Multi-parameter reconstruction of the past 400 years of Carpathian temperatures from tree rings

Instrumental data derived from meteorological stations provide a fairly reliable record of climate variability for at least the last century for most parts of Europe. Proxy-based climate reconstructions have been extensively developed throughout the continent over recent decades to extend these records further back in time. However, to date, parts of central and eastern Europe remain underrepresented, leading to gaps in high-resolution climatic information even in recent centuries. This issue is predominantly linked to large uncertainties in existing records and limitations in data quality associated with a generally weak climatic sensitivity of available proxy records. The REPLICATE project, presented here, aims to address this deficiency by utilizing various tree-ring parameters from temperature-sensitive Norway spruce (Picea abies). The samples, collected from treeline or near-treeline environments, will be used to develop a set of temperature reconstructions across four sub-regions of the Carpathian Mountains. By doing so, we aim to contribute to filling in the spatial paleoclimatic and data quality gap in central-eastern Europe. To improve the climatic signal, we utilized a combination of tree ring width (TRW) corrected for non-climatic (disturbance) trends and blue intensity (BI) series derived from scanned images as a surrogate for maximum latewood density. We also developed a novel tree-ring parameter similar to BI based on high-resolution reflected light microscope images of the tree sample surface – termed surface intensity (SI) – which accounts for resolution and color bias limitations commonly encountered in BI datasets. Additionally, traditional thin section-based quantitative wood anatomy (QWA) parameters and their reflected light surface imaging-based counterparts (sQWA) were also included. Integrating this range of tree-ring parameters in a complementary fashion helps isolate, optimize and extract stronger climatic signals by accounting for and minimizing a range of parameter-specific limitations and biases, yielding improved calibration with a more accurate representation of low-frequency climatic trends and high-frequency extremes. From these multi-parameter tree-ring chronologies, annually resolved, robust, high-quality summer temperature reconstructions, extending to the early to mid-17th century, are under development for four Carpathian locations (i.e., northern Slovakia, western Ukraine, northern and central Romania). Initial results indicate that the reconstructions based on such a multi-parameter approach can produce paleoclimatic records with reduced uncertainty that explain between 50% and 60% of the regional temperature variability. These reconstructions will contribute to a more highly resolved temperature dataset in a part of Europe with considerable research potential, resulting in an improved spatial representation of past European temperature fluctuations. Also, by providing a reliable historical context to evaluate return periods and magnitudes of temperature extremes, they will contribute to assessing potential future socioeconomic impacts of climate change (e.g., on agriculture) and developing possible mitigation solutions.