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Gordon S Hamilton - One of the best experts on this subject based on the ideXlab platform.
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climate variability in west antarctica derived from annual Accumulation Rate records from itase firn ice cores
Annals of Glaciology, 2004Co-Authors: Susan Kaspari, Paul Andrew Mayewski, Daniel A Dixon, Vandy Blue Spikes, Sharon B Sneed, Michael Handley, Gordon S HamiltonAbstract:Thirteen annually resolved Accumulation-Rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean Accumulation since 1970 at each site to the long-term mean indicates an increase in Accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean Accumulation at most sites. Correlations of the Accumulation-Rate records with sea-level pressure (SLP) and the SOI suggest that Accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in Accumulation coupled with strong SLP–Accumulation-Rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.
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Topographic control of regional Accumulation Rate variability at South Pole and implications for ice-core interpretation
Annals of Glaciology, 2004Co-Authors: Gordon S HamiltonAbstract:Snow-Accumulation Rates are known to be sensitive to local changes in ice-sheet surface slope because of the effect of katabatic winds. These topographic effects can be preserved in ice cores that are collected at non-ice-divide locations. The trajectory of an ice-core site at South Pole is reconstructed using measurements of ice-sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years. Recent Accumulation Rates, derived from shallow firn cores, vary along this trajectory according to surface topography, so that on a relatively steep flank mean annual Accumulation is 18% smaller than on a nearby topographic depression. These modern Accumulation Rates are used to reinterpret the cause of Accumulation Rate variability with time in the long ice-core record as an ice-dynamics effect and not a climate-change signal. The results highlight the importance of conducting ancillary ice-dynamics measurements as part of ice-coring programs so that topographic effects can be deconvolved from potential climate signals.
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Mass Balance and Accumulation Rate Across Siple Dome, West Antarctica
Annals of Glaciology, 2002Co-Authors: Gordon S HamiltonAbstract:Snow-Accumulation Rates and Rates of ice-thickness change (mass balance) are studied at several sites on Siple Dome,West Antarctica. Accumulation Rates are derived from analyses of grossbeta radioactivity in shallow firn cores located along a 60 km transect spanning both flanks and the crest of the dome. There is a north^south gradient in snow-Accumulation Rate across the dome that is consistent with earlier radar mappingof internalstratigraphy. Orographicprocessesprobablycontrolthisdistribution. Mass balance is inferred from the difference between global positioning system (GPS)- derived vertical velocities and snow-Accumulation Rates for sites close to the firn-core locations. Results indicatethatthere is virtually no netthicknesschangeat fourof thefive sites. The exception is at the northernmost site where a small amount of thinning is detected, that appearstobe inconsistentwith other studies. A possiblecause ofthisanom- alousthinning is recent retreatof the grounding line of Ice Stream D.
Yuki Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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drug sensitivity of single cancer cells is predicted by changes in mass Accumulation Rate
Nature Biotechnology, 2016Co-Authors: Mark M Stevens, Cecile L Maire, Nigel Chou, Mark A Murakami, David S Knoff, Yuki Kikuchi, Robert J Kimmerling, Huiyun Liu, Samer HaidarAbstract:Assays that can determine the response of tumor cells to cancer therapeutics could greatly aid the selection of drug regimens for individual patients. However, the utility of current functional assays is limited, and predictive genetic biomarkers are available for only a small fraction of cancer therapies. We found that the single-cell mass Accumulation Rate (MAR), profiled over many hours with a suspended microchannel resonator, accuRately defined the drug sensitivity or resistance of glioblastoma and B-cell acute lymphocytic leukemia cells. MAR revealed heterogeneity in drug sensitivity not only between different tumors, but also within individual tumors and tumor-derived cell lines. MAR measurement predicted drug response using samples as small as 25 μl of peripheral blood while maintaining cell viability and compatibility with downstream characterization. MAR measurement is a promising approach for directly assaying single-cell therapeutic responses and for identifying cellular subpopulations with phenotypic resistance in heterogeneous tumors.
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drug sensitivity of single cancer cells is predicted by changes in mass Accumulation Rate
Nature Biotechnology, 2016Co-Authors: Mark M Stevens, Cecile L Maire, Nigel Chou, Mark A Murakami, David S Knoff, Yuki Kikuchi, Robert J Kimmerling, Samer Haidar, Nicholas L CalistriAbstract:The efficacy of cancer drugs is profiled by measuring changes in the mass of single tumor cells.
Paul Andrew Mayewski - One of the best experts on this subject based on the ideXlab platform.
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snow Accumulation Rate on qomolangma mount everest himalaya synchroneity with sites across the tibetan plateau on 50 100 year timescales
Journal of Glaciology, 2008Co-Authors: Susan Kaspari, Shugui Hou, Paul Andrew Mayewski, Roger Leb Hooke, Shichang Kang, Dahe QinAbstract:Annual-layer thickness data, spanning AD 1534-2001, from an ice core from East Rongbuk Col on Qomolangma (Mount Everest, Himalaya) yield an age-depth profile that deviates systematically from a constant Accumulation-Rate analytical model. The profile clearly shows that the mean Accumulation Rate has changed every 50-100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale Rates. The model was used to obtain a time series of annual Accumulation. The mean annual Accumulation Rate decreased from ∼0.8m ice equivalent in the 1500s to ∼0.3m in the mid-1800s. From ∼1880 to ∼1970 the Rate increased. However, it has decreased since ∼1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in Accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in Accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology.
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climate variability in west antarctica derived from annual Accumulation Rate records from itase firn ice cores
Annals of Glaciology, 2004Co-Authors: Susan Kaspari, Paul Andrew Mayewski, Daniel A Dixon, Vandy Blue Spikes, Sharon B Sneed, Michael Handley, Gordon S HamiltonAbstract:Thirteen annually resolved Accumulation-Rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean Accumulation since 1970 at each site to the long-term mean indicates an increase in Accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean Accumulation at most sites. Correlations of the Accumulation-Rate records with sea-level pressure (SLP) and the SOI suggest that Accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in Accumulation coupled with strong SLP–Accumulation-Rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.
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Post-depositional movement of methanesulphonic acid at Law Dome, Antarctica, and the influence of Accumulation Rate
Annals of Glaciology, 2002Co-Authors: Mark A. J. Curran, Anne S. Palmer, Tas D. Van Ommen, Vin Morgan, Katrina L. Phillips, Alison J. Mcmorrow, Paul Andrew MayewskiAbstract:A series of ice cores from sites with different snow-Accumulation Rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. The precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the Accumulation Rate. At the low-Accumulation-Rate W20k site (0.17 m ice equivalent), MSA was completely relocated from the summer to winter layer. ModeRate movement was observed at the intermediate-Accumulation-Rate site (0.7 m ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-Accumulation-Rate DE08 site (1.4. m ice equivalent). The main DSS record of MSA covered the epoch AD 1727-2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed in the surface layers, outside of the main summer MSA peak, which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770-1800) with high summer nitRate levels. A complex interaction between the gradients in nss-sulphate, nitRate and sea salts (which are influenced by Accumulation Rate) is believed to control the Rate and extent of movement of MSA.
Hideaki Motoyama - One of the best experts on this subject based on the ideXlab platform.
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post bubble close off fractionation of gases in polar firn and ice cores effects of Accumulation Rate on permeation through overloading pressure
Atmospheric Chemistry and Physics, 2015Co-Authors: Takuro Kobashi, Tomoko Ikedafukazawa, M Suwa, Jakob Schwander, Takao Kameda, J Lundin, A Hori, Hideaki Motoyama, Michael DoringAbstract:Abstract. Gases in ice cores are invaluable archives of past environmental changes (e.g., the past atmosphere). However, gas fractionation processes after bubble closure in the firn are poorly understood, although increasing evidence indicates preferential leakages of smaller molecules (e.g., neon, oxygen, and argon) from the closed bubbles through the ice matrix. These fractionation processes are believed to be responsible for the observed millennial δO2/N2 variations in ice cores, linking ice core chronologies with orbital parameters. In this study, we investigated high-resolution δAr/N2 of the GISP2 (Greenland Ice Sheet Project 2), NGRIP (North Greenland Ice Core Project), and Dome Fuji ice cores for the past few thousand years. We find that δAr/N2 at multidecadal resolution on the "gas-age scale" in the GISP2 ice core has a significant negative correlation with Accumulation Rate and a positive correlation with air contents over the past 6000 years, indicating that changes in overloading pressure induced δAr/N2 fractionation in the firn. Furthermore, the GISP2 temperature and Accumulation Rate for the last 4000 years have nearly equal effects on δAr/N2 with sensitivities of 0.72 ± 0.1 ‰ °C−1 and −0.58 ± 0.09 ‰ (0.01 m ice year−1)−1, respectively. To understand the fractionation processes, we applied a permeation model for two different processes of bubble pressure build-up in the firn, "pressure sensitive process" (e.g., microbubbles: 0.3–3 % of air contents) with a greater sensitivity to overloading pressures and "normal bubble process". The model indicates that δAr/N2 in the bubbles under the pressure sensitive process are negatively correlated with the Accumulation Rate due to changes in overloading pressure. On the other hand, the normal bubbles experience only limited depletion (
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post bubble close off fractionation of gases in polar firn and ice cores effects of Accumulation Rate on permeation through overloading pressure
Atmospheric Chemistry and Physics, 2015Co-Authors: Takuro Kobashi, Tomoko Ikedafukazawa, M Suwa, Jakob Schwander, Takao Kameda, J Lundin, A Hori, Hideaki Motoyama, Michael DoringAbstract:Gases in ice cores are invaluable archives of past environmental changes (e.g., the past atmosphere). However, gas fractionation processes after bubble closure in the firn are poorly understood, although increasing evidence indicates preferential leakages of smaller molecules (e.g., neon, oxygen, and argon) from the closed bubbles through the ice matrix. These fractionation processes are believed to be responsible for the observed millennial δO 2 /N 2 variations in ice cores, linking ice core chronologies with orbital parameters. In this study, we investigated high-resolution δAr/N 2 of the GISP2 (Greenland Ice Sheet Project 2), NGRIP (North Greenland Ice Core Project), and Dome Fuji ice cores for the past few thousand years. We find that δAr/N 2 at multidecadal resolution on the "gas-age scale" in the GISP2 ice core has a significant negative correlation with Accumulation Rate and a positive correlation with air contents over the past 6000 years, indicating that changes in overloading pressure induced δAr/N 2 fractionation in the firn. Furthermore, the GISP2 temperature and Accumulation Rate for the last 4000 years have nearly equal effects on δAr/N 2 with sensitivities of 0.72 ± 0.1 ‰ °C −1 and −0.58 ± 0.09 ‰ (0.01 m ice year −1 ) −1 , respectively. To understand the fractionation processes, we applied a permeation model for two different processes of bubble pressure build-up in the firn, "pressure sensitive process" (e.g., microbubbles: 0.3–3 % of air contents) with a greater sensitivity to overloading pressures and "normal bubble process". The model indicates that δAr/N 2 in the bubbles under the pressure sensitive process are negatively correlated with the Accumulation Rate due to changes in overloading pressure. On the other hand, the normal bubbles experience only limited depletion ( 2 through thicker firn. The pressure sensitive bubbles are so depleted in δAr/N 2 at the bubble close-off depth that they dominate the total δAr/N 2 changes in spite of their smaller air contents. The model also indicates that δAr/N 2 of ice cores should have experienced several per mil of depletion during the storage 14–18 years after coring. Further understanding of the δAr/N 2 fractionation processes in the firn, combined with nitrogen and argon isotope data, may lead to a new proxy for the past temperature and Accumulation Rate.
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effect of Accumulation Rate on water stable isotopes of near surface snow in inland antarctica
Journal of Geophysical Research, 2014Co-Authors: Yu Hoshina, Koji Fujita, Fumio Nakazawa, Yoshinori Iizuka, Takayuki Miyake, Motohiro Hirabayashi, Takayuki Kuramoto, Shuji Fujita, Hideaki MotoyamaAbstract:[1] Postdepositional changes in water stable isotopes in polar firn were investigated at three sites characterized by different Accumulation Rates along the East Antarctic ice divide near Dome Fuji. Water stable isotopes, major ion concentrations, and tritium contents of three 2–4 m deep pits were measured at high resolution (2 cm). Temporally, the snow pits cover the past 50 years with snow Accumulation Rates in the range of 29–41 kg m−2 a−1 around Dome Fuji. Oxygen isotopic profiles in the three pits do not show annual fluctuations, but instead exhibit multiyear cycles. These multiyear cycles are lower in frequency at Dome Fuji as compared with the other two sites. Peaks of water stable isotopes in the multiyear cycles correspond to some ion concentration minima in the pits, although such relationships are not observed in coastal regions. We propose that the extremely low Accumulation environment keeps the snow layer at the near surface, which result in postdepositional modifications of isotopic signals by processes such as ventilation and vapor condensation-sublimation. We estimate that oxygen isotopic ratios could be modified by >10‰ and that the original seasonal cycle could be completely overprinted under the Accumulation conditions at Dome Fuji. Moreover, stake measurements at Dome Fuji suggest that the large variability in snow Accumulation Rate is the cause of the multiyear cycles.
Samer Haidar - One of the best experts on this subject based on the ideXlab platform.
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drug sensitivity of single cancer cells is predicted by changes in mass Accumulation Rate
Nature Biotechnology, 2016Co-Authors: Mark M Stevens, Cecile L Maire, Nigel Chou, Mark A Murakami, David S Knoff, Yuki Kikuchi, Robert J Kimmerling, Huiyun Liu, Samer HaidarAbstract:Assays that can determine the response of tumor cells to cancer therapeutics could greatly aid the selection of drug regimens for individual patients. However, the utility of current functional assays is limited, and predictive genetic biomarkers are available for only a small fraction of cancer therapies. We found that the single-cell mass Accumulation Rate (MAR), profiled over many hours with a suspended microchannel resonator, accuRately defined the drug sensitivity or resistance of glioblastoma and B-cell acute lymphocytic leukemia cells. MAR revealed heterogeneity in drug sensitivity not only between different tumors, but also within individual tumors and tumor-derived cell lines. MAR measurement predicted drug response using samples as small as 25 μl of peripheral blood while maintaining cell viability and compatibility with downstream characterization. MAR measurement is a promising approach for directly assaying single-cell therapeutic responses and for identifying cellular subpopulations with phenotypic resistance in heterogeneous tumors.
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drug sensitivity of single cancer cells is predicted by changes in mass Accumulation Rate
Nature Biotechnology, 2016Co-Authors: Mark M Stevens, Cecile L Maire, Nigel Chou, Mark A Murakami, David S Knoff, Yuki Kikuchi, Robert J Kimmerling, Samer Haidar, Nicholas L CalistriAbstract:The efficacy of cancer drugs is profiled by measuring changes in the mass of single tumor cells.
