| 31. |
- Pohjola, Veijo, et al.
(författare)
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Potential to recover paleoclimatic data in temperate ice cores: an example from the small ice cap Riukojietna, Northern Scandinavia
- 2005
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 87:1, s. 259-270
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Tidskriftsartikel (refereegranskat)abstract
- We have studied a 33.7 m deep ice core from a small polythermal Scandinavian ice cap to determine whether it is possible to recover pre-20th century climatic information from the glacier. Ice structural studies show a significant change from clear ice above 11 m depth (superimposed ice indicating refreezing) to bubbly ice below 11 m depth, indicating this is the transition between Little Ice Age (LIA) and 20th century ice. Calculations with a Nye-age model, along with a mass balance reconstruction, show that this structural boundary likely formed in the last part of the LIA, which in this region ended about 1910. The ice below this boundary was sampled and analyzed for stable isotopic composition and ionic content, which both show significant variations with depth. The stable isotope record likely contains cycles of annual duration during the LIA. The chemistry in the ice core indicates that the information is useful, and can be used to interpret climatic and environmental variables during the LIA. A comparison of Riukojietna ion chemistry and oxygen isotope records to similar records from other glaciers in this region reveals a clear continental – maritime gradient. Changes in this gradient with time may be possible to resolve using such ice core records. Results from this study demonstrate that ice cores from glaciers in this climatic environment can be useful in revealing environmental conditions from climatically colder periods and yield pre-industrial benchmark values for chemical loading and oxygen isotopes, but that hiatuses complicate the depth-age relationship.
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| 32. |
- Ridefelt, Hanna, 1977-, et al.
(författare)
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56 years of solifluction measurements in the Abisko Mountains, northern Sweden : analysis of spatial and temporal variations of slow soil surface movements
- 2009
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 91:3, s. 215-232
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Tidskriftsartikel (refereegranskat)abstract
- Solifluction movement rates from 1952 to 2008 for the Abisko region, northern Sweden, have been compiled and analysed through correlation tests and multiple regression. The temporal analysis is based on two datasets (Lobe11 & gridAB and Line B) from Karkevagge. The dataset Lobe11 & gridAB show a strong correlation between movement rates and mean annual air temperature (MAAT) and MAAT is also identified as one of the significant contributing parameters in the multiple regression model. No significant correlations were found for the Line B dataset. The spatial analysis indicates generally higher movement rates in the western part of the region and at lower altitudes mainly between 700 and 900 m a.s.l., but the spatial variability is high. To reduce the influence of the temporal variation the data for the correlation tests of the spatial variations were divided into two parts: 1957 to 1980 and 1981 to 2008. The correlation analysis of the dataset 1957 to 1980 shows a significant negative correlation between annual average movement rates and permafrost probability and altitude. The dataset 1981 to 2008 shows a positive correlation between movement rates and wetness index. It is concluded that movement rates may increase with higher MAAT in the western part of the region (Karkevagge), the spatial variability of movement rates within the region is very high and that altitude (and/or permafrost) together with wetness index are the main controls on the regional spatial variation. The study highlights the limitations in establishing statistical relationships between movement rates and climate using data from different field empirical studies.
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| 33. |
- Rosell, Staffan, 1966, et al.
(författare)
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Rainfall change and its implications for Belg harvest in South Wollo, Ethiopia
- 2007
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Ingår i: Geografiska Annaler, Series A: Physical Geography. - : Taylor & Francis. - 1468-0459 .- 0435-3676. ; 89:4, s. 287-299
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Tidskriftsartikel (refereegranskat)abstract
- Most farmers in the Ethiopian highlands depend on rain-fed agriculture. Some areas have the favourable situation of having two rainy seasons, Belg (February-May) and the long rainy season Kiremt (June-October), which is the case in some parts of South Wollo. Tef (Eragrostis tef) is the staple crop that farmers prefer to grow and the 90-day variety is suitable for growing during the short rainy season. One out of eight Ethiopians lives in tef potential areas which have Belg rainfall. The aim in this study is to analyse rainfall variation in South Wollo, in particular the area east of the small town of Hayk, and to study its effect on the ability to grow tef during the Belg season. Results from interviews showed that a more difficult farming situation had emerged during the past 40 years, largely due to deterioration of physical resources such as rainfall. Rainfall is analysed by comparing daily rainfall data from four stations in two periods, 1963 to 1982 and 1984 to 2003, for changes in totals, seasonal distribution and variability. Coefficient of variance, rainy days, rainfall intensity and dry spells were analysed. Results from this study show that there have been minor rainfall changes but greater rainfall variability. During fieldwork key informants were asked if they were able to harvest tef during the past nine years, a period that has been used in a model of rainfall influence on tef cultivation during the Belg season. In both 20–year periods, farmers were able to grow tef every second year. In spite of a greater variability in rainfall the farmers proved their knowledge and flexibility and were able to harvest tef in the same number of years during both periods.
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| 34. |
- Stouge, Svend, et al.
(författare)
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Lower palaeozoic stratigraphy of Murchisonfjorden and Sparreneset, Nordaustlandet, Svalbard
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 209-226
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Tidskriftsartikel (refereegranskat)abstract
- The Lower Palaeozoic stratigraphy of the Kap Sparre Formation of Kulling (Hecla Hoek Succession) from Murchisonfjorden and eastern Nordaustlandet of Svalbard is described based on new field observations in the region. The investigated sedimentary succession is referred to the Upper quartzite series and Upper dolomite series of the Kap Sparre Formation. The observed sequence resembles that of the Oslobreen Group from central and northeastern Ny Friesland and the formal and well-established and more detailed stratigraphical framework used in Ny Friesland may apply for the strata at Sparreneset and in Murchisonfjorden, western Nordaustlandet. The lower Palaeozoic succession overlies the uppermost Precambrian sediments (Dracoisen Formation = the lower part of Kap Sparre Formation sensu Kulling) of the Polarisbreen Group with a cryptic unconformity, and a regional stratigraphical gap spanning the late Ediacaran developed on the platform. Additions to the previous descriptions of some of the existing units are presented. The new lithostratigraphical unit: Black shale and limestone unit is proposed informally. It is a Lower(?) to Middle Cambrian black shale with limestone nodules and lenses that is exposed on the northwest coast of Krossoya in Murchisonfjorden, Svalbard. In addition, a Dolostone-limestone unit, Middle(?) Cambrian to Lower Ordovician, composed of dolostone and dolomitized limestone and minor limestone, and a Limestone unit (Lower to Middle(?) Ordovician), which overlies the Upper dolomite series are added to the succession. The deposits as a whole show the development of an environmentally controlled carbonate platform that marked the transition from the inner to the outer shelf that evolved during the opening and spreading of the Iapetus Ocean.
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| 35. |
- Strömquist, Lennart, 1943-, et al.
(författare)
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Integrated landscape analyses of change of miombo woodland in Tanzania and its implication for environment and human livelihood
- 2009
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 91A:1, s. 31-45
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Tidskriftsartikel (refereegranskat)abstract
- Landscapes bear witness to past and present natural and societal processes influencing the environment and human livelihoods. By analysing landscape change at different spatial scales over time the effects on the environment and human livelihoods of various external and internal driving forces of change can be studied. This paper presents such an analysis of miombo woodland surrounding the Mkata plains in central Tanzania. The rich natural landscape diversity of the study area in combination with its historical and political development makes it an ideal observation ground for this kind of study. The paper focuses on long-term physical and biological changes, mainly based on satellite information but also on field studies and a review of documents and literature.The miombo woodlands are highly dynamic semi-arid ecosystems found on a number of nutrient-poor soil groups. Most of the woodlands are related to an old, low-relief geomorphology of erosion surfaces with relatively deep and leached soils, or to a lesser extent also on escarpments and steep Inselberg slopes with poor soils. Each period in the past has cast its footprints on the landscape development and its potential for a sustainable future use. On a regional level there has been a continual decrease in forest area over time. Expansion of agriculture around planned villages, implemented during the 1970s, in some cases equals the loss of forest area (Mikumi-Ulaya), whilst in other areas (Kitulangalo), the pre-independence loss of woodland was small; the agricultural area was almost the same during the period 1975–1999, despite the fact that forests have been lost at an almost constant rate over the same period. Illegal logging and charcoal production are likely causes because of the proximity to the main highway running through the area. Contrasting to the general regional pattern are the conditions in a traditional village (Ihombwe), with low immigration of people and a maintained knowledge of the resource potential of the forest with regards to edible plants and animals. In this area the local community has control of the forest resources in a Forest Reserve, within which the woody vegetation has increased in spite of an expansion of agriculture on other types of village land. The mapping procedure has shown that factors such as access to transport and lack of local control have caused greater deforestation of certain areas than during the colonial period. Planned villages have furthermore continued to expand over forest areas well after their implementation, rapidly increasing the landscape fragmentation. One possible way to maintain landscape and biodiversity values is by the sustainable use of traditional resources, based on local knowledge of their management as illustrated by the little change observed in the traditionally used area.
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| 36. |
- Boelhouwers, Jan, et al.
(författare)
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Critical assessment of the 2°C min−1 threshold for thermal stress weathering
- 2013
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 95:4, s. 285-293
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Tidskriftsartikel (refereegranskat)abstract
- Rock surface temperature changes in excess of 2°C min−1 have been argued to result in permanent strain in rock. The single threshold value and the supposed importance of a rate of 2°C min−1 rock temperature change is rejected, based on lack of a sufficient empirical basis, contrasting results from acoustic emission studies, varying strength properties of different rock types, lack of data on actual strain resulting from short-term temperature variations, and lack of notable long-term weathering effects in Nordic environments. Based on the presented discussion, the role of thermal shock weathering in cold regions is questioned and renewed emphasis is placed on the importance of absolute temperature and measurement of strain, as well as spatial temperature gradients.
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| 37. |
- Backéus, Ingvar
(författare)
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Flarks in the Maloti, Lesotho
- 1989
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - 0435-3676 .- 1468-0459. ; 71, s. 105-111
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Tidskriftsartikel (refereegranskat)abstract
- Flarks are reported to occur in mires in Qathlamba (the Drakensberg Range) of the Maloti, Lesotho at an altitude of 3200 m a.s.l. Flarks are not previously reported from Africa. Conditions for the formation and maintenance of flarks are discussed. It is argued that local waterlogging is a more likely explanation for the formation of flarks in Qathlamba than frost action.
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| 38. |
- Bai, M. W., et al.
(författare)
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Different responses of the radial growth of the planted and natural forests to climate change in humid subtropical China
- 2020
-
Ingår i: Geografiska Annaler Series a-Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 102:3, s. 235-246
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Tidskriftsartikel (refereegranskat)abstract
- China holds the world's largest area of planted forests, which play a crucial role in mitigating climate change. Knowledge gaps remain on the responses of the growth of planted forests to climate changes in China, particularly for their long-term changes. This study compared the long-term tree-ring growth patterns and their responses to climate between planted and natural forests. We developed four chronologies from two typical conifer species ofPinus massonianaandCunninghamia lanceolatafrom planted and natural forests in humid subtropical China. One chronology is to our knowledge the longest chronology from planted forests in China spanning since 1944. Tree growths of both natural and planted forests are generally limited by summer drought due to the hot and dry summer in this area. In general, tree rings of the natural forests are more sensitive to climate than planted forests as indicated by higher inter-series correlations, which agree with previous studies. The natural forests are more drought sensitive wheareas the planted forests are relatively more limited by temperature. TheC. lanceolataforests showed more significant correlations with the accumulated drought thanP. massonianafor both the natural and planted forests.
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| 39. |
- Barthel, Roland, 1967, et al.
(författare)
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Current understanding of groundwater recharge and groundwater drought in Sweden compared to countries with similar geology and climate
- 2021
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Ingår i: Geografiska Annaler: Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 103:4, s. 323-345
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Tidskriftsartikel (refereegranskat)abstract
- Recently, groundwater in Sweden has attracted media attention due to supply shortages caused by dry periods and low groundwater levels. About half of Swedish drinking water stems from groundwater. The small Swedish aquifers are highly dependent on frequent and sufficient recharge. Groundwater recharge forms the link between meteorological and groundwater drought and thus the main link between climate change and sustainable water supply. This study evaluated whether the current knowledge on groundwater recharge and groundwater drought is sufficient to mitigate the impacts of climate change. A review of international literature on groundwater recharge in regions with conditions similar to Sweden was performed. National literature was compared and links to international studies evaluated. A survey among Swedish groundwater experts complemented the study. Findings are that research on groundwater recharge has been scarce in Sweden over the last decades and Swedish experts seem to not have taken much notice of international literature. It is concluded that Sweden is not well prepared to predict the impact of climate change on groundwater resources, as the most crucial process linking climate to groundwater is not well understood. The study has a strong focus on Sweden, however, the results are also relevant for countries with similar geology and climate. One main conclusion is that groundwater recharge studies often remain unique, and thus hardly transferable and comparable. Two or more independent studies are rarely applied in parallel, verification based on direct groundwater observations is not common. This raises concerns about the reliability of climate change impact predictions on groundwater.
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| 40. |
- Boelhouwers, Jan, 1962-, et al.
(författare)
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Long-term frost weathering rates of limestone beach clasts, Fårö Island, Central Baltic Sea
- 2020
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Taylor & Francis Group. - 0435-3676 .- 1468-0459. ; 102:1, s. 12-32
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Tidskriftsartikel (refereegranskat)abstract
- The known post-glacial isostatic land rise rates at Fårö Island, Central Baltic Sea, allowed for the reliable estimation of frost weathering rates of limestone clasts along five beach profiles. Weathering rates measured by clast dimension change were quantified over periods ranging between 640 and 2090 years. While the deposited beach materials at each profile have varying lithostratigraphic compositions these attributes appear to have no direct influence on the long-term comminution rates. Mean clast size of initially deposited beach materials is suggested to be primarily a function of local wave energy and sourced from local rock platforms. Field observations, climate data and literature point to the beach materials in the upper 10–20 cm being fractured under an active diurnal to short-term frost environment that has persisted over the past 1000–2000 years. Pore water freezing by 9% volumetric expansion and the development of pore water expulsion and hydrofracture is suggested to increase pore volume and pore interconnectedness over time and facilitate ice segregation growth. Observed modes of clast fracture, bursting, flaking and granular disaggregation suggest different frost weathering mechanisms to operate on different limestone lithologies. Long term rates of break down appear however not differentiated by limestone composition.
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