Remote sensing of albedo-reducing snow algae and impurities in the Maritime Antarctica

Huovinen, Pirjo; Ramírez, Jaime; Gómez, Iván

doi:10.1016/j.isprsjprs.2018.10.015

Cited by 52 publications

(39 citation statements)

References 59 publications

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“…averaged) the reflectance measured with the ASD spectrometer to the spectral resolution of Sentinel-2. This sensor features a high spatial resolution (up to 10 m in the visible spectrum) 61 and it is promising for mapping glacier algae distribution from space 33 .…”

Section: Methodsmentioning

confidence: 99%

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Glacier algae foster ice-albedo feedback in the European Alps

Mauro

Garzonio

Baccolo

et al. 2020

Sci Rep

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the melting of glaciers and ice sheets is nowadays considered a symbol of climate change. Many complex mechanisms are involved in the melting of ice, and, among these processes, surface darkening due to organic material on bare ice has recently received attention from the scientific community. The presence of microbes on glaciers has been shown to decrease the albedo of ice and promote melting.Despite several studies from the Himalaya, Greenland, Andes, and Alaska, no quantitative studies have yet been conducted in the european Alps. in this paper, we made use of DnA sequencing, microscopy and field spectroscopy to describe the nature of glacier algae found at a glacier (Vadret da Morteratsch) of the European Alps and to evaluate their effect on the ice-albedo feedback. Among different algal species identified in the samples, we found a remarkable abundance of Ancylonema nordenskioeldii, a species that has never previously been quantitatively documented in the Alps and that dominates algal blooms on the Greenland ice Sheet. our results show that, at the end of the ablation season, the concentration of Ancylonema nordenskioeldii on the glacier surface is higher than that of other algal species (i.e. Mesotaenium berggrenii). Using field spectroscopy data, we identified a significant correlation between a reflectance ratio (750 nm/650 nm) and the algae concentration. This reflectance ratio could be useful for future mapping of glacier algae from remote sensing data exploiting band 6 (740 nm) and band 4 (665 nm) of the MultiSpectral Instrument (MSI) on board Sentinel-2 satellite. Here we show that the biological darkening of glaciers (i.e. the bioalbedo feedback) is also occurring in the european Alps, and thus it is a global process that must be taken into account when considering the positive feedback mechanisms related to glacier melting.Glaciers and ice sheets are not lifeless 1 . It has been demonstrated that several species of microorganisms, algae and small arthropods find their optimal environment on melting ice and snow. These organisms are also able to shape their environment, through a feedback cycle that involves the albedo. In fact, since these organisms are darker than snow and ice, their presence increases the light absorption and promotes the melting of underlying snow or ice 2-4 . On the surface of glaciers, such extremophiles often aggregate with inorganic material (i.e. mineral dust) to form cryoconite 5,6 . Cryoconite is a dark sediment 5,7 that increases the absorption of visible radiation 4,8 , and promotes the formation of characteristic cryoconite holes 9 which are globally recognized as an hot spot of biodiversity on ice 10 . Besides living organisms, cryoconite is known to concentrate pollutants such as contaminants and radionuclides 11,12 . This may represent a problem in the future, with a possible secondary release of these substances to the environment 13,14 .Cryoconite accumulated in cryoconite holes has a limited impact on glacier and ice sheet surface mass balance. Instead, the presen...

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Section: Methodsmentioning

confidence: 99%

“…Sentinel-2 is particularly suited for mapping spatial and temporal variability of the cryosphere at fine scale 44 , while Sentinel-3 allows a broader perspective 43 . Some studies have already exploited these data for mapping algae distribution in Maritime Antarctica 33 and Southwest Greenland 25,35 .…”

mentioning

confidence: 99%

Glacier algae foster ice-albedo feedback in the European Alps

Mauro

Garzonio

Baccolo

et al. 2020

Sci Rep

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“…When shortwave radiative energy fluxes dominate, a porous, low-density weathering crust develops as a consequence of radiative energy penetration to the sub-surface (Muller and Keeler, 1969;Munro, 1990). This, together with cryoconite hole formation punctuating the porous substrate (McIntyre, 1984;Cook et al, 2016), can allow supraglacially generated meltwater to drain into a shallow, depth-limited sub-surface water table (Irvine-Fynn et al, 2011;Cooper et al, 2018;Christner et al, 2018). This porous near-surface ice layer typically has numerous air-ice interfaces characterized by a rough surface topography, offering opportunities for high-angle light scattering, which increases albedo (Jonsell et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Algal growth and weathering crust state drive variability in western Greenland Ice Sheet ice albedo

et al. 2020

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Abstract. One of the primary controls upon the melting of the Greenland Ice Sheet (GrIS) is albedo, a measure of how much solar radiation that hits a surface is reflected without being absorbed. Lower-albedo snow and ice surfaces therefore warm more quickly. There is a major difference in the albedo of snow-covered versus bare-ice surfaces, but observations also show that there is substantial spatio-temporal variability of up to ∼0.4 in bare-ice albedo. Variability in bare-ice albedo has been attributed to a number of processes including the accumulation of light-absorbing impurities (LAIs) and the changing physical properties of the near-surface ice. However, the combined impact of these processes upon albedo remains poorly constrained. Here we use field observations to show that pigmented glacier algae are ubiquitous and cause surface darkening both within and outside the south-west GrIS “dark zone” but that other factors including modification of the ice surface by algal bloom presence, surface topography and weathering crust state are also important in determining patterns of daily albedo variability. We further use observations from an unmanned aerial system (UAS) to examine the scale gap in albedo between ground versus remotely sensed measurements made by Sentinel-2 (S-2) and MODIS. S-2 observations provide a highly conservative estimate of algal bloom presence because algal blooms occur in patches much smaller than the ground resolution of S-2 data. Nevertheless, the bare-ice albedo distribution at the scale of 20 m×20 m S-2 pixels is generally unimodal and unskewed. Conversely, bare-ice surfaces have a left-skewed albedo distribution at MODIS MOD10A1 scales. Thus, when MOD10A1 observations are used as input to energy balance modelling, meltwater production can be underestimated by ∼2 %. Our study highlights that (1) the impact of the weathering crust state is of similar importance to the direct darkening role of light-absorbing impurities upon ice albedo and (2) there is a spatial-scale dependency in albedo measurement which reduces detection of real changes at coarser resolutions.

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“…Third, there is uncertainty in spectral biomarkers unique to glacier algae. Theoretically, a simple band ratio, spectral feature 5 identification or spectral mixing technique could be used to detect glacier algae as has been achieved for snow algae (Takeuchi et al, 2015;Painter et al, 2001;Huovinen et al, 2018). However, absorption by Mesotaenium berggrenii and Ancylonema nordenskiöldii (Williamson et al, 2019), the species found on the GrIS, is dominated by phenolic compounds that absorb strongly across the visible wavelengths (Williamson et al, 2018;Remias et al, 2012) and obscure potentially diagnostic spectral features associated with other algal pigments (Cook et al, , 2019b.…”

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confidence: 99%

Algal growth and weathering crust structure drive variability in Greenland Ice Sheet ice albedo

Tedstone¹,

Cook²,

Williamson³

et al. 2019

Preprint

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One of the primary controls upon the melting of the Greenland Ice Sheet (GrIS) is albedo. There is a major difference in the albedo of snow-covered versus bare-ice surfaces, but observations also show that there is substantial spatio-temporal variability of up to ∼0.4 in bare-ice albedo. Variability in bare ice albedo has been attributed to a number of processes including the accumulation of Light Absorbing Impurities (LAIs) and the changing physical properties of the near-surface ice. However, the combined impact of these processes upon albedo remains poorly constrained. Here we use field observations to show 5 that among LAIs, pigmented glacier algae are ubiquitous and cause surface darkening both within and outside the southwest GrIS 'dark zone', but that other factors including modification of underlying ice properties by algal bloom presence, surface topography and weathering crust development are also important in determining patterns of daily albedo variability.We further use unmanned aerial system observations to examine the scale gap in albedo between ground versus remotelysensed measurements made by Sentinel-2 (S-2) and MODIS. S-2 observations provide a highly conservative estimate of algal 10 bloom presence because algal blooms occur in patches much smaller than the ground resolution of S-2 data. Nevertheless, the bare-ice albedo distribution at the scale of 20×20 m S-2 pixels is generally unimodal and unskewed. Conversely, bare ice surfaces have a left-skewed albedo distribution at MODIS MOD10A1 scales. Thus, when MOD10A1 observations are used as input to energy balance modelling then meltwater production can be under-estimated by ∼2%. Our study highlights that (1) the impact of physical ice surface processes is of similar importance to the direct darkening role of light-absorbing impurities 15 upon ice albedo and (2) there is a spatial scale dependency in albedo measurement which reduces detection of real changes at coarser resolutions.

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Remote sensing of albedo-reducing snow algae and impurities in the Maritime Antarctica

Cited by 52 publications

References 59 publications

Glacier algae foster ice-albedo feedback in the European Alps

Glacier algae foster ice-albedo feedback in the European Alps

Algal growth and weathering crust state drive variability in western Greenland Ice Sheet ice albedo

Algal growth and weathering crust structure drive variability in Greenland Ice Sheet ice albedo

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