bluuebunny/crossref_metadata_2025_split huggingface dataset:
LGM–Holocene changes and Holocene millennial-scale oscillations of dust particles in the EPICA Dome C ice core, East Antarctica
Authors: Delmonte Barbara , Petit Jean Robert , Maggi Valter 
Published: November 2007

AbstractMeasurements of the concentration and size distribution of dust particles found in the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core, East Antarctica, provide records covering the last 27000 years. the total concentration decreased drastically by a factor of 55 from the Last Glacial Maximum (LGM) (800 ppb) to the Holocene (15 ppb), with a well-marked absolute minimum around 11500–11600 years ago. This latter almost corresponds to the end of the Younger Dryas in Greenland, which was marked by a methane peak related to the expansion of tropical wetlands. Assuming that the source region forAntarctic dust is the southern part of South America, the Antarctic dust minimum suggests a larger geographical extent for this wet period. the volume (mass)-size distribution of the particles displays a mode which is close to 2 μm in diameter, shifting from 1.9 μm in the glacial period to 2.07 μm in the Holocene. As opposed to previous results from old Dome C, EPICA suggests a greater proportion of large particles in Holocene samples than in LGM samples. In addition, for the period 13 000–2000BP, structured millennial-scale oscillations of the dust mode appear. These are especially well marked before 5000 years ago, with higher frequencies also present. the difference between LGM and Holocene particle distributions may be related to changes in the pattern of dust transport to East Antarctica. At Dome C the greater proportion of coarse particles observed during the Holocene suggests greater direct meridional transport. During the LGM, atmospheric circulation was likely more zonal, causing a greater amount of large dust particles to be removed from the atmosphere before reaching Antarctica. Changes in atmospheric circulation could also be the cause of the millennial-scale dust-mode oscillations during the Holocene.
Ice-flow properties at Dome Summit South, Law Dome, East Antarctica
Authors: Wang Weili , Warner Roland C. , Budd William F. 
Published: November 2007

AbstractIce-flow properties within a polar ice sheet are examined using the comprehensive data gathered from ice-core drilling by Australian National Antarctic Research Expeditions (ANARE) at Dome Summit South (DSS), on Law Dome, East Antarctica. Using the shear strain rates derived from borehole inclination measurements we demonstrate the need to modify the ice-flow relations to treat enhanced shear deformation deep within the ice sheet. We show that the relation between enhanced flow and the measured crystallographic properties is generally in accord with expectations, at least in the upper parts of the ice sheet, but it becomes clear that nearer to the bedrock the situation is more complicated. We also compare the observed shear strain-rate profile with results from a model that describes flow enhancement as a function of the applied stresses.
Interannual variations of shallow firn temperature at Greenland summit
Authors: Jun Li , Wang Weili , Jay Zwally H. 
Published: November 2007

AbstractFirn-temperature profiles are calculated in a thermal model using continuous surface temperatures derived from automatic weather station data and passive-microwave data in the Greenland summit region during the period 1987–99. the results show that significant interannual variations of mean summer (June–August) and annual temperatures occur in the top 15 m, in addition to the normal seasonal cycle of firn temperature. At 5 m depth, the seasonal cycle is damped to 13% of the surface seasonal range, but even at 15m about 1% or 0.6˚C of the seasonal cycle persists. Both summer and mean annual temperatures decrease from 1987 to 1992, followed by a general increasing trend. Interannual variability is 5˚C at the surface, but is dampened to 3.2˚C at 5 m depth and 0.7˚C at 15 m depth. Dampening of the interannual variability with depth is slower than dampening of the seasonal cycle, because of the longer time constant of the interannual variation. the warmer spring and summer temperatures experienced in the top 5 m, due to both the seasonal cycle and interannual variations, affect the rate of firn densification, which is non-linearly dependent on temperature. During the 12 year period 1987–99, the annual mean surface temperature is –29.2˚C, and the annual mean 15 m temperature is –30.1˚C, which is >1˚C warmer than a 15 mborehole temperature representing the period around 1959 and warmer than the best-fit temperature history by Alley and Koci (1990) back to AD 1500.
Generalized view of source-region effects on δD and deuterium excess of ice-sheet precipitation
Authors: Kavanaugh Jeffrey L. , Cuffey Kurt M. 
Published: November 2007

AbstractIt is generally recognized at present that ice-core deuterium excess measurements are potentially useful for reconstructions of vapor source-region temperature and humidity history, and that such measurements provide a method for correcting isotopic paleothermometers for effects of source temperature variations. Here we use a zonally averaged vapor-transport and isotopic-distillation model to show that deuterium excess of precipitation on the ice sheets is sensitive to a wide variety of source-region climate changes in addition to those changes of temperature and humidity that affect the composition of evaporate. Moreover, it is demonstrated that this wide variety of source-region changes all cause anticorrelated changes in deuterium excess with δD and δ18O over the ice sheets, suggesting that deuteriu 14m excess is a generally more useful tool for correcting isotopic thermometers than is currently recognized.
Reconstruction of the historical temperature trend from measurements in a medium-length borehole on the Lomonosovfonna plateau, Svalbard
Authors: van de Wal Roderik S.W. , Mulvaney Robert , Isaksson Elisabeth , Moore John C. , Pinglot Jean Francis , Pohjola Veijo A. , Thomassen Martijn P. A. 
Published: November 2007

AbstractA medium-length ice core was drilled at the ice divide on the Lomonosovfonna plateau (1230 m a.s.l.), Svalbard, in May 1997. As part of this project, temperature measurements were performed in the 120m deep borehole. At this site the ice thickness based on radar measurements is 126.5 m and the mean annual accumulation rate is 380 kg m–3. the measurements over the 15–120m depth interval show a nearly isothermal profile with a mean value of –2.8˚C and a standard deviation of 0.2˚C. the measurements reveal a temperature minimum at approximately 70m depth and a temperature gradient of 0.011 ±0.004˚Cm–1 near the bottom. the temperature minimum and relatively low temperature gradient cannot be explained in terms of a steady-state climate. Numerical calculations with a simple one-dimensional diffusion–advection model show that the temperature increased at a maximum rate of 0.02–0.025Ka–1 over the last 100 years, the total temperature increase amounting to 2.0–3.0K. Forcing the model with the observed record at Svalbard airport revealed that in the 19th century the surface temperature was at most 2.5 K lower, and that the instrumental observations started during a period with temperatures comparable to the end of the 19th century. the data are of particular interest for historical simulations since often no other temperature data are available in polar areas.
Temperature and methane changes over the past 1000 years recorded in Dasuopu glacier (central Himalaya) ice core
Authors: Tandong Yao , Keqin Duan , Baiqing Xu , Ninglian Wang , Jianchen Pu , Shichang Kang , Xiang Qin , Thompson Lonnie G. 
Published: November 2007

AbstractIn 1997, three ice cores were recovered from Dasuopu glacier on the northern slope of the central Himalaya. the first core, 159.9 m long, was drilled at 7000ma.s.l. down the flowline from the top of the col. the second core, 149.2m long, was drilled on the col at 7200ma.s.l. the third core, 167.7 m long, was also drilled on the col at 7200ma.s.l., 100 maway from the second core. the present paper discusses the δ18O and methane results reconstructed for the past 1000 years based on the second core. the δ18O can be interpreted as an air-temperature signal. the methane concentration is mainly representative of atmospheric methane concentration. Both δ18O and methane records show an obvious increasing trend in the past 1000 years. Methane concentration in the record is similar to the fluctuations of δ18O, decreasing during cold periods and increasing during warm periods. the Little Ice Age was well recorded in the core by both δ18O and methane. the coldest period appeared in the late 18th century, accompanied by a decrease in methane concentration. the abrupt methane-concentration increase starting after the 18th century is no doubt due to anthropogenic input. the observed methane-concentration decrease during World Wars I and II clearly demonstrates the importance of the anthropogenic input to atmospheric methane concentration if further measurements prove that it is a true atmospheric signal.
Depth–age and temperature prediction at Dome Fuji station, East Antarctica
Authors: Hondoh Takeo , Shoji Hitoshi , Watanabe Okitsugu , Salamatin Andrey N. , Lipenkov Vladimir Ya. 
Published: November 2007

AbstractThe geophysical metronome (Milankovitch components of the past surface temperature variations) and the isotope–temperature transfer function deduced from the borehole temperature profile at Vostok station, Antarctica, are applied to date the 2500 mdeep ice core from Dome Fuji station, Antarctica, and to reconstruct paleoclimatic conditions at the drilling site on the basis of the local δ18O isotope record. Special attention is paid to consistency of this depth–age relation with the mass-balance reconstruction and predictions of ice-flow modeling. the present-day ice mass-balance rate at Dome Fuji is estimated as 3.2 cm a–1. the ice age at the borehole bottom (590m above the bedrock) is around 335 ± 4.5 kyr and may reach 2000 kyr at about 3000 mdepth.The difference in the ice-sheet surface temperatures between Holocene optimum and Last Glacial Maximum is found to be 17.8˚C at the temporal isotope/temperature slope, about 30% lower than the modern geographical estimates. A good agreement between modeled and measured (preliminary data) borehole temperatures is obtained at the geothermal flux 0.059 Wm–2 and ice-fusion temperature (–2˚C) at the ice–rock interface with minimum (zero) melt rates.
Modelling evolution of anisotropy in fabric and texture of polar ice
Authors: Faria Sérgio H. , Ktitarev Dimitri , Hutter Kolumban 
Published: November 2007

AbstractWe present a simulation tool, based on a cellular automaton algorithm developed by D. Ktitarev and others, for the modelling of fabric and texture evolution in polycrystalline ice. the numerical results for the case of vertical uniaxial compression are compared with data obtained from boreholes GRIP–GISP2 in Greenland. A reasonable agreement is obtained, and guidelines are presented for further formulation of more realistic simulations. In particular, we discuss the rise of girdle-type fabrics, as well as the importance of intra- and intercrystalline stresses, temperature and impurity effects on the evolving ice microstructure.
Linear and non-linear relations between the high-frequency-limit conductivity, AC-ECM signals and ECM signals of Dome F Antarctic ice core from a laboratory experiment
Authors: Fujita Shuji , Azuma Nobuhiko , Motoyama Hideaki , Kameda Takao , Narita Hideki , Matoba Sumito , Igarashi Maokto , Kohno Mika , Fujii Yoshiyuki , Watanabe Okitsugu 
Published: November 2007

AbstractLaboratory experiments were done to better understand the electrical conduction mechanisms of impure, polycrystalline ice as represented by the 2503 m Dome Fuji (Antarctica) ice core. Also, two electrical measurement techniques for ice cores were compared and their usefulness for determining the acidity of ice cores was studied. We measured the electrical conductivity and complex permittivity of 167 slab-ice samples at frequencies from 20 Hz to 1 MHz. Measurements were performed at –21˚C for all samples, and at –110˚ to –20˚C for several samples, to examine the effects of temperature. We found linear relations between the AC loss factor and the molarity of sulfuric acid, and between the high-frequency-limit conductivity and the AC loss factor. Thus, the acidity levels can be determined from the AC loss factor. In contrast, the electrical conductivity measurement (ECM) current correlated weakly with the other parameters; furthermore, the correlation worsens at larger signal. In several samples containing high acidity, the dielectric properties had distinct changes near –81˚C. We argue that these changes were caused by a change from a liquid-vein-mediated conduction mechanism above the eutectic point of the solute/water/ ice system to a solid-phase conduction mechanism at lower temperatures.
A 800 year record of nitrate from the Lomonosovfonna ice core, Svalbard
Authors: Kekonen Teija , Moore John C. , Mulvaney Robert , Isaksson Elisabeth , Pohjola Veijo , van de Wal Roderik S. W. 
Published: November 2007

AbstractDetailed chemical analysis of the 122 m, relatively high-altitude and low-melt Lomonosovfonna ice core provides the best-dated record of nitrate from Svalbard. A very significant non-linear trend present in the record shows: (a) a rise in concentrations from the 12th to the mid-16th century, (b) reasonably stable concentrations until the mid-19th century, (c) a rise in concentrations into the 20th century, with (d) a rapid rise in the 1950s and (e) a decrease after the mid-1980s. Nitrate is well correlated with ammonium before 1920 and after 1960 but not in the intervening period. the correlation between ammonium and nitrate concentrations indicates that ammonium nitrate (NH4NO3) has been common at Lomonosovfonna. There are also places in the core where nitrate is very closely associated with calcium.
A Monte Carlo-tuned model of the flow in the NorthGRIP area
Authors: Grinsted Aslak , Dahl-Jensen Dorthe 
Published: November 2007

AbstractThe North Greenland Icecore Project (NorthGRIP) drill site was chosen in order to obtain a good Eemian record. At the present depth, 3001 m, the Eemian interstadial has yet to be seen. Clearly the flow in this area is poorly understood and needs further investigation. After a review of specific features of the bottom topography, it is believed that the geology changes along the flowline. In order to investigate whether this explains the observed age–depth relationship at NorthGRIP, the inverse Monte Carlo method has been applied to a simple model. the inversion reveals that the main reason no Eemian is observed is a high basal melt rate (2.7 mma–1). the melting is a consequence of a higher geothermal heat flux than the expected 51 mWm–2 of the Precambrian shield. from our analyses it is concluded that the geothermal heat flux at NorthGRIP is 98 mWm–2.The high basal melt rate also gives rise to sliding at the bed. In addition to these results, an accumulation model has been established specifically for NorthGRIP. These results are essential for further modelling of the NorthGRIP flow and depth–age relationship.
Sulphate record from a northeast Greenland ice core over the last 1200 years based on continuous flow analysis
Authors: Bigler Matthias , Wagenbach Dietmar , Fischer Hubertus , Kipfstuhl Josef , Miller Heinrich , Sommer Stefan , Stauffer Bernhard 
Published: November 2007

AbstractA 150 m deep ice core from the low-accumulation area of northeast Greenland was analyzed for sulphate, calcium, sodium and electrolytical meltwater conductivity at a depth resolution of approximately 1 cm by continuous flow analysis (CFA). the calcium and sodium profiles are used to establish a relatively precise ice-core chronology by annual-layer counting back to AD 830. Inspection of the novel CFA method for sulphate revealed relative errors typically around 15%, but at least ±20 ng g–1, for concentrations 5130 ng g–1, and a current detection limit for routine ice-core analyses of 40 ng g–1. Annual sulphate peaks are shown to occur over almost the entire core, with only a small shift in seasonality between the modern and pre-industrial sections. Inspection of volcanic horizons allowed more accurate timing of these peaks and clear identification of calcium-rich events. Disregarding clear volcanic peaks, significant long-term changes of sulphate are only seen over the industrial period. However, a higher frequency of important volcanic inputs was identified around AD 1200.
1000 year ice-core records from Berkner Island, Antarctica
Authors: Mulvaney Robert , Oerter Hans , Peel David A. , Graf Wolfgang , Arrowsmith Carol , Pasteur Elizabeth C. , Knight Bruce , Littot Geneviève C. , Miners William D. 
Published: November 2007

AbstractTwo medium-depth ice cores were retrieved from Berkner Island by a joint project between the Alfred-Wegener-Institut and the British Antarctic Survey in the 1994/95 field season. A 151m deep core from the northern dome (Reinwarthhöhe) of Berkner Island spans 700 years, while a 181 m deep core from the southern dome (Thyssenhöhe) spans approximately 1200 years. Both cores display clear seasonal cycles in electrical conductivity measurements, allowing dating by annual-layer counting and the calculation of accumulation profiles. Stable-isotope measurements (both δ18O and δD), together with the accumulation data, allow us to estimate changes in climate for most of the past millennium: the data show multi-decadal variability around a generally stable long-termmean. In addition, a full suite of major chemistry measurements is available to define the history of aerosol deposition at these sites: again, there is little evidence that the chemistry of the sites has changed over the past six centuries. Finally, we suggest that the southern dome, with an ice thickness of 950 m, is an ideal site from which to gain a climate history of the late stages of the last glacial and the deglaciation for comparison with the records from the deep Antarctic ice cores, and with other intermediate-depth cores such as Taylor Dome and Siple Dome.
Variability in the climate of the Pacific Ocean and North America as expressed in the Mount Logan ice core
Authors: Moore G.W. Kent , Alverson Keith , Holdsworth Gerald 
Published: November 2007

AbstractIn this paper, we explore the climate signal contained in the annual snow-accumulation time series from a high-altitude ice core drilled on Mount Logan in the Saint Elias mountain range of western Canada. With the global meteorological fields from the U.S. National Centers for Environmental Prediction re-analysis, we construct composites of the atmospheric circulation and temperature patterns associated with anomalous snow accumulation at the Mount Logan site over the period 1948–87. These results confirm, with an independent method, previous work that identified the existence of a coherent upper-tropospheric circulation anomaly extending over much of the North Pacific Ocean and North America that is associated with snow accumulation at the site. This anomaly has a similar structure to that associated with the extratropical response to the El Niño–Southern Oscillation. Coherent structures consistent with this circulation pattern also exist in both air- and land-temperature fields. In particular, heavy (light) snow accumulation at the site is associated with warmer (colder) air and surface temperatures over the North Pacific Ocean and North America. Over the North Pacific, the sea-surface temperature anomaly associated with heavy snow accumulation at the site has a “horseshoe” pattern that is similar to that associated with the Pacific Decadal Oscillation.
Phase relationships between Antarctic and Greenland climate records
Authors: Steig Eric J. , Alley Richard B. 
Published: November 2007

AbstractComparison of climate records from Antarctic and Greenland ice cores shows that the two regions respond asynchronously during millennial-scale climate changes. the apparent out-of-phase relationship between the records has been described as a climate ``seesaw’’ in which cooling in the Northern Hemisphere is balanced by warming in the Southern Hemisphere. the same relationship has also been attributed to the initiation of climate-change events in the Southern Hemisphere, rather than the North Atlantic as is conventionally assumed. A simple statistical approach−band-pass filtering combined with lag–correlation tests−used to examine the phase relationships in more detail shows that neither an anti-phase nor a phase-lag relationship adequately describes the observations. Whereas Antarctic and Greenland climate records do exhibit approximate anti-phase behavior about 50% of the time, they are generally in phase during cooling. A phase lead of Southern Hemisphere climate of 1000–1600 years is statistically indistinguishable from a lag of 400–800 years, whether for Dansgaard–Oeschger, Heinrich or longer-duration events. the ``seesaw’’ or ``Southern lead’’ appearance of the data arises from the fundamentally different characteristics of the climate time series, most importantly the absence of rapid warming events in Antarctica comparable to those in Greenland. to be consistent with the observations, climate models will need to capture these characteristics, in addition to reproducing the correct phase relationships.
Nitrate in Greenland and Antarctic ice cores: a detailed description of post-depositional processes
Authors: Röthlisberger Regine , Hutterli Manuel A. , Wolff Eric W. , Mulvaney Robert , Fischer Hubertus , Bigler Matthias , Goto-Azuma Kumiko , Hansson Margareta E. , Ruth Urs , Siggaard-Andersen Marie-Louise , Steffensen Jørgen P. 
Published: November 2007

AbstractA compilation of nitrate (NO3–) data from Greenland has shown that recent NO3– concentrations reveal a temperature dependence similar to that seen in Antarctica. Except for sites with very low accumulation rates, lower temperatures tend to lead to higher NO3– concentrations preserved in the ice. Accumulation rate, which is closely linked to temperature, might influence the concentrations preserved in snow as well, but its effect cannot be separated from the temperature imprint. Processes involved in NO3– deposition are discussed and shown to be temperature- and/or accumulation-rate-dependent. Apart from scavenging of nitric acid (HNO3) during formation of precipitation, uptake of HNO3 onto the ice crystal’s surface during and after precipitation seems to contribute further to the NO3– concentrations found in surface snow. Post-depositional loss of NO3– from the top snow layers is caused by release of HNO3 and by photolysis of NO3–. It is suggested that photolysis accounts for considerable losses at sites with very low accumulation rates. Depending on the site characteristic, and given that the temperature and accumulation-rate dependence is quantified, it should be possible to infer changes in atmospheric HNO3 concentrations.