Cloud Cover Feedback Moderates Fennoscandian Summer Temperature Changes Over the Past 1,000 Years

Northern Fennoscandia has experienced little summer warming over recent decades, in 24 contrast to the hemispheric trend, which is strongly linked to greenhouse gas emissions. A likely25 explanation is the feedback between cloud cover and temperature. We establish the long- and26 short-term relationship between summer cloud cover and temperature over Northern27 Fennoscandia, by analysing meteorological and proxy climate data. We identify opposing28 feedbacks operating at different timescales. At short timescales, dominated by internal29 variability, the cloud cover-temperature feedback is negative; summers with increased cloud30 cover are cooler and sunny summers are warmer. However, over longer timescales, at which31 forced climate changes operate, this feedback is positive, rising temperatures causing increased32 regional cloud cover and vice versa. This has occurred both during warm (Medieval Climate33 Anomaly and at present) and cool (Little Ice Age) periods. This two-way feedback relationship34 therefore moderates Northern Fennoscandian temperatures during both warm and cool35 hemispheric periods

Autonomic modulation and antiarrhythmic therapy in a model of long QT syndrome type 3

AIMS: Clinical observations in patients with long QT syndrome carrying sodium channel mutations (LQT3) suggest that bradycardia caused by parasympathetic stimulation may provoke torsades de pointes (TdP). beta-Adrenoceptor blockers appear less effective in LQT3 than in other forms of the disease. METHODS AND RESULTS: We studied effects of autonomic modulation on arrhythmias in vivo and in vitro and quantified sympathetic innervation by autoradiography in heterozygous mice with a knock-in deletion (DeltaKPQ) in the Scn5a gene coding for the cardiac sodium channel and increased late sodium current (LQT3 mice). Cholinergic stimulation by carbachol provoked bigemini and TdP in freely roaming LQT3 mice. No arrhythmias were provoked by physical stress, mental stress, isoproterenol, or atropine. In isolated, beating hearts, carbachol did not prolong action potentials per se, but caused bradycardia and rate-dependent action potential prolongation. The muscarinic inhibitor AFDX116 prevented effects of carbachol on heart rate and arrhythmias. beta-Adrenoceptor stimulation suppressed arrhythmias, shortened rate-corrected action potential duration, increased rate, and minimized difference in late sodium current between genotypes. beta-Adrenoceptor density was reduced in LQT3 hearts. Acute beta-adrenoceptor blockade by esmolol, propranolol or chronic propranolol in vivo did not suppress arrhythmias. Chronic flecainide pre-treatment prevented arrhythmias (all P < 0.05). CONCLUSION: Cholinergic stimulation provokes arrhythmias in this model of LQT3 by triggering bradycardia. beta-Adrenoceptor density is reduced, and beta-adrenoceptor blockade does not prevent arrhythmias. Sodium channel blockade and beta-adrenoceptor stimulation suppress arrhythmias by shortening repolarization and minimizing difference in late sodium current.status: publishe

Dendroclimatology on Scots pine (Pinus sylvestris L.) in northern Norway

A total of ten tree-ring chronologies of Scots pine, Pinus sylvestris L., was constructed between the Vesterålen archipelago and the Finnmarksvidda in order to investigate the regional variability of radial growth and climate response of pine. The longest tree-ring chronology, located in Forfjorddalen in Vesterålen, was highly significant back to AD 1354. The study area was divided into three dendroecological zones; the coast, the inner Scandes and the Finnmarksvidda. In all regions, July temperature was the most important growth-determining factor. At the coast, pine showed a significant positive response also to August temperatures. A partial study in the inner Scandes showed that the radial growth at north-facing slopes was enhanced by high June temperatures, most likely due to the influence of the midnight sun. Evidence of environmental stress due to global warming was seen in reduced growth during periods of warm-moist mid winters at the coast and, particularly in the warm 1930s, in the Scandes. Also, there were indications of drought stress in summer in the intra-alpine valleys of the Scandes and at the edaphically dry coastal site, Stonglandseidet. On the basis of the tree-ring chronologies, July temperatures were reconstructed back to AD 1800 for northern Norway 69°N and July-August temperatures along the coast back to AD 1358. The 20th century since 1915 was a period of above-average temperatures and growth. In the present reconstruction, a comparable warm period occurred previously only AD 1470-1540. In the 19th century, cool summers prevailed about AD 1810, in the 1830s and from the late 1860s to 1910. The 17th century, the coolest interval of the ‘Little Ice Age’, experienced three intervals of cool summers around AD 1605, 1640 and 1680. There was evidence of a lack of pine regeneration in the first half of the 17th century. Major regional temperature differences were observed around AD 1760 with extraordinarily warm summers east of the Scandes, but average temperatures at the coast, and about AD 1800, when the coast was warm, but the inland cooling. An exploratory reconstruction of June temperatures from growth differences between northand south-facing slopes demonstrated the potential of site-related growth responses for refined climate reconstructions

Historical legacy of old-growth pine forest in Dividalen, nothern Scandes

The Dividalen (Sami: Dieváidvuovdi) valley in Troms county, North Norway, is well known for its old-growth pine forest, a biodiversity hotspot for dead wood-inhabiting fungi and lichens. The majority of the valley is protected within the Upper Dividalen Landscape Conservation Area and National Park. A general conception is that until the mid-nineteenth century when agriculture and forestry entered the valley, the landscape was entirely untouched by man and only used as a pathway for Sami and their reindeer herds on their annual migrations between Sweden and the Norwegian coast. Recent investigations on culturally modified trees and fossil pollen from mires have, however, revealed quite a different story. Sami reindeer pastoralism has affected the vegetation composition from the early seventeenth century to the nineteenth century, and traditional land use should be acknowledged as a long present factor in forming the landscape and cultural heritage. The climatic deterioration known as the Little Ice Age had a severe effect on the pine forest stand structure during the same centuries, forming the culmination of a period of climatic stress initiated already in the thirteenth century. Both long-term cultural and climatic factors are thus important to understand the vegetation dynamics and resulting biodiversity within the protected areas

Historical legacy of the old-growth pine forest in Dividalen, northern Scandes

The Dividalen (Sami: Dieváidvuovdi) valley in Troms county, North Norway, is well known for its old-growth pine forest, a biodiversity hotspot for dead wood-inhabiting fungi and lichens. The majority of the valley is protected within the Upper Dividalen Landscape Conservation Area and National Park. A general conception is that until the mid-nineteenth century when agriculture and forestry entered the valley, the landscape was entirely untouched by man and only used as a pathway for Sami and their reindeer herds on their annual migrations between Sweden and the Norwegian coast. Recent investigations on culturally modified trees and fossil pollen from mires have, however, revealed quite a different story. Sami reindeer pastoralism has affected the vegetation composition from the early seventeenth century to the nineteenth century, and traditional land use should be acknowledged as a long present factor in forming the landscape and cultural heritage. The climatic deterioration known as the Little Ice Age had a severe effect on the pine forest stand structure during the same centuries, forming the culmination of a period of climatic stress initiated already in the thirteenth century. Both long-term cultural and climatic factors are thus important to understand the vegetation dynamics and resulting biodiversity within the protected areas

Non-stationary Response of Tree Growth to Climate Trends Along the Arctic Margin

Climate change modulates cold-marginal forest ecosystems through changing growth constraints. Understanding spatiotemporal variations in climate– growth relationships is essential to project forest ecosystem dynamics, and climate–environmental feedbacks. We explored variations in growth and climate–growth relationships, along the Arctic margin in north-western Europe, using Scots pine radial growth chronologies, climate data and links between the geographical origin of dominant air masses and growth-controlling variables. Analyses covered nineteenth century to early twenty-first century, with emphasis on two separate warming periods (early twentieth century, and late twentieth to early twenty-first century) and the intervening cooling period. The analyses revealed spatiotemporally unstable growth responses to climate along the Arctic margin. Spatial growth patterns were most similar during the cooling period. However, climate trends (warming, cooling) were weak drivers of growth-limiting climate variables. Instead, a transition in growth-limiting variables occurred throughout the analysed period. A wide range of growing season and non-growing season climate variables limited growth during the early twentieth century. Thereafter the number of growth-limiting variables progressively decreased. This change was accompanied by a contraction in the spatial correspondence between growth and climate, and by a shift in the geographical origin of dominant air masses. This was particularly emphasized close to the Atlantic during recent warming period. The weak association between growth-limiting variables and climate trends question projections of future ecosystem dynamics based on climate variables identified during specific periods (for example, recent warming period). Such projections may be misleading as the diversity of climate conditions constraining cold-marginal forests will be underestimated. climate trends; cold-marginal forests; dendroclimatology; growth-controlling climate; tree-climate interactions; Pinus sylvestris; spatiotemporal growth responses.publishedVersio

Growth variability of Scots pine (Pinus sylvestris) along a West-East gradient across northern Fennoscandia: a dendroclimatic approach

We performed a spatiotemporal analysis of a network of 21 Scots pine (Pinus sylvestris) ring-width chronologies in northern Fennoscandia by means of chronology statistics and multivariate analyses. Chronologies are located on both sides (western and eastern) of the Scandes Mountains (67°N-70°N, 15°E-29°E). Growth relationships with temperature, precipitation, and North Atlantic Oscillation (NAO) indices were calculated for the period 1880-1991. We also assessed their temporal stability. Current July temperature and, to a lesser degree, May precipitation are the main growth limiting factors in the whole area of study. However, Principal Component Analysis (PCA) and mean interseries correlation revealed differences in radial growth between both sides of the Scandes Mountains, attributed to the Oceanic-Continental climatic gradient in the area. The gradient signal is temporally variable and has strengthened during the second half of the 20th century. Northern Fennoscandia Scots pine growth is positively related to early winter NAO indices previous to the growth season and to late spring NAO. NAO/growth relationships are unstable and have dropped in the second half of the 20th century. Moreover, they are noncontinuous through the range of NAO values: for early winter, only positive NAO indices enhance tree growth in the next growing season, while negative NAO does not. For spring, only negative NAO is correlated with radial growth

Little Ice Age summer temperatures in Western Norway from a 700-year tree-ring chronology

A ring-width Pinus sylvestris chronology from Sogndal in western Norway was created, covering the period AD 1240–2008 and allowing for reconstruction of monthly mean July temperatures. This reconstruction is the first of its kind from western Norway and it aims to densify the existing network of temperature-sensitive tree-ring proxy series to better understand past temperature variability in the ‘Little Ice Age’ and diminish the spatial uncertainty. Spatial correlation reveals strong agreement with temperatures in southern Norway, especially on the western side of the Scandinavian Mountains. Five prominent cold periods are identified on a decadal timescale, centred on 1480, 1580, 1635, 1709 and 1784 and ‘Little Ice Age’ cooling spanning from 1450 to the early 18th century. High interannual and decadal agreement is found with an independent temperature reconstruction from western Norway, which is based on data from grain harvests and terminal moraines. The reconstructed temperatures also correlate with other tree-ring-based temperature reconstructions from Fennoscandia, most strongly with data from central Sweden. Tree growth in Sogndal is correlated to the Scandinavian teleconnection index in the summer months, at least in the last half of the 20th century, and is positively correlated to the summer expression of the North Atlantic Oscillation in the early half of the 20th century. A significant response to major volcanic forcing in the Northern Hemisphere was found, and extreme years seem to be related to the dominance of high and low geopotential height that in turn represents variability in the path of the storm tracks over Fennoscandia. When compared with the variation in frontal positions with time of Nigardsbreen, an eastern outlet glacier from the Jostedalsbreen glacier in western Norway, cold summers in the early 18th century relates to the culmination of a rapid glacial advance that lead up to the 1748 ‘Little Ice Age’ maximum extent

Middelalderfiske, fellefangst og fraflytting – en dendrokronologisk undersøkelse av et 1300-talls stasjonært fiskeanlegg i Nord-Mesna, Sørøst-Norge

&lt;p&gt;Vedlegg 1 og 2 til artikkelen "Middelalderfiske, fellefangst og fraflytting – en dendrokronologisk undersøkelse av et 1300-talls stasjonært fiskeanlegg i Nord-Mesna, Sørøst-Norge"&lt;/p&gt;&lt;p&gt;Attachment 1 and 2 to the article "Medieval fishing and abandonment – a dendrochronological investigation of a 14th-century stationary fishing trap in Lake Nord-Mesna, in the interior of Scandinavia"&lt;/p&gt;&lt;p&gt;Abstrct to article, submitted to the journal Fornvännen (https://www.vitterhetsakademien.se/english/the-royal-swedish-academy-of-letters-history-and-antiquities/publications/fornvannen.html):&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Medieval fishing and abandonment – a dendrochronological investigation of a 14th-century stationary fishing trap in Lake Nord-Mesna, in the interior of Scandinavia&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Fishing in rivers and lakes has traditionally been a longstanding and dependable means of sustenance for the people of inland Scandinavia. However, our understanding of pre-modern fishing traditions has been hampered by fragmented and rare written sources, as well as a scarcity of comprehensive archaeological records. Nevertheless, a recent excavation and thorough dendrochronological analysis of a fish trapping enclosure system in Lake Nord-Mesna (520 masl.), situated in the boreal forests of inland Norway, has provided unique and detailed insights into freshwater fishing traditions, techniques, organization and its historical significance.&lt;/p&gt;&lt;p&gt;The examined structure, believed to be a fish weir with lath screen traps set into shallow water, was established in the late 1200s, and in the following years it was regularly used and maintained in the spring/early summer.&nbsp;The last documented repair was in 1343, followed by an abandonment interpreted as a tangible manifestation of the recession that affected inland areas of Scandinavia in the 1300s, likely induced by factors such as plague and climatic deterioration. These results provide archaeological evidence of medieval utilization of effective enclosure traps in the region, contradicting the prevailing notion that this form of fishing was later introduced by Forest Finns who migrated to the area in the 17th century. Finally, and of significant importance, the findings offer fresh insights into the organization, practice, and outcomes of medieval fishing in inland Scandinavia.&lt;/p&gt