Implementation of counted layers for coherent ice core chronology

Abstract. A recent coherent chronology has been built for four Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a Bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice core chronology, the AICC2012 chronology for NGRIP was forced to fit exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core, as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited for constraints deduced from layer counting: the duration constraints. Estimating the global error on chronology due to such markers is not straightforward and implies some assumption on the correlation between individual counting errors for each interval of duration. We validate this new methodological implementation by conducting twin experiments and a posteriori diagnostics on the NGRIP ice core. Several sensitivity tests on marker sampling and correlation between counting errors were performed to provide some guidelines when using such a method for future dating experiments. Finally, using these markers for NGRIP in a five-core dating exercise with Datice leads to new chronologies that do not differ by more than 410 years from AICC2012 for Antarctic ice cores and 150 years from GICC05 for NGRIP over the last 60 000 years.

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Optimisation of glaciological parameters for ice core chronology by implementing counted layers between identified depth levels

Climate of the Past Discussions ◽

10.5194/cpd-10-3585-2014 ◽

2014 ◽

Vol 10 (4) ◽

pp. 3585-3616 ◽

Cited By ~ 4

Author(s):

L. Bazin ◽

B. Lemieux-Dudon ◽

A. Landais ◽

M. Guillevic ◽

P. Kindler ◽

...

Keyword(s):

Bayesian Approach ◽

Accumulation Rate ◽

Ice Core ◽

Ice Cores ◽

Age Difference ◽

Sensitivity Tests ◽

New Type ◽

Lock In ◽

Ice Core Dating

Abstract. A~recent coherent chronology has been built for 4 Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice cores chronology, it has been imposed that the AICC2012 chronology for NGRIP should respect exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited to constraints deduced from layer counting: the markers of age-difference. Using this type of markers for NGRIP in a 5 cores dating exercise with Datice, we have performed several sensitivity tests and show that the new ice core chronologies obtained with these new markers do not differ by more than 400 years from AICC2012 for Antarctic ice cores and by more than 130 years from GICC05 for NGRIP over the last 60 000 years. With this new parameterization, the accumulation rate and lock-in depth associated with NGRIP are more coherent with independent estimates than those obtained in AICC2012. While these new chronologies should not be used yet as new ice core chronologies, the improved methodology presented here should be considered in the next coherent ice core dating exercise.

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Progress on absolute dating of ice cores with Argon isotopes

10.5194/egusphere-egu21-14405 ◽

2021 ◽

Author(s):

Anais Orsi ◽

Ilaria Crotti ◽

Roxanne Jacob ◽

Amaelle Landais ◽

Elise Fourré

Keyword(s):

Ice Core ◽

Ice Cores ◽

Significant Advance ◽

Large Sample Size ◽

Argon Isotopes ◽

Absolute Dating ◽

Dating Method ◽

A New Technique ◽

Ice Core Dating ◽

Key Parameter

<p>In the search for very old ice, finding the age of the ice is a key parameter necessary for its interpretation. Most ice core dating method are based on chronological markers that require the ice to be in stratigraphic order. However, the oldest ice is likely to be found at the bottom of ice sheets, where the stratigraphy is disturbed, or in ablation areas, where the classical methods cannot be used. Absolute dating techniques have recently been developed to provide new constraints on the age of old ice, but their development in the context of ice cores is limited by the large sample size required. Here, we discuss the analytical performances of a new technique for 40Ar dating, which allows us to provide a reliable age with 80g of ice rather than 800g, as previously published. We present an application to the dating of the bottom of the TALDICE and Dome C ice cores. This method represents a significant advance for its application to the very precious ice at the bottom of ice cores.</p>

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Himalayan ice-core dating with snow algae

Journal of Glaciology ◽

10.3189/172756500781832918 ◽

2000 ◽

Vol 46 (153) ◽

pp. 335-340 ◽

Cited By ~ 38

Author(s):

Yoshitaka Yoshimura ◽

Shiro Kohshima ◽

Nozomu Takeuchi ◽

Katsumoto Seko ◽

Koji Fujita

Keyword(s):

Vertical Profile ◽

Algal Biomass ◽

Ice Core ◽

Algal Growth ◽

Ice Cores ◽

Late Summer ◽

Layer Formation ◽

Snow Algae ◽

Potential Use ◽

Ice Core Dating

AbstractSnow algae in shallow ice cores (7 m long) from Yala Glacier in the Langtang region of Nepal were examined for potential use in ice-core dating. Ice-core samples taken at 5350 m a.s.l. in 1994 contained more than seven species of snow algae. In a vertical profile of the algal biomass, 11 distinct algal layers were observed. Seasonal observation in 1996 at the coring site indicated most algal growth occurred from late spring to late summer. Pit observation in 1991, 1992 and 1994 indicated that algal layer formation takes place annually. δ18O, chemical ions (Na+, Cl−, SO42− and NO3−) and microparticles failed to show any clear seasonal variation, particularly at depths exceeding 2 m, possibly due to heavy meltwater percolation. Snow algae in ice cores would thus appear to be accurate boundary markers of annual layers and should prove useful for ice-core dating in Himalayan-type glaciers.

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Ice-core dating and chemistry by direct-current electrical conductivity

Journal of Glaciology ◽

10.3189/s0022143000002215 ◽

1992 ◽

Vol 38 (130) ◽

pp. 325-332 ◽

Cited By ~ 4

Author(s):

Kenorick Taylor ◽

Richard Alley ◽

Joe Fiacco ◽

Pieter Grootes ◽

Gregg Lamorey ◽

...

Keyword(s):

Electrical Conductivity ◽

Ice Core ◽

Low Frequency ◽

Ice Cores ◽

Quantitative Comparison ◽

Quantitative Interpretation ◽

Conductivity Measurements ◽

Temperature Variations ◽

The Core ◽

Ice Core Dating

AbstractAlthough quantitative interpretation of the low-frequency electrical conductivity of ice cores from central Greenland is complicated by temperature variations of the measured core, annual layers can be recognized in sections of the core that are not impacted by non-seasonal features. Ambiguities in counting of annual layers can be minimized by comparing the electrical conductivity measurements to measurements of dust concentration and visual stratigraphy. A non-linear relationship between applied voltage and the current measured across two electrodes complicates the quantitative comparison of measurements made with different equipment, but does not affect the overall shape of the observed features.

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Exploitation of chemical profiles by conjugate variable analysis: application to the dating of a tropical ice core (Nevado Illimani, Bolivia)

Climate of the Past Discussions ◽

10.5194/cpd-9-3399-2013 ◽

2013 ◽

Vol 9 (3) ◽

pp. 3399-3447

Author(s):

M. Gay ◽

M. De Angelis ◽

J.-L. Lacoume

Keyword(s):

Ice Core ◽

Ice Cores ◽

Ion Concentration ◽

Depth Profiles ◽

Conjugate Variable ◽

Chemical Profiles ◽

Analysis Application ◽

The Relationship ◽

Concentration Depth Profiles ◽

Ice Core Dating

Abstract. Ice core dating is a key parameter for the interpretation of the ice archives. However, the relationship between ice depth and age can generally not be easily established and requires to combine a large number of investigations and/or modeling effort. This paper presents a new approach of ice core dating based on conjugate variable (depth and spatial frequency) analysis of chemical profiles. The relationship between the depth of a given ice layer and the date it was deposited is determined using ion concentration depth profiles obtained along a one hundred-meters deep ice core recovered in the summit area of the Nevado Illimani (6350 m a.s.l.), located in the Eastern Bolivian Andes (16°37' S, 67°46' W). The results of Fourier conjugate analysis and wavelet tranforms are first compared. Both methods are applied to nitrate concentration depth profile. The resulting chronologies are checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points, demonstrating the efficiency of Fourier conjugate analysis when tracking the natural variability of chemical proxies. The Fourier conjugate analysis is then applied to concentration depth profiles of seven other ions thus providing information on the suitability of each of them for dating studies of tropical Andean ice cores.

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Dating a tropical ice core by time–frequency analysis of ion concentration depth profiles

Climate of the Past ◽

10.5194/cp-10-1659-2014 ◽

2014 ◽

Vol 10 (5) ◽

pp. 1659-1672

Author(s):

M. Gay ◽

M. De Angelis ◽

J.-L. Lacoume

Keyword(s):

Frequency Analysis ◽

Ice Core ◽

Ice Cores ◽

Ion Concentration ◽

Ice Age ◽

Time Frequency Analysis ◽

Time Frequency ◽

Depth Profiles ◽

Concentration Depth Profiles ◽

Ice Core Dating

Abstract. Ice core dating is a key parameter for the interpretation of the ice archives. However, the relationship between ice depth and ice age generally cannot be easily established and requires the combination of numerous investigations and/or modelling efforts. This paper presents a new approach to ice core dating based on time–frequency analysis of chemical profiles at a site where seasonal patterns may be significantly distorted by sporadic events of regional importance, specifically at the summit area of Nevado Illimani (6350 m a.s.l.), located in the eastern Bolivian Andes (16°37' S, 67°46' W). We used ion concentration depth profiles collected along a 100 m deep ice core. The results of Fourier time–frequency and wavelet transforms were first compared. Both methods were applied to a nitrate concentration depth profile. The resulting chronologies were checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points. With this first experiment, we demonstrated the efficiency of Fourier time–frequency analysis when tracking the nitrate natural variability. In addition, we were able to show spectrum aliasing due to under-sampling below 70 m. In this article, we propose a method of de-aliasing which significantly improves the core dating in comparison with annual layer manual counting. Fourier time–frequency analysis was applied to concentration depth profiles of seven other ions, providing information on the suitability of each of them for the dating of tropical Andean ice cores.

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Ice-core dating and chemistry by direct-current electrical conductivity

Journal of Glaciology ◽

10.1017/s0022143000002215 ◽

1992 ◽

Vol 38 (130) ◽

pp. 325-332 ◽

Cited By ~ 53

Author(s):

Kenorick Taylor ◽

Richard Alley ◽

Joe Fiacco ◽

Pieter Grootes ◽

Gregg Lamorey ◽

...

Keyword(s):

Electrical Conductivity ◽

Ice Core ◽

Low Frequency ◽

Ice Cores ◽

Quantitative Comparison ◽

Quantitative Interpretation ◽

Conductivity Measurements ◽

Temperature Variations ◽

The Core ◽

Ice Core Dating

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Spatial variations of local climate at Taylor Dome, Antarctica: implications for paleoclimate from ice cores

Annals of Glaciology ◽

10.1017/s0260305500016487 ◽

1994 ◽

Vol 20 ◽

pp. 219-225 ◽

Cited By ~ 4

Author(s):

E.D. Waddington ◽

D.L. Morse

Keyword(s):

Spatial Variability ◽

Source Region ◽

Ice Core ◽

Ice Cores ◽

Temperature Inversion ◽

Related Factors ◽

Local Climate ◽

Air Masses ◽

Air Temperatures ◽

Inversion Strength

10m firn temperatures are commonly used on the Antarctic plateau to estimate mean annual air temperatures. 10m firn temperatures measured at Taylor Dome (also referred to as McMurdo Dome in the literature), Antarctica, are influenced by a factor other than altitude and latitude that varies systematically across Taylor Dome. Some inter-related factors possibly contributing to the modern temperature variability are differences in sensible heat from warm or cold air masses, differences in wind strength and source region, differences in temperature inversion strength and differences in cloudiness. Our preliminary data are compatible with spatially variable katabatic winds that could control the winter temperature inversion strength to provide a large part of the signal. This has implications for paleoclimate studies.(1) Variations of the stable isotopes δ18O and δD from ice cores are a proxy for paleotemperature. The isotope thermometer is calibrated by comparing local isotope ratios with corresponding measured temperatures. In order to derive a useful isotope-temperature calibration, we must understand the processes that control the modern spatial variability of temperature. (2) In order to quantify past changes in local climate, we must understand processes that influence local spatial variability. If those processes differed in the past, ice-core climate reconstruction would be affected in two ways: through alteration of the geochemical record and through alteration of deep ice and firn temperatures.

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A Synoptic Scale Perspective on Greenland Ice Core δ18O Variability and Related Teleconnection Patterns

Atmosphere ◽

10.3390/atmos12030294 ◽

2021 ◽

Vol 12 (3) ◽

pp. 294

Author(s):

Norel Rimbu ◽

Monica Ionita ◽

Gerrit Lohmann

Keyword(s):

Ice Core ◽

Ice Cores ◽

Synoptic Scale ◽

Local Climate ◽

Rossby Wave Breaking ◽

Weather Patterns ◽

Teleconnection Patterns ◽

Climate Anomalies ◽

The North ◽

Oxygen Isotope Ratios

The variability of stable oxygen isotope ratios (δ18O) from Greenland ice cores is commonly linked to changes in local climate and associated teleconnection patterns. In this respect, in this study we investigate ice core δ18O variability from a synoptic scale perspective to assess the potential of such records as proxies for extreme climate variability and associated weather patterns. We show that positive (negative) δ18O anomalies in three southern and central Greenland ice cores are associated with relatively high (low) Rossby Wave Breaking (RWB) activity in the North Atlantic region. Both cyclonic and anticyclonic RWB patterns associated with high δ18O show filaments of strong moisture transport from the Atlantic Ocean towards Greenland. During such events, warm and wet conditions are recorded over southern, western and central part of Greenland. In the same time the cyclonic and anticyclonic RWB patterns show enhanced southward advection of cold polar air masses on their eastern side, leading to extreme cold conditions over Europe. The association between high δ18O winters in Greenland ice cores and extremely cold winters over Europe is partly explained by the modulation of the RWB frequency by the tropical Atlantic sea surface temperature forcing, as shown in recent modeling studies. We argue that δ18O from Greenland ice cores can be used as a proxy for RWB activity in the Atlantic European region and associated extreme weather and climate anomalies.

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Improved estimates of preindustrial biomass burning reduce the magnitude of aerosol climate forcing in the Southern Hemisphere

Science Advances ◽

10.1126/sciadv.abc1379 ◽

2021 ◽

Vol 7 (22) ◽

pp. eabc1379

Author(s):

Pengfei Liu ◽

Jed O. Kaplan ◽

Loretta J. Mickley ◽

Yang Li ◽

Nathan J. Chellman ◽

...

Keyword(s):

Southern Hemisphere ◽

Radiative Forcing ◽

Ice Core ◽

Ice Cores ◽

Terrestrial Ecosystems ◽

Rapid Expansion ◽

Past Century ◽

Fire Emissions ◽

The Past ◽

Fire Activity

Fire plays a pivotal role in shaping terrestrial ecosystems and the chemical composition of the atmosphere and thus influences Earth’s climate. The trend and magnitude of fire activity over the past few centuries are controversial, which hinders understanding of preindustrial to present-day aerosol radiative forcing. Here, we present evidence from records of 14 Antarctic ice cores and 1 central Andean ice core, suggesting that historical fire activity in the Southern Hemisphere (SH) exceeded present-day levels. To understand this observation, we use a global fire model to show that overall SH fire emissions could have declined by 30% over the 20th century, possibly because of the rapid expansion of land use for agriculture and animal production in middle to high latitudes. Radiative forcing calculations suggest that the decreasing trend in SH fire emissions over the past century largely compensates for the cooling effect of increasing aerosols from fossil fuel and biofuel sources.

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