Low-frequency patterns in Late-Holocene tree-ring records from northern Fennoscandia

Northern Fennoscandia is a cradle of tree-ring based climate reconstructions. These Late-Holocene data come from several types of tree-ring proxies and are typically used for discussing the extent of past climate excursions such as the Medieval Climate Anomaly and Little Ice Age, relative to the modern temperatures. This article compares tree-ring records published from the region over the past two decades with those produced here by recalculations, focussing on their low-frequency temperature patterns. Paleoclimate evidence fully independent of trees (sedimentary chironomid data) was used to assess the dendroclimatic records. Chironomid record correlated best with anatomy (maximum latewood radial-cell-wall thickness) data averaged over the region (A-FEN) when the latewood (maximum) anatomy was not tuned by earlywood (minimum) anatomy values. While all the examined tree-ring records are highly sensitive to high-frequency summer temperature variability, non-temperature factors likely play a role in modifying their low-frequency patterns. As a result, the subsets of A-FEN (representing NW and NE Fennoscandian sites i.e. Torneträsk region and Finnish Lapland) did not correlate, unlike the subsets of the maximum density data, for which reason the regionally averaged A-FEN seems to underestimate the temperature amplitudes during the Medieval Climate Anomaly. The findings contribute to the discussion on low-frequency patterns in millennia-long tree-ring chronologies.