Karoline Saubrekka

• Thiele, Stefan; Vader, Anna; Thomson, Stuart; Saubrekka, Karoline; Petelenz-Kurdziel, Elzbieta Anna & Müller, Oliver [Vis alle 8 forfattere av denne artikkelen] (2023). Seasonality of the bacterial and archaeal community composition of the Northern Barents Sea. Frontiers in Microbiology. ISSN 1664-302X. 14. doi: 10.3389/fmicb.2023.1213718. Fulltekst i vitenarkiv Vis sammendrag

  The Barents Sea is a transition zone between the Atlantic and the Arctic Ocean. The ecosystem in this region is highly variable, and a seasonal baseline of biological factors is needed to monitor the effects of global warming. In this study, we report the results from the investigations of the bacterial and archaeal community in late winter, spring, summer, and early winter along a transect through the northern Barents Sea into the Arctic Ocean east of Svalbard using 16S rRNA metabarcoding. Winter samples were dominated by members of the SAR11 clade and a community of nitrifiers, namely Cand. Nitrosopumilus and LS-NOB (Nitrospinia), suggest a prevalence of chemoautotrophic metabolisms. During spring and summer, members of the Gammaproteobacteria (mainly members of the SAR92 and OM60(NOR5) clades, Nitrincolaceae) and Bacteroidia (mainly Polaribacter, Formosa, and members of the NS9 marine group), which followed a succession based on their utilization of different phytoplankton-derived carbon sources, prevailed. Our results indicate that Arctic marine bacterial and archaeal communities switch from carbon cycling in spring and summer to nitrogen cycling in winter and provide a seasonal baseline to study the changes in these processes in response to the effects of climate change.

• Thiele, Stefan; Vader, Anna; Thomson, Stuart; Saubrekka, Karoline; Petelenz-Kurdziel, Elzbieta Anna & Rief Armo, Hilde [Vis alle 10 forfattere av denne artikkelen] (2023). The summer bacterial and archaeal community composition of the northern Barents Sea. Progress in Oceanography. ISSN 0079-6611. 215, s. 1–9. doi: 10.1016/j.pocean.2023.103054. Fulltekst i vitenarkiv Vis sammendrag

  Climate change related alterations in the Arctic have influences on the marine ecosystems, in particular on phytoplankton bloom dynamics. Since phytoplankton blooms are the main provider of carbon sources to the microbial loop, the bacterial and archaeal community are affected by the changes as well. Warmer water and less sea ice can lead to an earlier onset of phytoplankton blooms and consequently also to changes in the bacterial and archaeal community dynamics throughout Arctic summers. Here, we compared the bacterial and archaeal community composition during three summers (2018, 2019, and 2021) along a transect from the Barents Sea to the Arctic Ocean north of Svalbard. We used 16S rRNA gene sequencing to investigate changes in the communities in time and space. The main results showed that, Gammaproteobacteria (Nitrincolaceae), Bacteroidia (Polaribacter), and Alphaproteobacteria (SAR11 clade 1a members) dominated the bacterial and archaeal community in the surface waters but varied in abundance patterns between the years. The variations are potentially a result of different phytoplankton bloom stages and consequently differences in the availability of carbon sources. The distinctly different deep water communities were dominated by Candidatus Nitrosopumilus, Marinimicrobia, and members of the SAR324 clade in all years. The results indicate that changes in phytoplankton bloom dynamics can influence bacterial and archaeal community and thereby marine carbon cycling in surface waters, although direct links to the effects of global warming remain uncertain.

• Kohlbach, Doreen; Goraguer, Lucie; Bodur, Yasemin V.; Müller, Oliver; Amargant Arumí, Martí & Blix, Katalin [Vis alle 23 forfattere av denne artikkelen] (2023). Tidligere havissmelting forlenger den oligotrofe sommerperioden i Barentshavet med lav algebiomasse og vertikal fluks. Progress in Oceanography. ISSN 0079-6611. 213. doi: 10.1016/j.pocean.2023.103018. Fulltekst i vitenarkiv Vis sammendrag

  Havisen i Arktis minker i utstrekning og tykkelse som et resultat av klimaoppvarming. Dette påvirker tidspunkt, lengde, størrelse og sammensetning av fytoplankton og planktonproduksjon med påfølgende effekter på det arktiske, marine næringsnettet, og på biogeokjemiske sykluser. I dette studie dokumenterer vi miljødrivere som påvirker sammensetning, tetthet, biomasse, trofisk nivå, og den vertikale strømmen av encellete eukaryoter (protister) og fytoplankton i Barentshavet, sent i august 2018 og 2019. Disse to årene var karakterisert av ulike havisforhold. I august 2018 hadde iskanten trukket seg bort fra sokkelkanten og inn i Nansen bassenget nord for 82 °N, mens det i 2019 var mye is i den nordvestre delen av Barentshavet nord for 79 °N. Våre resultater viser at de varierende isforholdene bidro til markerte forskjeller i strukturen i de pelagiske protistsamfunnene i disse havområdene. I august 2018 var protistsamfunnet i et avsluttet blomstringsstadium, karakterisert av næringsfattig overflatevann som på de fleste stasjonene var dominert av små fytoplanktonarter og protister, i første rekke flagellater og ciliater. I 2019 var det et større innslag av autotrofe arter med store celler, særlig diatoméer, som medførte at den totale protistbiomassen hadde høyrere innhold av klorofyll a, noe som indikerte at protistsamfunnet fremdeles var i en sen oppblomstringsfase. Diatoméer utgjorde en høyrere andel av protistbiomassen på isdekte stasjoner i begge årene sammenliknet med stasjoner i åpent vann. Dette mønsteret var også synlig ved å ha en større vertikalstrøm av protistbiomasse i 2019, dominert av dinoflagellater og diatoméer, sammenliknet med 2018. Resultatene indikerer at den forutsatte overgangen til det isfrie Barentshavet vil forlenge den næringsfattige sommerperioden, med en lav algebiomasse og redusert vertikal transport.

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• Saubrekka, Karoline; Vader, Anna; Supraha, Luka & Edvardsen, Bente (2023). Diversity and distribution of Arctic protists in pelagic and sympagic habitats in the northern Barents Sea as revealed by metabarcoding. Vis sammendrag

  Protists play crucial roles in the marine ecosystems and in a rapidly changing Arctic it is important to reveal who are there, when and where, for future research and management. The aim of this study was to describe and compare the composition of protist communities in sea ice and pelagic habitats from samples collected in the northern Barents Sea along a transect in August 2018 with low sea-ice extent and 2019 with high sea-ice extent. Metabarcoding targeting the 18S rRNA gene revealed 3682 unique amplicon sequence variants (ASVs), a proxy for species, and clear difference in ASV composition in ice and pelagic habitats. The pelagic community showed interannual differences. In 2018 the community was dominated by dinoflagellates and nano- and pico-plankton such as Micromonas polaris. In 2019 a community with more centric diatoms was observed at ice edge stations. Members of the class Chrysophyceae dominated in melt ponds, whereas communities within the ice were dominated by dinoflagellates and pennate diatoms. The community changed from top to bottom of the ice cores and the diversity was higher in thick than thin ice. Just below the ice, dinoflagellate ASVs dominated together with Phaeocystis. Our results indicate that protist communities are distinct and specialized by habitat. With further ocean warming, pelagic communities may shift towards smaller flagellates, and thinning of the sea ice may lead to a loss of habitats and diversity.

• Edvardsen, Bente; Supraha, Luka; Egge, Elianne Dunthorn & Saubrekka, Karoline (2023). Diversity and distribution of marine protists in the Arctic explored by a polyphasic approach.
• Saubrekka, Karoline; Vader, Anna; Supraha, Luka; Andersen, Tom & Edvardsen, Bente (2023). Diversity and Distribution of Arctic Protists in Pelagic and Sympagic Habitats in the Northern Barents Sea as Revealed by Metabarcoding.
• Kwasniewski, Slawomir; Altenburger, Andreas; Assmy, Philipp Kurt Wolf; Bluhm, Bodil Annikki Ulla Barbro; Dabrowska, Anna Maria & Edvardsen, Bente [Vis alle 25 forfattere av denne artikkelen] (2023). Biodiversity in the northern Barents Sea and adjacent Nansen Basin – towards an updated inventory. Vis sammendrag

  Biodiversity patterns shape and drive ecosystem processes and functions in the global ocean. Given the changing climate and recent agreements to protect ocean regions, current estimates of biodiversity must be assembled. Here, we present new estimates and spatial patters of taxon richness from microbes to mammals from a shelf-to-basin transect in the northern Barents Sea and southern Nansen Basin from seasonal sampling in 2018-2022 by the Nansen Legacy project. We find that estimates of taxon richness are higher on the shelf than in the basin for pelagic protists, zooplankton, and benthic macrobenthos, nematodes, and prokaryotes, but not for sympagic protists. Taxon richness varied seasonally for pelagic prokaryotes, protists, and zooplankton, but little for sympagic meiofauna, benthic prokaryotes and macrobenthos. Unsurprisingly, taxon richness was generally highest for single-celled taxa. Taxon-rich groups included: sympagic diatoms; pelagic prokaryotes (e.g., Alphaproteobacteria), diatoms, dinoflagellates, copepods; and benthic prokaryotes (with abundant taxa, e.g., Candidatus nitrosopumilus and Woesia), nematodes, and polychaetes. Unexpectedly absent - though known from earlier studies - were, for example, nematodes in sea ice. Ironically, at top (and perhaps other) trophic levels species richness is likely to be enhanced regionally for some time, while losses of Arctic (endemic) species will impact global biodiversity, and potentially Arctic ecosystem functioning

• Saubrekka, Karoline (2021). The hidden forest in the Arctic.
• Dankel, Eli; Supraha, Luka; Edvardsen, Bente; Eikrem, Wenche & Saubrekka, Karoline (2023). Arktiske kalkflagellater: et morfologisk og molekylært dypdykk i det nordlige Barentshavet. Universitetet i Oslo. Vis sammendrag

  Oppblomstringer av kalkflagellater utgjør et viktig fundament for næringskjeden i Barentshavet. Fjernanalyse med satellittbilder har de siste tiårene dokumentert at denne oppblomstringen beveger seg nordover i takt med økende klimaendringer. Det er likevel fortsatt uvisst hva som skjer på artsnivå. Å forstå hvordan forekomsten til den enkelte art forandrer seg i møte med endrede miljøbetingelser, som redusert is og økende temperatur, gjør at man enklere kan forutse hvordan fytoplanktonsamfunnet vil respondere på et fremtidig, varmere Arktis. For denne oppgaven ble det hentet inn vannprøver fra syv stasjoner på et sør-nord-transekt i Barentshavet i august 2018 og 2019 under tokt i regi av forskningsprosjektet Arven etter Nansen (AeN). 2018 var globalt et av de varmeste årene på mange tiår, og Barentshavet var dermed isfritt den sommeren. I 2019 derimot var større deler av Barentshavet dekket av is. Prøver tatt for både svepeelektronmikroskopi (scanning electron microscopy, forkortet «SEM») og metastrekkoding (metabarcoding) ble brukt i oppgaven slik at resultatene fra metodene kunne sammenlignes. Formålet med SEM var å utføre både en kvalitativ og kvantitativ analyse av kalkflagellater. Metastrekkoding ble brukt til sekvensering av 18S rRNA-genet. I SEM fant jeg i prøvene fra 2018 Emiliania huxleyi, Coccolithus pelagicus, Papposphaera sarion, Papposphaera arctica, Wigwamma annulifera og Porsildia acerviphora. Utenom Coccolithus pelagicus og Wigwamma annulifera, ble de samme artene funnet i 2019. I tillegg ble Syracosphaera Marginiporata funnet i prøver fra et AeN-tokt i november-desember 2019. Artene fra 2018 var hovedsakelig til stede på den sørligste stasjonen i transektet, mens artene fra 2019 generelt ble funnet på flere forskjellige stasjoner. Fra metastrekkoding ble det registrert 13 OTUer (Operational Taxonomic Units) som er bestemt til kalkflagellat-taksa. Ettersom det stort sett mangler referansesekvenser for arktiske kalkflagellater, ble de fleste OTUene kun klassifisert til klasse eller orden. OTUene var for det meste til stede i prøvene fra den sørligste, og de to nordligste stasjonene. Det ble ikke observert et nevneverdig mønster i sammenheng med isdekket. Det ble derimot både for SEM og metastrekkoding observert at de fleste artene var til stede på stasjoner som i ulik grad ble påvirket av Den nordatlantiske havstrømmen. Resultatene er likevel ikke holdbare nok til å trekke en konklusjon om hvordan kalkflagellatsamfunnet i Barentshavet vil se ut i fremtiden. Ettersom de fleste OTUene viste lav taksonomisk oppløsning, og alle celler funnet i SEM ble bestemt til artsnivå, anbefaler jeg at SEM forblir den foretrukne metoden for kvalitativ og kvantitativ analyse av kalkflagellater.

• Walbækken, Hanna Myhre; Eikrem, Wenche; Edvardsen, Bente; Saubrekka, Karoline & Hofgaard, Antje (2023). Dinoflagellate diversity in the Barents Sea: a comparative identification analysis. Universitetet i Oslo. Vis sammendrag

  An important group in the protist community in marine habitats are dinoflagellates. In this study the diversity of dinoflagellates in a transect of seven pelagic sea stations in the Northern Barents Sea in August 2018 and August 2019 was assessed. The two sampling periods were characterized with low and high sea-ice extent, respectively. I have studied the diversity and presence of dinoflagellate species in the sample transect using the molecular method DNA metabarcoding, and the morphological methods light microscopy (LM), and scanning electron microscopy (SEM). The results from species identification were used to observe and compare potential differences in the two sampling years. It was shown that the morphological methods were limited in identification success by little amount of material in several of the vertical net haul samples, resulting in some bias when these results were compared with DNA metabarcoding that revealed a high number of OTU (operational taxonomic unit) reads assigned to division Dinoflagellata. Species classification by DNA metabarcoding was shown to be limited by the availability of reference sequences in the curated protist ribosomal database PR2. It yielded a rough overview of the composition of dinoflagellate species in the sampling transect that could be closer examined with more time to study single OTUs. Identification done by LM and SEM revealed the presence of genera in certain stations that was not revealed in metabarcoding, and vice versa. I also found that Lugol’s solution functioned well for the preservation of cell structure for sample analysis in SEM. Climate change is shown to cause more and rapid alterations in the Arctic, and the loss of sea-ice is an important consequence of a warmer climate. Regarding interannual differences in 2018 and 2019, the morphological methods showed some differences in species composition with genus Protoperidinium more often identified in 2018 than other species, and the same for Gymnodiniales species in 2019. This could potentially show a shift in phytoplankton communities in a changing environment, although time-series are necessary to predict the future compositions of dinoflagellate species. As phytoplankton makes up the fundament for the Arctic food chain, studies of changing environmental conditions are valuable for ecological reasons.

• Edvardsen, Bente; Gryn, Khrystyna; Šupraha, Luka; Eikrem, Wenche & Saubrekka, Karoline (2023). Biodiversity and distribution of Arctic phytoplankton and ice algae. Universitetet i Oslo. Vis sammendrag

  The project aims to enhance our understanding of Arctic marine ecosystems by researching the diversity, distribution, and functioning of phytoplankton and ice algae in response to rapid environmental changes. The diversity and biogeography of phytoplankton and ice algae from the Barents Sea were studied by combining algal cultivation and 18S and 28S rRNA gene sequencing. During the Nansen legacy project cruise in August 2019 (AeN706), a total of 46 algal strains were isolated from stations along a S-N transect in the Barents Sea into the Arctic Ocean. The identifications obtained from DNA sequencing, phylogenetic analysis and morphological examination indicated the presence of common Arctic algal species, such as Attheya septentrionalis, Thalassiosira gravida, and Chaetoceros neogracilis, among the identified genotypes. Additionally, this study has also characterised potentially novel species or species that have not been adequately described before. Taxonomic identification of the strains was performed using molecular and morphological approaches, and the biogeographic distribution was mapped using a global compilation of published metabarcoding datasets. It was demonstrated by the biogeographic analyses that four general biogeographic distribution types exist for arctic phytoplankton and ice algae: polar, arctic, arctic-temperate, and cosmopolitan. Genotypes with arctic-temperate distribution was most common among the characterised strains, and genotypes endemic to the arctic was also found. Only two genotypes with cosmopolitan distribution and one genotype with polar distribution were discovered. The results highlight that the phytoplankton and ice algal communities in the Barents Sea and Arctic Ocean consist of genotypes endemic to the Arctic and genotypes with broader biogeographic distributions.

• Røsbak, Silje K.; Edvardsen, Bente; Eiler, Alexander; Saubrekka, Karoline & Fon, Mathias (2023). Mikrobielt samfunn i kulturer av Chrysochromulina leadbeateri og relaterte svepeflagellater undersøkt med metastrekkoding. Universitetet i Oslo. Vis sammendrag

  Skadelige marine algeoppblomstringer er et tilbakevendende problem over hele verden, der skadene har en påvirkning på økosystemer og lokal økonomi. Chrysochromulina leadbeateri var årsak til en massiv fiskedød i 2019, men mekanismene bak denne oppblomstringen er fortsatt ukjent. Målet med oppgaven var å undersøke bakteriediversiteten i kulturer av den fiske-giftige Chrysochromulina leadbeateri, og sammenligne denne mot andre beslektede svepeflagellater, både hos potensielt giftige og ikke-giftige arter. I tillegg til dette ble bakteriediversiteten av mikrobiomet mellom fastsittende bakterier på algecellene og frittlevende bakterier i kultur undersøkt. I denne oppgaven ble det prokaryote mikrobiomet i kulturer av tre stammer av Chryochromulina leadbeateri og 6 stammer av beslektede svepeflagellatarter analysert. Dette ble gjort ved metastrekkoding av det ribosomale 16S rRNA-genet. Det ble påvist et mangfoldig mikrobiom der hele bakteriedatasettet inneholdt 3 rekker, 14 ordener og 53 slekter. Bakteriesamfunnets sammensetning bestod hovedsakelig av medlemmer i rekken Proteobacteria etterfulgt av medlemmer av rekken Bacteroidota, og kun noen få ASVer i rekken Actinobacteria. Av de 14 ordenene var Rhodobacterales, Flavobacteriales, Caulobacterales, Rhiszobiales og Cytophagales de mest vanlige. Av de 53 slektene var Marivita (Rhodobacterales) den mest abundante, etterfulgt av Roseovarius (Rhodobacterales), Jannaschia (Rhodobacterales), Hoefla (Rhizobiales), Seohaeicola (Rhodobacterales), Hyphomonas (Rhodobacterales) og Sulfitobacter (Rhodobacterales). Taksonomisk fordeling av bakterieslekter mellom de potensielt giftige og ikke-giftige svepeflagellatene viste forskjeller, der de potensielt giftige hadde flest unike identifiserte bakterieslekter. Når det gjelder alfadiversitet (forskjeller innad i et samfunn) viser de to gruppene derimot ingen store forskjeller i mikrobiomet. Det ble funnet en svak signifikant sammenheng i mikrobiomets betadiversitet (forskjeller mellom samfunn) mellom kulturer av potensielt giftige og ikke-giftige svepeflagellater, der svepeflagellatens giftighet innen slekt hadde en svak effekt i denne studien. I tillegg viste slekten til svepeflagellaten til å ha en signifikant betydning for hvilke bakteriearter som ble funnet i algekulturer. Ved en sammenligning av fordelingen av bakterieslekter som er fastsittende til algecellen og frittlevende i algekultur, deler de to gruppene 80 % av bakterieslektene, og har dermed høy likhet. De frittlevende bakteriene har høyest antall ASVer, noe som indikerer at de fleste bakterie-typene lever fritt i kultur. Dette vises også ved de statistiske analysene, der alfadiversiteten for de IV frittlevende bakteriene i kultur har et signifikant rikere mikrobiom i forhold til fastsittende bakterier til algecellen. Betadiversiteten mellom fastsittende og frittlevende bakterier viser derimot ingen signifikante forskjeller, som vil si at mikrobiom-sammensetningen ikke kan forklares ut ifra om det er fastsittende på algecellene eller frittlevende i kultur.

• Reigstad, Marit; Gabrielsen, Tove M.; Amargant-Arumi, Marti; Amundsen, Rita; Bluhm, Bodil & Bodur, Yasemin V. [Vis alle 37 forfattere av denne artikkelen] (2022). Seasonal Cruise Q3: Cruise Report . Septentrio Academic Publishing. ISSN 2703-7525. Vis sammendrag

  The Nansen Legacy Q3 cruise, 5-27 August 2019, initiated the seasonal investigations of the Nansen Legacy transect. The transect represent an environmental gradient going through the northern Barents Sea, and included 7 process stations (P1-P7) lasting 6-53 hrs. CTD stations were taken to increase the hydrographic resolution on the transect. The program included measurements and sampling from the atmosphere, sea ice, ocean and sea floor. Data collected ranged from physical observations, chemical, biological and geological data collection, and the aim was to link observations and measurements to improve our understanding of the systems involving both climate, human impacts and the ecosystems. Deployment of moorings and gliders extended the observational capacity in time and space, outside the cruise period.

• Ludvigsen, Martin; Assmy, Philipp; Adams, Matthew James Samuel; Arumi, Marti A.; Mo-Bjørkelund, Tore & Bodur, Yasemin V. [Vis alle 35 forfattere av denne artikkelen] (2022). Seasonal cruise Q2 2021: Cruise Report . Septentrio Academic Publishing. ISSN 2703-7525. Vis sammendrag

  The spring season was the target for the Nansen Legacy cruise organized in late April and first half of May 2021 following the transect defined for this series of cruises to capture the variations of the year sampling physical, biological and chemical conditions in the ice and the sea. The transect went through both open water and ice. Seven process stations were visited (P1 through P7) together with smaller NLEG stations according to the program for the seasonal investigations. The first station (P1) was in open waters, while the remaining six main station had ice coverage of varying degree. Each of the process stations lasted 24 hours or more to allow a full diurnal cycle. Sampling included ice physics, ice samples, phytoplankton, zooplankton, marine chemistry and eco toxicology using acoustic, optical and robotics methods together with lab analyses of physical samples. Remote sensing data were also matched with in situ observations of both sea and ice conditions.

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