling Mountains plays a decisive role. The temperature on the northern slope exhibits a higher amplitude at the interannual and interdecadal scales than does that on the southern slope, and temporal differences occur at the quasi-century scale. The temperature achieves the strongest correlation with the original Atlantic Multidecadal Oscillation (AMO) sequence during the entire study period. In addition, the different time scales reveal that a significant response relationship exists between the temperature at the interannual scale and the May sea temperature in the NINO3.4 area, which lags by one year. At the different time scales and various time ranges, the Qinling early spring temperature responds differently to the climate signals, which is an important factor leading to a lower correlation during the entire study period.

Influence of large-scale climate signals on the precipitation variability over Iran

Influence of large-scale climate signals on the precipitation variability over Iran

Using environmental tracers to evaluate the preservation of palaeoclimate signals in aquifers of the London Basin, UK

The concept of aquifer basins as palaeoclimate archives has existed for some decades, yet few detailed studies comparing aquifer types have been carried out. To assess the potential of a particular aquifer as an archive, its hydrogeochemical characteristics must be thoroughly investigated, ideally in comparison to an adjacent aquifer which can be shown to substantially preserve its ice-age endowment at depth. The London Basin (UK) presents such an opportunity, containing two main aquifers of contrasting type: the Chalk, a fractured microporous limestone, and the Lower Greensand, a porous sandstone. Despite intensive exploitation of both, evidence for Devensian (late-glacial) water remains at depth, though this differs between aquifer type. To understand the reasons for this, a suite of environmental tracers has been applied. In addition to hydrochemistry, stable isotopes (δ18O, δ2H), carbon isotopes (δ13C-DIC, 14C-DIC) and noble gases (He, Ne, Ar, Kr and Xe), two tracers new to the basin (CFCs and 14C-DOC) have been used. In effect the Lower Greensand appears to be the ‘reference aquifer’, preserving recharge from prior to the Last Glacial Maximum (LGM), while the Chalk contains mixed water, with no remaining trace of the undiluted pre-LGM end member even at depth in remote parts of the confined basin. Whereas both aquifers had in the past given maximum 14C-DIC model ages ≥ 30kyr (the effective limit of that method), in the present study the use of 14C-DOC has reduced this to 23.4 kyr (Lower Greensand) and 17.2 kyr (Chalk). Similar contrasts in maximum stable isotope depletions (−8.2 ‰ and −7.8 ‰ δ18O) and noble-gas-derived recharge temperature minima (2.6° and 4.1 °C) were also observed. CFCs were found at all Chalk sites, with traces detectable even at 40 km from outcrop, so some climate signal degradation appears inevitable throughout the Chalk aquifer of the basin. A correlation between 14C activity and excess 4He suggests that deep saline water in the Lower Greensand could be ≥ 50kyr old. The use of 14C-DOC in particular appears to be key to understanding how reliable these individual aquifers are as palaeoarchives.

Impacts of climate and tree morphology on tree-ring stable isotopes in central Mongolia.

Recent climate extremes in Mongolia have ignited a renewed interest in understanding past climate variability over centennial and longer time scales across north-central Asia. Tree-ring width records have been extensively studied in Mongolia as proxies for climate reconstruction, however, the climate and environmental signals of tree-ring stable isotopes from this region need to be further explored. Here, we evaluated a 182-year record of tree-ring δ13C and δ18O from Siberian Pine (Pinus sibirica Du Tour) from a xeric site in central Mongolia (Khorgo Lava) to elucidate the environmental factors modulating these parameters. First, we analyzed the climate sensitivity of tree-ring δ13C and δ18O at Khorgo Lava for comparison with ring-width records, which have been instrumental in reconstructing hydroclimate in central Mongolia over two millennia. We also compared stable isotope records of trees with partial cambial dieback ('strip-bark morphology'), a feature of long-lived conifers growing on resource-limited sites, and trees with a full cambium ('whole-bark morphology'), to assess the inferred leaf-level physiological behavior of these trees. We found that interannual variability in tree-ring δ13C and δ18O reflected summer hydroclimatic variability, and captured recent, extreme drought conditions, thereby complementing ring-width records. The tree-ring δ18O records also had a spring temperature signal and thus expanded the window of climate information recorded by these trees. Over longer time scales, strip-bark trees had an increasing trend in ring-widths, δ13C (and intrinsic water-use efficiency, iWUE) and δ18O, relative to whole-bark trees. Our results suggest that increases in iWUE at this site might be related to a combination of leaf-level physiological responses to increasing atmospheric CO2, recent drought, and stem morphological changes. Our study underscores the potential of stable isotopes for broadening our understanding of past climate in north-central Asia. However, further studies are needed to understand how stem morphological changes might impact stable isotopic trends.

Coastal environmental and atmospheric data reduction in the Southern North Sea supporting ecological impact studies

Coastal climate impact studies make increasing use of multi-source and multi-dimensional atmospheric and environmental datasets to investigate relationships between climate signals and the ecological response. The large quantity of numerically simulated data may, however, include redundancy, multi-colinearity and excess information not relevant to the studied processes. In such cases techniques for feature extraction and identification of latent processes prove useful. Using dimensionality reduction techniques this research provides a statistical underpinning of variable selection to study the impacts of atmospheric processes on coastal chlorophyll-a concentrations, taking the Dutch Wadden Sea as case study. Dimension reduction techniques are applied to environmental data simulated by the Delft3D coastal water quality model, the HIRLAM numerical weather prediction model and the Euro-CORDEX climate modelling experiment. The dimension reduction techniques were selected for their ability to incorporate (1) spatial correlation via multi-way methods (2), temporal correlation through Dynamic Factor Analysis, and (3) functional variability using Functional Data Analysis. The data reduction potential and explanatory value of these methods are showcased and important atmospheric variables affecting the chlorophyll-a concentration are identified. Our results indicate room for dimensionality reduction in the atmospheric variables (2 principle components can explain the majority of variance instead of 7 variables), in the chlorophyll-a time series at different locations (two characteristic patterns can describe the 10 locations), and in the climate projection scenarios of solar radiation and air temperature variables (a single principle component function explains 77% of the variation for solar radiation and 57% of the variation for air temperature). It was also found that solar radiation followed by air temperature are the most important atmospheric variables related to coastal chlorophyll-a concentration, noting that regional differences exist, for instance the importance of air temperature is greater in the Eastern Dutch Wadden Sea at Dantziggat than in the Western Dutch Wadden Sea at Marsdiep Noord. Common trends and different regional system characteristics have also been identified through dynamic factor analysis between the deeper channels and the shallower intertidal zones, where the onset of spring blooms occurs earlier. The functional analysis of climate data showed clusters of atmospheric variables with similar functional features. Moreover, functional components of Euro-CORDEX climate scenarios have been identified for radiation and temperature variables, which provide information on the dominant mode (pattern) of variation and its uncertainties. The findings suggest that radiation and temperature projections of different Euro-CORDEX scenarios share similar characteristics and mainly differ in their amplitudes and seasonal patterns, offering opportunities to construct statistical models that do not assume independence between climate scenarios but instead borrow information (“borrow strength”) from the larger pool of climate scenarios. The presented results were used in follow up studies to construct a Bayesian stochastic generator to complement existing Euro-CORDEX climate change scenarios and to quantify climate change induced trends and uncertainties in phytoplankton spring bloom dynamics in the Dutch Wadden Sea.

100 k.y. pacing of the East Asian summer monsoon over the past five glacial cycles inferred from land snails

Abstract The effects of orbital forcing on the East Asian summer monsoon (EASM) after the mid-Pleistocene transition are controversial. Chinese cave δ18O records only show low-latitude ∼20 k.y. cycles, while pedogenic proxy records from Chinese loess are dominated by highlatitude 100 k.y. cycles. This discrepancy may result from the multicomponent origin of proxies, particularly for pedogenic signals in loess deposits, where the primary climatic signals are modified by pedogenic smoothing, leaching, and changes in sedimentation rate, and the latter are also being forced by 100 k.y. cycles. We present an EASM record spanning the past 470 k.y. from the central Chinese Loess Plateau based on the δ13C values of land snail shells (δ13Cshell), which eliminates the influence of the above processes and exclusively records the local past EASM precipitation. The δ13Cshell record is dominated by the 100 k.y. cycle, with more depleted values during interglacials compared to glacials. At the end of marine isotope stage (MIS) 11, δ13Cshell-based precipitation remained at an interglacial level following the MIS 11 super-interglacial climate in the Northern Hemisphere, although a glacial period had commenced on a global basis. Overall, our δ13Cshell record is highly coupled with high-northern-latitude ice-volume variations, possibly supporting the high-latitude forcing of the EASM.

Dynamics Changes in Basal Area Increment, Carbon Isotopes Composition and Water Use Efficiency in Pine as Response to Water and Heat Stress in Silesia, Poland.

Trees can be used as archives of changes in the environment. In this paper, we present the results of the analysis of the impact of water stress and increase in air temperature on BAI and carbon stable isotopic composition and water use efficiency of pine. Dendrochronological methods together with mass spectrometry techniques give a possibility to conduct a detailed investigation of pine growing in four industrial forests in Silesia (Poland). Detailed analysis-based bootstrap and moving correlation between climatic indices (temperature, precipitation, and Standardized Precipitation-Evapotranspiration Index) and tree parameters give the chance to check if the climatic signals recorded by trees can be hidden or modified over a longer period of time. Trees have been found to be very sensitive to weather conditions, but their sensitivity can be modified and masked by the effect of pollution. Scots pine trees at all sites systematically increased the basal area increment (BAI) and the intrinsic water use efficiency (iWUE) and decreased δ13C in the last century. Furthermore, their sensitivity to the climatic factor remained at a relatively high level. Industrial pollution caused a small reduction in the wood growth of pines and an increase in the heterogeneity of annual growth responses of trees. The main factors influencing the formation of wood in the pines were thermal conditions in the winter season and pluvial conditions in the previous autumn, and also in spring and summer in the year of tree ring formation. The impact of thermal and pluvial conditions in the year of tree ring formation has also been reflected in the isotopic composition of tree rings and water use efficiency. Three different scenarios of trees' reaction link to the reduction of stomata conductance or changes in photosynthesis rate as the response to climate changes in the last 40 years have been proposed.

Climate change impacts on wind power generation for the Italian peninsula

Wind energy is one of the key renewable resources contributing to climate change mitigation policies in national and international energy transition strategies. However, climate change itself can affect the availability of wind resources, due to possible future changes in large-scale circulation pattern. This study aims to understand whether how and to what extent current and future climate change is affecting wind producibility in Italy. In this analysis, the 10 m wind speed from Euro-CORDEX regional climate models was bias-corrected using MERIDA meteorological reanalysis and the wind producibility is calculated, using a reference turbine chosen among the most commonly installed in Italian wind farms. The changes in the availability of wind resources from the reference period 1986–2005 for the short (2021–2050), medium (2051–2080), and long term (2071–2100) are analyzed, considering both the RCP 4.5 and RCP 8.5 scenarios. The results show a prevalently weak and not statistically significant climate signal for the RCP 4.5 scenario, while a more pronounced and significant signal is highlighted for the RCP 8.5 scenario in the medium and long term, indicating a decrease in wind producibility. Specifically, the conclusions suggest that future planning of wind producibility should mainly focus in some specific areas of the eastern Italian coast and in the south-east Italian regions, mostly in the off-shore areas. In these regions, indeed, the RCP 8.5 scenario shows the lowest decrease in the overall annual producibility, while, for the RCP 4.5 scenario, the medium and the long term foresee a slight increase in wind producibility at the annual level, while, in the short term, an increasing trend is observed mostly in the spring season.

Alpine shrubs have benefited more than trees from 20th century warming at a treeline ecotone site in the French Pyrenees

Mountain ecosystems are particularly sensitive to climate change, which in part causes encroachment of woody plants at the treeline ecotone, with repercussions on treeline advance and ecosystem carbon balance. Yet, studies investigating the long-term trends in radial growth as well as year-to-year response of several tree and shrub species to climate change are scarce, especially in the Pyrenees where dendroecological studies are hitherto critically lacking. Here, we estimate and compare the long-term growth trends of two shrub (Rhododendron ferrugineum and Juniperus communis) and one tree (Pinus uncinata) species, and investigate their year-to-year growth response to changing climatic conditions and advancing snow melt-out timings. We used the Age-Class Isolation method (ACI) to derive growth trends from the ring width series of trees and shrubs. Climate-growth relationships were evaluated using fixed- and moving-window bootstrap correlation functions with the aim to determine the effects of changing climate and snowpack on shrub and tree growth. Overall, our results show that all species at our site, especially shrubs, have grown increasingly well over at least the last century, probably in response to increasing temperatures during the growing season and earlier snow melt-out dates. Nevertheless, the two shrub species differ quite strongly in their response to climate. Whereas the climate signal of J. communis has been relatively stable in recent decades despite the persistent and significant warming trend, R. ferrugineum shows a strong shift in climate sensitivity and is increasingly affected negatively by climate change. Altogether, our results address the different climate sensitivity of the two most common shrubs in the Pyrenees. They also contribute to a better understanding of vegetation dynamics in the Pyrenean treeline ecotone in the context of global change.

Ring-width and blue-light chronologies of Podocarpus lawrencei from southeastern mainland Australia reveal a regional climate signal

Abstract. High-resolution palaeoclimate proxies are fundamental to our understanding of the diverse climatic history of the Australian mainland, particularly given the deficiency in instrumental datasets spanning more than a century. Annually resolved, tree-ring-based proxies play a unique role in addressing limitations in our knowledge of interannual to multi-decadal temperature and hydroclimatic variability prior to the instrumental period. Here we present cross-dated ring-width (RW) and minimum blue-intensity (BI) chronologies spanning 70 years (1929–1998) for Podocarpus lawrencei Hook.f., the Australian mainland's only alpine conifer, based on nine full-disc cross-sections from Mount Loch in the Victorian Alps. Correlations with climate variables from observation stations and gridded data across the 1929–1998 period reveal a significant positive relationship between RW and mean monthly maximum temperatures in winter throughout central Victoria (r=0.62, p<0.001) and a significant negative correlation to winter precipitation (r=-0.51, p<0.001). We also found significant negative correlations between RW and monthly snow depth at Spencer Creek in New South Wales (r=-0.60, p<0.001). Of the assessed BI parameters, delta blue intensity (ΔBI; the difference between early- and late-wood BI) displayed the greatest sensitivity to climate, with robust spatial correlations with mean October to December maximum and minimum monthly temperatures (r=-0.43, p<0.001; r=-0.51, p<0.001) and July precipitation (r=0.44, p<0.001), across large areas of northern Victoria. These promising findings highlight the utility of this species for future work. With the very limited availability of suitable long-lived and cross-datable species on the Australian mainland, these results have significant implications for advancing high-resolution palaeoclimate science in southeastern Australia and for improving our understanding of past climate in the region.