Abstract: Background and aims – Despite the ongoing taxonomical revision of the entire (sub)-Antarctic diatom flora, our knowledge on the ecology and community associations of moss-inhabiting diatoms is still rather limited. In the present study, our research aim was to survey the diversity together with the environmental factors structuring the epiphytic moss diatom communities on Ile Amsterdam (TAAF), a small volcanic island in the southern Indian Ocean.Material and methods – A morphology-based dataset and (physico)chemical measurements were used for the ecological and biogeographical analysis of moss-inhabiting diatom flora from Ile Amsterdam. In total, 148 moss samples were examined using light microscopy.Key results – The analysis revealed the presence of 125 diatom taxa belonging to 38 genera. The uniqueness of the Ile Amsterdam diatom flora is mainly reflected by the species composition of the dominant genera Pinnularia, Nitzschia, Humidophila, and Luticola, with a large number of unknown and often new species. This highly specific diatom flora, together with differences in the habitats sampled and the isolated position of the island, resulted in very low similarity values between Ile Amsterdam and the other islands of the Southern Ocean. From a biogeographical point of view, 40% of the taxa have a typical cosmopolitan distribution, whereas 22% of all observed species can be considered endemic to Ile Amsterdam, with another 17% species showing a restricted sub-Antarctic distribution. The NMDS analysis, based on a cluster dendrogram, divides the samples into six main groups. For each group, indicator species were determined. Both environmental data and diatom distributions indicate that apart from elevation, specific conductance, pH, and moisture are the major factors determining the structure of moss-inhabiting diatom communities on Ile Amsterdam.Conclusion – The isolated geographic position and unique climatological and geological features of the island shaped the presence of a unique diatom flora, characterised by many endemic species. The results of the study are of prime importance for further (palaeo-)ecological and biogeographical research.

Abstract: Abstract. Atmospheric Information Embedded In Ice-core Nitrate Is Disturbed By Post-depositional Processing. Here We Used A Layered Snow Photochemical Column Model To Explicitly Investigate The Effects Of Post-depositional Processing On Snow Nitrate And Its Isotopes (δ15n And Δ17o) At Summit, Greenland, Where Post-depositional Processing Was Thought To Be Minimal Due To The High Snow Accumulation Rate. We Found Significant Redistribution Of Nitrate In The Upper Snowpack Through Photolysis, And Up To 21 % Of Nitrate Was Lost And/or Redistributed After Deposition. The Model Indicates Post-depositional Processing Can Reproduce Much Of The Observed δ15n Seasonality, While Seasonal Variations In δ15n Of Primary Nitrate Are Needed To Reconcile The Timing Of The Lowest Seasonal δ15n. In Contrast, Post-depositional Processing Can Only Induce Less Than 2.1 ‰ Seasonal Δ17o Change, Much Smaller Than The Observation (9 ‰) That Is Ultimately Determined By Seasonal Differences In Nitrate Formation Pathway. Despite Significant Redistribution Of Snow Nitrate In The Photic Zone And The Associated Effects On δ15n Seasonality, The Net Annual Effect Of Post-depositional Processing Is Relatively Small, Suggesting Preservation Of Atmospheric Signals At The Annual Scale Under The Present Summit Conditions. But At Longer Timescales When Large Changes In Snow Accumulation Rate Occur This Post-depositional Processing Could Become A Major Driver Of The δ15n Variability In Ice-core Nitrate.

Abstract: While most precipitation in Antarctica falls as snow, little is known about liquid precipitation, although it can have ecological and climatic impacts. This study combines meteorological reports at 10 stations with the ERA5 reanalysis to provide a climatological characterization of rainfall occurrence over Antarctica. Along the East Antarctic coast, liquid precipitation occurs 22 days per year at most and coincides with maritime intrusions and blocking anticyclones. Over the north-western Antarctic Peninsula, rainfall occurs more than 50 days per year on average and the recent summer cooling was accompanied by a decrease of −35 annual rainy days per decade between 1998 and 2015 at Faraday-Vernadsky. Projections from seven latest-generation climate models reveal that Antarctic coasts will experience a warming and more frequent and intense rainfall by the end of the century. Rainfall is expected to impact new regions of the continent, increasing their vulnerability to melting by the preconditioning of surface snow.

Abstract: Year-round records of the ionic composition of Antarctic aerosol were obtained at the inland Dome C (DC) and coastal Neumayer (NM) sites, with additional observations of black carbon (BC) at NM. Discussions focus on the origin of ammonium in Antarctica. This first Antarctic atmospheric study of several species emitted by biomass burning (BB) indicates that BC and oxalate reach a maximum in October in relation to BB activity in the southern hemisphere. Ammonium reaches a maximum 2 months later, suggesting that BB remains a minor ammonium source there. The ammonium maximum in December coincides with the occurrence of diatom blooms in the austral ocean, suggesting that oceanic ammonia emissions are the main source of ammonium in Antarctica. The ammonium to sulfur-derived biogenic species molar ratio of 0.15 in summer suggests far lower ammonia emissions from the Antarctic oceans than midlatitude southern oceans.

Abstract: Sea stars (Echinodermata: Asteroidea) are a key component of Southern Ocean benthos, with 16% of the known sea star species living there. In temperate marine environments, sea stars commonly play an important role in food webs, acting as keystone species. However, trophic ecology and functional role of Southern Ocean sea stars are still poorly known, notably due to the scarcity of large-scale studies. Here, we report 24,332 trophic marker (stable isotopes and elemental contents of C, N, and S of tegument and/or tube feet) and biometric (arm length, disk radius, arm to disk ratio) measurements in 2,456 specimens of sea stars. Samples were collected between 12 January 1985 and 8 October 2017 in numerous locations along the Antarctic littoral and subantarctic islands. The spatial scope of the data set covers a significant portion of the Southern Ocean (47.717° S to 86.273° S; 127.767° W to 162.201° E; depth, 6–5,338 m). The data set contains 133 distinct taxa, including 72 currently accepted species spanning 51 genera, 20 families, and multiple feeding guilds/functional groups (suspension feeders, sediment feeders, omnivores, predators of mobile or sessile prey). For 505 specimens, mitochondrial CO1 genes were sequenced to confirm and/or refine taxonomic identifications, and those sequences are already publicly available through the Barcode of Life Data System. This number will grow in the future, as molecular analyses are still in progress. Overall, thanks to its large taxonomic, spatial, and temporal extent, as well as its integrative nature (combining genetic, morphological, and ecological data), this data set can be of wide interest to Southern Ocean ecologists, invertebrate zoologists, benthic ecologists, and environmental managers dealing with associated areas. Please cite this data paper in research products derived from the data set, which is freely available without copyright restrictions.