Two centuries-long dendroclimatic reconstruction based on Low Arctic Betula pubescens from Tromso Region, Northern Norway

This study presents the results of dendrochronological and dendroclimatological research of Betula pubescens from four sites in northern Norway (Kvaloya Island, Tromsoya Island and Storelva Valley), which provided a 193-year chronology. Our results highlight the importance of the site selection in dendroclimatological studies. We demonstrated that activity of geomorphic processes connected with local topography could led to reduced strength of climatic signal embedded in tree-ring data. Negative pointer years, triggered mainly by unfavourable climatic conditions and insect outbreaks, were common for all site chronologies in 1945, 1955, 1965, 1975, 1986, 2004. However, some site-specific differences were also distinguished. Response function analysis confirmed that June, July and August temperatures were positively correlated with tree-ring widths. This climate-growth relationship was stable throughout the years 1925-2000. From summer temperature reconstruction back to AD 1820, two colder (c. 1835-1850 and 1890-1920) and two warmer (c. 1825-1835 and 1920-1940) periods were identified. The tree-ring record from the Tromso Region, well correlated between series, sites and climate variables, is an important element of a large-scale reconstruction of pre-instrumental climate variation in the northeastern part of the Atlantic Ocean. Our dendroclimatic reconstruction corresponds well with other climate proxy data, like fluctuations of mountain glaciers in Scandinavia or sea ice extent.