Sea ice algae as food source- High trophic dependency of important energy transmitters in the central Arctic Ocean

Polar ecosystems thrive significantly on carbon synthesized by sea ice-associated microalgae during long periods of the year. Continued alterations of the sea ice system might not only have dramatic consequences for the sympagic (ice-associated) ecosystem, but will also have a large impact on the pelagic food web due to the close connectivity between the sea ice and the pelagic system. Thus, it is crucial to identify to which extent ecologically important species in the Arctic Ocean trophically depend on ice algae-produced carbon versus carbon produced by pelagic phytoplankton

Dependency of Arctic zooplankton on pelagic food sources: New insights from fatty acid and stable isotope analyses

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

Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba

Antarctic krill Euphausia superba (“krill”) constitute a fundamental food source for Antarctic seabirds and mammals, and a globally important fisheries resource. The future resilience of krill to climate change depends critically on the winter survival of young krill. To survive periods of extremely low production by pelagic algae during winter, krill are assumed to rely partly on carbon produced by ice algae. The true dependency on ice algae-produced carbon, however, is so far unquantified. This confounds predictions on the future resilience of krill stocks to sea ice decline. Fatty acid (FA) analysis, bulk stable isotope analysis (BSIA), and compound-specific stable isotope analysis (CSIA) of diatom- and dinoflagellate-associated marker FAs were applied to quantify the dependency of overwintering larval, juvenile, and adult krill on ice algae-produced carbon (αIce) during winter 2013 in the Weddell-Scotia Confluence Zone. Our results demonstrate that the majority of the carbon uptake of the overwintering larval and juvenile krill originated from ice algae (up to 88% of the carbon budget), and that the dependency on ice algal carbon decreased with ontogeny, reaching <56% of the carbon budget in adults. Spatio-temporal variability in the utilization of ice algal carbon was more pronounced in larvae and juvenile krill than in adults. Differences between αIce estimates derived from short- vs. long-term FA-specific isotopic compositions suggested that ice algae-produced carbon gained importance as the winter progressed, and might become critical at the late winter-spring transition, before the phytoplankton bloom commences. Where the sea ice season shortens, reduced availability of ice algae might possibly not be compensated by surplus phytoplankton production during wintertime. Hence, sea ice decline could seriously endanger the winter survival of recruits, and subsequently overall biomass of krill

Snowmelt contribution to Arctic first-year ice ridge mass balance and rapid consolidation during summer melt

An assessment of potential groundwater areas in the Ifni basin, located in the western AntiAtlas range of Morocco, was conducted based on a multicriteria analytical approach that integrated a set of geomorphological and hydroclimatic factors influencing the availability of this resource. This approach involved the use of geographic information systems (GIS) and hierarchical analytical process (AHP) models. Different factors were classified and weighted according to their contribution to and impact on groundwater reserves. Their normalized weights were evaluated using a pairwise comparison matrix. Four classes of potentiality emerged: very high, high, moderate, and low, occupying 15.22%, 20.17%, 30.96%, and 33.65%, respectively, of the basin’s area. A groundwater potential map (GWPA) was validated by comparison with data from 134 existing water points using a receiver operating characteristic (ROC) curve. The AUC was calculated at 80%, indicating the good predictive accuracy of the AHP method. These results will enable water operators to select favorable sites with a high groundwater potential

Snowmelt contribution to Arctic first-year ice ridge mass balance and rapid consolidation during summer melt

Sea ice ridges are one of the most under-sampled and poorly understood components of the Arctic sea ice system. Yet, ridges play a crucial role in the sea ice mass balance and have been identified as ecological hotspots for ice-associated flora and fauna in the Arctic. To better understand the mass balance of sea ice ridges, we drilled and sampled two different first-year ice (FYI) ridges in June–July 2020 during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). Ice cores were cut into 5 cm sections, melted, then analyzed for salinity and oxygen (d18O) isotope composition. Combined with isotope data of snow samples,we used a mixing model to quantify the contribution of snow to the consolidated sea ice ridge mass. Our results demonstrate that snow meltwater is important for summer consolidation and overall ice mass balance of FYI ridges during the melt season, representing 6%–11% of total ridged ice mass or an ice thickness equivalent of 0.37–0.53 m.These findings demonstrate that snowmelt contributes to consolidation of FYI ridges and is a mechanism resulting in a relative increase of sea ice volume in summer. This mechanism can also affect the mechanical strength and survivability of ridges, but also contribute to reduction of the habitable space and light levels within FYI ridges. We proposed a combination of two pathways for the transport of snow meltwater and incorporation into ridge keels: percolation downward through the ridge and/or lateral transport from the under-ice meltwater layer. Whether only one pathway or a combination of both pathways is most likely remains unclear based on our observations, warranting further research on ridge morphologypublishedVersio

Earlier sea-ice melt extends the oligotrophic summer period in the Barents Sea with low algal biomass and associated low vertical flux

The decrease in Arctic sea-ice extent and thickness as a result of global warming will impact the timing, duration, magnitude and composition of phytoplankton production with cascading effects on Arctic marine food-webs and biogeochemical cycles. Here, we elucidate the environmental drivers shaping the composition, abundance, biomass, trophic state and vertical flux of protists (unicellular eukaryotes), including phytoplankton, in the Barents Sea in late August 2018 and 2019. The two years were characterized by contrasting sea-ice conditions. In August 2018, the sea-ice edge had retreated well beyond the shelf break into the Nansen Basin (>82°N), while in 2019, extensive areas of the northwestern Barents Sea shelf (>79°N) were still ice-covered. These contrasting sea-ice conditions resulted in marked interannual differences in the pelagic protist community structure in this area. In August 2018, the protist community was in a post-bloom stage of seasonal succession characterized by oligotrophic surface waters and dominance of small-sized phytoplankton and heterotrophic protists (predominantly flagellates and ciliates) at most stations. In 2019, a higher contribution of autotrophs and large-celled phytoplankton, particularly diatoms, to total protist biomass compared to 2018 was reflected in higher chlorophyll a concentrations and suggested that the protist community was still in a late bloom stage at some stations. It is noteworthy that particularly diatoms contributed a considerably higher proportion to the protist biomass at the ice-covered stations in both years compared to the open-water stations. This pattern was also evident in the higher vertical protist biomass flux in 2019, dominated by dinoflagellates and diatoms, compared to 2018. Our results suggest that the predicted transition toward an ice-free Barents Sea will lengthen the oligotrophic summer period with low algal biomass and associated low vertical flux.publishedVersio