Ice Algae Research Articles

Darkening of the Greenland Ice Sheet: Fungal Abundance and Diversity Are Associated With Algal Bloom.

Recent studies have highlighted the importance of ice-algal blooms in driving darkening and therefore surface melt of the Greenland Ice Sheet (GrIS). However, the contribution of fungal and bacterial communities to this microbially driven albedo reduction remains unconstrained. To address this significant knowledge gap, fungi were isolated from key GrIS surface habitats (surface ice containing varying abundance of ice algae, supraglacial water, cryoconite holes, and snow), and a combination of cultivation and sequencing methods utilized to characterize the algal-associated fungal and bacterial diversity and abundance. Six hundred and ninety-seven taxa of fungi were obtained by amplicon sequencing and more than 200 fungal cultures belonging to 46 different species were isolated through cultivation approaches. Basidiomycota dominated in surface ice and water samples, and Ascomycota in snow samples. Amplicon sequencing revealed that bacteria were characterized by a higher diversity (883 taxa detected). Results from cultivation as well as ergosterol analyses suggested that surface ice dominated by ice algae and cryoconite holes supported the highest fungal biomass (104–105 CFU/100 ml) and that many fungal taxa recognized as endophytes and plant pathogens were associated with dark ice characterized by a high abundance of ice algae. This paper significantly advances this field of research by investigating for the first time the fungal abundance and diversity associated with algal blooms causing the darkening of the GrIS. There is a strong association between the abundance and diversity of fungal species and the blooming of algae on the surface ice of the Greenland Ice Sheet.

オホーツク海紋別沖において採集した流氷中の微細藻類（アイスアルジー）の生物量と分類群組成（短報）

オホーツク海紋別沖において採集した流氷中の微細藻類（アイスアルジー）の生物量と分類群組成（短報）

Microbial Ecology of Snow Reveals Taxa-Specific Biogeographical Structure.

Snows that persist late into the growing season become colonized with numerous metabolically active microorganisms, yet underlying mechanisms of community assembly and dispersal remain poorly known. We investigated (Illumina MiSeq) snow-borne bacterial, fungal, and algal communities across a latitudinal gradient in Fennoscandia and inter-continental distribution between northern Europe and North America. Our data indicate that bacterial communities are ubiquitous regionally (across Fennoscandia), whereas fungal communities are regionally heterogeneous. Both fungi and bacteria are biogeographically heterogeneous inter-continentally. Snow algae, generally thought to occur in colorful algae blooms (red, green, or yellow) on the snow surface, are molecularly described here as an important component of snows even in absence of visible algal growth. This suggests that snow algae are a previously underestimated major biological component of visually uncolonized snows. In contrast to fungi and bacteria, algae exhibit no discernible inter-continental or regional community structure and exhibit little endemism. These results indicate that global and regional snow microbial communities and their distributions may be dictated by a combination of size-limited propagule dispersal potential and restrictions (bacteria and fungi) and homogenization of ecologically specialized taxa (snow algae) across the globe. These results are among the first to compare inter-continental snow microbial communities and highlight how poorly understood microbial communities in these threatened ephemeral ecosystems are.

Snow algae communities in Antarctica: metabolic and taxonomic composition.

Summary Snow algae are found in snowfields across cold regions of the planet, forming highly visible red and green patches below and on the snow surface. In Antarctica, they contribute significantly to terrestrial net primary productivity due to the paucity of land plants, but our knowledge of these communities is limited. Here we provide the first description of the metabolic and species diversity of green and red snow algae communities from four locations in Ryder Bay (Adelaide Island, 68°S), Antarctic Peninsula.During the 2015 austral summer season, we collected samples to measure the metabolic composition of snow algae communities and determined the species composition of these communities using metabarcoding.Green communities were protein‐rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Both communities also contained bacteria, protists and fungi.These data show the complexity and variation within snow algae communities in Antarctica and provide initial insights into the contribution they make to ecosystem functioning.

Melt Procedure Affects the Photosynthetic Response of Sea Ice Algae

The accuracy of sea ice algal production estimates is influenced by the range of melting procedures used in studies to obtain a liquid sample for incubation, particularly in relation to the duration of melt and the approach to buffering for osmotic shock. In this research, ice algal photophysiology from 14C incubations was compared in field samples prepared by three melt procedures: i) a rapid ≤ 4 h melt of the bottommost (< 1 cm) ice algal layer scraped into a large volume of filtered seawater (salinity 27 - 30), ii) melt of a bottom 5 cm section diluted into a moderate volume of filtered seawater over 24 h (salinity 20 - 24), and iii) melt of a bottom 5 cm section without any filtered seawater dilution over about 48 h (salinity 10 -12). Maximum photosynthetic rate, photosynthetic efficiency and production at zero irradiance were significantly affected by the melt treatment employed in experiments. All variables were greatest in the highly diluted scrape sample and lowest in the bulk-ice samples melted in the absence of filtered seawater. Laboratory experiments exposing cultures of the common sea ice diatom Nitzschia frigida to different salinities and light conditions suggested that the field-based responses can be attributed to the rapid (< 4 h) adverse effects of exposing cells to low salinities during melt without dilution. The observed differences in primary production between melt treatments were estimated to account for over 60% of the variability in production estimates reported for the Arctic. Future studies are strongly encouraged to replicate salinity conditions representative of in situ values during the melting process to minimize hypoosmotic stress, thereby most accurately estimating primary production.

Mismatch between microalgae and herbivorous copepods due to the record sea ice minimum extent of 2012 and the late sea ice break-up of 2013 in the Beaufort Sea

The unprecedented pace of warming of the Arctic Ocean affects a wide range of pelagic processes, from primary production to fish recruitment. Sequential sediment traps deployed on oceanographic moorings at the Beaufort Sea shelf break were used to investigate the impact of variations in physical conditions on the phenology of microalgae and herbivorous copepods. Water temperature, salinity, microalgal fluxes, and zooplankton fluxes were monitored over 6 of the 7 annual cycles from September 2009 to September 2016 with a hiatus from September 2013 to August 2014. Satellite-derived sea ice concentration and snow depth were retrieved for the same period. For 5 of the 6 cycles, a consistent interval between the vernal abundance of the Calanus species (C. glacialis and C. hyperboreus), the export of the ice alga Nitzschia frigida, and peak in nauplii abundance and diatom export, reflected a match between microalgae and herbivorous copepods. Drastic changes in water temperatures and ice conditions during the 2012–2013 cycle affected this synchronization. In 2012, the record sea ice minimum extent led to anomalously high upper water temperatures during autumn and winter that led to a shoaling of the vertical distribution of C. hyperboreus females and to the production of their nauplii at shallower depths several weeks before diatom export. Due to several oceanic and atmospheric forcing, the record sea ice minimum extent was followed in 2013 by a rebound in ice cover that delayed snowmelt, sea ice melt, and ice algae export. This delay resulted in a mismatch between C. glacialis females and N. frigida fluxes and in fewer C. glacialis nauplii in June and July 2013. These mismatch events likely had a negative impact on Calanus recruitment and on the subsequent transfer of energy to carnivorous zooplankton and fish. It is crucial to maintain mooring deployments to accurately assess the wide range of effects of climate warming on the marine ecosystems.

Abiotic degradation of highly branched isoprenoid alkenes and other lipids in the water column off East Antarctica

In some previous studies, the ratio between a di-unsaturated highly branched isoprenoid (HBI) lipid termed IPSO25 and a structurally related tri-unsaturated counterpart (HBI III) (viz. IPSO25/HBI III) has been used as a proxy measure of variable sea ice cover in the Antarctic owing to their production by certain sea ice algae and open water diatoms, respectively. To investigate this further, we quantified selected lipids and their photo- and autoxidation products in samples of suspended particulate matter (SPM) collected at different water depths in the polynya region west of the Dalton Iceberg Tongue (East Antarctica). The results obtained confirm the high efficiency of photo- and autoxidation processes in diatoms from the region. The systematic increase of the ratio IPSO25/HBI III with water depth in the current samples appeared to be dependent on the sampling site and was due to both (i) a relatively higher contribution of ice algae to the deeper samples resulting from their increased aggregation and therefore higher sinking rate, or (ii) a stronger abiotic degradation of HBI III during settling through the water column. Analyses of samples taken from the water-sediment interface and some underlying near-surface sediments revealed a further increase of the ratio IPSO25/HBI III, indicative of further differential oxidation of the more unsaturated HBI. Unfortunately, specific oxidation products of HBI III could not be detected in the strongly oxidized SPM and sediment samples, likely due to their lability towards further oxidation. In contrast, oxidation products of HBI III were detected in weakly oxidized samples of phytoplanktonic cells collected from Commonwealth Bay (also East Antarctica), thus providing more direct evidence for the involvement of photo- and/or autoxidation of HBI III in the region. This oxidative alteration of the ratio IPSO25/HBI III between their source and sedimentary environments might need to be considered more carefully when using this parameter for palaeo sea ice reconstruction purposes in the Antarctic.

Characteristics of particle fluxes in the Prydz Bay polynya, Eastern Antarctica

The settling of particulate carbon in seawater is a key component of the ocean carbon cycle. We deployed a set of sediment trap in the polynya of Prydz Bay from December 2010 to December 2011 to investigate the seasonal variations in particle fluxes. There was a clear seasonal variation in the particle fluxes, with maximum and minimum fluxes recorded during the summer and winter, respectively. The average total flux over the sampling period was 193.58 mg m−2 d−1, and the average fluxes of organic carbon (Corg), inorganic carbon (Cinorg), and biogenic silica (Sibio) were 721.78, 28.67, and 2382.80 μmol m−2 d−1, respectively. Sibio was the main contributor to the total mass flux, and strongly correlated with Corg. The high Sibio/Corg molar ratios (>1) suggest that Corg was transported to deep sea in association with Sibio. By comparing remote sensing data of sea ice and chlorophyll in the upper water column, we found that the dynamics of carbon fluxes were closely related to changes in sea ice. Algae in sea ice may have a key role in biological pump processes in early summer. Apart from the ice algae bloom period, variations in carbon fluxes generally corresponded with phytoplankton blooms in the upper water. The ballast effect controlled the particle settling velocity and the efficiency of the biological pump. Sea ice rafts initiated the first particle export event and enhanced the particle settling efficiency during melting period. As diatoms might become less dominant in the ice-free area, sea ice loss may cause the efficiency of the biological pump efficiency to decrease over the long term.

Exploring the composition of macromolecular organic matter in Arctic Ocean sediments under a changing sea ice gradient

Arctic sea ice has been affected by climate change, leading to reductions in summer sea ice extent over the past few decades, impacting nutrient dynamics, ocean temperature fluxes and the biological communities present in the ocean. Marine organic matter is a complex mixture of differentially degraded terrestrial and marine organisms from a range of sources and time periods. In this study pyrolysis-gas chromatography-mass spectrometry (Py-GC–MS) has been used to quantify the solvent-insoluble component of marine organic matter in surface sediments to gain a more holistic understanding of the macromolecular composition at five stations along a south to north transect in the Arctic Barents Sea, east of Svalbard (depths 288–334 m.b.s.l). Two methods were compared to identify the effectiveness of rapid screening, in contrast to grouping similar pyrolysis products. There were changes in macromolecular composition of marine surface sediments across the S-N transect using both methods, highlighting the varying benthic and pelagic communities north of the Polar Front and across the variable sea ice margin, corresponding to differing biological communities (e.g. fish, phytoplankton, ice algae, zooplankton). All five stations across the changing sea ice transect were interpreted as having primarily marine surface sediment macromolecular signatures, given their locations far from major terrestrial inputs and the more subtle changes when compared with previous investigations on the East Siberian Artic shelf. Fluctuations in macromolecular compositions across the transect included increasing N-containing compounds (including pyridines) and n-alkene/n-alkane doublet pyrolysis products from sediments collected in stations with the greatest average ice cover. If the future position of the Polar Front moves northwards then deposition of labile organic matter which appears to be efficiently processed will move further north, meaning greater deposition of organic carbon under areas of open ocean. Future research needs to understand how this OC will be buried and if it is regionally significant, given anticipated weakening stratification and a more Atlantic influenced northern Barents Sea.

Response of the Arctic Marine Inorganic Carbon System to Ice Algae and Under‐Ice Phytoplankton Blooms: A Case Study Along the Fast‐Ice Edge of Baffin Bay

AbstractPast research in seasonally ice‐covered Arctic seas has suggested that ice algae play a role in reducing dissolved inorganic carbon (DIC) during spring, preconditioning surface waters to low dissolved CO2 (pCO2sw), and uptake of atmospheric CO2 during the ice‐free season. The potential role of under‐ice phytoplankton blooms on DIC and pCO2sw has not often been considered. In this study we examined the inorganic carbon system beneath landfast sea ice starting midway through a bottom ice algae bloom and concluding in the early stages of an under‐ice phytoplankton bloom. During most of the ice algae bloom we observed a slight increase in DIC/pCO2sw in surface waters, as opposed to the expected reduction. Biomass calculations confirm that the role of ice algae on DIC/pCO2sw in the study region were minor and that this null result may be widely applicable. During snow melt, we observed an under‐ice phytoplankton bloom (to 10 mg/m3 Chl a) that did reduce DIC and pCO2sw. We conclude that under‐ice phytoplankton blooms are an important biological mechanism that may predispose some Arctic seas to act as a CO2 sink at the time of ice breakup. We also found that pCO2sw was undersaturated at the study location even at the beginning of our sampling period, consistent with several other studies that have measured under‐ice pCO2sw in late winter or early spring. Finally, we present the first measurements of carbonate saturation states for this region, which may be useful for assessing the vulnerability of a local soft‐shelled clam fishery to ocean acidification.

Taxonomic re-examination of "Chloromonas nivalis (Volvocales, Chlorophyceae) zygotes" from Japan and description of C. muramotoi sp. nov.

Recent molecular data has strongly suggested that field-collected cysts of snow algae that are morphologically identifiable as the zygotes of Chloromonas nivalis are composed of multiple species. Motile vegetative cells, however, have not been directly obtained from these cysts because of the difficulties involved in inducing their germination. Recently, our comparative molecular analyses, using both field-collected and cultured materials, demonstrated that one Japanese lineage of “C. nivalis zygotes” belongs to C. miwae. Herein, we examined another Japanese lineage of field-collected “C. nivalis zygotes” and a new strain originating from Japan. Our molecular data demonstrated that these two different life cycle stages are conspecific, and that they represent a new species that we herein describe as C. muramotoi sp. nov., based on the vegetative and asexual morphological characteristics of the strain. Multigene phylogenetic analyses showed that this new species was sister to C. miwae. Scanning electron microscopy demonstrated that the cysts of C. muramotoi are different from those of C. miwae, based on the arrangement of the flanges developing on the cell wall.

Analyzing carotenoids of snow algae by Raman microspectroscopy and high-performance liquid chromatography.

We tested the potential of Raman microspectroscopy to determine carotenoid pigments - both primary (lutein, beta-carotene) and secondary (astaxanthin) carotenoids - in the different species and life-cycle stages of snow algae from the order Chlamydomonadales (Chlorophyta). We compared the performance of Raman spectrometry to a reference method of biological pigment analysis, high-performance liquid chromatography (HPLC). The three main carotenoid Raman bands of the astaxanthin-rich red cysts were located at 1520, 1156 and 1006 cm-1. The shifts (orange aplanozygotes and green motile cells with flagella) in the position of the ν1(CC) Raman band of the polyenic chain is consistent with the expected changes in the ratios of the various carotenoid pigments. Flagellated green cells commonly contain lutein as a major carotenoid, together with minor amounts of β‑carotene and varying amounts of antheraxanthin, violaxanthin and neoxanthin. Aplanozygotes contain mixtures of both primary and secondary carotenoids. In most cases, the ν1(CC) band is an overlapping set of bands, which is due to the signal of all carotenoid pigments in the sample, and a deconvolution along with the band position shifts (mainly ν1) could be used to characterize the mixture of carotenoids. However, the ability of Raman spectroscopy to discriminate between structurally slightly differing carotenoid pigments or several carotenoids in an admixture in an unknown biological system remains limited.

Nieves penitentes are a new habitat for snow algae in one of the most extreme high-elevation environments on Earth

ABSTRACTNieves penitentes are pinnacle-shaped ice structures found at high elevations in the dry Andes. Here we report, using molecular and microscopic approaches, the first description of snow algae communities inhabiting penitente ice at 5,277 m a.s.l., demonstrating a new habitat for snow algae in one of the most extreme environments on Earth. Red ice patches on penitentes contained a microbial community dominated by algae in the genera Chlamydomonas and Chloromonas, both of which were closely related to known snow algae from alpine and polar environments. In contrast, we obtained few snow algae sequences from clear ice, but we did find cyanobacteria sequences and evidence of aeolian-deposited organic matter. Tephra (“soil”) within and just downhill from the penitente field hosted more complex bacterial and eukaryotic communities that were significantly different from ice communities in terms of both alpha and beta diversity. In this environment penitentes provide both water and shelter from harsh winds, high UV radiation, and thermal fluctuations, creating an oasis in an otherwise extreme landscape. Intriguingly, recent planetary investigations have suggested the existence of penitente-like structures on other planetary bodies of our solar system. Therefore, penitentes and the harsh environment that surrounds them provide a new terrestrial analog for astrobiological studies of life beyond Earth.

Enhanced bottom-ice algal biomass across a tidal strait in the Kitikmeot Sea of the Canadian Arctic

Sea ice algae are an important contributor of primary production in the Arctic ecosystem. Within the bottom-ice environment, access to nutrients from the underlying ocean is a major factor controlling production, phenology, and taxonomic composition of ice algae. Previous studies have demonstrated that tides and currents play an important role in driving the flux of nutrients to bottom-ice algal communities when biological demand during the spring bloom is high. In this study we investigate how surface currents under landfast first-year ice influence nutrient supply based on stoichiometric composition, algal chlorophyll a biomass and species composition during spring 2016, in Dease Strait, Nunavut. Stronger water dynamics over a shoaled and constricted strait dominated by tidal currents (tidal strait) supported turbulent flow more than 85% of the deployment duration in comparison to outside the tidal strait in an embayment where turbulent flow was only evidenced a small percentage (&amp;lt;15%) of the time. The system appeared to be nitrate-depleted with surface water concentrations averaging 1.3 μmol L–1. Increased currents were correlated significantly with a decrease in ice thickness and an increase in ice algal chlorophyll a. Furthermore, pennate diatoms dominated the ice algal community abundance with greater contribution within the strait where currents were greatest. These observations all support the existence of a greater nutrient flux to the ice bottom where currents increased towards the center of the tidal strait, resulting in an increase of bottom ice chlorophyll a biomass by 5–7 times relative to that outside of the strait. Therefore, expanding beyond the long identified biological hotspots of open water polynyas, this paper presents the argument for newly identified hotspots in regions of strong sub-ice currents but persistent ice covers, so called “invisible polynyas”.

Upward transport of bottom-ice dimethyl sulfide during advanced melting of arctic first-year sea ice

This paper presents the first empirical estimates of dimethyl sulfide (DMS) gas fluxes across permeable sea ice in the Arctic. DMS is known to act as a major potential source of aerosols that strongly influence the Earth’s radiative balance in remote marine regions during the ice-free season. Results from a sampling campaign, undertaken in 2015 between June 2 and June 28 in the ice-covered Western Baffin Bay, revealed the presence of high algal biomass in the bottom 0.1-m section of sea ice (21 to 380 µg Chl a L–1) combined with the presence of high DMS concentrations (212–840 nmol L–1). While ice algae acted as local sources of DMS in bottom sea ice, thermohaline changes within the brine network, from gravity drainage to vertical stabilization, exerted strong control on the distribution of DMS within the interior of the ice. We estimated both the mean DMS molecular diffusion coefficient in brine (5.2 × 10–5 cm2 s–1 ± 51% relative S.D., n = 10) and the mean bulk transport coefficient within sea ice (33 × 10–5 cm2 s–1 ± 41% relative S.D., n = 10). The estimated DMS fluxes ± S.D. from the bottom ice to the atmosphere ranged between 0.47 ± 0.08 µmol m–2 d–1 (n = 5, diffusion) and 0.40 ± 0.15 µmol m–2 d–1 (n = 5, bulk transport) during the vertically stable phase. These fluxes fall within the lower range of direct summer sea-to-air DMS fluxes reported in the Arctic. Our results indicate that upward transport of DMS, from the algal-rich bottom of first-year sea ice through the permeable sea ice, may represent an important pathway for this biogenic gas toward the atmosphere in ice-covered oceans in spring and summer.

Temporal evolution of IP25 and other highly branched isoprenoid lipids in sea ice and the underlying water column during an Arctic melting season

In recent years, certain mono- and di-unsaturated highly branched isoprenoid (HBI) alkene biomarkers (i.e., IP25 and HBI IIa) have emerged as useful proxies for sea ice in the Arctic and Antarctic, respectively. Despite the relatively large number of sea ice reconstructions based on IP25 and HBI IIa, considerably fewer studies have addressed HBI variability in sea ice or in the underlying water column during a spring bloom and ice melt season. In this study, we quantified IP25 and various other HBIs at high temporal and vertical resolution in sea ice and the underlying water column (suspended and sinking particulate organic matter) during a spring bloom/ice melt event in Baffin Bay (Canadian Arctic) as part of the Green Edge project. The IP25 data are largely consistent with those reported from some previous studies, but also highlight: (i) the short-term variability in its production in sea ice; (ii) the release of ice algae with high sinking rates following a switch in sea ice conditions from hyper- to hyposaline within the study period; and (iii) the occurrence of an under-ice phytoplankton bloom. Outcomes from change-point analysis conducted on chlorophyll a and IP25, together with estimates of the percentage of ice algal organic carbon in the water column, also support some previous investigations. The co-occurrence of other di- and tri-unsaturated HBIs (including the pelagic biomarker HBI III) in sea ice are likely to have originated from the diatom Berkeleya rutilans and/or the Pleurosigma and Rhizosolenia genera, residing either within the sea ice matrix or on its underside. Although a possible sea ice source for HBIs such as HBI III may also impact the use of such HBIs as pelagic counterparts to IP25 in the phytoplankton marker-IP25 index, we suggest that the impact is likely to be small based on HBI distribution data.

Snow algae drive productivity and weathering at volcanic rock-hosted glaciers

Abstract Earth has experienced periodic local to global glaciation for nearly 3 billion years, providing supra- and subglacial environments for colonization by microbial communities. A number of studies have reported on the role of microbial communities in glacial ecosystems including their influence on element cycling and weathering, but there is a paucity data on volcanic rock-hosted glacial ecosystems. Glaciers on stratovolcanoes in the Pacific Northwest override silica-rich rocks which represent analogues to an early Martian cryosphere. On these glaciers, blooms of photosynthetic snow algae support supraglacial microbial communities as has been observed on snowfields, glaciers, and ice sheets. In subglacial environments of volcanic rock-hosted glacial systems, weathering is driven, at least in part, by carbonic acid, suggesting a link between supraglacial carbon sources and subglacial heterotrophic microbial communities. Here, we report inorganic carbon assimilation and microbial community composition on glaciers across three stratovolcanoes ranging in composition from dacitic to mafic in the Pacific Northwest of the United States to begin to constrain the role of supraglacial primary productivity in subglacial weather processes. These data, coupled to contextual carbon and nitrogen isotope analyses of biomass and aqueous geochemistry, indicate snow algae drive light dependent carbon uptake across supraglacial and periglacial environments. Furthermore, snow algae microbial communities are supported by fixed nitrogen predominantly from deposition via precipitation. Our data highlight intense cycling of carbon and nitrogen driven by supraglacial microbial communities that feeds subglacial microbial communities which in turn may drive weathering processes. These results further underscore the role of glacial ecosystems in global biogeochemical cycling, especially during past global glaciations. Finally, these results lend support for glaciers as refugia for biodiversity on Earth and potentially on other bodies such as Mars where evidence exists for widespread and long-lived cryosphere including glaciers and ice sheets.

Seasonal and spatial variability of sea ice and phytoplankton biomarker flux in the Chukchi sea (western Arctic Ocean)

Sediment traps were deployed at 870 m water-depth from August 2008 to September 2009 at station DM in the Chukchi Sea (western Arctic Ocean) in an area covered by sea ice in winter to determine seasonal fluxes of HBIs and phytoplankton sterols in order to improve our understanding of sea ice proxies. HBI-III fluxes and PIIIIP25 are for the first time documented in the Arctic Ocean to evaluate their significance for paleoclimate reconstructions. Highest mass fluxes were found from mid-July 2009 to September 2009 contrasting with low values during all other months (i.e., December 2008 to early July 2009). Indeed, during the winter months IP25 was not detected but increased by a factor of nine over summer 2009 reflecting sea ice algae and pelagic phytoplankton production at the sea ice edge. High HBIs and low sterol fluxes at the end of summer 2008 are consistent with the complete melting of sea ice and post-bloom conditions. We found that HBI-III was more abundant in the early stage of sea ice retreat that characterizes the marginal ice zone. These sea ice biomarkers were also measured in surface sediments across a wide range of sea ice cover in the western Arctic region. Higher IP25 values were found in the southeastern Chukchi Sea and decreased westwards where sea ice conditions are less severe. Stronger positive linear relationship were found between the sea ice proxy indexes PBIP25 and PIIIIP25 and spring sea ice concentrations than with IP25 in agreement with earlier findings from other Arctic and sub-Arctic regions.

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

Snow algae have been proposed to play a key role in climate change as they can reduce albedo (“bioalbedo”) and thus accelerate the melting of snow and ice fields. Although satellite-derived data has opened opportunities for larger scale observations, remote sensing of snow algae has been scarce and is methodologically challenging due to the presence of other light-absorbing impurities (LAIs). So far the studies on the role of LAIs in reducing albedo and increasing melting have been strongly focused on the Arctic ice sheets. The aims of the present study were to compare the relative impact of microalgae and other LAIs in reducing albedo in the snow of Fildes Peninsula, King George Island, Maritime Antarctica, using Spectral Mixture Analysis (SMA), which allows mapping sub-pixel fractions of multiple components in mixed pixels from satellite-derived data (Sentinel-2A). Also, the applicability of band ratios previously proposed for classifying snow algae (Red-Green band ratio) and impurities (Snow Darkening Index (SDI)) was tested and compared with SMA. Ground validation was made by characterizing the composition of snow algae (through chlorophyll a fluorescence) and by measurements of spectral absorption of solar radiation in red and green snow. SMA resulted a reliable method to classify snow algae and impurities with low amount of false positives (user accuracy 92–93%). However, omission error derived from dominant type (>50% abundance) confusion matrix was higher (producer accuracy for algae 63% and impurity 53%). In contrast, classification with band ratios resulted in large number of false positives (user accuracy for SDI 36%, for R/G 46%), and even higher omission error for R/G (producer accuracy 36%), whereas SDI had better producer accuracy (68%). SMA provided higher precision in separating dominant LAIs than the band ratios, which resulted in widely overlapping signals. Reduced albedo could be related with SMA-derived snow algae and impurity abundancies at albedo levels >45% for algae and >30% for impurities.

Mapping Ice Algal Blooms in Southwest Greenland From Space

AbstractQuantifying the distribution and abundance of ice algae is fundamental for understanding the evolving processes of algal blooms in supraglacial environments, particularly over the Greenland ice sheet, given the role of algal impurities in modulating surface albedo and meltwater production. Field observations of ice algae in Greenland are very limited over space and time. Here we show for the first time the regional variability in algal abundance across the dark zone in southwest Greenland, derived from Sentinel‐3 images acquired during the summertime in 2016 and 2017. We demonstrate the capacity of Sentinel‐3 imagery to characterize the spatial pattern of algal abundance using the reflectance ratios between 709‐ and 673‐nm bands, highly consistent with field measurements. The estimated algal abundance reveals a significant linear growth pattern of algal population with time after the peak of dark ice presence, shown to be tightly linked to surface runoff and meltwater production.