Description: The Arctic is warming 2–3 times faster than the global average, leading to a decrease in Arctic sea ice extent, thickness, and associated changes in sea ice structure. These changes impact sea ice habitat properties and the ice-associated ecosystems. Sea-ice algal blooms provide various algal-derived carbon sources for the bacterial and archaeal communities within the sea ice. Here, we detail the transition of these communities from winter through spring to early summer during the Norwegian young sea ICE (N-ICE2015) expedition. The winter community was dominated by the archaeon Candidatus Nitrosopumilus and bacteria belonging to the Gammaproteobacteria (Colwellia, Kangiellaceae, and Nitrinocolaceae), indicating that nitrogen-based metabolisms, particularly ammonia oxidation to nitrite by Cand. Nitrosopumilus was prevalent. At the onset of the vernal sea-ice algae bloom, the community shifted to the dominance of Gammaproteobacteria (Kangiellaceae, Nitrinocolaceae) and Bacteroidia (Polaribacter), while Cand. Nitrosopumilus almost disappeared. The bioinformatically predicted carbohydrate-active enzymes increased during spring and summer, indicating that sea-ice algae-derived carbon sources are a strong driver of bacterial and archaeal community succession in Arctic sea ice during the change of seasons. This implies a succession from a nitrogen metabolism-based winter community to an algal-derived carbon metabolism-based spring/ summer community.

Description: Global warming causes dramatic environmental change to Arctic ecosystems. While pelagic primary production is initiated earlier and its intensity can be increased due to earlier ice melt and extended open-water periods, sea-ice primary production is progressively confined on a spatio-temporal scale, leading to unknown consequences for the ice-associated (sympagic) food web. Understanding ecological responses to changes in the availability and composition of pelagic and sympagic food sources is crucial to determine potential changes of food-web structure and functioning in Arctic marine communities under increasingly ice-free conditions. Focus was placed on the importance of suspended particulate organic matter vs. sympagic organic matter for 12 zooplankton species with different feeding modes covering five taxonomic groups (copepods, krill, amphipods, chaetognaths, and appendicularians) at two ice-covered, but environmentally different, stations in the north-western Barents Sea in August 2019. Contributions of diatom- and flagellate-associated fatty acids (FAs) to total lipid content and carbon stable isotopic compositions of these FAs were used to discriminate food sources and trace flows of organic matter in marine food webs. Combination of proportional contributions of FA markers with FA isotopic composition indicated that consumers mostly relied, directly (herbivorous species), or indirectly (omnivorous and carnivorous species), on pelagic diatoms and flagellates, independently of environmental conditions at the sampling locations, trophic position, and feeding mode. Differences were nevertheless observed between species. Contrary to other studies demonstrating a high importance of sympagic organic matter for food-web processes, our results highlight the complexity and variability of trophic structures and dependencies in different Arctic food webs.

Description: Seasonal plankton time-series data are presented from Kongsfjorden from two years with contrasting environmental conditions. Kongsfjorden (west coast of Spitsbergen – 79◦N) integrates inputs from Atlantic and Arctic waters, and glacier run-off, and is thus a prime location to study impacts on ecosystem dynamics of key environmental drivers that are relevant across the Arctic. Despite extensive research in Kongsfjorden, seasonally resolved data are scarce. From late April/early May to early September 2019 and 2020, we conducted pelagic sampling at a mid-fjord station at mostly weekly to bi-weekly resolution investigating the environmental drivers of phyto- and zooplankton community composition and phenology. During spring 2019, Atlantic water masses with temperatures 〉 1 ◦C were found throughout the upper 250 m of the water column, and little sea ice occurred in the fjord. Spring 2020, in turn, was characterized by the presence of local water masses with sub-zero temperatures and relatively extensive sea-ice cover. The most striking contrast between the two years was the difference in phytoplankton spring bloom composition. In 2019, the spring bloom was dominated by the colonial stage of the haptophyte Phaeocystis pouchetii and diatoms played a minor role, while the spring bloom in 2020 was dominated by diatoms of the genus Thalassiosira succeeded by P. pouchetii. Selective grazing by large copepods and water mass structure seem to have been the decisive factors explaining the marked difference in diatom spring bloom biomass between the years while similar spring abundances of P. pouchetii in both years indicated that this species was less impacted by those factors. Our data suggest that differences in spring bloom composition impacted trophic transfer and carbon export. Recruitment of the dominant copepods Calanus finmarchicus and C. glacialis, Cirripedia and euphausiid larvae as well as the export of carbon to the seabed was more efficient during the diatom-dominated compared to the P. pouchetii–dominated spring bloom. In summer, the plankton composition shifted towards a flagellate-dominated community characterized by mixo- and heterotrophic taxa adapted to a lower nutrient regime and strong top-down control by copepod grazers. However, residual silicic acid after the P. pouchetii–dominated spring bloom fueled a late summer diatom bloom in 2019. Our data provide a first glimpse into the environmental drivers of plankton phenology and underline that high resolution monitoring over many annual cycles is required to resolve the ephemeral variations of plankton populations against the backdrop of climate change.

Description: We investigated diets of 24 Barents Sea zooplankton taxa to understand pelagic food-web processes during late summer, including the importance of sea ice algae-produced carbon. This was achieved by combining insights derived from multiple and complementary trophic marker approaches to construct individual aspects of feeding. Specifically, we determined proportions of algal-produced fatty acids (FAs) to reflect the reliance on diatom- versus dinoflagellate-derived carbon, highly branched isoprenoid (HBI) lipids that distinguish between ice-associated and pelagic carbon sources, and sterols to indicate the degree of carnivory. Copepods had the strongest diatom signal based on FAs, while a lack of sea ice algae-associated HBIs (IP25, IPSO25) suggested that they fed on pelagic rather than ice-associated diatoms. The amphipod Themisto libellula and the ctenophores Beroë cucumis and Mertensia ovum had a higher contribution of dinoflagellate-produced FAs. There was a high degree of carnivory in this food web, as indicated by the FA carnivory index 18:1(n−9)/18:1(n−7) (mean value 〈 1 only in the pteropod Clione limacina), the presence of copepod-associated FAs in most of the taxa, and the absence of algal-produced HBIs in small copepod taxa, such as Oithona similis and Pseudocalanus spp. The coherence between concentrations of HBIs and phytosterols within individuals suggested that phytosterols provide a good additional indication for algal ingestion. Sea ice algae-associated HBIs were detected in six zooplankton species (occurring in krill, amphipods, pteropods, and appendicularians), indicating an overall low to moderate contribution of ice-associated carbon from late-summer sea ice to pelagic consumption. The unexpected occurrence of ice-derived HBIs in pteropods and appendicularians, however, suggests an importance of sedimenting ice-derived material at least for filter feeders within the water column at this time of year.

Description: The Southern Ocean is a major sink of anthropogenic CO2 and an important foraging area for top trophic level consumers. However, iron limitation sets an upper limit to primary productivity. Here we report on a considerably dense late summer phytoplankton bloom spanning 9000 km2 in the open ocean of the eastern Weddell Gyre. Over its 2.5 months duration, the bloom accumulated up to 20 g C m−2 of organic matter, which is unusually high for Southern Ocean open waters. We show that, over 1997–2019, this open ocean bloom was likely driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of Warm Deep Water enriched in hydrothermal iron and, possibly, other iron sources. This recurring open ocean bloom likely facilitates enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hot spots for marine birds and baleen whales.

Description: Challenge 4. 9

Description: Published

Description: Refereed

Description: The data has been collected during the the year-long drift expedition "Multidisciplinary drifting Observatory for the Study of Arctic Climate" (MOSAiC) from September 2019 to September 2020 on research vessel Polarstern. The samples were collected with Niskin bottles attached to a CTD rosette, an Apstein net with 20 µm mesh size, a hand pump or a pump mounted on a ROV. The samples were preserved using a few drops of Lugol and hexamethylenetetramine-buffered formalin at a final concentration of 1%. The samples were collected with Niskin bottles attached to a CTD rosette at the following depths: 5, 10, 30, 60, 90 m and deep chlorophyll max (DCM). Protists were identified and counted with light microscopy using the Utermöhl method and the result are given as cells per liter (cells/L) called Abundance.

Description: The data has been collected during the expedition "Multidisciplinary drifting Observatory for the Study of Arctic Climate" (MOSAiC) from September 2019 to September 2020 on research vessel Polarstern. The dataset contains abundance of sea ice protists, including ice algae (autotrophic) and protozoa (heterotrophic). Protists were identified and counted with light microscopy using the Utermöhl method and the result are given as cells per liter (cells/L) called Abundance. Sea ice samples were collected with a 9 cm diameter ice corer (Kovacs Enterprise) from both level and ridge ice. The samples were collected from the bottom part of the ice core and generally sectioned from 0-3 cm, 3-10 cm and in 10 cm intervals thereafter. With some exceptions, ice core sections were melted in filtered sea water at 4°C. Melted samples were preserved using Lugol-formaldehyde mixture with a few drops of acidic Lugol solution and hexamethylenetetramine-buffered formalin at a final concentrations of 1%.

Description: The data has been collected during the year-long drift expedition "Multidisciplinary drifting Observatory for the Study of Arctic Climate" (MOSAiC) from September 2019 to September 2020 on research vessel Polarstern. The dataset contains abundance of pelagic marine and sea ice protists, including algae (autotrophic) and protzoa (heterotrophic). Protists were identified and counted with light microscopy using the Utermöhl method and the result are given as cells per liter (cells/L) called Abundance. The samples were collected with short-term sediment traps deployed at 3-4 depths (1, 5, 15 and 50 m) below level ice and near sea-ice ridges. The samples were preserved with a few drops of Lugol and hexamethylenetetramine-buffered formalin at a final concentrations of 1%.

Description: Here we present concentrations of chlorophyll a, phaeopigments, particulate organic carbon and nitrogen from water samples collected at discrete depths with a CTD-rosette during the European Iron Fertilization Experiment (EIFEX). The experiment was carried out from February 11 to March 20, 2004 in the 60-km diameter, rotating core of an eddy, formed by a meander of the Antarctic Polar Front (centred at around 49°10' S and 2°10' E). Samples were taken within the eddy inside and outside the fertilized patch, and in a few cases outside the eddy.Chlorophyll concentrations were determined by fluorometry using a Turner Design Model 10-AU digital fluorometer. Sampling, measurements and calibration of the fluorometer was carried out following the JGOFS protocol procedure (Knap et al, 1996). Results of the fluorometer calibration diverged by 5% between beginning and end of the cruise. Chlorophyll a content was calculated using average parameter values from the two calibrations. Measurement uncertainty was estimated from triplicate water samples taken from depths ranging between 10 and 100 m depth and averaged 5% of measured values. Samples for particulate organic carbon and nitrogen (POC and PON) were filtered onto precombusted Whatman GF/F filters and processed following recommendations by Lorrain et al. (2003). Samples were measured independently on three different analysers: a CN2500 CHN Analyser (Thermo Finnigan MAT) coupled to a Delta+ mass spectrometer (Thermo Finnigan MAT) via Conflo II interface (Thermo Finnigan MAT), a Carlo-Erba NA-1500 Series II elemental analyzer coupled to a Finnegan Delta+ mass spectrometer and a Euro EA Elemental Analyser. Differences due to methods were within the range of measurement variability (below 2%). The particulate organic phosphorus (POP) content was determined colorimetrically using the method from Hansen and Koroleff (1999; measurement variability 4%). Biogenic silica (BSi) was measured following the wet alkaline digestion method according to Müller and Schneider (1993; measurement variability 2%).

Description: Vertical export fluxes of particulate organic carbon (POC) and nitrogen (PON), chlorophyll a and phaeopigments from sediment trap sampling in the Artic Ocean north of Svalbard, the Nansen Basin and Yermak Plateau, during the N-ICE2015 research project (led by the Norwegian Polar Institute). The dataset includes 8 deployments of short-term cylindrical sediment traps (KC Denmark AS) in the time period between 30.01.2015 until 16.06.2015. Samples were used to study the drivers of the biological carbon pump in the region north of Svalbard (Dybwad et al. 2021: doi10.3389/fmars.2020.525800).