Tree-ring based reconstruction of winter minimum temperatures in the south-western Caspian Sea since 1879

Abstract

In the context of global warming, winter temperature variability exhibits marked regional differences and has become a central focus in climate research. This study reconstructs winter minimum temperatures (WMT) since AD 1879 using a tree-ring width index chronology of Taxus baccata L., sampled at 1500–1600 m elevation in the south-western Caspian Sea region. It also offers preliminary insights into the mechanisms driving winter temperature variability. The results show that tree radial growth is significantly and positively correlated with both late spring to early summer precipitation and winter temperatures, with the strongest association observed with WMT. The reconstructed WMT series reveals distinct interannual and decadal fluctuations over the past century. Prolonged warm periods (lasting five or more consecutive years) occurred during 1886–1890, 1914–1918, 1921–1925, 1933–1939, 1961–1965, 1975–1980, and 1997–2005. Despite a warming trend since the 1980s, a cooling signal has emerged in the early 21st century, and reconstructed temperatures remain within the range of historical variability. Spatial correlation analysis indicates that the reconstruction captures winter temperature variability across westerly-dominated regions of Central and Western Asia. Wavelet analyses further reveal a phase-dependent relationship with the North Atlantic Oscillation (NAO) in the 6–12-year band, and significant coherence with Niño 3.4 sea surface temperatures (SST) in the 4–8-year band during specific periods. Overall, WMT variability appears to be modulated by the combined influence of NAO and ENSO at multiple scales, although other regional processes may also contribute.

Graphical abstract

Keywords

tree rings / winter minimum temperature / the south-western Caspian Sea

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