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- Melles, Martin, et al.
(författare)
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2.8 million years of arctic climate change from Lake El'gygytgyn, NE Russia
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 337:6092, s. 315-320
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Tidskriftsartikel (refereegranskat)abstract
- The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are similar to 4 degrees to 5 degrees C and similar to 300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.
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- Nowaczyk, N. R., et al.
(författare)
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Chronology of Lake El'gygytgyn sediments - a combined magnetostratigraphic, palaeoclimatic and orbital tuning study based on multi-parameter analyses
- 2013
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 9:6, s. 2413-2432
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Tidskriftsartikel (refereegranskat)abstract
- A 318-metre-long sedimentary profile drilled by the International Continental Scientific Drilling Program (ICDP) at Site 5011-1 in Lake El'gygytgyn, Far East Russian Arctic, has been analysed for its sedimentologic response to global climate modes by chronostratigraphic methods. The 12 km wide lake is sited off-centre in an 18 km large crater that was created by the impact of a meteorite 3.58 Ma ago. Since then sediments have been continuously deposited. For establishing their chronology, major reversals of the earth's magnetic field provided initial tie points for the age model, confirming that the impact occurred in the earliest geomagnetic Gauss chron. Various stratigraphic parameters, reflecting redox conditions at the lake floor and climatic conditions in the catchment were tuned synchronously to Northern Hemisphere insolation variations and the marine oxygen isotope stack, respectively. Thus, a robust age model comprising more than 600 tie points could be defined. It could be shown that deposition of sediments in Lake El'gygytgyn occurred in concert with global climatic cycles. The upper similar to 160m of sediments represent the past 3.3 Ma, equivalent to sedimentation rates of 4 to 5 cm ka(-1), whereas the lower 160m represent just the first 0.3 Ma after the impact, equivalent to sedimentation rates in the order of 45 cm ka(-1). This study also provides orbitally tuned ages for a total of 8 tephras deposited in Lake El'gygytgyn.
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| 11. |
- Tarasov, P. E., et al.
(författare)
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A pollen-based biome reconstruction over the last 3.562 million years in the Far East Russian Arctic - new insights into climate-vegetation relationships at the regional scale
- 2013
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9332. ; 9:6, s. 2759-2775
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Tidskriftsartikel (refereegranskat)abstract
- The recent and fossil pollen data obtained under the frame of the multi-disciplinary international El'gygytgyn Drilling Project represent a unique archive, which allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could be potentially present in this region during the past. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) long phases of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals in the study region within the past million years. During the late Pliocene-early Pleistocene interval (i.e., similar to 3.562-2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation from generally warmer/wetter environments of the earlier (i. e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction indicates that the taxon-rich cool mixed and cool conifer forest biomes are mostly characteristic of the time prior to MIS G16, whereas the tundra biome becomes a prominent feature starting from MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to similar to 2.730 Ma. The cold-and drought-tolerant steppe biome first appears in the reconstruction similar to 3.298 Ma during the tundra-dominated MIS M2, whereas the tundra biome initially occurs between similar to 3.379 and similar to 3.378 Ma within MIS MG4. Prior to similar to 2.800 Ma, several other cold stages during this generally warm Pliocene interval were characterized by the tundra biome.
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- Paloneva, J., et al.
(författare)
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CNS manifestations of Nasu-Hakola disease : a frontal dementia with bone cysts
- 2001
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Ingår i: Neurology. - 0028-3878 .- 1526-632X. ; 56:11, s. 1552-8
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Nasu-Hakola disease or polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL) is a genetically heterogeneous disease characterized by a combination of systemic bone cysts and dementia. OBJECTIVE: The authors present a neurologic, neuroradiologic, and neuropathologic analysis of a series of PLOSL patients in which the diagnosis has been confirmed by molecular genetic methods. METHODS: Clinical, neurophysiologic, and imaging follow-up data on eight patients as well as autopsy samples of three patients were analyzed in this study. All eight patients were homozygous for a loss-of-function mutation in the DAP12 gene. RESULTS: In most patients, the disease debuted with pain in ankles and wrists after strain during the third decade, followed by fractures caused by cystic lesions in the bones of the extremities. Frontal lobe syndrome and dementia began to develop by age 30, leading to death by age 40. Neuroimaging disclosed abnormally high and progressively increasing bicaudate ratios and calcifications in the basal ganglia as well as increased signal intensities of the white matter on T2-weighted MR images even before the appearance of clinical neurologic symptoms. Three patients who had undergone autopsies showed an advanced sclerosing leukoencephalopathy with frontal accentuation, widespread activation of microglia, and microvascular changes. CONCLUSIONS: Although PLOSL in most patients manifests by bone fractures, some patients do not show any osseous symptoms and signs before the onset of neurologic manifestations. Consequently, patients with frontal-type dementia of unknown origin should be investigated by x-ray of ankles and wrists. The current results suggest early basal ganglia involvement in PLOSL.
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| 14. |
- Ranki, A., et al.
(författare)
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Abundant expression of HIV Nef and Rev proteins in brain astrocytes in vivo is associated with dementia
- 1995
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Ingår i: AIDS. - 0269-9370 .- 1473-5571. ; 9:9, s. 1001-8
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To relate the expression of HIV regulatory proteins and HIV-specific mRNA in the brain cells of infected individuals with clinical neurological disease. DESIGN: Formalin-fixed postmortem brain tissue from 14 HIV-infected adult patients, with previous repeated neurological and neuroradiological examinations, was studied by immunohistochemical and molecular biological methods. Samples from non-infected brains served as controls. METHODS: Immunohistochemistry with monoclonal antibodies (MAb) was combined with in situ RNA hybridization. Target cells were identified with MAb to glial fibrillary acidic protein (GFAP; astrocytes), CD68 (activated macrophages) and Ricinus communis agglutinin (RCA-1; microglia, endothelial cells). For HIV, a panel of MAb against HIV Nef, Tat, Rev and Env proteins or probes specific for all classes of mRNA (nef), for singly or non-spliced mRNA (env) and for non-spliced mRNA (gag/pol) were used. RESULTS: Nef protein was detected in subcortical or subpial astrocytes in seven out of 14 samples, and in multinucleated giant cells in two cases. Gag/pol or env mRNA-expressing astrocytes were detected in four cases. In four out of five cases studied, HIV Rev, but not Tat, was also expressed in astrocytes. Six out of the seven patients with Nef-positive astrocytes had suffered from moderate to severe dementia. The patient with most rapidly progressing severe dementia showed extensive HIV mRNA expression together with Nef and Rev expression in astrocytes. CONCLUSION: In adult human brain, astrocytes are infected by HIV and preferentially express HIV Nef and Rev proteins but are also sometimes productively infected. Astrocyte infection is associated with moderate to severe dementia which agrees with recent knowledge on the housekeeping activities of astrocytes and their eventual role in learning and memory.
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