Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr BP

Parrenin, Frédéric; Petit, J. R.; Masson‐Delmotte, Valérie; Wolff, Eric W.; Basile‐Doelsch, Isabelle; Jouzel, Jean; Lipenkov, V. Ya.; Rasmussen, S. O.; Schwander, Jakob; Severi, Mirko; Udisti, Roberto; Vereș, Daniel; Vinther, Bo M.

doi:10.5194/cp-8-1031-2012

Cited by 52 publications

(74 citation statements)

References 49 publications

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“…This result obtained with our associated appropriate parameterization is in agreement with the study of Parrenin et al (2012) showing that the classical firn densification model overestimates LID during the last glacial period at EDC. With our revised model, the simulated age is also significantly decreased for the glacial periods at low accumulation and temperature sites on the East Antarctic plateau (Dome C, Vostok, and Dome Fuji).…”

Section: Discussionsupporting

confidence: 80%

“…The latest results are in good agreement with the recent determination of age within the AICC2012 timescale: 3920 years for EDC 21 ka (ice age) and 5100 years for Vostok 21 ka (ice age). This is not unexpected since the EDC LID in the construction of the AICC2012 timescale is deduced from the EDC δ 15 N scenario, a hypothesis supported by the available gas and ice stratigraphic markers over the last deglaciation (Parrenin et al, 2012).…”

Section: Discussionmentioning

confidence: 91%

“…We use a 2 m convective zone for all sites, except Vostok, where we use 13 m, in accordance with firn measurements (Bender et al, 2006). We assume that the convective zone did not evolve during the last deglaciation, consistent with dating constraints at Dome C and at Vostok during Termination 2 (Parrenin et al, 2012;Bazin et al, 2013;Landais et al, 2013). Table S4).…”

Section: Input Scenariosmentioning

confidence: 99%

“…This hypothesis can explain the mismatch between modelled and measured δ 15 N at EPICA Dronning Maud Land (EDML) during the glacial period by invoking a 10 m convective zone (Landais et al, 2006). However, it has been ruled out for explaining the strong mismatch between model and δ 15 N data at EPICA Dome C (EDC) for the last glacial period (Parrenin et al, 2012). Fourth, firn densification is very sensitive to changes in temperature and accumulation rate so that uncertainties in the surface climate parameters can lead to a biased value of the modelled LID and hence δ 15 N. Fifth, a significant thermal fractionation signal can affect the total δ 15 N signal.…”

Section: Introductionmentioning

confidence: 99%

“…The decrease in the LID in the models is caused by the increase in temperature during the deglaciation, which has a stronger impact than the increase in the accumulation rate. The differences in modelled and measured δ 15 N for glacial periods at cold sites on the East Antarctic plateau have important consequences for the age estimate and hence the ice core chronology: using the firn densification models, the modelled age for the glacial period at Vostok and Dome C is too large by several centuries Parrenin et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

et al. 2017

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Abstract. The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas-ice age difference is essential to documenting the phasing between CO 2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ 15 N of air measured in ice cores.All firn densification models applied to deglaciations show a large disagreement with δ 15 N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ 15 N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model-data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ 15 N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ 15 N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and measured δ 15 N evolution at Greenland and Antarctic sites with high accumulation unless threshold effects are taken into account. We thus do not provide a definite solution to the firnification at very cold Antarctic sites but propose potential pathways for future studies.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 91%

Section: Input Scenariosmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

et al. 2017

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Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations

et al. 2014

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Acidity is an important chemical variable that impacts atmospheric and snowpack chemistry.Here we describe composite time series and the spatial pattern of acidity concentration (Acy = H + À HCO 3 À ) during the last 2000 years across the Dronning Maud Land region of the East Antarctic Plateau using measurements in seven ice cores. Coregistered measurements of the major ion species show that sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), and hydrochloric acid (HCl) determine greater than 98% of the acidity value. The latter, also described as excess chloride (ExCl À ), is shown mostly to be derived from postdepositional diffusion of chloride with little net gain or loss from the snowpack. A strong inverse linear relationship between nitrate concentration and inverse accumulation rate provides evidence of spatially homogenous fresh snow concentrations and reemission rates of nitrate from the snowpack across the study area. A decline in acidity during the Little Ice Age (LIA, 1500-1900 Common Era) is observed and is linked to declines in HNO 3 and ExCl À during that time. The nitrate decline is found to correlate well with published methane isotope data from Antarctica (δ 13 CH 4 ), indicating that it is caused by a decline in biomass burning. The decrease in ExCl À concentration during the LIA is well correlated to published sea surface temperature reconstructions in the Atlantic Ocean, which suggests increased sea salt aerosol production associated with greater sea ice extent.

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Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study

2013

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[1] Reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core-derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional. We test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the MAECHAM5-HAM aerosol-climate model. An ensemble of 70 simulations is analyzed, with SO 2 injections ranging from 8.5 to 700 Tg, with eruptions in January and July. Modeled sulfate deposition flux to Antarctica shows excellent spatial correlation with ice core-derived estimates for Pinatubo and Tambora, although the comparison suggests the modeled flux to the ice sheets is 4-5 times too large. We find that Greenland and Antarctic deposition efficiencies (the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden) vary as a function of the magnitude and season of stratospheric sulfur injection. Changes in simulated sulfate deposition for large SO 2 injections are connected to increases in aerosol particle size, which impact aerosol sedimentation velocity and radiative properties, the latter leading to strong dynamical changes including strengthening of the winter polar vortices, which inhibits the transport of stratospheric aerosols to high latitudes. The resulting relationship between Antarctic and Greenland volcanic sulfate deposition is nonlinear for very large eruptions, with significantly less sulfate deposition to Antarctica than to Greenland. These model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of Tambora-magnitude and larger.Citation: Toohey, M., K. Kru¨ger, and C. Timmreck (2013), Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study,

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Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr BP

Cited by 52 publications

References 49 publications

Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations

Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study

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