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Abstract Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea‐ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under‐ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immatureB. saidaand the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth ofB. saidain this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immatureB. saidamay be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival ofB. saidawill not depend on prey presence alone, but also on prey catchability, digestibility, and energy content. 

Abstract Microalgae are the main source of the omega‐3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), essential for the healthy development of most marine and terrestrial fauna including humans. Inverse correlations of algal EPA and DHA proportions (% of total fatty acids) with temperature have led to suggestions of a warming‐induced decline in the global production of these biomolecules and an enhanced importance of high latitude organisms for their provision. The cold Arctic Ocean is a potential hotspot of EPA and DHA production, but consequences of global warming are unknown. Here, we combine a full‐seasonal EPA and DHA dataset from the Central Arctic Ocean (CAO), with results from 13 previous field studies and 32 cultured algal strains to examine five potential climate change effects; ice algae loss, community shifts, increase in light, nutrients, and temperature. The algal EPA and DHA proportions were lower in the ice‐covered CAO than in warmer peripheral shelf seas, which indicates that the paradigm of an inverse correlation of EPA and DHA proportions with temperature may not hold in the Arctic. We found no systematic differences in the summed EPA and DHA proportions of sea ice versus pelagic algae, and in diatoms versus non‐diatoms. Overall, the algal EPA and DHA proportions varied up to four‐fold seasonally and 10‐fold regionally, pointing to strong light and nutrient limitations in the CAO. Where these limitations ease in a warming Arctic, EPA and DHA proportions are likely to increase alongside increasing primary production, with nutritional benefits for a non‐ice‐associated food web. 

The Multi-disciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), was conducted from October 2019 to September 2020. The Research Vessel Polarstern was frozen into the ice in the Central Arctic Ocean north of Norway and drifted with the prevailing currents from north to south, traversing multiple Arctic basins and regimes and serving as a floating laboratory for an international, multidisciplinary program focusing on multiple facets of ice, ocean, atmosphere, biogeochemistry, and ecosystem responses to ongoing changing environmental conditions. Zooplankton ecology was investigated as part of the ecosystem team program. Abundance data from the area has been limited, particularly for the winter season. Weekly net tows were scheduled with multiple nets (mesh sizes 53, 150 and 1000 microns (µm)) to add to that data. This data set contains zooplankton abundance data (individuals per cubic meter) for the 53 µm ring net samples, sampling location and net depth information. Abundant zooplankton were identified to species and stage, including nauplii. Less abundant specimens were identified to subgroup, genus, group or family. 

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition was conducted from October 2019-September 2020. During this ~1 year period, the Research Vessel (R/V) Polarstern was frozen into the ice in the Central Arctic Ocean north of Norway and drifted with the prevailing currents from north to south, traversing multiple Arctic basins and regimes, and was re-located in late July to near the North Pole after drifting through Fram Strait. The ship served as a floating laboratory for an international, multidisciplinary program focusing on multiple facets of ice, ocean, atmosphere, biogeochemistry, and ecosystem responses to ongoing changing environmental conditions. Zooplankton ecology was investigated as part of the ecosystem team program. Here we present data on key zooplankton rate processes collected over the period of the drift including: respiration, feeding, and reproduction. 

Abundance (ind. m-3) of zooplankton taxa was calculated from samples of Polarstern cruise PS122 (MOSAiC). Samples were taken with a Ring net with an opening area of 0.79 m2 and a mesh size of 1000 µm. Samples were analysed via image-based ZooScan analysis. The classified images are available at the web application EcoTaxa: https://ecotaxa.obs-vlfr.fr/prj/9966. 

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition was conducted from October 2019-September 2020. During this ~1 year period, the Research Vessel (R/V) Polarstern was frozen into the ice in the Central Arctic Ocean north of Norway and drifted with the prevailing currents from north to south, traversing multiple Arctic basins and regimes, and was re-located in late July to near the North Pole after drifting through Fram Strait. The ship served as a floating laboratory for an international, multidisciplinary program focusing on multiple facets of ice, ocean, atmosphere, biogeochemistry, and ecosystem responses to ongoing changing environmental conditions. Zooplankton ecology was investigated as part of the ecosystem team program. Here we present data on key zooplankton morphological and compositional parameters collected over the period of the drift. This data set contains the carbon and nitrogen content (micrograms [µg]) and lengths for individuals or groups of calanoid copepods and other taxa (e.g., amphipods, chaetognaths), width (micrometers [µm]) for copepods, and body area (micrometers squared [µm2]) and lipid sac area (µm2) for Calanus spp. copepods collected in different water depth intervals at approximately weekly intervals during the period of the drift. 

The international and interdisciplinary sea-ice drift expedition “The Multidisciplinary drifting Observatory for the Study of Arctic Climate” (MOSAiC) was conducted from October 2019 to September 2020. The aim of MOSAiC was to study the interconnected physical, chemical, and biological characteristics and processes from the atmosphere to the deep sea of the central Arctic system. The ecosystem team addressed current knowledge gaps and explored unknown biological properties over a complete seasonal cycle focusing on three major research areas: biodiversity, biogeochemical cycles, and linkages to the environment. In addition to the measurements of core properties along a complete seasonal cycle, dedicated projects covered specific processes and habitats, or organisms on higher taxonomic or temporal resolution in specific time windows. A wide range of sampling instruments and approaches, including sea-ice coring, lead sampling with pumps, rosette-based water sampling, plankton nets, remotely operated vehicles, and acoustic buoys, was applied to address the science objectives. Further, a broad range of process-related measurements to address, for example, productivity patterns, seasonal migrations, and diversity shifts, were made both in situ and onboard RV Polarstern. This article provides a detailed overview of the sampling approaches used to address the three main science objectives. It highlights the core sampling program and provides examples of habitat- or process-specific sampling. The initial results presented include high biological activities in wintertime and the discovery of biological hotspots in underexplored habitats. The unique interconnectivity of the coordinated sampling efforts also revealed insights into cross-disciplinary interactions like the impact of biota on Arctic cloud formation. This overview further presents both lessons learned from conducting such a demanding field campaign and an outlook on spin-off projects to be conducted over the next years. 

Atlantic predatory nekton resides further north than expected, adding a trophic level to the central Arctic ecosystem model. 

These files contain metadata describing the samples used in 18S ribosomal DNA sequencing of gut contents from zooplankton collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Raw sequence data along with these files are deposited in the Sequence Read Archive (SRA), and will be accessible through National Center for Biotechnology Information (NCBI), BioProject Identification (ID) PRJNA789896 upon manuscript publication (expected December 2022). The study looks at the Eukaryotic organisms in the guts of Arctic zooplankton collected through the year-long drift survey. The majority of the samples used were female copepods (Calanus glacialis, Calanus hyperboreus, and Metridia longa), with a few other organisms and life stages included.