scholarly journals Investigating the past and recent δ<sup>18</sup>O-accumulation relationship seen in Greenland ice cores

2012 ◽  
Vol 8 (6) ◽  
pp. 2053-2059 ◽  
Author(s):  
S. L. Buchardt ◽  
H. B. Clausen ◽  
B. M. Vinther ◽  
D. Dahl-Jensen
Keyword(s):  
Temperature Rise ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Data Set ◽  
The Past

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.

scholarly journals Investigating the past and recent δ<sup>18</sup>O-accumulation relationship seen in Greenland ice cores

2012 ◽  
Vol 8 (4) ◽  
pp. 4105-4120
Author(s):  
S. L. Buchardt ◽  
H. B. Clausen ◽  
B. M. Vinther ◽  
D. Dahl-Jensen
Keyword(s):  
Temperature Rise ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Data Set ◽  
The Past ◽  
Show Evidence

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.

scholarly journals Post-bubble close-off fractionation of gases in polar firn and ice cores: effects of accumulation rate on permeation through overloading pressure

2015 ◽  
Vol 15 (24) ◽  
pp. 13895-13914 ◽  
Author(s):  
T. Kobashi ◽  
T. Ikeda-Fukazawa ◽  
M. Suwa ◽  
J. Schwander ◽  
T. Kameda ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Accumulation Rate ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Significant Negative Correlation ◽  
Orbital Parameters ◽  
The Past ◽  
Pressure Sensitive ◽  
Core Project

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 (< 0.5 ‰) in the firn. Colder temperatures in the firn induce more depletion in δAr/N2 through thicker firn. The pressure sensitive bubbles are so depleted in δAr/N2 at the bubble close-off depth that they dominate the total δAr/N2 changes in spite of their smaller air contents. The model also indicates that δAr/N2 of ice cores should have experienced several per mil of depletion during the storage 14–18 years after coring. Further understanding of the δAr/N2 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.

scholarly journals Topographic control of regional accumulation rate variability at South Pole and implications for ice-core interpretation

2004 ◽  
Vol 39 ◽  
pp. 214-218 ◽  
Author(s):  
Gordon S. Hamilton
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Topographic Effects ◽  
South Pole ◽  
Accumulation Rates ◽  
Surface Slope ◽  
Ice Dynamics

AbstractSnow-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.

scholarly journals Variability in accumulation rates from GPR profiling on the West Antarctic plateau

2004 ◽  
Vol 39 ◽  
pp. 238-244 ◽  
Author(s):  
Vandy B. Spikes ◽  
Gordon S. Hamilton ◽  
Steven A. Arcone ◽  
Susan Kaspari ◽  
Paul A. Mayewski
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Track Length ◽  
Flow Profile ◽  
Accumulation Rates ◽  
West Antarctica ◽  
West Antarctic ◽  
Ground Penetrating ◽  
Along Track

AbstractIsochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25–185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed.

scholarly journals Interpolation methods for Antarctic ice-core timescales: application to Byrd, Siple Dome and Law Dome ice cores

2014 ◽  
Vol 10 (3) ◽  
pp. 1195-1209 ◽  
Author(s):  
T. J. Fudge ◽  
E. D. Waddington ◽  
H. Conway ◽  
J. M. D. Lundin ◽  
K. Taylor
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Linear Interpolation ◽  
Atmospheric Methane ◽  
Interpolation Methods ◽  
The Past ◽  
Annual Layer ◽  
Siple Dome ◽  
Abrupt Changes

Abstract. Antarctic ice cores have often been dated by matching distinctive features of atmospheric methane to those detected in annually dated ice cores from Greenland. Establishing the timescale between these tie-point ages requires interpolation. While the uncertainty at tie points is relatively well described, uncertainty of the interpolation is not. Here we assess the accuracy of three interpolation schemes using data from the WAIS Divide ice core in West Antarctica; we compare the interpolation methods with the annually resolved timescale for the past 30 kyr. Linear interpolation yields large age errors (up to 380 years) between tie points, abrupt changes in duration of climate events at tie points, and an age bias. Interpolations based on the smoothest accumulation rate (ACCUM) or the smoothest annual-layer thickness (ALT) yield timescales that more closely agree with the annually resolved timescale and do not have abrupt changes in duration at tie points. We use ALT to assess the uncertainty in existing timescales for the past 30 kyr from Byrd, Siple Dome, and Law Dome. These ice-core timescales were developed with methods similar to linear interpolation. Maximum age differences exceed 1000 years for Byrd and Siple Dome, and 500 years for Law Dome. For the glacial–interglacial transition (21 to 12 kyr), the existing timescales are, on average, older than ALT by 40 years for Byrd, 240 years for Siple Dome, and 150 years for Law Dome. Because interpolation uncertainty is often not considered, age uncertainties for ice-core records are often underestimated.

scholarly journals How well can we parameterize past accumulation rates in polar ice sheets?

1997 ◽  
Vol 25 ◽  
pp. 418-422 ◽  
Author(s):  
Eric J. Steig
Keyword(s):  
Accumulation Rate ◽  
Order Approximation ◽  
Ice Core ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
First Order Approximation

An important component of models of the cryosphere is the calculation of accumulation rates over polar ice sheets. As a first-order approximation, many models rely on the assumption that temperature is the main controlling factor for precipitation. However, compilation of available ice-core data, including a new core from Taylor Dome, East Antarctica, suggests that precipitation is significantly decoupled from temperature for a large proportion of both the Greenland and Antarctic ice sheets. While the estimated glacial-to-interglacial change in temperature does not differ greatly among ice cores from each ice sheet, the estimated change in accumulation rate varies by more than a factor of 2. A simple vapor-pressure parameterization gives reasonable estimates of accumulation in the ice-sheet interior, but this is not necessarily the case close to the ice-sheet margin, where synoptic weather systems are important.

scholarly journals A 485 year record of atmospheric chloride, nitrate and sulfate: results of chemical analysis of ice cores from Dyer Plateau, Antarctic Peninsula

1995 ◽  
Vol 21 ◽  
pp. 182-188 ◽  
Author(s):  
Jihong Cole Dai ◽  
Lonnie G. Thompson ◽  
Ellen Mosley-Thompson
Keyword(s):  
Sea Water ◽  
Accumulation Rate ◽  
Linear Regression Analysis ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Sea Salt ◽  
Volcanic Emissions ◽  
Data Set ◽  
Snow Chemistry

Detailed ionic analyses of Dyer Plateau snow show that major soluble impurities in snow consist of sodium (Na+), chloride (Cl−), nitrate (NO3−), sulfate (SO42−), and acidity (H+). The ratios of Na+ to Cl− concentrations are close to that of sea water, indicating little or no fractionation of sea-salt aerosols. The analyses of core sections from three sites along a 10 km transect show that local spatial variation of snow chemistry in this area is minimal and that temporal (decadal, inter-annual and sub-annual) variations in snow chemistry are very well preserved.Anion analyses of the upper 181 m section of two 235 m ice cores yield a data set of 485 years (1505-1989) of annual snow accumulation and fluxes of Cl−, NO3−, and non-sea-salt (nss) SO42−. No significant long-term trends are observed in any of the anion fluxes. This is consistent with other Antarctic ice-core records showing no significant anthropogenic atmospheric pollution in the high southern latitudes. Linear regression analysis shows that Cl− flux is independent of snow-accumulation rate. Significant positive correlations are found between accumulation rate and both NO3− flux and background nss-SO42− flux. These results suggest that dry deposition is primarily responsible for air-to-ground Cl− flux while wet deposition dominates the NO3− and nss-SO42− flux (≥90% and ≥75%, respectively). The nss-S042− fluxes provide a chronology of explosive volcanic emissions reaching the Antarctic region for the past 485 years.

scholarly journals Spatial and temporal variability of snow accumulation using ground-penetrating radar and ice cores on a Svalbard glacier

2002 ◽  
Vol 48 (162) ◽  
pp. 417-424 ◽  
Author(s):  
Anja Pälli ◽  
Jack C. Kohler ◽  
Elisabeth Isaksson ◽  
John C. Moore ◽  
Jean Francis Pinglot ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Spatial And Temporal Variability ◽  
Accumulation Rates ◽  
Radar Reflection ◽  
Ground Penetrating ◽  
Horizontal Layers

AbstractA 50 MHz ground-penetrating radar was used to detect horizontal layers in the snowpack along a longitudinal profile on Nordenskjöldbreen, a Svalbard glacier. The profile passed two shallow and one deep ice-core sites. Two internal radar reflection layers were dated using parameters measured in the deep core. Radar travel times were converted to water equivalent, yielding snow-accumulation rates along the profile for three time periods: 1986–99, 1963–99 and 1963–86. The results show 40–60% spatial variability in snow accumulation over short distances along the profile. The average annual accumulation rate for 1986–99 was found to be about 12% higher than for the period 1963–86, which indicates increased accumulation in the late 1980s and 1990s.

scholarly journals Stratigraphic analysis of Dome Fuji Antarctic ice core using an optical scanner

2004 ◽  
Vol 39 ◽  
pp. 467-472 ◽  
Author(s):  
Morimasa Takata ◽  
Yoshinori Iizuka ◽  
Takeo Hondoh ◽  
Shuji Fujita ◽  
Yoshiyuki Fujii ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Scattered Light ◽  
Ice Core ◽  
Ice Cores ◽  
Core Sample ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
Scanning Method ◽  
Scattering Intensity ◽  
Optical Scanner

AbstractLong-term changes of snow-accumulation rate in Antarctica are a major uncertainty in our understanding of past climate. Because the visible strata in polar ice are due to variations in the sizes and concentrations of air inclusions and microparticles, the scattered light intensity from an ice core yields valuable information on the stratification, which is likely to provide estimates of the annual accumulation rates. Identification of each layer is therefore necessary, and we developed an optical scanner apparatus to record detailed visible strata of ice cores. The apparatus records the two-dimensional distribution of light-scattering intensity along ice-core samples and produces an image of the whole ice-core sample by an image analysis process. These images showed that ice from Dome Fuji ice core contained a large number of layers. Volcanic layers were also well identified. We processed the scattering intensity on the enhanced intensity images to produce an intensity profile. This profile showed that the period of the intensity variations is consistent with a core-dating model applied to the Dome Fuji ice core. We also found that the intensity peaks are closely correlated to peaks in Ca2+ ion concentrations. Thus, our scanning method is a promising approach to measuring annual-layer thickness and, as a result, may be used to infer past accumulation rates in Antarctica.

scholarly journals Spatial and temporal distributions of surface mass balance between Concordia and Vostok stations, Antarctica, from combined radar and ice core data: first results and detailed error analysis

2018 ◽  
Vol 12 (5) ◽  
pp. 1831-1850 ◽  
Author(s):  
Emmanuel Le Meur ◽  
Olivier Magand ◽  
Laurent Arnaud ◽  
Michel Fily ◽  
Massimo Frezzotti ◽  
...  
Keyword(s):  
Error Analysis ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Time Averaging ◽  
Accumulation Rates ◽  
Accumulation Pattern ◽  
Surface Mass ◽  
First Results

Abstract. Results from ground-penetrating radar (GPR) measurements and shallow ice cores carried out during a scientific traverse between Dome Concordia (DC) and Vostok stations are presented in order to infer both spatial and temporal characteristics of snow accumulation over the East Antarctic Plateau. Spatially continuous accumulation rates along the traverse are computed from the identification of three equally spaced radar reflections spanning about the last 600 years. Accurate dating of these internal reflection horizons (IRHs) is obtained from a depth–age relationship derived from volcanic horizons and bomb testing fallouts on a DC ice core and shows a very good consistency when tested against extra ice cores drilled along the radar profile. Accumulation rates are then inferred by accounting for density profiles down to each IRH. For the latter purpose, a careful error analysis showed that using a single and more accurate density profile along a DC core provided more reliable results than trying to include the potential spatial variability in density from extra (but less accurate) ice cores distributed along the profile. The most striking feature is an accumulation pattern that remains constant through time with persistent gradients such as a marked decrease from 26 mm w.e. yr−1 at DC to 20 mm w.e. yr−1 at the south-west end of the profile over the last 234 years on average (with a similar decrease from 25 to 19 mm w.e. yr−1 over the last 592 years). As for the time dependency, despite an overall consistency with similar measurements carried out along the main East Antarctic divides, interpreting possible trends remains difficult. Indeed, error bars in our measurements are still too large to unambiguously infer an apparent time increase in accumulation rate. For the proposed absolute values, maximum margins of error are in the range 4 mm w.e. yr−1 (last 234 years) to 2 mm w.e. yr−1 (last 592 years), a decrease with depth mainly resulting from the time-averaging when computing accumulation rates.

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