Spectral Characterization, Radiative Forcing, and Pigment Content
of Coastal Antarctic Snow Algae: Approaches to Spectrally
Discriminate Red and Green Communities and Their Impact on
Snowmelt

Khan, Alia L.; Dierssen, Heidi M.; Scambos, T. A.; Höfer, Juan; Cordero, Raúl R.

doi:10.5194/tc-2020-170

Cited by 9 publications

(16 citation statements)

References 46 publications

(80 reference statements)

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“…Our work builds upon previous use of Sentinel 2 imagery to study snow algae in Antarctica (Huovinen et al, 2018;Gray et al, 2020;Khan et al, 2020Khan et al, , 2021 and shows the advantage gained by using high spatial and spectral resolution satellites, such as WorldView 2 or 3. Figure 12 compares snow algae identified through the methodology presented here, with that used in Gray et al (2020), which used coarser-resolution Sentinel 2 satellite imagery.…”

Section: Worldview Satellites To Map Snow Algaementioning

confidence: 82%

“…Moreover, this analysis focused only on a snapshot of growth from 1 year's worth of imagery at each bloom location. The problem of red bloom detection in Sentinel 2 imagery has been somewhat addressed by the work of Khan et al (2020), yet large uncertainties remain when deriving area and biomass estimates from 10 m spatial resolution pixels. Key to using remotely sensed observations to study Antarctic terrestrial ecology lies in this balance between spatial resolution and area coverage.…”

Section: Introductionmentioning

confidence: 99%

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Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites

et al. 2021

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Snow algae are an important group of terrestrial photosynthetic organisms in Antarctica, where they mostly grow in low lying coastal snow fields. Reliable observations of Antarctic snow algae are difficult owing to the transient nature of their blooms and the logistics involved to travel and work there. Previous studies have used Sentinel 2 satellite imagery to detect and monitor snow algal blooms remotely, but were limited by the coarse spatial resolution and difficulties detecting red blooms. Here, for the first time, we use high-resolution WorldView multispectral satellite imagery to study Antarctic snow algal blooms in detail, tracking the growth of red and green blooms throughout the summer. Our remote sensing approach was developed alongside two Antarctic field seasons, where field spectroscopy was used to build a detection model capable of estimating cell density. Global Positioning System (GPS) tagging of blooms and in situ life cycle analysis was used to validate and verify our model output. WorldView imagery was then used successfully to identify red and green snow algae on Anchorage Island (Ryder Bay, 67°S), estimating peak coverage to be 9.48 × 104 and 6.26 × 104 m2, respectively. Combined, this was greater than terrestrial vegetation area coverage for the island, measured using a normalized difference vegetation index. Green snow algae had greater cell density and average layer thickness than red blooms (6.0 × 104 vs. 4.3 × 104 cells ml−1) and so for Anchorage Island we estimated that green algae dry biomass was over three times that of red algae (567 vs. 180 kg, respectively). Because the high spatial resolution of the WorldView imagery and its ability to detect red blooms, calculated snow algal area was 17.5 times greater than estimated with Sentinel 2 imagery. This highlights a scaling problem of using coarse resolution imagery and suggests snow algal contribution to net primary productivity on Antarctica may be far greater than previously recognized.

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Section: Worldview Satellites To Map Snow Algaementioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites

et al. 2021

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“…Snow-covered surfaces in the interior of the Antarctic continent can enhance the downwelling UV irradiance by up to 50% due to the extremely high albedo (about 95% in the UV part of the spectrum) 36 . Although the albedo is considerably lower at coastal sites on King George Island, where the snow is often thin and patchy in late spring 37 , it may have contributed to enhance the surface UV over the period Nov. 24th–Dec. 4th.…”

Section: Resultsmentioning

confidence: 99%

Persistent extreme ultraviolet irradiance in Antarctica despite the ozone recovery onset

Cordero

Féron

Damiani

et al. 2022

Sci Rep

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Attributable to the Montreal Protocol, the most successful environmental treaty ever, human-made ozone-depleting substances are declining and the stratospheric Antarctic ozone layer is recovering. However, the Antarctic ozone hole continues to occur every year, with the severity of ozone loss strongly modulated by meteorological conditions. In late November and early December 2020, we measured at the northern tip of the Antarctic Peninsula the highest ultraviolet (UV) irradiances recorded in the Antarctic continent in more than two decades. On Dec. 2nd, the noon-time UV index on King George Island peaked at 14.3, very close to the largest UV index ever recorded in the continent. On Dec. 3rd, the erythemal daily dose at the same site was among the highest on Earth, only comparable to those recorded at high altitude sites in the Atacama Desert, near the Tropic of Capricorn. Here we show that, despite the Antarctic ozone recovery observed in early spring, the conditions that favor these extreme surface UV events persist in late spring, when the biologically effective UV radiation is more consequential. These conditions include long-lasting ozone holes (attributable to the polar vortex dynamics) that often bring ozone-depleted air over the Antarctic Peninsula in late spring. The fact that these conditions have been occurring at about the same frequency during the last two decades explains the persistence of extreme surface UV events in Antarctica.

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“…Thus, natural selection appears to favor albedo-reducing pigmentation that strikes a balance between melt-inducing coloration and all-absorbing black that would overheat cells and disrupt their function (Dial et al, 2018). Because snow and ice algae generate liquid from frozen water, a positive feedback loop between them and the ice features they inhabit may be critical to cryosphere decline (Anesio et al, 2017;Ganey et al, 2017;Hotaling et al, 2017b;Khan et al, 2020;Stibal et al, 2012;Takeuchi, 2009). However, snow and ice algae contribution to BAR is highly variable.…”

Section: Snow and Ice Algaementioning

confidence: 99%

Biological albedo reduction on ice sheets, glaciers, and snowfields

Hotaling¹,

Lutz²,

Dial³

et al. 2021

Preprint

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The global cryosphere, Earth's frozen water, is in precipitous decline. The ongoing and predicted impacts of cryosphere loss are diverse, ranging from disappearance of entire biomes to crises of water availability. Covering approximately one-fifth of the Earth, mass loss from the terrestrial cryosphere is driven primarily by a warming atmosphere but reductions in albedo (the proportion of reflected light) also contribute by increasing absorption of solar radiation. In addition to dust and other abiotic impurities, biological communities substantially reduce albedo worldwide. In this review, we provide a global synthesis of biological albedo reduction (BAR) in terrestrial snow and ice ecosystems. We first focus on known drivers-algal blooms and cryoconite (granular sediment on the ice that includes both mineral and biological material)-as they account for much of the biological albedo variability in snow and ice habitats. We then consider an array of potential drivers of BAR whose impacts may be overlooked, such as arthropod deposition, resident organisms (e.g., dark-bodied glacier ice worms), and larger vertebrates, including humans, that visit the cryosphere. We consider both primary (e.g., BAR due to the presence of pigmented algal cells) and indirect (e.g., nutrient addition from arthropod deposition) effects, as well as interactions among biological groups (e.g., birds feeding on ice worms). Collectively, we highlight that in many cases, overlooked drivers and interactions among factors have considerable potential to alter BAR, perhaps rivaling the direct effects of algal blooms and cryoconite. We conclude by highlighting knowledge gaps for the field and detailing a global framework for long-term BAR monitoring. Introduction:The global cryosphere-the compilation of Earth's frozen water-is in rapid, accelerating decline (IPCC, 2019). Covering approximately one-fifth of the Earth's surface at present, mass loss from the terrestrial cryosphere is driven primarily by a warming atmosphere (Fountain et al., 2012;Hock et al., 2019). Over the last 50 years, spring snow cover on land in the Arctic has

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Spectral Characterization, Radiative Forcing, and Pigment Content of Coastal Antarctic Snow Algae: Approaches to Spectrally Discriminate Red and Green Communities and Their Impact on Snowmelt

Cited by 9 publications

References 46 publications

Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites

Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites

Persistent extreme ultraviolet irradiance in Antarctica despite the ozone recovery onset

Biological albedo reduction on ice sheets, glaciers, and snowfields

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