Rovaniemi Research Unit

Rovaniemi, Finland

Rovaniemi Research Unit

Rovaniemi, Finland

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Lindholm M.,Rovaniemi Research Unit | Aalto T.,Rovaniemi Research Unit | Grudd H.,University of Stockholm | Mccarroll D.,University of Swansea | And 2 more authors.
Journal of Quaternary Science | Year: 2012

Four Nordic temperature proxies based on tree growth at the northern timberline - ring-width from Sweden and Finland, maximum latewood density from Sweden, and height increment from Finland - were compared. Three indexing methods were used to enhance the low (centennial and above), medium (decadal-to-multidecadal) and high (decadal-to-interannual) frequencies. The proxies are shown to have a strong temperature signal (common variance) at the interannual-to-multidecadal scale, while the multidecadal-to-centennial trends are less coherent, perhaps reflecting intra-regional differences in growing conditions but more likely due to the more noisy regional curve standardization method used to retain the longest trends. Various methods of combining the four proxy series were explored and tested by comparison with four long temperature records from northern Fennoscandia. Only relatively high-frequency, spline-indexed series produced consistently positive verification statistics as a reconstruction model for summer temperature using all four proxies. © 2012 John Wiley & Sons, Ltd.


Loader N.J.,University of Swansea | Jalkanen R.,Rovaniemi Research Unit | McCarroll D.,University of Swansea | Moberg A.,University of Stockholm
Journal of Quaternary Science | Year: 2011

A reconstruction of spring (April-May) temperature for northern Fennoscandia developed from the Tornionjoki (Tornio river) long cryophenological record of ice break-up dates, back to AD 1693, is presented. The record is strongly climatically sensitive and explains 67% of the variance in the instrumental data over the last 150 years. The record exhibits a stepped decrease in the duration of the river's ice cover by 14 days, equivalent to an increase in April-May mean temperature of approximately 2.5°C over the last three centuries. The relationship between the date of ice break-up, and accumulated daily mean temperatures (>0°C) is investigated. Uncertainty in the observation of ice break-up is also considered in addition to the potential of this time series for regional climate model validation. © 2011 John Wiley & Sons, Ltd.


Ogurtsov M.,RAS Ioffe Physical - Technical Institute | Lindholm M.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit | Veretenenko S.,Saint Petersburg State University
Advances in Space Research | Year: 2015

Time evolution of growing season temperatures in the Northern Hemisphere was analyzed using both wavelet and Fourier approaches. A century-scale (60-140 year) cyclicity was found in the summer temperature reconstruction from the Taymir peninsula (∼72° N, ∼105° E) and other high-latitude (60-70° N) regions during the time interval AD 1576-1970. This periodicity is significant and consists of two oscillation modes, 60-70 year and 120-140 year variations. In the summer temperatures from the Yamal peninsula (∼70° N, ∼67° E) only a shorter-term (60-70 year) variation is present. A comparison of the secular variation in the Northern Hemisphere temperature proxies with the corresponding variations in sunspot numbers and the fluxes of cosmogenic 10Be in Greenland ice shows that a probable cause of this variability is the modulation of temperature by the century-scale solar cycle of Gleissberg. This is consistent with the results obtained previously for Northern Fennoscandia (67°-70° N, 19°-33° E). Thus, evidence for a connection between century-long variations in solar activity and climate was obtained for the entire boreal zone of the Northern Hemisphere. © 2014 Published by Elsevier Ltd. on behalf of COSPAR.


Ogurtsov M.,RAS Ioffe Physical - Technical Institute | Lindholm M.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit
Monthly Notices of the Royal Astronomical Society | Year: 2014

Proxies of solar activity, based on radiocarbon and beryllium, covering most of the Holocene were statistically analysed using both wavelet and Fourier approaches. It was shown that a significant tri-centennial (300-400 yr) cyclicity is present in the both series. Evidence for the same kind of variation was found in data on flux of 10Be in Dye-3 (South Greenland, AD 1424-1985) and NGRIP (Central Greenland, AD 1389-1994) ice cores. Possible origins of the revealed quasi-300-year periodicity are discussed. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ogurtsov M.,RAS Ioffe Physical - Technical Institute | Lindholm M.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit | Veretenenko S.V.,RAS Ioffe Physical - Technical Institute
Advances in Space Research | Year: 2013

A new summer temperature proxy was built for northern Fennoscandia in AD 1000-2004 using parameters of tree growth from a large region, extending from the Swedish Scandes to the Kola Peninsula. It was found that century-scale (55-140 year) cyclicity is present in this series during the entire time interval. This periodicity is highly significant and has a bi-modal structure, i.e. it consists of two oscillation modes, 55-100 year and 100-140 year variations. A comparison of the century-long variation in the northern Fennoscandian temperature proxy with the corresponding variations in Wolf numbers and concentration of cosmogenic 10Be in glacial ice shows that a probable cause of this periodicity is the modulation of regional climate by the secular solar cycle of Gleissberg. This is in line with the results obtained previously for a more limited part of the region (Finnish Lapland: 68-70 N, 20-30 E). Thus the reality of a link between long-term changes in solar activity and climate in Fennoscandia has been confirmed. Possible mechanisms of solar influence on the lower troposphere are discussed. © 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.


Lindholm M.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit
Holocene | Year: 2012

Height-increment and tree-ring width data of Scots pine from northern Fennoscandia were updated and their sample replication increased considerably. Standard chronologies as well as low-frequency chronologies were built and compared during their common period in ad 745-2007. The two chronologies correlate significantly (r = 0.58) with each other and have several extreme years in common, e.g. 1089 and 1601. The low-frequency chronologies indicate four significant periods of above-average growth and eight periods of below-average growth, which occur in both chronologies. These include the early 20th century growth surges that occurred during 1917-1955 in height increment and during 1919-1961 in ring width. In both chronologies, this latest increasing trend unequivocally turns to a fall and comes to an end by the 1960s. Tree-ring chronologies of Scots pine from northern Sweden and the Khibiny Low Mountains region (northwestern Russia) as well as from Siberia show coincidence in the decadal- to century-scale with our chronologies. © The Author(s) 2011.


Seo J.-W.,University of Hamburg | Salminen H.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit | Eckstein D.,University of Hamburg
Baltic Forestry | Year: 2010

The phenophases of Scots pine, from bud break up to the end of cambium activity, at two sites (approx. 80 and 300 km, respectively, south of the forest border) in the northern boreal zone of Finland were monitored with high time resolution during three growing seasons. Averaged over the study sites and years, bud break occurred in the first half of May. Height growth started in the second half of May and radial growth followed around end of May/beginning of June. Both processes culminated in the second half of June, clearly before the warmest period of the year. Height growth finished by end of June/early July. Lastly, radial growth was completed by end of July/mid-August. Hence, the growing season from bud break to the end of radial growth took on average 87 days. However, annual shoot length and tree-ring width were independent from the duration of height and radial growth as well as from the onset dates for height growth and cambium activity, respectively.


Lindholm M.,Rovaniemi Research Unit | Jalkanen R.,Rovaniemi Research Unit | Salminen H.,Rovaniemi Research Unit | Aalto T.,Rovaniemi Research Unit | Ogurtsov M.,RAS Ioffe Physical - Technical Institute
Holocene | Year: 2011

New data have allowed us to extend a previous height-increment chronology of Scots pine (Pinus sylvestris L.) at the northern Fennoscandian timberline 817 years backwards in time, from 1561 to 745. Our final transfer model accounts for 31% of the dependent instrumental (mean June-August) temperature variance between 1908 and 2007. According to the 1263 yr long summer temperature proxy, the most severe summers were experienced in 1601, 1790 and 782. Correspondingly, the summers of 1689, 885 and 1123 were the most favourable for growth. Two drastic shifts in temperature variability were also found. The twentieth century experienced a multidecadal change as the cold 1905-1914 period was immediately followed by a warm period from 1915 to 1944. An even more prominent shift occurred in the Middle Ages, as the most severe cold spell during 1135-1164 was preceded by the warmest period only a decade earlier, during 1115-1124. The Fourier spectrum of the reconstruction shows significant concentrations of variance around 33.3, 23.3 and 11 years, and between 2.6 and 3.0 years. The wavelet spectrum was able to date several centres of fluctuating periodicities between 745 and 2007. Furthermore, daily temperature records allowed us to define the major growth forcing climatic factor in more detail than in previous response analyses. The mean temperature during a 53 day season from 14 June to 6 August produced the strongest positive growth response (r 2 = 0.36). © The Author(s) 2010.

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