Fennoscandia revisited: a spatially improved tree-ring reconstruction of summer temperatures for the last 900 years
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Despite the spatially homogenous summer temperaturepattern in Fennoscandia, there are large spreadsamong the many existing reconstructions, resulting in anuncertainty in the timing and amplitude of past changes.Also, there has been a general bias towards northernmostFennoscandia. In an attempt to provide a more spatiallycoherent view of summer (June–August, JJA) temperaturevariability within the last millennium, we utilized sevendensity and three blue intensity Scots pine (Pinus sylvestrisL.) chronologies collected from the altitudinal (ScandinavianMountains) and latitudinal (northernmost part) treeline.To attain a JJA temperature signal as strong as possible,as well as preserving multicentury-scale variability,we used a new tree-ring parameter, where the earlywoodinformation is removed from the maximum density andblue intensity, and a modified signal-free standardizationmethod. Two skilful reconstructions for the period 1100–2006 CE were made, one regional reconstruction basedon an average of the chronologies, and one field (gridded)reconstruction. The new reconstructions were shown tohave much improved spatial representations compared tothose based on data from only northern sites, thus makingit more valid for the whole region. An examination of some of the forcings of JJA mean temperatures in the regionshows an association with sea-surface temperature over theeastern North Atlantic, but also the subpolar and subtropicalgyres. Moreover, using Superposed Epoch Analysis, asignificant cooling in the year following a volcanic eruptionwas noted, and for the largest explosive eruptions, theeffect could remain for up to 4 years. This new improvedreconstruction provides a mean to reinforce our understandingof forcings on summer temperatures in the NorthEuropean sector.
|Research areas and keywords||
Subject classification (UKÄ) – MANDATORY
|Publication status||Published - 2014|