A long-term Arctic snow depth record from Abisko, northern Sweden, 1913–2004     

Jack Kohler  Ola Brandt  Margareta Johansson  Terry Callaghan 《Polar research》2006,25(2):91-113

A newly digitized record of snow depth from the Abisko Scientific Research Station in northern Sweden covers the period 1913-present. Mean snow depths were taken from paper records of measurements made on a profile comprising 10 permanent stakes. This long-term record yields snow depths consistent with two other shorter term Abisko records: measurements made at another 10-stake profile (1974-present) and at a single stake (1956-present). The measurement interval is variable, ranging from daily to monthly, and there are no data for about half of the winter months in the period 1930-1956. To fill the gaps, we use a simple snowpack model driven by concurrent temperature and precipitation measurements at Abisko. Model snow depths are similar to observed; differences between the two records are comparable to those between profile and single stake measurements. For both model and observed snow depth records, the most statistically significant trend is in winter mean snow depths, amounting to an increase of about 2 cm or 5 % of the mean per decade over the whole measurement period, and 10% per decade since the 1930-40s, but all seasonal means of snow depth show positive trends on the longest timescales. However, the start, end, and length of the snow season do not show any statistically significant long-term trends. Finally, the relation between the Arctic Oscillation index and Abisko temperature, precipitation and snow depth is positive and highly significant, with the best correlations for winter.  相似文献   

Isotopic composition of phanerozoic ore leads from the Swedish segment of the Fennoscandian Shield     

Åke Johansson  David Rickard 《Mineralium Deposita》1984,19(4):249-255

95 analyses of ore lead isotope ratios from 23 Phanerozoic ore deposits from the Swedish segment of the Fennoscandian Shield form a marked linear trend on a ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb diagram. The line may be interpreted in a two-stage model, the lead being derived from 1.8±0.15 Ga old Svecokarelian basement and mineralization occurring at 0.4±0.15 Ga. The initial composition of the Svecokarelian rock lead was similar to the lead in early Proterozoic volcanogenic sulfide ores in Sweden. — The large spread in the isotope ratios was caused by a combination of selective leaching of different minerals in the source rocks, mixing with less radiogenic Caledonian lead, and local or regional variations in the U, Th and Pb contents of the basement. As a consequence, conventional methods of identifying source rocks from lead isotopic data (e.g. mu-values, Th/U ratios) may not be directly applicable. Phanerozoic ore lead development in the Swedish section of the Fennoscandian Shield was ensialic. That is, the ore lead was almost entirely derived from the Precambrian basement, although this basement does not appear to be anomalously enriched in Pb. No juvenile or mantle lead was apparently contributed to this section of the crust after the Precambrian, except for that mechanically transported onto the western edge of the Shield by the Caledonian nappes. However, some of Europe's largest lead deposits are included in these Swedish Phanerozoic mineralizations, suggesting that it was the nature of the processes involved rather than the richness of the source, that determined their formation.  相似文献   

Field measurements of emission of nitric oxide from fertilized and unfertilized forest soils in Sweden   总被引：3，自引：0，他引：3  

C. Johansson 《Journal of Atmospheric Chemistry》1984,1(4):429-442

Application of nitrate fertilizers on two types of forest soils led to a marked increase in the NO emission rate indicating a large potential for NO production in these soils. The largest fluxes on the fertilized plots were up to 60 ng NO–N m^–2 s^–1. About 0.35% of the applied nitrogen was lost as NO within about 14 days after fertilization. The fluxes from the unfertilized forest soils were in the range 0.1 to 0.8 ng NO–N m^–2 s^–1 with a median value of 0.3 ng NO–N m^–2 s^–1. If this value, obtained during June and August to September, is representative for the growing season (150 days), it corresponds to an annual emission of 0.04 kg NO–N ha^–1. This is about 30% of the value obtained for an unfertilized agricultural soil. Because of the large areas occupied by forests in Sweden the flux of NO from forest soils represents a significant contribution to the total flux of NO from soils in Sweden.Earlier observations of equilibrium concentrations for NO have been verified. These were found to range from 0.2 to 2 ppbv for an unfertilized forest soil and up to 170 ppbv for a fertilized soil. At the rural site in Sweden where these measurements were performed the ambient concentrations where found to be less than this equilibrium concentration, and consequently there was generally a net emission of NO.There are still large uncertainties about the global flux of NO from soils. Using direct measurements on three different types of ecosystems and estimates based on a qualitative discussion for the remaining land areas, a global natural source for NO of the order of 1 Tg N a^–1 was obtained. If 0.35% of the total annual production of fertilizer nitrogen is lost as NO, fertilization of soils may contribute with 20% to the natural flux from soils.  相似文献   

Increased photosynthesis compensates for shorter growing season in subarctic tundra—8 years of snow accumulation manipulations     

Julia Bosiö  Christian Stiegler  Margareta Johansson  Herbert N. Mbufong  Torben R. Christensen 《Climatic change》2014,127(2):321-334

This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots.  相似文献   

Ecological aspects of fin whale and humpback whale distribution during summer in the Norwegian Sea     

Leif Nøttestad  Lise D. Sivle  Bjørn A. Krafft  Lise Langård  Valantine Anthonypillai  Matteo Bernasconi  Herdis Langøy  Bjørn E. Axelsen 《Marine Ecology》2014,35(2):221-232

The Norwegian Sea is a migration and feeding ground for fin whales (Balaenoptera physalus) and humpback whales (Megaptera novaeangliae) in summer. During the last decade, significant structural changes in the prey community, including northerly expansion and movement in the distribution of pelagic fish species, have been reported from this ecosystem. However, little information on whale feeding ecology exists in the Norwegian Sea and surrounding waters. A total of 59 fin whales and 48 humpback whales were sighted during 864 h of observation over an observation distance of about 8200 nmi (15,200 km) in the Norwegian Sea from 15 July to 6 August 2006 and 2007. The fin whale group size, as mean (±SD), varied between one and five individuals (2.1 ± 1.2 ind.) and humpback whale group size varied between one and six individuals (2.5 ± 1.7 ind.). Fin‐ and humpback whales were observed mainly in the northern part of the study area, and were only found correlated with the presence of macro‐zooplankton in cold Arctic water. Humpback whales were not correlated with the occurrence of adult Norwegian spring‐spawning herring (Clupea harengus) except for the northernmost areas. Despite changes in the whale prey communities in the Norwegian Sea, no apparent changes in fin‐ or humpback whale distribution pattern could be found in our study compared to their observed summer distribution 10–15 years ago.  相似文献   

Early Holocene Tree Growth at a High Elevation Site in the Northernmost Scandes of Sweden (Lapland): A Palaeobiogeographical Case Study Based on Megafossil Evidence   总被引：2，自引：0，他引：2  

Leif Kullman 《Geografiska Annaler: Series A, Physical Geography》1999,81(1):63-74

The paper focuses on early Holocene tree growth and alpine tree-limits in the northernmost Swedish Scandes (Lapland). Megafossil wood remnants in peats and lakes were searched for over a large area at elevations high above the modern tree-limits. Wood of Pinus sylvestris, Betula pubescens spp. tortuosa and Alnus incana was discovered near the shore of a small lake (999 m a.s.l.) c. 500 m higher than today's tree-limit of Pinus sylvestris in this region. Radiocarbon dating yielded values of unprecedented age, c. 8500–8100 ¹⁴C years BP for all three species and in addition 5400–4500 ¹⁴C years BP for Betula and Alnus. The highest position of the Pinus tree-limit occurred during the early Holocene, which compares well with the situation reconstructed by megafossils in the southern Scandes. It now appears that the long-term tree-limit and climate histories are broadly the same in entire mid- and northern Fennoscandia. Corrected for glacio-isostatic land uplift, the tree-limit record suggests that the summers were c. 2.4°C warmer than today at 8500 ¹⁴C years BP . A dry continental climate with substantial seasonal contrasts is likely to have prevailed during this period, which restricted the occurrence of glaciers and glacier activity. Most circumstances point to the overriding importance of the Milankovitch orbital theory for pacing or forcing the long-term postglacial climate change. The results are inconsistent with most inferences based on pollen, certain macrofossil records and general circulation simulations. These proxy environmental histories have frequently advocated a mid-Holocene thermal optimum and an oceanic and humid climate in northern and western Fennoscandia during the early Holocene. The uncovered discrepancy between the outcome of the objective and factual megafossil method and more subjective/inferential microfossil methods should be important for Quaternary plant ecology in general, stressing the usefulness of megafossil studies.  相似文献