Effects of bubbles, cracks, and volcanic tephra on the spectral albedo of bare ice near the Transantarctic Mountains: Implications for sea glaciers on Snowball Earth

Dadić, Ruzica; Mullen, Peter C.; Schneebeli, Martin; Brandt, Richard E.; Warren, Stephen G.

doi:10.1002/jgrf.20098

Cited by 72 publications

(113 citation statements)

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“…Dang et al, 2015). Moreover, we are also considering using the firn/ice albedo parameterization of Dadic et al (2013), based on measurements covering the range of densities from 400 to 900 kg m −3 . Surface-based measurements are needed to test satelliteretrieved albedo and to quantify the drivers behind albedo changes in different areas of Greenland.…”

Section: Discussionmentioning

confidence: 99%

The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

et al. 2016

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Abstract. The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using space-borne multispectral data collected during the 3 decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade −1 between 1996 and 2012. Over the same period, albedo modelled by the Modèle Atmosphérique Régionale (MAR) also shows a decrease, though at a lower rate (∼ −0.01 decade −1 ) than that obtained from space-borne data. We suggest that the discrepancy between modelled and measured albedo trends can be explained by the absence in the model of processes associated with the presence of light-absorbing impurities. The negative trend in observed albedo is confined to the regions of the GrIS that undergo melting in summer, with the drysnow zone showing no trend. The period 1981-1996 also showed no statistically significant trend over the whole GrIS. Analysis of MAR outputs indicates that the observed albedo decrease is attributable to the combined effects of increased near-surface air temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, and to trends in light-absorbing impurities (LAI) on the snow and ice surfaces. Neither aerosol models nor in situ and remote sensing observations indicate increasing trends in LAI in the atmosphere over Greenland. Similarly, an analysis of the number of fires and BC emissions from fires points to the absence of trends for such quantities. This suggests that the apparent increase of LAI in snow and ice might be related to the exposure of a "dark band" of dirty ice and to increased consolidation of LAI at the surface with melt, not to increased aerosol deposition. Albedo projections through to the end of the century under different warming scenarios consistently point to continued darkening, with albedo anomalies averaged over the whole ice sheet lower by 0.08 in 2100 than in 2000, driven solely by a warming climate. Future darkening is likely underestimated because of known underestimates in modelled melting (as seen in hindcasts) and because the model albedo scheme does not currently include the effects of LAI, which have a positive feedback on albedo decline through increased melting, grain growth, and darkening.

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Section: Discussionmentioning

confidence: 99%

The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

et al. 2016

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“…Equivalent radiative transfer schemes for glacier ice are scarce, perhaps due to the diverse range of glacier surface types. Smooth ice is best represented as a bulk medium of ice with air bubbles and cracks of known size distribution and specular reflection from the upper surface (Gardner and Sharp, 2010;Dadic et al, 2013). In contrast, weathered ice is best described as a collection of ice grains in a bulk medium of air (or water in the case of saturated ice) and is therefore more optically similar to very coarse snow.…”

Section: Radiative Transfer Modellingmentioning

confidence: 99%

“…The same may be true for NIR (0.7-1.3 µm) photographic methods (Yamaguchi et al, 2014). Other options include microcomputed tomography (Micro-CT: Dadic et al, 2013), although this requires cores to remain completely frozen through extraction, transport and analysis. Grain sizes could be determined using a polarising hand lens (Hubbard and Glasser, 2005;Negi et al, 2010) -although the error can be high (Painter et al, 2007) -or semi-automated analysis of photographs of thin/thick sections (Dadic et al, 2013) or the sample surface.…”

Section: Characterising Snow or Ice Optical Characteristicsmentioning

confidence: 99%

“…Other options include microcomputed tomography (Micro-CT: Dadic et al, 2013), although this requires cores to remain completely frozen through extraction, transport and analysis. Grain sizes could be determined using a polarising hand lens (Hubbard and Glasser, 2005;Negi et al, 2010) -although the error can be high (Painter et al, 2007) -or semi-automated analysis of photographs of thin/thick sections (Dadic et al, 2013) or the sample surface. Non-spherical grain shapes can influence the surface albedo (Dang et al, 2016) and can be simulated in the radiative transfer scheme TARTES .…”

Section: Characterising Snow or Ice Optical Characteristicsmentioning

confidence: 99%

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Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

et al. 2017

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Abstract. The darkening effects of biological impurities on ice and snow have been recognised as a control on the surface energy balance of terrestrial snow, sea ice, glaciers and ice sheets. With a heightened interest in understanding the impacts of a changing climate on snow and ice processes, quantifying the impact of biological impurities on ice and snow albedo ("bioalbedo") and its evolution through time is a rapidly growing field of research. However, rigorous quantification of bioalbedo has remained elusive because of difficulties in isolating the biological contribution to ice albedo from that of inorganic impurities and the variable optical properties of the ice itself. For this reason, isolation of the biological signature in reflectance data obtained from aerial/orbital platforms has not been achieved, even when ground-based biological measurements have been available. This paper provides the cell-specific optical properties that are required to model the spectral signatures and broadband darkening of ice. Applying radiative transfer theory, these properties provide the physical basis needed to link biological and glaciological ground measurements with remotely sensed reflectance data. Using these new capabilities we confirm that biological impurities can influence ice albedo, then we identify 10 challenges to the measurement of bioalbedo in the field with the aim of improving future experimental designs to better quantify bioalbedo feedbacks. These challenges are (1) ambiguity in terminology, (2) characterising snow or ice optical properties, (3) characterising solar irradiance, (4) determining optical properties of cells, (5) measuring biomass, (6) characterising vertical distribution of cells, (7) characterising abiotic impurities, (8) surface anisotropy, (9) measuring indirect albedo feedbacks, and (10) measurement and instrument configurations. This paper aims to provide a broad audience of glaciologists and biologists with an overview of radiative transfer and albedo that could support future experimental design.

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“…The low heat capacity of the ice surface allows large seasonal shifts of the Hadley circulation, yielding an indirect annual-mean circulation and, in contrast to Earth's modern climate, a zone of net evaporation around the equator Abbot et al, 2013). The equatorial net evaporation zone lowers the equatorial surface albedo because bare ice has a much lower albedo than snow (Brandt et al, 2005;Warren and Brandt, 2006;Dadic et al, 2013) and because of accumulation of surface dust. Both factors facilitate the deglaciation of a hard Snowball Earth Le Hir et al, 2010).…”

Section: A Voigt: Dynamics Of the Snowball Earth Hadley Circulationmentioning

confidence: 99%

The dynamics of the Snowball Earth Hadley circulation for off-equatorial and seasonally varying insolation

Voigt

2013

Earth Syst. Dynam.

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Abstract. I study the Hadley circulation of a completely icecovered Snowball Earth through simulations with a comprehensive atmosphere general circulation model. Because the Snowball Earth atmosphere is an example of a dry atmosphere, these simulations allow me to test to what extent dry theories and idealized models capture the dynamics of realistic dry Hadley circulations. Perpetual off-equatorial as well as seasonally varying insolation is used, extending a previous study for perpetual on-equatorial (equinox) insolation. Vertical diffusion of momentum, representing the momentum transport of dry convection, is fundamental to the momentum budgets of both the winter and summer cells. In the zonal budget, it is the primary process balancing the Coriolis force. In the meridional budget, it mixes meridional momentum between the upper and the lower branch and thereby decelerates the circulation. Because of the latter, the circulation intensifies by a factor of three when vertical diffusion of momentum is suppressed. For seasonally varying insolation, the circulation undergoes rapid transitions from the weak summer into the strong winter regime. Consistent with previous studies in idealized models, these transitions result from a mean-flow feedback, because of which they are insensitive to the treatment of vertical diffusion of momentum. Overall, the results corroborate previous findings for perpetual on-equatorial insolation. They demonstrate that descriptions of realistic dry Hadley circulations, in particular their strength, need to incorporate the vertical momentum transport by dry convection, a process that is neglected in most dry theories and idealized models. An improved estimate of the strength of the Snowball Earth Hadley circulation will also help to better constrain the climate of a possible Neoproterozoic Snowball Earth and its deglaciation threshold.

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Effects of bubbles, cracks, and volcanic tephra on the spectral albedo of bare ice near the Transantarctic Mountains: Implications for sea glaciers on Snowball Earth

Cited by 72 publications

References 93 publications

The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

The dynamics of the Snowball Earth Hadley circulation for off-equatorial and seasonally varying insolation

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