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South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia-New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisture transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions.

ABSTRACT Existing high-resolution reconstructions of hydroclimate variability in Europe are lacking natural proxy data from European Russia. For this reason, developing new hydroclimate proxies for this vast region is crucial. It is even more important, because drought evidences from the forest-steppe region of European Russia will elucidate the eastern borders of large-scale meteorological events that had been covering large parts of Europe in the past. In this study, we provide new tree-ring chronologies of Pinus sylvestris L. for the site in the southernmost natural pine forest in European Russia. Based on these chronologies, we develop a quantitative drought reconstruction and disclose the driest years in the region since 1790s. The reconstruction of Standardized Precipitation Evapotranspiration Index explains 29-39% of instrumental period variability, it adequately tracks low-frequency (30-50 years) variations of drought indices as well as extreme events. Collection of historical evidences from periodicals of the 19th century and other historical evidences helped to verify the new reconstruction. Using gridded precipitation reconstruction over Europe, we showed a possible existence of large-scale hydroclimate events that had occurred in the East European forest-steppe region in the 19th century. Possible connections of drought events in European Russia with Atlantic Multidecadal Oscillation and Scandinavian teleconnection pattern are discussed. We argue that being a complex natural archive, ring width of pine in Voronezh region can be successfully used as an estimator of prolonged droughts (1-2 years). [ABSTRACT FROM AUTHOR]

Although European part of Russia is the largest forest-covered part of Europe, dendroclimatic data for high-resolution climate reconstructions are still scarce in this region. Climatic response of 62 tree-ring width chronologies of pine (Pinus sylvestris), spruce (Picea abies, Picea obovata) and larch (Larix sibirica) was analysed over a large area in the northern and central parts of European Russia (54-70° N, 29-57° E). The use of several climatic archives including the data from meteorological stations and gridded datasets allowed identifying the most important climatic parameters impacting the radial growth of conifers in the study region. Our results showed that all conifers growing to the north of 60°N react positively to summer temperature. To the south, at the latitude of 54-56° N, the signal is changing and the ring width depends on the combination of two parameters -- warmth and humidity (precipitation, Palmer Drought Severity Index, soil moisture). These findings are in correspondence with analogous studies from nearby regions (Europe and Fennoscandia) and large-scale studies for the whole Northern Hemisphere. Although three genera of conifers were studied, pine is much better represented in the analysed network, and the results for spruce and larch have to be confirmed in further studies. The negative correlation of the spruce-ring width with the temperature of previous growing season has been defined for 16 of 17 studied chronologies. [ABSTRACT FROM AUTHOR]

Here we propose a new method for dendroclimatic reconstructions. This DIrect REConstruction Technique (DIRECT) performs modelling of the age-dependent association between climate and growth in three-dimensional space and directly transforms the raw tree-ring values (on the scale of original growth units) into climate variability while considering the effect of age in this relationship. DIRECT was applied to maximum latewood density (MXD) data from Finnish/Swedish Lapland. The new DIRECT reconstruction was compared with a reconstruction produced using regional curve standardization (RCS), a method that is often used to preserve the low-frequency variability in tree-ring proxy data. Comparison of the DIRECT and RCS methods showed that both produced summer temperature reconstructions with approximately equal amounts of low-frequency palaeoclimate information. The DIRECT method avoids traditional detrending techniques by considering the cambial age of each tree when building the statistical climate–proxy model and identifying non-linear relationships between climate and tree growth. DIRECT provides objective consideration and removal of differential growth rates and age-related noise without losing the low-frequency portion of palaeoclimate variability. It is anticipated that DIRECT will prove to be a useful tool in regions where strong climate control enables the use of tree rings for palaeoclimate reconstructions. [ABSTRACT FROM AUTHOR]

A 15th century Russian icon from the Novgorod region was analyzed using both dendrochronological and radiocarbon methods [liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS)]. This orthodox icon represents the Mother of God (Dexiokratusa). Fine art experts attribute the icon to between the late 14th to the early 15th centuries. The last complete tree ring was dated to AD 1409. There are indications that the trees were cut down during the summer of AD 1410. Taking into account the time for seasoning (about 8 months), the icon would have been painted in AD 1411. Wiggle-matching of the six AMS samples failed. Two of six AMS dates correspond to dendrochronological dates, while four of the six AMS dates showed differences with the dendrochronological dates by 5-39 yr. This discrepancy raises the issue of a possible regional offset from the calibration curve for the 13th century AD in NW Russia. [ABSTRACT FROM AUTHOR]