| 1. |
- Andresen, Camilla Snowman, et al.
(author)
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Early Holocene terrestrial climatic variability along a North Atlantic Island transect: palaeoceanographic implications
- 2007
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:15-16, s. 1989-1998
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Journal article (peer-reviewed)abstract
- A synthesis of the early Holocene climatic development in the North Atlantic region is presented, based on three previously published lake records from southern Greenland (Lake N14), Iceland (Lake Torfadalsvatn) and the Faroe Islands (Lake Lykkjuvotn). The interval 11500-8500 cal BP has been divided into five phases with respect to the inferred strength of the North Atlantic Current (NAC) and Irminger Currents (IC). Phase 1 (11 500-10 750 cal BP) was characterised by the first establishment of the NAC and IC in the vicinity of the studied sites, interrupted by the Preboreal Oscillation around 11 200cal BP. Phase 2 (10 750-10 100 cal BP) was marked by a further warming step in southern Greenland rather concordant with a change into colder and more variable winters on the Faroe Islands. It is proposed that this could partly be related to a series of melt water outbursts disturbing the thermohaline circulation in the eastern Atlantic Ocean, resulting in a warming trend in the western region. During Phase 3 (10 100-9400cal BP) the strength of the IC reaching northwestern Iceland intensified. A more stable regime in surface circulation was established at the onset of Phase 4 (9400-8900 cal BP) in southern Greenland and was followed by a change towards further warm conditions on Iceland at the onset of Phase 5 (8900-8500 cal BP). (C) 2007 Elsevier Ltd. All rights reserved.
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| 2. |
- Andresen, Camilla Snowman, et al.
(author)
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Rapid Holocene climate changes in the North Atlantic: evidence from lake sediments from the Faroe Islands
- 2006
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In: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 35:1, s. 23-34
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Journal article (peer-reviewed)abstract
- Holocene records from two lakes on the Faroe Islands were investigated to determine regional climatic variability: the fairly wind-exposed Lake Starvatn on Streymoy and the more sheltered Lake Lykkjuvotn on Sandoy. Sediment cores were analysed for content of biogenic silica, organic carbon and clastic material, and magnetic susceptibility. In addition, a new qualitative proxy for past lake ice cover and wind activity was developed using the flux of clastic grains that are larger than 255 mu m. Both long-term and short-term climatic developments were similar between the two lakes, suggesting a response to a regional climate signal. The long-term climate development is characterized by early Holocene rapid warming followed by Holocene climatic optimum conditions ending around 8300 cal. yr BP. A more open landscape as evidenced from increased sand grain influx in the period 8300-7200 cal. yr BP could reflect the aftermath of the 8200 cal. yr BP event, although the event itself is not recognized in either of the two lake records. From around 7200 cal. yr BP the mid-Holocene climate deterioration is observed and from 4200 cal. yr BP the climate deteriorated further with increased amplitude of centennial cooling episodes.
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| 3. |
- Jessen, Catherine, et al.
(author)
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Abrupt climatic changes and an unstable transition into a late Holocene Thermal Decline: a multiproxy lacustrine record from southern Sweden
- 2005
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In: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 20:4, s. 349-362
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Journal article (peer-reviewed)abstract
- The transition from a middle Holocene relatively warm and stable climate to a cooler and unstable late Holocene climate is reconstructed using sediments from Lake Igelsjon, south-central Sweden. This multiproxy study illustrates local, regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and/or wetter conditions around 4000 cal. yr BP. The results suggest that between ca. 4600 and ca. 3400 cal. yr BP, the environment around and within the lake responded in two major, well-defined steps: the first between 4450 and 4350 cal. yr BP and the second between 4000 and 3800 cal. yr BP. A series of rapid fluctuations of short duration were superimposed on the general cooling trend, with the most severe aquatic response peaking at ca. 3800 cal. yr BP. Pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and Corylus pollen influx in the period of 4000-3500 cal. yr BP. Stomatal-based reconstruction of atmospheric CO2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal. yr BP.
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| 4. |
- Jessen, Catherine, et al.
(author)
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Climate forced atmospheric CO2 variability in the early Holocene: A stomatal frequency reconstruction
- 2007
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In: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 57:3-4, s. 247-260
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Journal article (peer-reviewed)abstract
- The dynamic climate in the Northern Hemisphere during the early Holocene could be expected to have impacted on the global carbon cycle. Ice core studies however, show little variability in atmospheric CO2. Resolving any possible centennial to decadal CO2 changes is limited by gas diffusion through the firn layer during bubble enclosure. Here we apply the inverse relationship between stomatal index (measured on sub-fossil leaves) and atmospheric CO2 to complement ice core records between 11,230 and 10,330 cal. yr BP. High-resolution sampling and radiocarbon dating of lake sediments from the Faroe Islands reconstruct a distinct CO2 decrease centred on ca. 11,050 cal. yr BP, a consistent and steady decline between ca. 10,900 and 10,600 cal. yr BP and an increased instability after ca. 10,550 cal. yr BP. The earliest decline lasting ca. 150 yr is probably associated with the Preboreal Oscillation, an abrupt climatic cooling affecting much of the Northern Hemisphere a few hundred years after the end of the Younger Dryas. In the absence of known global climatic instability, the decline to ca. 10,600 cal. yr BP is possibly due to expanding vegetation in the Northern Hemisphere. The increasing instability in CO2 after 10,600 cal. yr BP occurs during a period of increasing cooling of surface waters in the North Atlantic and some increased variability in proxy climate indicators in the region. The reconstructed CO2 changes also show a distinct similarity to indicators of changing solar activity. This may suggest that at least the Northern Hemisphere was particularly sensitive to changes in solar activity during this time and that atmospheric CO2 concentrations fluctuated via rapid responses in climate. (c) 2006 Elsevier B.V. All rights reserved.
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| 5. |
- Jessen, Catherine, et al.
(author)
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Variability and seasonality of North Atlantic climate during the early Holocene: evidence from Faroe Island lake sediments
- 2008
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 18:6, s. 851-860
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Journal article (peer-reviewed)abstract
- Based on their position in relation to major ocean currents, palaeoclimatic archives in the Faroe Islands are expected to be sensitive recorders of variations in North Atlantic circulation. The multiproxy analysis ( magnetic susceptibility, total carbon, nitrogen and sulphur, biogenic silica, grains > 255 mu m) of a lacustrine record with both winter and summer climate indicators illustrates the variability of Faroese climate during the early Holocene (c. 11 300-10 240 cal. yr BP) and allows comparison with other records in the region. Our high-resolution record suggests a period of predominantly winter cooling and increased storminess centred at c. 11 150 cal. yr BP followed by a period of stability between c. 11 000 and 10 680 cal. yr BP, which correlates with a time when the North Atlantic was particularly free of meltwater incursions. After c. 10 680 cal. yr BP, both winter and summer indicators show an increase in variability broadly synchronous with increased variability at other North Atlantic sites. Within this time period, a predominantly winter cooling centred at c. 10 600 cal. yr BP, a winter/summer cooling centred at c. 10 450 cal. yr BP and a winter/summer cooling centred at c. 10 300 cal. yr BP are recorded. These distinctive coolings correspond to periods of ice core delta O-18 inferred lowered atmospheric temperatures over Greenland and the reoccurrence of meltwater outbursts at c. 10 600, 10 500 and 10 350 cal. yr BP.
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| 6. |
- Kokfelt, Ulla, et al.
(author)
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Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments
- 2009
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 15:7, s. 1652-1663
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Journal article (peer-reviewed)abstract
- Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake-water, and changes in δ13C and C, N and δ15N to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake-water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June–September (JJAS) precipitation and that the increase in lake-water TOC concentration reflects an increase in total annual precipitation. A significant depletion in 13C of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake-sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.
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| 7. |
- Loader, N J, et al.
(author)
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The role of inter-specific, micro-habitat and climatic factors on the carbon isotope (delta C-13) variability of a modern leaf assemblage from northern Scandinavia: implications for climate reconstruction
- 2006
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In: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 35:2, s. 188-201
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Journal article (peer-reviewed)abstract
- To provide a basis for the interpretation of past climatic conditions from Quaternary leaf records, leaf carbon isotope (delta C-13) results are presented for 12 northern European dwarf-shrub, shrub and tree species growing across a network of 18 sites in northern Scandinavia. The role of micro-habitat (hummock/hollow) on carbon isotope trends is explored in addition to a comparison of the carbon isotope composition of both cellulose and wholeleaf material. The data are also examined against local meteorological variables (temperature, precipitation and vapour pressure deficit) at both species and genus levels. Results exhibit only modest coherence between selected plant species and low-order correlations with external climate forcings consistent with accepted models for carbon isotope fractionation. Potential for the analysis and interpretation of stable isotopic time series may still be identified; however, factors such as inter-plant variability, senescence, diagenesis and homogeneity need to be thoroughly addressed before such an approach may be used for palaeoenvironmental reconstructions. These findings highlight the complexities and limitations of spatial calibration methods.
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| 8. |
- Rügheimer, Louise, 1970-
(author)
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Kidney Hyaluronan : Regulatory Aspects During Different States of Body Hydration, Nephrogenesis & Diabetes
- 2008
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Doctoral thesis (other academic/artistic)abstract
- The kidney regulates the excretion of water and electrolytes, which maintains homeostasis and enables control of arterial blood pressure. Hyaluronan, a large negatively charged interstitial glucosaminoglycan, is heterogeneously distributed within the kidney, primarily found in the medulla.Medullary hyaluronan content changes depending on the state of body hydration and plays a part in fluid regulation through its water binding and viscoelastic properties. The aim of this thesis was to provide new insight into the regulation of intrarenal hyaluronan during different states of body hydration, during completion of kidney development, and during diabetes mellitus.Dehydration reduces medullary interstitial hyaluronan in parallel with reduced hyaluronan synthase 2 gene expression and increased urinary hyaluronidase activity. Acute hydration results in an increase in medullary hyaluronan, an increase that requires nitric oxide and prostaglandins. Urinary hyaluronidase activity decreases during hydration. The elevation of hyaluronan is important for reducing water permeability of the interstitium i.e. favoring diuresis.Changes in hyaluronan concentration constitute a morphoregulatory pathway that plays a key role in nephrogenesis. The reduction in neonatal hyaluronan depended on an angiotensin II mediated process that does not appear dependent on lymph vessel formation. If angiotensin II is blocked with an ACE inhibitor, hyaluronan accumulates, which results in structural and functional abnormalities in the kidney. Renomedullary hyaluronan is elevated during uncontrolled diabetes, which coincides with induction of hyaluronan synthase 2 mRNA, hyperglycemia, glucosuria, proteinuria and overt diuresis. The levels of hyaluronan are probably at a terminus ad quem as no further response was seen during hydration. The higher interstitial expression of hyaluronan during diabetes may be involved in the progression of diabetic nephropathy.This thesis in physiology provides new mechanistic insights into the regulation of renal hyaluronan during various aspects of fluid handling.
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| 9. |
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| 10. |
- Rundgren, Mats, et al.
(author)
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Last interglacial atmospheric CO2 changes from stomatal index data and their relation to climate variations
- 2005
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In: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 49:1-2, s. 47-62
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Journal article (peer-reviewed)abstract
- A high-resolution atmospheric CO2 reconstruction based on stomatal index data obtained from Betula and Quercus leaf fragments extracted from the Danish Hollerup lake sediment section provides a unique insight into last interglacial CO2 dynamics. According to pollen stratigraphic correlations the CO2 record covers the first c. 7400 years of the Eemian, as palaeobotanically defined in northwestern Europe. The first c. 3000 years of the reconstruction are characterised by centennial to millennial CO2 variability in the interval 250-290 ppmv, while the remaining part of the record is generally more stable with slightly higher values (290-300 ppmv). According to pollen stratigraphic correlations this shift in CO2 dynamics is coincident with the end of the early Eemian climatic optimum in northwestern Europe. Pollen data from this region indicate that early Eemian CO2 instability may be linked to vegetation succession following deglaciation in Europe, but vegetation dynamics on other northern continents were probably also important. In addition, palaeoceanographic records from the Nordic seas indicate an influence of oceanic processes on the reconstructed Eemian CO2 evolution. A 300-year period of rapid CO2 oscillations immediately before the establishment of stable conditions is synchronous with a dry and cool event previously inferred from proxy data from the same sediment sequence, suggesting that this was a climatic event of regional or global significance. The presented CO2 reconstruction is in general agreement with previous ice core and stomatal-based CO2 data, although a larger variability compared with Vostok ice core data is evident. This may be explained partly by the different resolution of the two records and the inherent smoothing of ice core gas records.
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| 11. |
- Rundgren, Mats
(author)
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Stratigraphy of peatlands in central and northern Sweden: evidence of Holocene climatic change and peat accumulation
- 2008
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In: GFF. - 2000-0863. ; 130:Part 2, s. 95-107
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Journal article (peer-reviewed)abstract
- Early peat surveys demonstrated the potential to detect Holocene climatic changes in southern Sweden through analysis of the degree of decomposition of Sphagnum peat and motivated systematic collection of peat-strati graphic information during subsequent geological mappings in central and northern Sweden. The resulting (published and unpublished) data was compiled and reanalysed, taking into account unpublished radiocarbon data and developments in radiocarbon calibration and pollen-stratigraphic dating. Data from 61 carefully selected sites indicate a peat initiation maximum centred in the north 9500-8000 cal. BP and interpreted to primarily reflect climatic change. The cause for a secondary maximum 6000-5500 cal. BP centred further south is less clear. Peat deposition data show a continuous increase in the period 10 500-2000 cal. BP, with almost constant values during recent millennia, indicating that peatlands in the region acted as a long-term Holocene carbon sink and increasingly so until c. 2000 years ago. Sphagnum peat decomposition data display a long-term trend towards wetter conditions after 5000 cal. BP interpreted to primarily reflect progressively stronger westerly airflow and an accompanying increase in precipitation. These data also show that wet shifts occurred more frequently across the region around 3300, 2500-2100 and 1300 cal. BP. The timing of peak frequencies of wet shifts is similar to that of supposedly climate-related wet shifts identified in southern Sweden. Variability in frequency of wet shifts is most strongly pronounced in the south-west, with an apparent periodicity of 800-1000 years believed to reflect regular changes in westerly airflow during the mid and late Holocene.
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| 12. |
- Virchenko, Olena, 1975-, et al.
(author)
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Early Achilles tendon healing in sheep
- 2008
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In: Archives of Orthopaedic and Trauma Surgery. - : Springer Science and Business Media LLC. - 0936-8051 .- 1434-3916. ; 128:9, s. 1001-1006
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Journal article (peer-reviewed)abstract
- Introduction: The biomechanics of early tendon healing is important for designing post-injury training, but this has not been described in an animal model, similar to humans in size. We measured elastic and viscoelastic properties of a tendon regenerate in sheep, in a study designed to see the effects of exogenously applying the growth and differentiation factor CDMP-2. This is the first description of early tendon healing in sheep Achilles tendons. Materials and methods: Twenty female sheep underwent Achilles tendon transection without suturing or immobilization. Two hours after the operation, 100 μg of CDMP-2 or placebo was injected into the hematoma. The sheep were slaughtered after 3 weeks, and tendon regenerates tested for viscoelastic properties by cyclical loading, before a destructive tensile test. Thereafter, all specimens were examined by high resolution computerized tomography (CT), and histology. Results: The tendon regenerate formed a sleeve, around the tendon stumps. Failure occurred between the regenerate sleeve and the tendon stumps. There was an unexpectedly large variation in force at failure. In the CDMP-2 group, force correlated with regenerate transverse area, but not in the controls. Thus, the variation in maximum stress was smaller in the CDMP-2 group (P = 0.009). Although the force at failure was only a tenth of normal, the capacity to store elastic energy was already near normal (hysteresis 16%). The mean transverse area, force at failure and stiffness were all about 30% larger in the CDMP-2 group, but this was not significant. There were no signs of bone or cartilage formation on CT or histology. Conclusions: Results are compatible with a positive effect of CDMP-2, but the power was too low to demonstrate any such effect. Considering that spontaneous ruptures in humans are likely to have a more variable geometry than in this model, humans can also be expected to vary a lot in early mechanical characteristics. This emphasizes the importance of individualized rehabilitation programs. The low hysteresis suggests that the energy storing capacity is rather easy for the tissues to develop, possibly it is harder to create appropriate energy dissipation, in order to avoid re-rupture. © Springer-Verlag 2008.
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| 13. |
- Wastegård, Stefan, et al.
(author)
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Age, geochemistry and distribution of the mid-Holocene Hekla-S/Kebister tephra
- 2008
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 18:4, s. 539-549
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Journal article (peer-reviewed)abstract
- The middle Holocene Hekla-S/Kebister tephra originates in the Hekla volcanic system on SW Iceland. The distal distribution of the tephra includes the Faroe Islands, Shetland and Central Sweden, indicating a main dispersal towards the east. The chemical composition of the tephra follows the pattern of other major eruptions of Hekla, and ratios between selected oxides may in some cases allow separation from other major Holocene tephras from Hekla. Tephra from the Plinian phase dominates in eastern sites, while tephra also from later phases is found in the Faroe sites. Wiggle-matching of radiocarbon dates around the tephra in a Swedish peat-bog suggests an age around 3720 cal. yr BP (3750-3700 cal. yr BP), which is in accordance with previous attempts to date this tephra. This is within a period with significant climate changes in NW Europe and opens possibilities for exact comparisons of peat and lake sediment records from different geographical areas.
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