Fig. 3: Paleo evidence links Scandinavian blocking to Common Era flood events in Svalbard.

a The Scandinavian (Scand) reconstructed summer temperatures from the N-TREND tree-ring dataset (in red; data were area-weight averaged over 12–30°E and 65–70°N³¹) and the Northern Scandinavian reconstructed temperature (in green; N. Scand) from Esper et al.⁶⁰ compared to the Calcium variability at Linnévatnet (in black). For visibility only the 1-750CE time interval is shown for the N. Scand⁶⁰ ((a); green) as the two Scand reconstructions exhibit strong co-variablity during their overlapping period (750 CE-2006 CE, annual: r = 0.87). b Spatial correlation between the Scand temperature reconstruction³¹ and atmospheric pressure at 500 hPa geopotential height (Z500)⁶¹. The blue star denotes the location of Linnévatnet in Svalbard. c Reconstructed sea ice concentration from the Nordic Seas³⁶ (blue) compared to the Calcium at Linnévatnet. Periods of lower and higher sea ice concentration (SIC) are highlighted in red and blue, respectively. d Spatial correlation between the Scand temperature reconstruction³¹ and sea surface temperature from HadISST. Blue area delimits the location of the targeted reconstructed SIC from the Nordic Seas in (c). The tree-ring and sea-ice time series were filtered using 5-year running mean to improve visibility. Correlations shown (b, d) are significant with a P < 0.1.