Sea ice primary production is a key component supplying carbon to higher trophic levels when few other resources are available. In bottom-ice habitats, this production is limited by light availability and nutrient supply from underlying seawater. Reports of low sea ice primary production from Greenland have reinforced the view that landfast ice is regionally unimportant. Here, we document a single early-spring observation of intense algal production in sea ice adjacent to marine terminating glaciers in West Greenland, an environment rarely examined in ice studies. The bloom included abundant pennate diatoms, including Nitzschia frigida, and reached a daily primary production of 146 ± 4.8 mg C m⁻² d⁻¹ and biomass accumulation of 42.4 ± 1.6 mg Chlorophyll a (Chl a) m⁻², exceeding previous Greenland observations. A biomass-specific production of 3.40 mg C mg Chl a⁻¹ d⁻¹ and maximum quantum yield (ΦPSII_max) of 0.44 indicated an active community. Strong silicic acid depletion in the presence of significant nitrate and phosphate concentrations suggested that silicic acid was the primary limiting nutrient within the ice. We propose that inflow-driven fjord circulation likely enhanced nutrient availability beneath the ice, while turbulence-driven fluxes across the ice-ocean interface represent a plausible mechanism for sustaining the observed high sympagic production during this sampling event. Sea ice in fjords with marine-terminating glaciers may therefore support high early-season production under favorable local conditions.

Across much of the Arctic, climate warming has reduced the extent of thicker and more persistent sea ice and increased the prevalence of thinner first-year ice. Thin first-year landfast sea ice is ecologically important because reduced ice thickness can increase light transmission to the ice–water interface, while the associated brine conditions, including salinity and permeability, can strongly influence algal biomass accumulation and photophysiology. This thin (0.24–0.55 m), short-lived, seasonal, first-year landfast sea ice already dominates Nuup Kangerlua fjord, southwest Greenland, making it a useful natural example of ice conditions that may become more common in parts of the future Arctic. We focused on late February–early March because this period captures the seasonal transition from very low winter irradiance toward increasing spring light, when sea ice algal communities begin photosynthetic acclimation prior to the main bloom period. Using this site as an example of future Arctic-like conditions, we investigated chlorophyll a (Chl a) concentration and the photobiology of sea ice algal communities during five sampling events between 2017 and 2022. The vertical distribution of Chl a concentration and photobiological parameters measured with variable chlorophyll fluorescence differed between years, as did Chl a concentrations, with integrated biomass ranging from 0.08 to 0.78 mg Chl a m−2. Direct under-ice PAR measurements showed transmittance values ranging from 0.013 to 0.29. Bottom-ice communities were acclimated to relatively high light intensities, with Ek often exceeding 200 µmol photons m−2 s−1, and we detected no clear evidence of photoinhibition in the fluorescence data. Boosted regression tree models identified brine salinity as the main predictor of both Chl a concentration, explaining 42.0% of the variation, and, ΦPSII_max, the maximum dark-adapted photosynthetic efficiency, explaining 86.1% of the variation. Both parameters decreased exponentially with increasing sea ice brine salinity (p < 0.0001), indicating that higher brine salinity was associated with reduced algal biomass and lower photosynthetic efficiency. These results show that short-lived first-year landfast sea ice can support physiologically active sea ice algal communities despite relatively low biomass, and suggest that algal performance in this ice type was more strongly associated with brine salinity during the late-winter to early spring sampling period, while light availability also varied substantially among years. As thin and short-lived sea ice conditions become more common in parts of the Arctic, this habitat may represent an increasingly important, though temporally variable, component of Arctic marine primary production.

Sea ice physical, biological, and chemical properties vary across a wide range of spatial scales, from meters to hundreds or thousands of meters. This spatial variability is commonly attributed to differ-ences in air and ice temperatures, light availability, snow cover thickness, grazing by protozoa, and ocean currents. In situ time series experiments on sea ice are widely used to examine temporal changes in ice algal biomass and photo-physiology in response to specific drivers and light particu-larly. A key assumption in such studies is that observed temporal changes reflect changes in the driving factors rather than spatial variability within the experimental area. Here, we investigate the spatial variability of sea ice physical, chemical properties, ice algal biomass, and algal photobiology at the small spatial scale commonly applied in in situ experiments. Measurements were conducted at 16 sites within a 6 × 6 m plot on land-fast first-year sea ice in Malene Bight, SW Greenland. Sea ice temperature, bulk salinity, Chlorophyll a concentration, and photobiological parameters derived from Pulse Amplitude Modulated (PAM) fluorometry were assessed on the bottom 5 cm of sea ice along with snow depth and sea ice thickness. No statistically significant spatial variability was de-tected for any of the measured parameters, but significant negative correlations were observed be-tween snow depth and maximum quantum yield (ΦPSII_max), and between snow depth and ice thick-ness. The ice algal community was dominated by flagellates (50.4

Nutrient inputs from upwelling, ocean currents, advection, and terrestrial sources play a crucial role in driving primary production in Arctic fjords and coastal areas. This study analyzes more than two decades of field measurements across a terrestrial-river-coastal continuum in Arctic Greenland, showing how shifts in coastal inflows, glacial meltwater, and terrestrial inputs control changes in nutrient dynamics in the fjord. Our data indicate oligotrophication, with nitrate concentrations decreasing by similar to 49% and phytoplankton biomass by similar to 60% over the study period. These changes are associated with a similar to 12% increase in catchment vegetation greening, which likely reduced terrestrial nitrate input to the fjord by similar to 65%. Nutrient dynamics in the fjord were also influenced by inflows of fresher coastal waters, providing nitrate-poor, silicate-rich waters. Silicate concentrations in the fjord have risen by similar to 115% over the past two decades, suggesting increased input from all these sources. Whether these patterns are unique to this fjord or representative of broader Arctic trends remains uncertain and our study highlights the need to further explore the cross-boundary ecological impacts of climate change on Arctic marine and coastal ecosystems.

The dramatic loss of sea ice due to global warming is changing light conditions for marine primary production, but exactly how is not well understood. Previous studies revealed that small peaks in the absorption spectrum of liquid water, due to molecular vibrations of H2O, delineate a series of spectral niches for aquatic photosynthesis. Ice, however, has a smoother absorption spectrum and scatters light much more strongly than liquid water. Here, we show with a radiative transfer model that the loss of sea ice causes a pronounced blue shift, narrowing light spectra in the euphotic zone to shorter wavelengths. Furthermore, ice cover yields a smooth continuum of light spectra, whereas open water creates distinct spectral niches selecting for phytoplankton species with different photosynthetic pigments. These results indicate that the loss of sea ice will cause major changes in both the pigment and species composition of primary producers in polar ecosystems.

Aerosols, including biological aerosols, exert a significant influence on cloud formation, influencing the global climate through their effects on radiative balance and precipitation. The Arctic region features persistent mixed-phase clouds, which are impacted by ice nucleating particles (INPs) that modulate the phase transitions within clouds, affecting their lifetime and impacting the region's climate. An increasing number of studies document that Arctic soils harbor numerous biogenic INPs (bioINPs), but these have yet to be linked to their microbial producers. In addition, the transfer of bioINPs from soils into freshwater and marine systems has not been quantified. This study aimed to address these open questions by analyzing soil and freshwater samples from northeast Greenland to determine the microbial composition along with the INP concentrations and size distributions. We found that soils contained between 3.19×104 and 1.55×106 INP g−1 soil, which was on the lower side of what has previously been reported for active-layer soils. The composition of INPs varied widely across locations and could have originated from bacterial and fungal sources. We detected Mortierella, a fungal genus known to produce ice nucleating proteins, at nearly all locations. Spearman correlations between soil taxa and INP concentrations pointed at lichenized fungi as a possible contributor to soil INP. Additionally, based on the INP size distribution, we suggest that soil INPs were bound to soil particles or microbial membranes at some locations, while other locations showed a variety of soluble INPs with different molecular sizes. In streams, INP concentrations were comparable to what has previously been measured in streams from temperate regions. Interestingly, stream INP concentrations showed a positive association with soil INP concentrations. The potential release and aerosolization of these bioINPs into the atmosphere – whether directly from the soil, from streams into which they are washed, or from the oceans where they might be transported – could impact cloud formation and precipitation patterns in the Arctic. This research contributes valuable knowledge to the understanding of microbial communities and the potential microbial producers of highly active bioINPs in Arctic soils and their connectivity with Arctic streams.

Open water leads in the sea ice covering the Polar regions are becoming more frequent and cover larger areas as a result of the warming and thinning of the ice. Refreezing of the leads advances the occurrence of young and newly formed sea ice (nilas), which has a thickness of < 10 cm and is characterized by a highly saline surface brine. Due to the growth of fragile frost flowers exposed at its surface, nilas can become a significant source of bromine, mercury, sea salt aerosols, bioaerosols, and ice nucleating particles for the atmosphere. Here we report the results of a study where we investigated the initial formation phase of a 3-6 mm-thick nilas in cleared sea ice ponds. Samples for quantifications of macronutrients, microorganisms, Chlorophyll a (Chl a) and photobiology were collected from seawater, nilas, and brine 5 and 24 h, after the experiment commenced. The concentration changes between constituents were scaled relative to changes in salinity with the enrichment index (I). Nilas was enriched in microalgae and Chl a and the brine was highly enriched in bacteria, virus like particles (VLPs) and algae after only 5 h. We did not find a significant further enrichment between 5 and 24 h of nilas formation. This indicates that the initial formation phase of the nilas is an important step in distributing nutrients and microorganisms in nilas and brine. Only particulate matter was enriched in nilas and brine and none of the macronutrients. Photosynthetic microalgae were strongly impaired in the nilas and the brine, where no fluorescence signal could be detected supposedly due to a combination of excessive light at the surface and high brine salinity. The reasons for the observed differences in enrichments are evaluated and discussed including concentration of particulate matter, evaporation of surface brine, microbial growth and concentration of microorganisms in the sea surface microlayer (SML). Further studies are needed to decipher which of the proposed mechanisms were predominantly responsible for the observed enrichments as well as how these enrichments affect firstly the frost flowers and secondly the atmosphere.

Light attenuation is of fundamental importance for photosynthesis in marine and freshwater environments and quantified as Kd(PAR). A 30-year (1992-2021) long time-series of Kd(PAR) (n = 945) from Aarhus Bay, at the North Sea - Baltic Sea transition obtained with 1-5 measurements per month is analyzed. The time-series showed a weak but not statistically significant positive trend with an average Kd(PAR) of 0.30 +/- 0.08 m-1. Monthly based time-series of Kd(PAR) showed, in comparison, significant differences with average maximum values in March of 0.38 +/- 0.09 m-1 compared to a minimum in June of 0.26 +/- 0.03 m-1. There were statistically significant positive Kd(PAR) trends in April and December and a negative trend in October. Accordingly, the depth limit of eelgrass and macroalgae decreased from 8 to 5 m in April. The strong variability in Kd(PAR) in February and March related to the phytoplankton spring bloom in Aarhus Bay both in timing and strength, given the strong and significant correlation between Chl a and Kd(PAR). Partitioning showed that non-Chl a attenuation related to CDOM and suspended matter increased from 0.20 m-1 to 0.29 m-1 between 1992 and 2007 but was constant from then on. The Chl a specific attenuation coefficient varied around an average of 0.019 +/- 0.008 m2 (mg Chl a)-1 and showed only small variations over time. The frequency of CTD casts and light measurements decreased between 1992 (n = 52 per year) and 2022 (n = 15 per year) but no parallel trends in average Kd(PAR) were observed. No significant trend (1992-2021) in annual average Chl a concentrations in Aarhus Bay was detected. The importance of high-resolution measurements in time are emphasized and at least monthly to track the strong seasonal variation.

The sea ice spring bloom is crucial for sustaining Arctic marine food webs, with sea ice algae serving as primary carbon sources for higher trophic levels. Despite the prevailing dominance of diatom species in sea ice spring blooms, our study highlights a notable deviation, showcasing a bloom driven by dinoflagellates. Through field sampling of first-year sea ice cores and subsequent analysis of physical and biogeochemical parameters, combined with amplicon sequencing of the 18S rRNA gene, we investigated the occurrence and implications of this significant dinoflagellate bloom, with a particular focus on Polarella glacialis. Our findings reveal that high irradiances at the top of the ice core, coupled with elevated nutrient availability and warm ice conditions, are key drivers of this phenomenon, as elucidated by redundancy analysis. Moreover, our results suggest a potential climate-driven decline in snow cover on sea ice, increased open leads, and thinner sea ice, which may favor the proliferation of dinoflagellates over diatoms. This alternative dinoflagellate-dominated bloom could have profound ecological consequences, given the enriched omega-3 fatty acid content of dinoflagellates, thereby influencing energy transfer within the Arctic marine food web. Furthermore, our study identifies the presence of not only Polarella glacialis but also Chytridinium, an ectoparasite on copepod eggs, and the green algae Ulothrix in relatively high abundances within the sea ice. These findings shed light on the intricate interplay between environmental factors and microbial community dynamics within Arctic sea ice ecosystems.

The novel concept of the review is a focus on the organisms living in the sea ice and what mechanisms they have developed for their existence. The review describes the physical environment of the sea ice and the microorganisms living there as microalgae, bacteria, virus, fungi, meio- and macrofauna where they inhabit the brine channels and exposed to low temperatures as down to −25 °C and high salinities—up to 300. Nutrients, O2, CO2, pH, light, and UV are also identified as stressors regarding the metabolism of the microorganisms. It is argued that sea ice must be recognized as an extreme environment as based on records of very high or very low concentrations or intensities of the stressors that living organisms in the ice are exposed to and able to endure. Each taxonomic group of organisms in the sea ice are dealt with in detail in terms of the explicit stressors the group is exposed to, and specifically what known mechanisms that the organisms have amended to secure existence and life. These mechanisms are known for some group of organisms as autotrophs, bacteria, meio- and macrofauna but less so for virus and fungi. The review concludes that sea ice is an extreme environment where the stressors vary significantly in both space and time, both in consort and solitary, classifying organisms living there as polyextremophiles and extremophiles. The review relates further to extraterrestrial moons covered with sea ice and these habitats and points toward sea ice on Earth for prospective studies until further technological advances.

The Arctic is a region that is particularly vulnerable to climate change, as it is warming at a much faster rate than the rest of the globe. This warming causes a decline in multiyear sea ice cover, which results in an increase in ice-free waters with a much lower albedo compared to ice, therefore leading to a positive feedback and enhanced warming. Another factor that plays a role in regulating the temperature in the Arctic is the type and extent of cloud cover. Aerosols, that can serve as cloud condensation nuclei or ice nucleating particles (INPs), are key for cloud formation and aggregation state of water; liquid or ice. Some microorganisms produce INPs, but it is not well understood which microorganisms are most relevant, which environments they inhabit, and how active they are. In this study, we investigated the partitioning of INPs between the Arctic marine and atmospheric environment by combining in situ measurements with laboratory experiments, deploying cold-stage INP measurements and amplicon sequencing of the bacterial and eukaryotic communities. First, we determined if sea ice acts as a reservoir for INPs and, whether the INPs are partitioned into the sea ice during its formation or whether they are produced by microorganisms within the sea ice. We used a modified ice-finger to grow sea ice using sea water collected in West Greenland. We found that INPs are not enriched in the ice, but they stochastically incorporate into the ice fraction during sea ice formation. Next, we studied the temporal and spatial dynamics of INPs in Arctic sea ice cores that were collected before and during the spring sea ice phytoplankton bloom. We observed a higher concentration of INPs active at -10 °C (INP-10) present towards the bottom of the sea ice core with concentrations 10-100-fold higher than those in the under-ice water. Finally, we determined the potential of sea-ice as a source of atmospheric INP. In separate experiments, we filled bulk water and water from melted sea ice from Nuuk and Station Nord into a temperature-controlled sea spray simulation chamber and quantified the microorganisms and INPs present in the bulk water and air before and after the water bubbling. We observed that the highly active INPs are efficiently aerosolized by bubble-bursting together with specific bacterial and eukaryotic taxa. In light of these findings, this study provides new insights into the role of Arctic sea ice as a reservoir for INPs and the microorganisms that potentially produce them. Additionally, it explores the mechanisms by which INPs are released into the Arctic atmosphere. Last, these results can be used to improve cloud and climate model predictions in the Arctic region.

Land-terminating glaciers and submarine melting of marine-terminating glaciers are significant fea-tures in Arctic regions and are foreseen to become more frequent as marine-terminating glaciers ultimately develop into a land-terminated state. A transition driven by the continuous rise in Arctic air temperatures, and emphasizes the importance of studies of land-terminating glaciers their bio-optical properties and biogeochemistry. Kangerlussuaq in west Greenland with a land-terminating glaciers and was selected for this study. During a research cruise we measured spectral and PAR attenuation, particulate matter concentrations, salinity, nutrient concentrations, Chla, and phytoplank-ton species composition, along a transect from river outlet to open marine waters. Results showed that surface waters in Kangerlussuaq were strongly influenced by meltwater with low salinities, high particulate matter concentrations, high PAR and spectral light attenuation coefficients, and low nutrient concentrations. Spectral composition was also affected by the particulate matter. PAR photic depths varied between 4 and 9 m dependent on particulate matter concentrations. There was a decrease with distance from outlet in silicate concentrations, and opposite for phosphate, which increased significantly from river outlet to the marine. Phytoplankton species number (42) and diversity were high at the marine station but low (3) in turbid waters dominated by the diatom Skeletonema costatum in high numbers. A meltwater plume covered about 50 % of the Kangerlussuaq at average discharges in early August. Primary production was quantified with a simple model based on light attenuation coefficients, and showed a near exponential decrease in production with increase in attenuation.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Nutrients supplied by upwelling, mixing, and inflow from adjacent oceans and terrestrial nutrient inputs are key factors regulating primary production in Arctic fjords and coastal areas. However, the contribution of terrestrial nutrient input to marine primary production remains poorly understood. Tundra biomes are highly sensitive to climate change, and vegetation responses to warming such as Arctic greening could modify terrestrial nutrient inputs to fjords and coastal areas. Here we analyze long–term measurements from northeast Greenland, revealing that climate–induced terrestrial greening has increased by 20% from 1999–2021, leading to a 77% decline in terrestrially–derived nitrate input from land to the coastal ecosystem, and a 39% decrease in phytoplankton biomass in the coastal ecosystem. These changes indicate an overall climate–driven decline in nitrate export via terrestrial rivers to the sea, and this oligotrophication may have major consequences for future Arctic coastal ecosystems.

The aims of this review are to elucidate the spatial variation in the primary production rates and biomasses (Chl a) of sea ice algae in the Canadian Arctic–Greenland region, characterized by its comparable physical settings. A database was compiled from 30 studies of the production rates and biomasses (Chl a) of sea ice algae, the snow and ice thicknesses, ice types, nutrients (Si(OH)4, PO4, (NO3 + NO2)), and NH4 concentrations in the ice and below the ice from the region. Production rates were significantly higher (463 mg C m−2 d−1) in Resolute Bay and Northern Baffin Bay (317 mg C m−2 d−1), both in the Canadian Arctic, compared to a rate of 0.2 mg C m−2 d−1 in northeast Greenland. The biomasses reached 340 mg Chl a m−2 in Resolute Bay in comparison to 0.02 mg Chl a m−2 in southwest Greenland. Primary production at other Canadian and Greenland sites was comparable, but sea ice Chl a was higher (15.0 ± 13.4 mg Chl a m−2) at Canadian sites compared to Greenland ones (0.8 ± 0.5 mg Chl a m−2). Resolute and Northern Baffin Bay production rates were significantly higher when compared to other Arctic Ocean sites outside the studied region. The review concludes that the high production rates and biomasses in Resolute and Northern Baffin Bay are related to the inflow and mixing of nutrient-rich waters of Pacific origin. A conceptual model with drivers and inhibitors of the primary production of sea ice algae is proposed, and the database is compiled into a dataset of published data for further studies.

Blooms of pigmented algae darken the surface of glaciers and ice sheets, thereby enhancing solar energy absorption and amplifying ice and snow melt. The impacts of algal pigment and community composition on surface darkening are still poorly understood. Here, we characterise glacier ice and snow algal pigment signatures on snow and bare ice surfaces and study their role in photophysiology and energy absorption on three glaciers in Southeast Greenland. Purpurogallin and astaxanthin esters dominated the glacier ice and snow algal pigment pools (mass ratios to chlorophyll a of 32 and 56, respectively). Algal biomass and pigments impacted chromophoric dissolved organic matter concentrations. Despite the effective absorption of astaxanthin esters at wavelengths where incoming irradiance peaks, the cellular energy absorption of snow algae was 95% lower than anticipated from their pigmentation, due to pigment packaging. The energy absorption of glacier ice algae was consequently ~ 5 × higher. On bare ice, snow algae may have locally contributed up to 13% to total biological radiative forcing, despite contributing 44% to total biomass. Our results give new insights into the impact of algal community composition on bare ice energy absorption and biomass accumulation during snow melt.

Arctic summer sea ice extent is decreasing and thinning, forming melt ponds that cover more than 50% of the sea ice area during the peak of the melting season. Despite of this, ice algal communities in melt ponds are understudied and so are their contribution to the Arctic Ocean primary production and carbon turnover. While melt ponds have been considered as low productive, recent studies suggest that accumulated ice algal potentially facilitate high and yet overlooked rates of carbon turnover. Here we report on ice algal communities forming dense mats not previously described, collected from melt ponds in the northern Barents Sea in July. We document on distinct layered and brown colored mats with high carbon assimilation and net primary production rates compared to ice algal communities and aggregates, in fact comparable to benthic microalgae at temperate tidal flats. Rates of gross and net primary production, as well as community respiration rates were obtained from oxygen micro profiling, and carbon assimilation calculations were supported by 14 C incubations, pigment analysis and light microscopy examinations. The melt pond algal mats consisted of distinct colored layers and differed from aggregates with a consisted layered structure. We accordingly propose the term melt pond algal mats, and further speculate that these dense ice algal mats may provide an important yet overlooked source of organic carbon in the Arctic food-web. A foodweb component likely very sensitive to climate driven changes in the Arctic Ocean and pan-Arctic seas.

Cervical cancer (CC) is one of the most common cancers in women worldwide in which most cases are diagnosed with the Human Papilloma Virus (HPV). At the present time, there is neither a vaccine nor a drug to prevent or to effectively treat HPV infection. In the recent decades, compounds originated from marine organisms are well known for their novel chemical structures and wide range of biological activities. In the frame of our ongoing program to identify natural compounds endowed with anticancer bioactivities, this study conducted in silico assessment of 502 compounds originated from marine organisms against E6 protein of HPV for potential inhibition activity. The tertiary structure of targeted protein was constructed using SWISS-MODEL in which obtained Ramachandran plot proved the high quality of the protein model with 87.7% residues located in the most favored region and 11.6% residues allocated in the allowed region. All studied compounds were evaluated for drug-like and pharmacokinetic properties. AutoDock 4.2.6 and AutoDock Vina 1.2.0 were utilized to investigate the docking conformation of studied compounds towards E6 protein. High correlation coefficient between the dock score of AutoDock 4.2.6 and AutoDock Vina 1.2.0 was recorded with the value of R = 0.62. Docking outcomes in combination with ADMET studies identified compounds 153, 185 and 500 are the top “hits” for further drug development based on dock score ranking and docking conformation analysis, in particularly, compound 153 could be considered with caution due to its potent in causing mutation.

Upwelling and downwelling spectral (320–920 nm) distributions and photosynthetic active radiation (PAR) intensities were measured below a first-year land-fast sea ice in a western Greenland fjord with and without a snow cover. Time-series of surface upwelling PAR, downwelling PAR, and under-ice PAR were also obtained. Spectral distributions of upwelling and downwelling irradiances were similar except for reduced intensities in the UV, the red, and NIR parts of the spectrum when the ice was snow-covered. Upwelling PAR amounted to about 10% of downwelling intensities, giving 5.1 µmol photons m−2 s−1 at the bottom of the ice with a snow cover and 8.2 µmol photons m−2 s−1 without. PAR partitioning analyses showed that the upwelling was related to scattering by suspended particles in the water column. A snow melt increased under-ice daily maximum downwelling PAR from 50 to 180 µmol photons m−2 s−1 and overall under-ice PAR of 55 and 198 µmol photons m−2 s−1 with 10% upwelling. It is concluded that upwelling PAR below sea ice might be an important factor regarding sea ice algae photophysiology and performance with a 10% higher PAR; specifically when PAR > Ek the light saturation point of the sea ice algae.

Snow cover on sea ice is the most important factor controlling light availability for sea ice algae, but it is predicted by climate models to become more variable and stochastic. Here, we document effects of a sudden, complete loss of the entire snow cover on first-year sea ice at Kangerlussuaq Fjord, West Greenland, due to a natural Föhn wind event that caused a ca. 17 °C air temperature increase over 36 h. We applied Imaging-PAM fluorometry to examine effects of snow cover on algal distribution and photobiology and observed a rapid decrease in algal biomass associated with loss of the skeletal ice crystal layer on the underside of the ice that had supported most of the visible algae. Furthermore, the remaining algae were photobiologically stressed, as seen in a significant decrease in the dark-acclimated fluorescence yield (ΦPSII_max) from 0.55 before snow loss to 0.41 after. However, recovery in the dark suggested that non-photosynthetic quenching was successfully dissipating excess energy in the community and that there was little photodamage. An observed decrease in the photosynthetic efficiency α from 0.22 to 0.16 µmol é m−2 s−1 is therefore likely to be due to photoacclimation and the change in community composition. Centric diatoms and flagellates were the main taxa lost in the snow loss event, whereas the sea ice specialist Nitzschia frigida increased in numbers. These observations are similar to those seen in artificial snow-clearing experiments and consistent with snow clearing being a useful approach for investigating the complex interactions between snow cover, irradiance fluctuations, and ice algal performance.

Greenland fjords are currently undergoing large ecosystem changes due to unprecedented melting of the Greenland Ice Sheet (GrIS). The rapidly increasing discharge of meltwater and ice not only influences circulation patterns and stratification of the water column, but it also introduces large fluxes of allochthonous carbon and nutrients into the Greenland coastal environment, as well as transports large quantities of inorganic particles and suspended sediments which could limit light availability to primary producers. However, data is still limited for most Greenland fjord systems and the east coast of Greenland is especially understudied. During this cruise we investigated 3 different fjord systems of East Greenland in August 2018 aboard the HDMS Lauge Koch. We aimed to describe the physical, chemical and biological variability from glaciers to the shelf. This data set consists of 84 CTD profiles that were obtained with a Seabird SBE25 conductivity, temperature, depth (CTD) instrument. In addition to measuring pressure, conductivity, and temperature, the CTD recorded chlorophyll-a fluorescence, photosynthetically available radiation (PAR), dissolved oxygen, turbidity and pH. The instrument was factory calibrated before the cruise. The CTD recorded variables at 16 Hz and the raw data were processed using Seabird standard workflow to produce 0.1 m binned profiles using the downcast data only. This dataset compiles all CTD variables measured from all profiles into a single comma separated CSV file. We would like to thank the captain and crew of HDMS Lauge Koch for excellent collaboration. The cruise was funded by the Danish Center for Marine Research and by the EU Horizon2020 funded project INTAROS (grant no. 727890) and the Danish Cooperation for Environment in the Arctic.