Archival processes of the water stable isotope signal in East Antarctic ice cores

Casado, Mathieu; Landais, A.; Picard, Ghislain; Münch, Thomas; Laepple, Thomas; Stenni, Barbara; Dreossi, Giuliano; Ekaykin, Alexey; Arnaud, Laurent; Genthon, Christophe; Touzeau, Alexandra; Masson‐Delmotte, Valérie; Jouzel, Jean

doi:10.5194/tc-12-1745-2018

Cited by 74 publications

(100 citation statements)

References 81 publications

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“…This analysis suggests that HSSW

_{R o n n e}

interacted with an older ice, formed at higher altitude than the ice that interacted with HSSW

_{B e r k n e r}

. Only very few ice cores have measured

δ^{18}

O on FRIS, but we note that

δ^{18}

O of order

-

40‰ are typical values recorded at depth in ice cores over the ice sheet (Casado et al, ) and that

δ^{18}

O of order

-

20‰ are values consistent with those recorded in an ice core near the front of FRIS (Graf et al, ). While much uncertainty exists in the spatial variability of basal

δ^{18}

O characteristics of ice, lower values of

δ^{18}

O could be associated with ice closer to the ice front (consistent with][and arguably because ice nearer the ice‐front might locally form on the ice shelf by ice compaction ; Graf et al, ).…”

Section: Resultssupporting

confidence: 78%

Ice Shelf Basal Melt and Influence on Dense Water Outflow in the Southern Weddell Sea

et al. 2020

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We use new observations of stable water isotopes from a research cruise in early 2017 to highlight ocean‐ice interactions occurring under Filchner‐Ronne Ice Shelf, the largest Antarctic ice shelf. In particular, we investigate the properties of Ice Shelf Water with temperature lower than the surface freezing point, in the Filchner Depression. We identify two main flavors of Ice Shelf Water emerging from beneath the Filchner Ice Shelf, which originate from High Salinity Shelf Water end members with distinct characteristics. Furthermore, these two High Salinity Shelf Water end members interact with areas of the ice shelves with different basal properties to produce different versions of Ice Shelf Water. These water masses are associated with different rates of basal melting and refreezing, which we quantify. Ice Shelf Water types that flow out of the ice shelf cavity are composed of 0.4% of mass from ice shelf (melt minus freeze) when sampled at the front of Filchner Ice Shelf. The slightly lighter Ice Shelf Water version mixes directly with ambient water masses as it flows northward on the continental shelf. The resulting Ice Shelf Water mixture with temperature below the surface freezing point ultimately sinks along the continental slope into the deep ocean, as a precursor of the Weddell Sea bottom waters.

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“…This analysis suggests that HSSW

_{R o n n e}

interacted with an older ice, formed at higher altitude than the ice that interacted with HSSW

_{B e r k n e r}

. Only very few ice cores have measured

δ^{18}

O on FRIS, but we note that

δ^{18}

O of order

-

40‰ are typical values recorded at depth in ice cores over the ice sheet (Casado et al, ) and that

δ^{18}

O of order

-

20‰ are values consistent with those recorded in an ice core near the front of FRIS (Graf et al, ). While much uncertainty exists in the spatial variability of basal

δ^{18}

O characteristics of ice, lower values of

δ^{18}

O could be associated with ice closer to the ice front (consistent with][and arguably because ice nearer the ice‐front might locally form on the ice shelf by ice compaction ; Graf et al, ).…”

Section: Resultssupporting

confidence: 78%

Ice Shelf Basal Melt and Influence on Dense Water Outflow in the Southern Weddell Sea

et al. 2020

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“…In a study by Casado et al (2018), the authors combine a comprehensive dataset consisting of several years of precipitation collection from Dome C, Antarctica with δ 18 O records from snow pits. A clear discrepancy between the average precipitation isotopic composition and the average snow pit isotopic composition was observed.…”

Section: Citationmentioning

confidence: 99%

Evidence of Isotopic Fractionation During Vapor Exchange Between the Atmosphere and the Snow Surface in Greenland

et al. 2019

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Several recent studies from both Greenland and Antarctica have reported significant changes in the water isotopic composition of near‐surface snow between precipitation events. These changes have been linked to isotopic exchange with atmospheric water vapor and sublimation‐induced fractionation, but the processes are poorly constrained by observations. Understanding and quantifying these processes are crucial to both the interpretation of ice core climate proxies and the formulation of isotope‐enabled general circulation models. Here, we present continuous measurements of the water isotopic composition in surface snow and atmospheric vapor together with near‐surface atmospheric turbulence and snow‐air latent and sensible heat fluxes, obtained at the East Greenland Ice‐Core Project drilling site in summer 2016. For two 4‐day‐long time periods, significant diurnal variations in atmospheric water isotopologues are observed. A model is developed to explore the impact of this variability on the surface snow isotopic composition. Our model suggests that the snow isotopic composition in the upper subcentimeter of the snow exhibits a diurnal variation with amplitudes in δ 18 O and δD of ~2.5‰ and ~13‰, respectively. As comparison, such changes correspond to 10–20% of the magnitude of seasonal changes in interior Greenland snow pack isotopes and of the change across a glacial‐interglacial transition. Importantly, our observation and model results suggest, that sublimation‐induced fractionation needs to be included in simulations of exchanges between the vapor and the snow surface on diurnal timescales during summer cloud‐free conditions in northeast Greenland.

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“…The width of the kernel is set by the diffusion length σ , which is site-specific and a function of depth. For modelling the time uncertainty we use the approach of Comboul et al (2014). Model parameters are the rates of missing and double-counted annual layers, which we set to match the reported time uncertainties of the isotope records.…”

Section: Transfer Functions For Vapour Diffusion and Time Uncertaintymentioning

confidence: 99%

“…However, the interpretation of isotope records in terms of local atmospheric temperatures is complicated by a multitude of processes that distort the original relationship present in precipitation (e.g. Fujita and Abe, 2006;Sjolte et al, 2011;Steen-Larsen et al, 2011;Touzeau et al, 2016;Casado et al, 2018). To a first approximation, changes in isotopic composition are only recorded in the ice if there is snowfall, while the role of water vapour exchange processes in between precipitation events is still debated (Steen-Larsen et al, 2011;Stenni et al, 2016; Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Section: Introductionmentioning

confidence: 99%

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What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?

Münch

Laepple

2018

Clim. Past

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Abstract. Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, we find an increase in the SNR by nearly 1 order of magnitude (∼0.2 at decadal and ∼1.0 at multi-centennial scales). The estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.

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Archival processes of the water stable isotope signal in East Antarctic ice cores

Cited by 74 publications

References 81 publications

Ice Shelf Basal Melt and Influence on Dense Water Outflow in the Southern Weddell Sea

Ice Shelf Basal Melt and Influence on Dense Water Outflow in the Southern Weddell Sea

Evidence of Isotopic Fractionation During Vapor Exchange Between the Atmosphere and the Snow Surface in Greenland

What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?

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