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Search Results: 1 - 10 of 494865 matches for " B. M. Vinther "
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Greenland ice core evidence of the 79 AD Vesuvius eruption
C. Barbante,N. M. Kehrwald,P. Marianelli,B. M. Vinther
Climate of the Past Discussions , 2012, DOI: 10.5194/cpd-8-5429-2012
Abstract: Volcanic tephra are indepenent age horizons and can synchronize strata of various paleoclimate records including ice and sediment cores. Before such paleoclimate records can be synchronized, it is essential to first confidently identify individual independent marker horizons. The Greenland Ice Core Project (GRIP) ice core from Central Greenland is often used as a "golden spike" to synchronize Northern Hemisphere paleoclimte records. The Holocene section of the GRIP ice core is dated by multi-parameter annual layer counting, and contains peaks in acidity, SO42 and microparticle concentrations at a depth of 428.4 to 429.6 m, which have not previously been definitively ascribed to a volcanic eruption. Here, we identify tephra particles and determine that volcanic shards extracted from a depth of 429.2 m in the GRIP ice core are likely due to the 79 AD Vesuvius eruption. The chemical compositon of the tephra particles is consistent with the K-phonolitic composition of the Vesuvius juvinile ejecta and differs from the chemical composition of other major eruptions (≥VEI 4) between 50–100 AD.
Adeno-Associated Vector mediated gene transfer of Transforming Growth Factor-beta1 to normal and osteoarthritic human chondrocytes stimulates cartilage anabolism
Ulrich-Vinther M.,Stengaard C.,Schwarz E. M.,Goldring M. B.
European Cells and Materials (ECM) , 2005,
Abstract: The objective of the present study was to investigate whether cartilage anabolism in human primary osteoarthritic chondrocytes could be improved by adeno-associated virus (AAV) vector-mediated gene transduction of transforming growth factor TGF-beta1 (TGF-beta1). A bi-cistronic AAV-TGF-beta1-IRES-eGFP (AAV-TGF-beta1) vector was generated and used for transduction of a normal human articular chondrocyte cell line (tsT/AC62) and primary human osteoarthritic articular chondrocytes harvested from 8 patients receiving total knee joint arthroplasty. Transduction efficiency was detected by fluorescent microscopy for gene expression of enhanced green fluorescent protein (eGFP). TGF-beta1 synthesis was determined by ELISA. To assess the influence of TGF-beta1 gene therapy on chondrocyte cartilage metabolism, mRNA expressions of type II collagen, aggrecan, and matrix metalloproteinase 3 (MMP-3) were determined by quantitative real-time PCR. AAV-TGF-beta1 transduction resulted in increased synthesis of TGF-beta1 in both osteoarthritic chondrocytes and the normal articular chondrocyte cell line. The expression levels of the transduced genes were correlated to "multiplicity of infection" (MOI) and post-infectious time. In both osteoarthritic chondrocytes and the normal articular chondrocyte cell line, AAV-TGF-beta1 treatment increased mRNA expression of both type II collagen and aggrecan, but decreased MMP-3 mRNA expression. Osteoarthritic chondrocytes and the normal articular chondrocyte cell line could be transduced with equal efficiencies. In conclusion, it was demonstrated that AAV-TGF-beta1 gene transfer stimulates cartilage anabolism and decreases expression of enzymes responsible for cartilage degradation in human osteoarthritic chondrocytes. The results indicate that the AAV vector is an efficient mediator of growth factors to human articular chondrocytes, and that it might be useful in future chondrocyte gene therapy.
Investigating the past and recent δ18O-accumulation relationship seen in Greenland ice cores
S. L. Buchardt, H. B. Clausen, B. M. Vinther,D. Dahl-Jensen
Climate of the Past (CP) & Discussions (CPD) , 2012,
Abstract: Decadal means of δ18O and accumulation rates from 52 ice core locations in Greenland are presented. The accumulation rates are derived from annual layers determined in the δ18O curve. Investigation of the δ18O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of δ18O and accumulation rate on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four records in the data set contain sufficient recent data that the period of observed temperature rise from the 1990s and onwards can be investigated. All four records are from locations close to the ice divide in Northern Greenland and while three of them show increased temperatures, no conclusive statement can be made about the accumulation rate from these data.
Investigating the past and recent δ18O-accumulation relationship seen in Greenland ice cores
S. L. Buchardt,H. B. Clausen,B. M. Vinther,D. Dahl-Jensen
Climate of the Past (CP) & Discussions (CPD) , 2012, DOI: 10.5194/cp-8-2053-2012
Abstract: Decadal means of δ18O and accumulation rates from 52 ice core locations in Greenland are presented. The accumulation rates are derived from annual layers determined in the δ18O curve. Investigation of the δ18O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of δ18O and accumulation rate on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four records in the data set contain sufficient recent data that the period of observed temperature rise from the 1990s and onwards can be investigated. All four records are from locations close to the ice divide in Northern Greenland and while three of them show increased temperatures, no conclusive statement can be made about the accumulation rate from these data.
Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes
S. B. Simonsen,S. J. Johnsen,T. J. Popp,B. M. Vinther
Climate of the Past Discussions , 2011, DOI: 10.5194/cpd-7-921-2011
Abstract: A new ice core paleothermometer is introduced based on the temperature dependent diffusion of the stable water isotopes in the firn. A new parameter called differential diffusion length is defined as the difference between the diffusion length of the two stable water isotopes 18O and deuterium. A model treatment of the diffusion process of the firn and the ice is presented along with a method of retrieving the diffusion signal from the ice core record of water isotopes using spectral methods. The model shows how the diffusion process is highly dependent on the inter-annual variations in the surface temperatures resulting in a longer diffusion length than by assuming an isothermal firn. The longer diffusion length can be explained by the strong non-linearly behavior of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on δ18O and δD measurements, spanning the transition from the last glacial to the holocene, from the NorthGRIP ice core. The surface temperature reconstruction based on the differential diffusion resembles other temperature reconstructions for the NorthGRIP ice core. However, the Aller d warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behavior are not fully understood. The method shows the need of an expansion of high resolution stable water isotopes data sets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight in past climate, through the physical process of isotope diffusion in the firn column of ice sheets.
Investigating the past and recent δ18O-accumulation relationship seen in Greenland ice cores
S. L. Buchardt,H. B. Clausen,B. M. Vinther,D. Dahl-Jensen
Climate of the Past Discussions , 2012, DOI: 10.5194/cpd-8-4105-2012
Abstract: Decadal means of δ18O and accumulation rates from 52 ice core sites in Greenland are presented. The accumulation rates are derived from annual layers determined in the δ18O curve. Investigation of the δ18O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of δ18O and accumulation on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four sites in the data set contain sufficient recent data that the period of observed temperature rise from the 1990's and onwards can be investigated. All four sites are located close to the ice divide in Northern Greenland and while three sites show increased temperatures, none show evidence of increased accumulation.
Supporting Online Material to the manuscript: "Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years - glaciological and paleoclimatic implications."
Vasileios Gkinis,Sebastian B. Simonsen,Susanne L. Buchardt,James W. C. White,Bo M. Vinther
Physics , 2014,
Abstract: This is the supporting online material for the manuscript arXiv:1404.4201 "Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years - glaciological and paleoclimatic implications."
Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years - glaciological and paleoclimatic implications
Vasileios Gkinis,Sebastian B. Simonsen,Susanne L. Buchardt,James W. White,Bo M. Vinther
Physics , 2014, DOI: 10.1016/j.epsl.2014.08.022
Abstract: A high resolution (0.05 m) water isotopic record ($\delta^{18}\mathrm{O}$) is available from the NorthGRIP ice core. In this study we look into the water isotope diffusion history as estimated by the spectral characteristics of the $\delta^{18}\mathrm{O}$ time series covering the last 16,000 years. The diffusion of water vapor in the porous medium of the firn pack attenuates the initial isotopic signal, predominantly having an impact on the high frequency components of the power spectrum. Higher temperatures induce higher rates of smoothing and thus the signal can be used as a firn paleothermometer. We use a water isotope diffusion model coupled to a steady-state densification model in order to infer the temperature signal from the site, assuming the accumulation and strain rate history as estimated using the GICC05 layer counted chronology and a Dansgaard--Johnsen ice flow model. The temperature reconstruction accurately captures the timing and magnitude of the B\o lling--Aller\o d and Younger Dryas transitions. A Holocene climatic optimum is seen between 7 and 9 ky b2k with an apparent cooling trend thereafter. Our temperature estimate for the Holocene climatic optimum, points to a necessary adjustment of the ice thinning function indicating that the ice flow model overestimates past accumulation rates by about 10\% at 8 ky b2k. Finally, the record presents a climatic variability over the Holocene spanning millennial and centennial scales with a profound cooling occurring at approximately 4000 years b2k. The new reconstruction technique is able to provide past temperature estimates by overcoming the issues apparent in the use of the classical $\delta^{18}\mathrm{O}$ slope method. It can in the same time resolve temperature signals at low and high frequencies.
Past surface temperatures at the NorthGRIP drill site from the difference in firn diffusion of water isotopes
S. B. Simonsen, S. J. Johnsen, T. J. Popp, B. M. Vinther, V. Gkinis,H. C. Steen-Larsen
Climate of the Past (CP) & Discussions (CPD) , 2011,
Abstract: A new ice core paleothermometer is introduced based on the temperature dependent diffusion of the stable water isotopes in the firn. A new parameter called differential diffusion length is defined as the difference between the diffusion length of the two stable water isotopologues 2H1H16O and 1H218O. A model treatment of the diffusion process of the firn and the ice is presented along with a method of retrieving the diffusion signal from the ice core record of water isotopes using spectral methods. The model shows how the diffusion process is highly dependent on the inter-annual variations in the surface temperatures. It results in a diffusion length longer than if the firn was isothermal. The longer diffusion length can be explained by the strong nonlinearly behaviour of the saturation pressure over ice in the range of the surface temperature fluctuations. The method has been tested on δ18O and δD measurements, spanning the transition from the last glacial to the holocene, from the NorthGRIP ice core. The surface temperature reconstruction based on the differential diffusion resembles other temperature reconstructions for the NorthGRIP ice core. However, the Aller d warming is seen to be significantly warmer than observed in other ice core based temperature reconstructions. The mechanisms behind this behaviour are not fully understood. The method shows the need of an expansion of high resolution stable water isotope datasets from ice cores. However, the new ice core paleothermometer presented here will give valuable insight into past climate, through the physical process of isotope diffusion in the firn column of ice sheets.
Sensitivity of interglacial Greenland temperature and δ18O: ice core data, orbital and increased CO2 climate simulations
V. Masson-Delmotte, P. Braconnot, G. Hoffmann, J. Jouzel, M. Kageyama, A. Landais, Q. Lejeune, C. Risi, L. Sime, J. Sjolte, D. Swingedouw,B. Vinther
Climate of the Past (CP) & Discussions (CPD) , 2011,
Abstract: The sensitivity of interglacial Greenland temperature to orbital and CO2 forcing is investigated using the NorthGRIP ice core data and coupled ocean-atmosphere IPSL-CM4 model simulations. These simulations were conducted in response to different interglacial orbital configurations, and to increased CO2 concentrations. These different forcings cause very distinct simulated seasonal and latitudinal temperature and water cycle changes, limiting the analogies between the last interglacial and future climate. However, the IPSL-CM4 model shows similar magnitudes of Arctic summer warming and climate feedbacks in response to 2 × CO2 and orbital forcing of the last interglacial period (126 000 years ago). The IPSL-CM4 model produces a remarkably linear relationship between TOA incoming summer solar radiation and simulated changes in summer and annual mean central Greenland temperature. This contrasts with the stable isotope record from the Greenland ice cores, showing a multi-millennial lagged response to summer insolation. During the early part of interglacials, the observed lags may be explained by ice sheet-ocean feedbacks linked with changes in ice sheet elevation and the impact of meltwater on ocean circulation, as investigated with sensitivity studies. A quantitative comparison between ice core data and climate simulations requires stability of the stable isotope – temperature relationship to be explored. Atmospheric simulations including water stable isotopes have been conducted with the LMDZiso model under different boundary conditions. This set of simulations allows calculation of a temporal Greenland isotope-temperature slope (0.3–0.4‰ per °C) during warmer-than-present Arctic climates, in response to increased CO2, increased ocean temperature and orbital forcing. This temporal slope appears half as large as the modern spatial gradient and is consistent with other ice core estimates. It may, however, be model-dependent, as indicated by preliminary comparison with other models. This suggests that further simulations and detailed inter-model comparisons are also likely to be of benefit. Comparisons with Greenland ice core stable isotope data reveals that IPSL-CM4/LMDZiso simulations strongly underestimate the amplitude of the ice core signal during the last interglacial, which could reach +8–10 °C at fixed-elevation. While the model-data mismatch may result from missing positive feedbacks (e.g. vegetation), it could also be explained by a reduced elevation of the central Greenland ice sheet surface by 300–400 m.
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