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

2014 ◽  
Vol 10 (1) ◽  
pp. 65-104 ◽  
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 yr) between tie points, abrupt changes in duration at tie points, and an age bias. Interpolation 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 the 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 yr for Byrd and Siple Dome, and 500 yr for Law Dome. For the glacial-interglacial transition (21 to 12 kyr), the existing timescales are, on average, older than ALT by 40 yr for Byrd, 240 yr for Siple Dome, and 150 yr for Law Dome. Because interpolation uncertainty is often not considered, age uncertainties for ice-core records are often underestimated.

scholarly journals A revised Law Dome age model (LD2017) and implications for last glacial climate

2017 ◽  
Author(s):  
Jason Roberts ◽  
Andrew Moy ◽  
Christopher Plummer ◽  
Tas van Ommen ◽  
Mark Curran ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Chemical Species ◽  
Linear Interpolation ◽  
Snow Accumulation ◽  
Volcanic Event ◽  
Last Glacial ◽  
Annual Layer ◽  
Abrupt Changes ◽  
Age Model

Abstract. Here we present a revised Law Dome, Dome Summit South (DSS) ice core age model (denoted LD2017) that significantly improves the chronology over the last 88 ka. An ensemble approach was used, allowing for the computation of both a median age and associated uncertainty as a function of depth. The revised chronology incorporates extended continuous annual layer counting to 853 m using chemical species with seasonally-varying behaviours. The annual layer counted age at 853 m is 2332 years before 2000 (y b2k) with an error of +13/−7 y, i.e. 2345–2325 y b2k . Below this depth, non-linear interpolation between age ties using a probability density function for age/depth is used to constrain and model the age of the ice. The ice-based age ties below the annual layer counted section are based on matching volcanic event markers, methane (CH4) gas concentration, isotopic composition of ice (δ18O) and the Last Glacial Maximum (LGM) dust peak to other records. For consistency, the timescale used for all matching is the AICC2012 timescale (Veres et al., 2013). The first ice-based age tie is the base of the annual layer counting record (2332 y b2k) and the age ties from ~ 2400–4000 y b2k are volcanic synchronised ice-based age ties. The detection of abrupt changes in CH4 gas concentrations within the DSS record provides further independent gas-based age ties, including the tightly constrained 8200 y b2k event. The improved age control between 9000 and 21000 y b2k is supplemented by CH4 and δ18O ice measurements (Pedro et al., 2011). Over the period 16600 to 18600 y b2k large changes in dust concentration, matched to the EDC dust record, are used to constrain two ice-based age ties. Unlike previous studies, where the modelling was used to simultaneously infer both age and snow accumulation rate, we made an independent estimate of the snow accumulation rate, where required, for the use of gas based age ties.

scholarly journals 1000 year ice-core records from Berkner Island, Antarctica

2002 ◽  
Vol 35 ◽  
pp. 45-51 ◽  
Author(s):  
Robert Mulvaney ◽  
Hans Oerter ◽  
David A. Peel ◽  
Wolfgang Graf ◽  
Carol Arrowsmith ◽  
...  
Keyword(s):  
Decadal Variability ◽  
Ice Core ◽  
Ice Cores ◽  
Aerosol Deposition ◽  
Climate History ◽  
Joint Project ◽  
The Past ◽  
Annual Layer ◽  
History Of ◽  
Field Season

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.

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 Secular Trends Of Accumulation Rate On Ice Cores From Dunde Ice Cap, China Over The Last 1000 Years

1990 ◽  
Vol 14 ◽  
pp. 363-363
Author(s):  
Wu Xiaoling ◽  
Li Zhongqin ◽  
Xie Zichu
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Surface Strain ◽  
Entire Length ◽  
Ice Age ◽  
Cooperative Research ◽  
Ice Cap ◽  
Annual Layer ◽  
Lanzhou Institute

Cooperative research programs were conducted on the Dunde Ice Cap (38°06′N, 96°26′E), China, in 1984, 1986, 1987, by the Lanzhou Institute of Glaciology and Geocryology (LIGG), China and the Byrd Polar Research Center (BPRC), U.S.A. This paper gives the preliminary results of the analysis on accumulation rate of the ice cap over the last 1000 years. Three ice cores were recovered to bedrock from the ice-cap summit (5324 m a.s.l.). Core D-1 (139.8 m long) was divided in the field along the entire length and was shared equally between LIGG and BPRC. Core D-2 (136.6 m long) was returned frozen complete to the LIGG for ice-core measurements. In Core D-3 (138.4 m long) the upper sectors were melted and bottled in the field and the lower sectors were returned frozen to the BPRC, U.S.A. Core D-1 was analyzed in China along the entire length for oxygen isotope, liquid conductivity and pH. A year-by-year dating of the ice cores has been made with Dansgaard-Johnsen’s flow pattern by using the data of surface strain-rate (August 1986 to August 1987) and tritium measurements. The resulting time-scales of the ice cores in Dunde Ice Cap yield an age of 4600 yr B.P. The annual layer thicknesses of core D-1 were measured mainly by δ18O analysis and liquid conductivity. The lower δ18O is generally associated with higher electrical conductivity. Annual layer thickness was converted to accumulation rates and compared with meteorological records from Delingxa Meteorological Station. The mean accumulation rate is 518 mm in ice-equivalent. Particular attention is given to the possible impact of the Little Ice Age. Based on spectral analysis of time series for the accumulation variation with depth, short-term (30, 33 year at 0.01 level) and intermediate-term variation (120 year) were discussed. The ice-core research program has been supported by the Chinese National Foundation of Natural Science under Grant DO125-4860011.

scholarly journals Secular Trends Of Accumulation Rate On Ice Cores From Dunde Ice Cap, China Over The Last 1000 Years

1990 ◽  
Vol 14 ◽  
pp. 363
Author(s):  
Wu Xiaoling ◽  
Li Zhongqin ◽  
Xie Zichu
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Surface Strain ◽  
Entire Length ◽  
Ice Age ◽  
Cooperative Research ◽  
Ice Cap ◽  
Annual Layer ◽  
Lanzhou Institute

Cooperative research programs were conducted on the Dunde Ice Cap (38°06′N, 96°26′E), China, in 1984, 1986, 1987, by the Lanzhou Institute of Glaciology and Geocryology (LIGG), China and the Byrd Polar Research Center (BPRC), U.S.A. This paper gives the preliminary results of the analysis on accumulation rate of the ice cap over the last 1000 years. Three ice cores were recovered to bedrock from the ice-cap summit (5324 m a.s.l.). Core D-1 (139.8 m long) was divided in the field along the entire length and was shared equally between LIGG and BPRC. Core D-2 (136.6 m long) was returned frozen complete to the LIGG for ice-core measurements. In Core D-3 (138.4 m long) the upper sectors were melted and bottled in the field and the lower sectors were returned frozen to the BPRC, U.S.A. Core D-1 was analyzed in China along the entire length for oxygen isotope, liquid conductivity and pH. A year-by-year dating of the ice cores has been made with Dansgaard-Johnsen’s flow pattern by using the data of surface strain-rate (August 1986 to August 1987) and tritium measurements. The resulting time-scales of the ice cores in Dunde Ice Cap yield an age of 4600 yr B.P. The annual layer thicknesses of core D-1 were measured mainly by δ18O analysis and liquid conductivity. The lower δ18O is generally associated with higher electrical conductivity. Annual layer thickness was converted to accumulation rates and compared with meteorological records from Delingxa Meteorological Station. The mean accumulation rate is 518 mm in ice-equivalent. Particular attention is given to the possible impact of the Little Ice Age. Based on spectral analysis of time series for the accumulation variation with depth, short-term (30, 33 year at 0.01 level) and intermediate-term variation (120 year) were discussed. The ice-core research program has been supported by the Chinese National Foundation of Natural Science under Grant DO125-4860011.

scholarly journals A 60 000 year Greenland stratigraphic ice core chronology

2007 ◽  
Vol 3 (6) ◽  
pp. 1235-1260 ◽  
Author(s):  
K. K. Andersen ◽  
M. Bigler ◽  
H. B. Clausen ◽  
D. Dahl-Jensen ◽  
S. J. Johnsen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Time Scale ◽  
Ice Core ◽  
Ice Cores ◽  
The Past ◽  
The North ◽  
Annual Layer ◽  
Absolute Age ◽  
Age Estimates ◽  
New Time

Abstract. The Greenland Ice Core Chronology 2005 (GICC05) is a time scale based on annual layer counting of high-resolution records from Greenland ice cores. Whereas the Holocene part of the time scale is based on various records from the DYE-3, the GRIP, and the NorthGRIP ice cores, the glacial part is solely based on NorthGRIP records. Here we present an 18 kyr extension of the time scale such that GICC05 continuously covers the past 60 kyr. The new section of the time scale places the onset of Greenland Interstadial 12 (GI-12) at 46.9±1.0 kyr b2k (before year AD 2000), the North Atlantic Ash Zone 2 layer in GI-15 at 55.4±1.2 kyr b2k, and the onset of GI-17 at 59.4±1.3 kyr b2k. The error estimates are derived from the accumulated number of uncertain annual layers and can be regarded as 1σ uncertainties. In the 40–60 kyr interval the new time scale has a discrepancy with the Meese-Sowers GISP2 time scale of up to 2.4 kyr, whereas GICC05 compares well to the dating of the Hulu Cave record with absolute age differences of less than 800 years throughout the 60 kyr period. The new time scale is generally in close agreement with other independently dated records and reference horizons, such as the Laschamp geomagnetic excursion and the Kleegruben speleothem record from the Austrian Alps, suggesting high accuracy of both event durations and absolute age estimates.

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

2015 ◽  
Vol 15 (11) ◽  
pp. 15711-15753
Author(s):  
T. Kobashi ◽  
T. Ikeda-Fukazawa ◽  
M. Suwa ◽  
J. Schwander ◽  
T. Kameda ◽  
...  
Keyword(s):  
Negative Correlation ◽  
Environmental Changes ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Significant Negative Correlation ◽  
Ice Crystals ◽  
Orbital Parameters ◽  
Air Content ◽  
The Past

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 ice crystals. 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. Herein, we found that δAr/N2 at decadal resolution on the gas age scale in the GISP2 ice core has a significant negative correlation with accumulation rate over the past 6000 years. Furthermore, the precise temperature and accumulation rate records over the past 4000 years are found to 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 yr−1)−1, respectively. To understand the fractionation processes, we applied a permeation model to "microbubbles (< 1 % of air content in the Vostok ice core)" and "normal bubbles" in the firn. The model indicates that δAr/N2 in the microbubbles is negatively correlated with the accumulation rate as found in the observation, due to changes in overloading pressure. Colder (warmer) temperatures in the firn induce more (less) depletions in δAr/N2. The microbubbles are so depleted in δAr/N2 at the bubble closeoff depth that they dominate the total δAr/N2 changes in spite of their smaller volumes. The model also indicates that δAr/N2 of GISP2 and NGRIP should have experienced several permil of depletion during the storage 14 years after coring. Further understanding of the δAr/N2 and δO2/N2 fractionation processes in the firn may lead to a new proxy for the past temperature and accumulation rate.

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.

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