Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low accumulation conditions

Abstract. We investigate for the first time through continuous measurements the loss and alteration of past atmospheric information from air trapping mechanisms under low accumulation conditions. Methane concentration changes were measured over the Dansgaard-Oeschger event 17 (D0-17, ~ 60,000 yrBP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale, unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values which aims at minimizing the bias in the overall signal. Once the layered-trapping induced anomalies are removed from the record, the DO-17 appears to be smoother than its equivalent record from the high accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However and surprisingly, the degree of smoothing appears similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than usually expected. We also developed a method to extract the gas age distributions in ice layers that can be applied even for sites without firn-air measurements. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low temperature and accumulation conditions.

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Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low-accumulation conditions

Climate of the Past ◽

10.5194/cp-13-1815-2017 ◽

2017 ◽

Vol 13 (12) ◽

pp. 1815-1830 ◽

Cited By ~ 17

Author(s):

Kévin Fourteau ◽

Xavier Faïn ◽

Patricia Martinerie ◽

Amaëlle Landais ◽

Alexey A. Ekaykin ◽

...

Keyword(s):

Ice Core ◽

Flow Analysis ◽

Atmospheric Composition ◽

Atmospheric Variability ◽

High Accumulation ◽

Antarctic Plateau ◽

Mixing Ratios ◽

Gas Trapping ◽

Continuous Flow Analysis ◽

Concentration Changes

Abstract. We investigate for the first time the loss and alteration of past atmospheric information from air trapping mechanisms under low-accumulation conditions through continuous CH4 (and CO) measurements. Methane concentration changes were measured over the Dansgaard–Oeschger event 17 (DO-17, ∼ 60 000 yr BP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale that are unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values that aims at minimizing the bias in the overall signal. Once the layered-trapping-induced anomalies are removed from the record, DO-17 appears to be smoother than its equivalent record from the high-accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However, the degree of smoothing appears surprisingly similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low-accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than previously expected. We also developed a numerical method to extract the gas age distributions in ice layers after the removal of the anomalous layers based on comparison with a weakly smoothed record. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low-temperature and low-accumulation conditions.

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On the occurrence of annual layers in Dome Fuji ice core early Holocene ice

Climate of the Past ◽

10.5194/cp-11-1127-2015 ◽

2015 ◽

Vol 11 (9) ◽

pp. 1127-1137 ◽

Cited By ~ 5

Author(s):

A. Svensson ◽

S. Fujita ◽

M. Bigler ◽

M. Braun ◽

R. Dallmayr ◽

...

Keyword(s):

Ice Core ◽

Flow Analysis ◽

Ice Cores ◽

Snow Accumulation ◽

Early Holocene ◽

High Temporal Resolution ◽

High Accumulation ◽

Data Set ◽

Antarctic Plateau ◽

Annual Layer

Abstract. Whereas ice cores from high-accumulation sites in coastal Antarctica clearly demonstrate annual layering, it is debated whether a seasonal signal is also preserved in ice cores from lower-accumulation sites further inland and particularly on the East Antarctic Plateau. In this study, we examine 5 m of early Holocene ice from the Dome Fuji (DF) ice core at a high temporal resolution by continuous flow analysis. The ice was continuously analysed for concentrations of dust, sodium, ammonium, liquid conductivity, and water isotopic composition. Furthermore, a dielectric profiling was performed on the solid ice. In most of the analysed ice, the multi-parameter impurity data set appears to resolve the seasonal variability although the identification of annual layers is not always unambiguous. The study thus provides information on the snow accumulation process in central East Antarctica. A layer counting based on the same principles as those previously applied to the NGRIP (North Greenland Ice core Project) and the Antarctic EPICA (European Project for Ice Coring in Antarctica) Dronning Maud Land (EDML) ice cores leads to a mean annual layer thickness for the DF ice of 3.0 ± 0.3 cm that compares well to existing estimates. The measured DF section is linked to the EDML ice core through a characteristic pattern of three significant acidity peaks that are present in both cores. The corresponding section of the EDML ice core has recently been dated by annual layer counting and the number of years identified independently in the two cores agree within error estimates. We therefore conclude that, to first order, the annual signal is preserved in this section of the DF core. This case study demonstrates the feasibility of determining annually deposited strata on the central East Antarctic Plateau. It also opens the possibility of resolving annual layers in the Eemian section of Antarctic ice cores where the accumulation is estimated to have been greater than in the Holocene.

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Estimation of gas record alteration in very low-accumulation ice cores

Climate of the Past ◽

10.5194/cp-16-503-2020 ◽

2020 ◽

Vol 16 (2) ◽

pp. 503-522

Author(s):

Kévin Fourteau ◽

Patricia Martinerie ◽

Xavier Faïn ◽

Alexey A. Ekaykin ◽

Jérôme Chappellaz ◽

...

Keyword(s):

High Resolution ◽

Ice Core ◽

Age Distribution ◽

Ice Cores ◽

Measured Signal ◽

Antarctic Plateau ◽

Average Value ◽

Mixing Ratios ◽

Gas Trapping ◽

Trapping Model

Abstract. We measured the methane mixing ratios of enclosed air in five ice core sections drilled on the East Antarctic Plateau. Our work aims to study two effects that alter the recorded gas concentrations in ice cores: layered gas trapping artifacts and firn smoothing. Layered gas trapping artifacts are due to the heterogeneous nature of polar firn, where some strata might close early and trap abnormally old gases that appear as spurious values during measurements. The smoothing is due to the combined effects of diffusive mixing in the firn and the progressive closure of bubbles at the bottom of the firn. Consequently, the gases trapped in a given ice layer span a distribution of ages. This means that the gas concentration in an ice layer is the average value over a certain period of time, which removes the fast variability from the record. Here, we focus on the study of East Antarctic Plateau ice cores, as these low-accumulation ice cores are particularly affected by both layering and smoothing. We use high-resolution methane data to test a simple trapping model reproducing the layered gas trapping artifacts for different accumulation conditions typical of the East Antarctic Plateau. We also use the high-resolution methane measurements to estimate the gas age distributions of the enclosed air in the five newly measured ice core sections. It appears that for accumulations below 2 cm ice equivalent yr−1 the gas records experience nearly the same degree of smoothing. We therefore propose to use a single gas age distribution to represent the firn smoothing observed in the glacial ice cores of the East Antarctic Plateau. Finally, we used the layered gas trapping model and the estimation of glacial firn smoothing to quantify their potential impacts on a hypothetical 1.5-million-year-old ice core from the East Antarctic Plateau. Our results indicate that layering artifacts are no longer individually resolved in the case of very thinned ice near the bedrock. They nonetheless contribute to slight biases of the measured signal (less than 10 ppbv and 0.5 ppmv in the case of methane using our currently established continuous CH4 analysis and carbon dioxide, respectively). However, these biases are small compared to the dampening experienced by the record due to firn smoothing.

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Estimation of gas record alteration in very low accumulation ice cores

10.5194/cp-2019-94 ◽

2019 ◽

Author(s):

Kévin Fourteau ◽

Patricia Martinerie ◽

Xavier Faïn ◽

Alexey A. Ekaykin ◽

Jérôme Chappellaz ◽

...

Keyword(s):

High Resolution ◽

Ice Core ◽

Age Distribution ◽

Ice Cores ◽

Measured Signal ◽

Antarctic Plateau ◽

Average Value ◽

Mixing Ratios ◽

Gas Trapping ◽

Chemical Content

Abstract. We measured the methane mixing ratios of enclosed air in five ice core sections drilled on the East Antarctic plateau. Our work aims to study two effects that affect the recorded gas concentrations in ice cores: layered gas trapping artifacts and firn smoothing. Layered gas trapping artifacts are due to the heterogeneous nature of polar firn, where some strata might close early and trap abnormally old gases that appear as spurious values during measurements. The smoothing is due to the combined effects of diffusive mixing in the firn and the progressive closure of bubbles at the bottom of the firn. Consequently, the gases trapped in a given ice layer span a distribution of ages. Concentration measurements thus only measure the average value in the ice layer, which removes the fast variability from the record. We focus on the study of East Antarctic plateau ice cores, as these low accumulation ice cores are particularly affected by both layering and smoothing. Our results suggest that the presence of layering artifacts in deep ice cores is linked with the chemical content of the ice. We use high-resolution methane data to parametrize a simple model reproducing the layered gas trapping artifacts for different accumulation conditions typical of the East Antarctic plateau. We also use the high-resolution methane measurements to estimate the gas age distributions of the enclosed air in the five newly measured ice core sections. It appears that for accumulations below 2 cm ie yr−1(ice equivalent) the gas records experience nearly the same degree of smoothing. We therefore propose to use a single gas age distribution to represent the firn smoothing observed in the glacial ice cores of the East Antarctic plateau. Finally, we used the layered gas trapping model and the estimation of glacial firn smoothing to estimate their potential impacts on a million-and-a-half years old ice core from the East Antarctic plateau. Our results indicate that layering artifacts are no longer individually resolved in the case of very thinned ice near the bedrock. They nonetheless contribute to slight biases of the measured signal (less than 10 ppbv and 0.5 ppmv in the case of methane and carbon dioxide). However, these biases are small compared to the dampening experienced by the record due to firn smoothing.

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On the occurrence of annual layers in Dome Fuji ice core early Holocene ice

Climate of the Past Discussions ◽

10.5194/cpd-11-805-2015 ◽

2015 ◽

Vol 11 (2) ◽

pp. 805-830

Author(s):

A. Svensson ◽

S. Fujita ◽

M. Bigler ◽

M. Braun ◽

R. Dallmayr ◽

...

Keyword(s):

Ice Core ◽

Flow Analysis ◽

Ice Cores ◽

Early Holocene ◽

High Temporal Resolution ◽

High Accumulation ◽

Antarctic Plateau ◽

Annual Layer ◽

Dronning Maud Land ◽

Seasonal Signal

Abstract. Whereas ice cores from high accumulation sites in coastal Antarctica clearly demonstrate annual layering, it is debated whether a seasonal signal is also preserved in ice cores from lower accumulation sites further inland and particularly on the East Antarctic Plateau. In this study, we examine five metres of early Holocene ice from the Dome Fuji (DF) ice core in high temporal resolution by continuous flow analysis. The ice was continuously analyzed for concentrations of dust, sodium, ammonium, liquid conductivity, and water isotopic composition. Furthermore, a dielectric profiling was performed on the solid ice. In most of the analyzed ice, the multi-parameter impurity dataset appears to resolve the seasonal variability although the identification of annual layers is not always unambiguous. A layer counting based on the same principles as those previously applied to the Greenland NGRIP and the Antarctic EPICA Dronning Maud Land (EDML) ice cores leads to a mean annual layer thickness for the DF ice of 3.0 ± 0.3 cm that compares well to existing estimates. The measured DF section is linked to the EDML ice core through a characteristic pattern of three significant acidity peaks that are present in both cores. The corresponding section of the EDML ice core has recently been dated by annual layer counting and the number of years identified independently in the two cores agree within error estimates. We therefore conclude that, to first order, the annual signal is preserved in this section of the DF core. This case study demonstrates the feasibility of determining annually deposited strata on the central Eastern Antarctic Plateau. It also opens the possibility of resolving annual layers in the Eemian section of the DF ice core where the accumulation is estimated to have been greater than in the Holocene.

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Continuous flow analysis of the Mount Brown South ice core

10.5194/egusphere-egu21-15782 ◽

2021 ◽

Author(s):

Margaret Harlan ◽

Helle Astrid Kjær ◽

Tessa Vance ◽

Paul Vallelonga ◽

Vasileios Gkinis ◽

...

Keyword(s):

Indian Ocean ◽

Size Distribution ◽

Continuous Flow ◽

Ice Core ◽

Flow Analysis ◽

East Antarctica ◽

Southern Indian Ocean ◽

Indian Ocean Region ◽

Continuous Flow Analysis ◽

Ocean Region

The Mount Brown South (MBS) ice core is an approximately 300-meter-long ice core, drilled in 2016-2017 to the south of Mount Brown, Wilhelm II Land, East Antarctica. This location in East Antarctica was chosen as it produces an ice core with well-preserved sub-annual records of both chemistry and isotope concentrations, spanning back over 1000 years. MBS is particularly well suited to represent climate variations of the Indian Ocean sector of Antarctica, and to provide information about regional volcanism in the Southern Indian Ocean region.A section of ice spanning the length of the MBS core was melted as part of the autumn 2019 continuous flow analysis (CFA) campaign at the Physics of Ice, Climate, and Earth (PICE) group at the University of Copenhagen. During this campaign, measurements were conducted for chemistry and impurities contained in the ice, in addition to water isotopes. The data measured in Copenhagen include measurements of H2O2, pH, electrolytic conductivity, and NH4+, Ca2+, and Na+&#160;ions, in addition to insoluble particulate concentrations and size distribution measured using an Abakus laser particle counter.Here, we present an overview of the CFA chemistry and impurity data, as well as preliminary investigations into the size distribution of insoluble particles and the presence of volcanic material within the ice. These initial chemistry and particulate size distribution data sets are useful in order to identify sections of the MBS core to subject to further analysis to increase our understanding of volcanic activity in the Southern Indian Ocean region.

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Calculating uncertainty for the RICE ice core continuous flow analysis water isotope record

Atmospheric Measurement Techniques ◽

10.5194/amt-11-4725-2018 ◽

2018 ◽

Vol 11 (8) ◽

pp. 4725-4736 ◽

Cited By ~ 2

Author(s):

Elizabeth D. Keller ◽

W. Troy Baisden ◽

Nancy A. N. Bertler ◽

B. Daniel Emanuelsson ◽

Silvia Canessa ◽

...

Keyword(s):

High Resolution ◽

Continuous Flow ◽

Ice Core ◽

Flow Analysis ◽

Calibration Error ◽

Data Set ◽

Total Uncertainty ◽

Continuous Flow Analysis ◽

Uncertainty Estimates ◽

Water Isotope

Abstract. We describe a systematic approach to the calibration and uncertainty estimation of a high-resolution continuous flow analysis (CFA) water isotope (δ2H, δ18O) record from the Roosevelt Island Climate Evolution (RICE) Antarctic ice core. Our method establishes robust uncertainty estimates for CFA δ2H and δ18O measurements, comparable to those reported for discrete sample δ2H and δ18O analysis. Data were calibrated using a time-weighted two-point linear calibration with two standards measured both before and after continuously melting 3 or 4 m of ice core. The error at each data point was calculated as the quadrature sum of three factors: Allan variance error, scatter over our averaging interval (error of the variance) and calibration error (error of the mean). Final mean total uncertainty for the entire record is δ2H=0.74 ‰ and δ18O=0.21 ‰. Uncertainties vary through the data set and were exacerbated by a range of factors, which typically could not be isolated due to the requirements of the multi-instrument CFA campaign. These factors likely occurred in combination and included ice quality, ice breaks, upstream equipment failure, contamination with drill fluid and leaks or valve degradation. We demonstrate that our methodology for documenting uncertainty was effective across periods of uneven system performance and delivered a significant achievement in the precision of high-resolution CFA water isotope measurements.

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PANDA, the French analytical platform dedicated to ice core

10.5194/egusphere-egu21-13253 ◽

2021 ◽

Author(s):

Sophie Darfeuil ◽

Patrick Ginot ◽

Joel Savarino ◽

Nicolas Caillon ◽

Xavier Faïn ◽

...

Keyword(s):

Trace Metals ◽

Major Ions ◽

Ice Core ◽

Flow Analysis ◽

Common Interest ◽

Continuous Flow Analysis ◽

Laser Spectrometry ◽

O Isotopes ◽

And Performance ◽

Analysis System

Since 2018, under the impetus of the IGE (Grenoble) and the LSCE (Saclay) and the common interest of the "Carottes de Glace France" consortium, an analytical platform dedicated to glacier archives was created to meet the growing analytical needs requested by projects involving French partners (Ice Memory, EAIIST, BE-OI ...) and international collaborations with a ten-year vision. Within this framework 5 modules have been developed between the IGE and the LSCE. 3 modules are installed at the IGE, including a CHEMISTRY module which includes a large number of instruments coupled to the CFA (Continuous Flow Analysis) system, allowing high-resolution multi tracer analysis on a single ice stick (water isotopes, dust, conductivity, colorimetry, black carbon, trace metals and gas) as well as several auto-samplers for discrete analyses (major ions, organic species, trace metals, sugars ...). The GAS module is shared between continuous analyses on the CFA system (laser spectrometry CH4/CO) and discrete analyses (Gas chromatography CH4/CO2). The ISOTOPY module allows the analysis of nitrogen (N), sulfur (S) and oxygen (O) isotopes. At the LSCE, the WATER ISOTOPY module allows continuous (Picarro coupled to a CFA line equipped with conductivity cells and auto-sampler) or discrete (Picarro or mass spectrometer) analyses for &#948;D, &#948;18O and &#948;17O in water. The AIR ISOTOPY module completes the platform for analyses by mass spectrometry of &#948;15N of N2, the triple isotopic composition of O2 and noble gases isotopes (36/38/40 Ar; 82/84/86 Kr; 129-132 Xe). An overview of the capacity and performance of the platform will be presented.

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Improved methodologies for continuous-flow analysis of stable water isotopes in ice cores

Atmospheric Measurement Techniques ◽

10.5194/amt-10-617-2017 ◽

2017 ◽

Vol 10 (2) ◽

pp. 617-632 ◽

Cited By ~ 14

Author(s):

Tyler R. Jones ◽

James W. C. White ◽

Eric J. Steig ◽

Bruce H. Vaughn ◽

Valerie Morris ◽

...

Keyword(s):

Continuous Flow ◽

Ice Core ◽

Flow Analysis ◽

Ice Cores ◽

Isotope Ratio Mass Spectrometry ◽

Absorption Spectrometry ◽

Isotopic Analysis ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Continuous Flow Analysis

Abstract. Water isotopes in ice cores are used as a climate proxy for local temperature and regional atmospheric circulation as well as evaporative conditions in moisture source regions. Traditional measurements of water isotopes have been achieved using magnetic sector isotope ratio mass spectrometry (IRMS). However, a number of recent studies have shown that laser absorption spectrometry (LAS) performs as well or better than IRMS. The new LAS technology has been combined with continuous-flow analysis (CFA) to improve data density and sample throughput in numerous prior ice coring projects. Here, we present a comparable semi-automated LAS-CFA system for measuring high-resolution water isotopes of ice cores. We outline new methods for partitioning both system precision and mixing length into liquid and vapor components – useful measures for defining and improving the overall performance of the system. Critically, these methods take into account the uncertainty of depth registration that is not present in IRMS nor fully accounted for in other CFA studies. These analyses are achieved using samples from a South Pole firn core, a Greenland ice core, and the West Antarctic Ice Sheet (WAIS) Divide ice core. The measurement system utilizes a 16-position carousel contained in a freezer to consecutively deliver ∼  1 m  ×  1.3 cm2 ice sticks to a temperature-controlled melt head, where the ice is converted to a continuous liquid stream and eventually vaporized using a concentric nebulizer for isotopic analysis. An integrated delivery system for water isotope standards is used for calibration to the Vienna Standard Mean Ocean Water (VSMOW) scale, and depth registration is achieved using a precise overhead laser distance device with an uncertainty of ±0.2  mm. As an added check on the system, we perform inter-lab LAS comparisons using WAIS Divide ice samples, a corroboratory step not taken in prior CFA studies. The overall results are important for substantiating data obtained from LAS-CFA systems, including optimizing liquid and vapor mixing lengths, determining melt rates for ice cores with different accumulation and thinning histories, and removing system-wide mixing effects that are convolved with the natural diffusional signal that results primarily from water molecule diffusion in the firn column.

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Sulphate record from a northeast Greenland ice core over the last 1200 years based on continuous flow analysis

Annals of Glaciology ◽

10.3189/172756402781817158 ◽

2002 ◽

Vol 35 ◽

pp. 250-256 ◽

Cited By ~ 40

Author(s):

Matthias Bigler ◽

Dietmar Wagenbach ◽

Hubertus Fischer ◽

Josef Kipfstuhl ◽

Heinrich Miller ◽

...

Keyword(s):

Continuous Flow ◽

Ice Core ◽

Flow Analysis ◽

Depth Resolution ◽

The Novel ◽

Small Shift ◽

Annual Layer ◽

Continuous Flow Analysis ◽

Clear Identification ◽

Relative Errors

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.

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