Seasonal and interannual variations of firn densification and ice-sheet surface elevation at the Greenland summit

Zwally, H. Jay; Li, Jun

doi:10.3189/172756502781831403

Cited by 134 publications

(209 citation statements)

References 38 publications

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“…The observed development of seasonal cycles in density, which increase with depth and which follow the Ca++ seasonality, shows that strong seasonal cycles in impurities can induce a seasonal cycle in firn density unrelated to the temperature. This contradicts the hypothesis that the deep firn seasonal density cycle is induced by temperature at the surface (for example Landais et al, 2006;Zwally and Li, 2002). The relative maximum in density variability in deeper firn (Freitag et al, 2004;Gerland et al, 1999;Hörhold et al, 2011) can likely be attributed to the impurity effect.…”

Section: Discussioncontrasting

confidence: 51%

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On the impact of impurities on the densification of polar firn

Hörhold

Laepple

Freitag

et al. 2012

Earth and Planetary Science Letters

153

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Editor: P. DeMenocalKeywords: polar firn density densification impurity density variability Understanding polar firn densification is crucial for reconstructing the age of greenhouse gas concentrations extracted from ice cores, and for the interpretation of air in ice as a dating tool or as a climate proxy. Firn densification is generally modeled as a steady burial and sintering process of defined layers, where the structure of the layering is maintained along the whole firn and ice column. However, available high-resolution density data, as well as firn air samples, question this picture and point to a lack of understanding of firn densification. Based on analysis of high-resolution density and calcium concentration records from Antarctic and Greenland ice cores, we show for the first time that also impurities may have a significant impact on the densification. Analysis of firn cores shows a correlation between density and the calcium ion (Ca++) concentration, and this correlation increases with depth. The existence of this relationship is independent of the local climatic conditions at the core sites analyzed. The strong positive correlation between the density and the logarithm of Ca++ concentration indicates that impurities induce softening and lead to faster densification over a wide range of concentrations. In one core, the impurity effect manifests itself so strongly that the density develops a seasonal cycle closely following the seasonal cycle of Ca++. Our results clearly show that the structure of the firn layering changes with depth and suggest that the increased variability in density observed in deep firn, recently described as a universal feature of polar firn, may arise from the influence of Ca++ and/or other impurities. The impurity effect is likely to have direct implications on our understanding of glacial firn densification and on glacial gas age estimates.

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Section: Discussioncontrasting

confidence: 51%

“…The seasonal temperature cycle is thought to be responsible for the creation of density variability (Alley, 1988;Gow, 1965;Zwally and Li, 2002). Firn models usually predict that seasonal variations in density decrease and fade out slowly with depth in the later stage of densification (Zwally and Li, 2002).…”

Section: Introductionmentioning

confidence: 99%

On the impact of impurities on the densification of polar firn

Hörhold

Laepple

Freitag

et al. 2012

Earth and Planetary Science Letters

153

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“…Fig. 2 in Zwally and Li, 2002). Therefore assuming the pole is anchored at the base, their measured velocity should be V fc (z base ) + V ice .…”

Section: Discussion Of Measurementsmentioning

confidence: 99%

“…Therefore assuming the pole is anchored at the base, their measured velocity should be V fc (z base ) + V ice . For a comparison of the relative magnitudes of V fc (z) and V ice in the steady state, for example, V fc (z = 0) ≈ 2.1V ice at the surface and the total surface velocity is V(z = 0) ≈ 3.1V ice , where V ice = <A>/ρ i and <A> is the mean surface accumulation (Zwally and Li, 2002). Considering the attention given to one measurement from Richter and others (2008), it would be interesting to see similar specific analysis for the other 56 markers and how their chosen accumulation rates for that large range of measured velocities might indicate a stable surface.…”

Section: Discussion Of Measurementsmentioning

confidence: 99%

Response to Comment by A. RICHTER, M. HORWATH, R. DIETRICH (2016) on ‘Mass gains of the Antarctic ice sheet exceed losses’ by H. J. Zwally and others (2015)

et al. 2016

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“…Vihma et al: Spatial and temporal variability in summer snow pack Information on snow density is required to convert satellite observations of changes in the ice sheet elevation to mass changes (McConnell et al, 2000;Zwally and Li, 2002) and to estimate the water equivalent surface mass balance on the basis of stake measurements (Takahashi and Kameda, 2007). Anomalies in snow temperature and accumulation are positively correlated but have an opposing effect on the firn layer thickness (Helsen et al, 2008).…”

mentioning

confidence: 99%

Spatial and temporal variability in summer snow pack in Dronning Maud Land, Antarctica

et al. 2011

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Abstract.To quantify the spatial and temporal variability in the snow pack, field measurements were carried out during four summers in Dronning Maud Land, Antarctica. Data from a 310-km-long transect revealed the largest horizontal gradients in snow density, temperature, and hardness in the escarpment region. On the local scale, day-to-day temporal variability dominated the standard deviation of snow temperature, while the diurnal cycle was of second significance, and horizontal variability on the scale of 0.4 to 10 m was least important. In the uppermost 0.2 m, the snow temperature was correlated with the air temperature over the previous 6-12 h, whereas at the depths of 0.3 to 0.5 m the most important time scale was 3 days. Cloud cover and radiative fluxes affected the snow temperature in the uppermost 0.30 m and the snow density in the uppermost 0.10 m. Both on the intra-pit and transect scales, the ratio of horizontal to temporal variability increased with depth. The horizontal standard deviation of snow density increased rapidly between the scales of 0.4 and 2 m, and more gradually from 10 to 100 m. Inter-annual variations in snow temperature and density were due to interannual differences in air temperature and the timing of the precipitation events.

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Seasonal and interannual variations of firn densification and ice-sheet surface elevation at the Greenland summit

Cited by 134 publications

References 38 publications

On the impact of impurities on the densification of polar firn

On the impact of impurities on the densification of polar firn

Response to Comment by A. RICHTER, M. HORWATH, R. DIETRICH (2016) on ‘Mass gains of the Antarctic ice sheet exceed losses’ by H. J. Zwally and others (2015)

Spatial and temporal variability in summer snow pack in Dronning Maud Land, Antarctica

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