Sedimentary ancient DNA sequences reveal marine ecosystem shifts and indicator taxa for glacial-interglacial sea ice conditions

Sedimentary ancient DNA (sedaDNA) analysis is a promising new approach for reconstructing the impact of past climate and environmental changes on marine paleobiodiversity. By recovering, amplifying, and sequencing taxonomically informative sedaDNA fragments preserved in sediments, it is possible to assess the response of a broad range of eukaryote taxa, including non-fossilizing lineages, to past climate change. Here we present a unique marine derived sedaDNA metabarcoding record, spanning the penultimate glacial-interglacial transition across Marine Isotope Stages 6 to 5d (>135–107 ka) from an Eirik Drift core-site in the Labrador Sea. We identified a range of marine groups including dinoflagellates, diatoms, coccolithophores, chlorophytes, and copepods. There were representatives of primary/secondary producers, grazers, and parasites, which may represent remnants of complex ecosystems and ancient food webs. There were significant biodiversity shifts following the penultimate deglaciation and changing sea ice conditions throughout the Last Interglacial. These shifts reflected the striking increase in community richness during periods of seasonal sea ice and reduction under extensive perennial sea ice cover and open ocean. We identify two potential sedaDNA indicator taxa sequences associated with past seasonal sea ice which are most likely pico-eukaryote representatives of Micromonas and Pyramimonas, both green algae with known sea ice associations in modern ecosystems. Our work demonstrates the importance of high resolution marine sedaDNA metabarcoding for unravelling climate-ecosystem linkages and strengthens the potential of sedaDNA signals for past sea ice reconstructions through indicator sequences.publishedVersio

Arctic Paleoceanography Cruise KH21-234 with R/V Kronprins Haakon

We set sail from Longyearbyen on 30.6.2021 to collect surface sediments, long sediment archives, water and plankton samples. The study area is located north of Svalbard, within the seasonal and permanent sea ice covered Arctic Ocean. We took stations N of Svalbard, near Nordaustlandet, Sophia Basin, Yermak Plateau and on the shelf east of Svalbard. In total, we had 52 stations. We deployed the multicorer at least once at every station and sampled the core tops already onboard. These samples will be included in the Arctic Surface Sediment DNA Database, which we will use to establish new aDNA based sea ice proxies. We recovered gravity cores from 12 stations that can be used to reconstruct the Arctic sea ice history in the Holocene, last glacial and likely also Last Interglacial. We collected ice and water and filtered these for eDNA and biomarkers, and water for tracing the isotope signal of the different water masses in the region (Atlantic Water, Polar Water).publishedVersio

A New Human Challenge Model for Testing Heat-Stable Toxin-Based Vaccine Candidates for Enterotoxigenic Escherichia Coli Diarrhea - Dose Optimization, Clinical Outcomes, and CD4+ T Cell Responses

Enterotoxigenic Escherichia coli (ETEC) are a common cause of diarrheal illness in young children and travelers. There is yet no licensed broadly protective vaccine against ETEC. One promising vaccine development strategy is to target strains expressing the heat-stable toxin (ST), particularly the human ST (STh), since infections with these strains are among the leading causes of diarrhea in children in low-and-middle income countries. A human challenge model based on an STh-only ETEC strain will be useful to evaluate the protective efficacy of new ST-based vaccine candidates. To develop this model, we experimentally infected 21 healthy adult volunteers with the epidemiologically relevant STh-only ETEC strain TW10722, identified a suitable dose, assessed safety, and characterized clinical outcomes and immune responses caused by the infection. Doses of 1×1010 colony-forming units (CFU) of TW10722 gave a suitable attack risk of 67% for moderate or severe diarrhea and an overall diarrhea attack risk of 78%. Non-diarrheal symptoms were mostly mild or moderate, and there were no serious adverse events. During the first month after ingesting the challenge strain, we measured significant increases in both activated CD4+ T cells and levels of serum IgG and IgA antibodies targeting coli surface antigen 5 (CS5) and 6 (CS6), as well as the E. coli mucinase YghJ. The CS5-specific CD4+ T cell and antibody responses were still significantly elevated one year after experimental infection. In conclusion, we have developed a safe STh-only ETEC-based human challenge model which can be efficiently used in Phase 2B trials to evaluate the protective efficacy of new ST-based vaccine candidates.publishedVersio

Sea Ice Variability in a Warmer Past: Last Interglacial Paleoceanography of the (Sub)Arctic Oceans

Det omfattende og permanente havisdekket som i dag karakteriserer det Arktiske havet er i rask endring med en havoverflate som uunngåelig er i endring fra hvit til blå. Forståelse for en slik omfattende endring og dets konsekvenser for hav, klima, og økosystemer i, og utenfor, de Arktisk og Subarktiske hav krever en forståelse for havisens naturlige variasjoner gjennom geologiske tid. Tidligere intervaller in jordens historie som var varme gir innsikt inn i hvordan klima og miljø responderer på et globalt varmere klima. Den Siste Interglasiale Perioden (LIG), Marine Isotop trinn (MIS) 5e, hadde mange karakteristikker som liknet på modellerte projeksjoner av vårt framtidige klima. Den hadde et varmere klima enn dagens, men også et mer ustabilt klima. En nøkkelfaktor som har potensial for å påvirke klima- og havvariasjoner er havis, men dets tilstedeværelse og utbredelse gjennom LIG er lite kjent. Hvilken rolle havis kan ha spilt i interglasial klimavariabilitet er dermed et uløst spørsmål. I tillegg, eksisterer det store uenigheter om tilstanden til Arktisk havis gjennom LIG, og den glasiale til interglasiale overgangen som er karakterisert av betydelig klima og miljøendringer. Havisen er intrikat knyttet til både variasjoner i havstrømmer og dynamiske isdekker gjennom tid. En forståelse for hvordan disse forskjellige parameterne i jordens is-hav-klima system henger sammen er viktig for å bedre forstå mekanismene som fører til havisvariasjoner, og i tillegg, forstå hvordan havisen kan påvirke de ulike komponentene i is-hav-klima systemet. Viktigheten av å forstå usikkerhetene knyttet til havisens variabilitet, og utbredelse, kombinert med usikkerhetene knyttet til interglasial klimavariasjoner utgjør det overordnede målet for denne avhandlingen; å bedre forstå hvilken rolle havis kan ha spilt i jorden is-hav-klima system gjennom den siste interglasiale perioden, og dets glasiale overganger. For å undersøke det overordnete målet løser denne doktorgradsavhandlingen årtusen til århundre skala LIG, og glasial til interglasial havisvariasjon og hydrografi i de Arktiske til Subarktiske havene. Dette inkluderer den siste delen av den glasiale perioden MIS 6 og dens avsmelting (Terminasjon II), MIS 5e/LIG og MIS 5d, noe som dekker en total tidsperiode fra ca. 140–90 tusen år siden. Fra marine sedimentkjerner analyserer vi fossile og geokjemiske rester av mikroorganismer som en gang levde i havisen og i overflatehavet. Disse danner nå et naturlig arkiv av tidligere havis- og hydrografisk variasjon. Spesifikt, er havisrekonstruksjonene basert p ̊a sedimentær mengder av isalge biomarkøren IP25, kombinert med fytoplanktonbiomarkører for åpent hav, og analyse av dinoflagellatcyster. Disse dataene sammenlignes med nye og tidligere publiserte proxirekonstruksjoner som avdekker et bredere bilde av den paleoseanografiske historien til (sub)Arktis. Denne doktorgradsavhandlingen inneholder to proxirekonstruksjoner fra Labradorhavet og Framstredet. Begge områdene avslører en utvikling av havis fra maksimale glasiale utbredelse, gjennom randis, til minimale interglasial havisutbredelse (Artikkel I og II). I artikkel I fra det subpolare Labradorhavet gir våre data et detaljert innblikk i interaksjonene mellom havis og dynamikken til overflatestrømmene som danner den subpolare gyren (SPG). I artikkel II gir våre proxirekonstruksjoner fra Framstredet innsikter om havisvariabilitet og produktivitet i sammenheng med isdekkedynamikk, dannelse av polynyaer og innstrømmende Atlanterhavsvann. I artikkel III gir våre data innsikt i mulig bruk av stabile oksygenisotoper fra kombinerte planktiske og bentiske foraminiferer for å avdekke havis, stratifisering og dypvannsdannelse i Labradorhavet. Resultatene presentert i denne avhandlingen gir ny kunnskap om utviklingen av havis gjennom den siste interglasiale perioden, og gir innsikt i evolusjonen av havis gjennom glasial til interglasiale klimaoverganger i en bredere kontekst av den paleoseanografiske historien til de Arktiske og Subarktiske regionene. Dessuten gir denne avhandlingen verdifull informasjon som kan brukes til å forbedre klimamodeller for mer nøyaktige projeksjoner av fremtidig klima, og tilbyr data for å evaluere nye proxier for havisrekonstruksjoner. Til sist, er disse dataene viktige for å bedre forstå interglasiale klima og naturlige havisvariasjoner, avgjørende for å bedre forstå konsekvensene assosiert med en fremtidig havisfri Arktisk sommer.The extensive to permanent state of the Arctic Ocean’s sea ice cover is changing rapidly, inevitably turning the surface of the Arctic Ocean from white to blue. Understanding this profound transformation and its implications for the climate, oceans and ecosystems in, and beyond, the Arctic and Subarctic regions requires an understanding of natural sea ice variability throughout geologic time. Past intervals of warming in Earth’s history provide insights into the climatic and environmental responses that may be triggered in a globally warming world. The Last Interglacial (LIG; 128–116 thousand years ago), Marine Isotope Stage (MIS) 5e, had many characteristics similar to model projections of our future climate. It had a warmer climate than present, but is also thought to have had a less stable climate. One key factor that has the potential to influence ocean and climate variability is sea ice, but its presence and extent throughout the LIG is poorly constrained. Thus, what role sea ice may have played in interglacial climate variability remains an unresolved question. Large discrepancies exist regarding the state of Arctic sea ice cover through the LIG, and the glacial-interglacial transitions characterised by large climatic and environmental shifts. Sea ice variability is intricately linked with the flow of surface ocean currents and dynamic ice sheets through time. Understanding how these different parameters of the Earth’s ice-ocean-climate system interact is crucial to ultimately understand better the mechanisms that lead to sea ice variability, and additionally understand how the sea ice may influence other components of the ice-ocean-climate system. The importance of elucidating the uncertainties related to sea ice variability, nature and extent, combined with uncertainties related to interglacial climate variability, makes up the overall aim of this thesis; to better understand the role of sea ice in the Earth’s ice-ocean-climate system throughout the LIG and its glacial transitions. To investigate the aim, this PhD thesis resolves millennial to centennial-scale LIG and glacial-interglacial sea ice variability and surface ocean hydrography in the Arctic and Subarctic Oceans. This includes the late glacial MIS 6, Termination II, MIS 5e/LIG, and MIS 5d covering a total time span from ca. 140–90 thousand years ago. From marine sediment cores, we analyze the fossil and geochemical remains of the microorganisms that once lived in the sea ice and surface ocean, now providing a natural archive of past sea ice and hydrographic variability. Specifically, sea ice reconstructions are based on the sedimentary abundance of the sea ice algae biomarker IP25 combined with open-water phytoplankton biomarkers, and dinoflagellate cyst assemblage analysis. These data are compared to new and previously published proxy-records that together provide new insights into the sea ice and paleoceanographic history of the (sub)Arctic Oceans. This PhD thesis includes two proxy reconstructions from the Labrador Sea and the Fram Strait regions. Both regions reveal an evolution of sea ice from maximum glacial extents, through marginal ice zone conditions, to minimum interglacial sea ice extents (Paper I and II). In paper I, our reconstruction from the subpolar Labrador Sea reveals a detailed insight into the connection between sea ice, and the dynamic surface circulation of the subpolar gyre (SPG). In paper II, our Fram Strait proxy-reconstruction reveals insights on sea ice variability and productivity in the context of ice sheet dynamics, polynya formation, and Atlantic water influence. In paper III, our data shed light on the potential use of coupled benthic and planktic foraminiferal stable oxygen isotopes to infer sea ice, stratification and deep convection in the subpolar Labrador Sea. The findings presented in this thesis contribute new insights into LIG sea ice variability, and into the evolution of sea ice across glacial to interglacial climates within the broader context of the paleoceanographic history of the Arctic and Subarctic. Furthermore, this thesis offers input information for enhancing the accuracy of climate model predictions of future climate, and it offers data for evaluating novel proxies for sea ice reconstructions. Ultimately, the findings are important for a better understanding of interglacial climates and natural sea ice variability, crucial for fully grasping the consequences associated with a future sea ice-free Arctic summer.Doktorgradsavhandlin

Deglasial isdynamikk på Vesterålenmarginen

Hvordan marinbaserte isdekker og isstrømmer responderer på endringer i miljø og klima er et stort usikkerhetsmoment i klimaforskning. Derfor er det viktig å studere hvordan tidligere isdekker og isstrømmer responderte på et varmere klima under den siste deglasiasjonen. I denne studien presenteres resultatene fra detaljerte sedimentologiske analyser av seks marine sedimentkjerner lokalisert i et langsgående transekt på øvre del av kontinentalskråningen utenfor Vesterålen, Nord-Norge. Kjernene er lokalisert c. 8 km nordvest for eggakanten og 40-50 km sør for utløpet til paleoisstrømmen som eksisterte i Andfjorden. Sedimentologiske tolkninger baserer seg på høyoppløslige tredimensjonale CT-avbildninger, kornstørrelsesanalyser ved Mastersizer 3000, element geokjemiske analyser ved XRF kjerneskanning samt radiokarbondatering av planktoniske foraminiferer. Nye dateringer, samt dateringer fra tidligere publisert litteratur, har blitt kalibrert med en ny kalibreringskurve for Norskehavet. Hovedformålet med studien er å rekonstruere og tidfeste ismarginfluktuasjonene og isstrømaktiviteten på kontinentalsokkelen utenfor Vesterålen. Et delmål er å diskutere de paleoseanografiske faktorene som kan ha bidratt til fluktuasjoner i ismargin og isstrømaktivitet, samt deglasiasjonen av isdekket fra kontinentalsokkelen. Sedimentkjernene fra kontinentalskråningen oppbevarer signaturer av sedimentære prosesser avsatt de siste 18,0–12,0 ka BP fra havbunnstrømmer, glasigene debrisstrømmer, isdroppet materiale fra isfjell og suspensjonsavsetning fra sedimentmettede smeltevannsplumer. Det Fennoskandiske isdekket rykket ut til eggakanten ved c. 16,8 ka BP (Heinrich hendelse 1.1) og 15,5 ka BP (Heinrich hendelse 1.2). Mellom disse fremrykkene, c. 16,5 ka BP, trakk ismarginen på Vesterålensokkelen seg tilbake, samtidig som Andfjordenisstrømmen var lokalisert ved eggakanten. Reaksjonene indikerer at det lokale isdekket på Vesterålenmarginen var mer sensitivt ovenfor miljø- og klimaendringer enn de omkringliggende isstrømmene som drenerte hovedisdekket. Fremrykkingen av isdekket under Heinrich stadial 1 er tolket til å ha foregått samtidig med etableringen av en stratifisert vannsøyle og et ekstensivt sjøisdekke i de nordiske hav. Deglasiasjonen av sokkelen og tilbaketrekningen av hovedisdekket på Vesterålenmarginen skjedde i begynnelsen av bøllingvarmingen, c. 14,8 ka BP. Tilbaketrekningen fant sted omtrent samtidig med at sjøisdekket ble redusert og atlantisk vann strømmet inn i Norskehavet ved en sterk AMOC. Disse overenstemmelsene tyder på at det er en sterk sammenheng mellom ismarginfluktuasjoner og dannelse av en stratifisert vannsøyle og sjøis, samt den endelige deglasiasjonen av isen på kontinentalsokkelen

Sea ice variability in the North Atlantic subpolar gyre throughout the last interglacial

The Last Interglacial period, Marine Isotope Stage 5e (MIS 5e ∼116–128 ka), is thought to have had a warmer, but less stable climate than the present interglacial. One key factor that has the potential to influence the ocean and climate is sea ice, but its presence and extent throughout MIS 5e is poorly constrained. Here we reconstruct the sea surface hydrography and sea ice variability in the Labrador Sea, a region influenced by the subpolar gyre (SPG) and where deep water formation occurs, in order to evaluate the potential of sea ice to drive or amplify ocean variability. We analysed biomarkers (highly branched isoprenoids, HBIs, and sterols), dinoflagellate cyst assemblages and stable oxygen isotopes from the late stages of MIS 6, throughout MIS 5e, into MIS 5d. Our results show that the late glacial MIS 6 was likely characterised by a thick multiyear sea ice cover. During the first phase of MIS 5e, the hydrography was highly variable. The initial 1500 years (128–126.5 ka) were characterised by the presence of a seasonal Marginal Ice Zone (MIZ) accompanied by subsurface warmth. As the sea ice retreated, cool, likely polar-sourced water dominated the surface and subsurface ocean (126.5–124 ka), until an abrupt surge of sea ice marked the final pulse of the remnants of the deglaciation. The second half of MIS 5e (124–116 ka) was characterised by a persistent inflow of warm water, only interrupted by incursions of cold water as summer insolation declined. Seasonal sea ice returned to the Eirik Drift during MIS 5d. We infer that sea ice variability throughout MIS 5e was coupled with the variability of the SPG. Especially the location of a proximal MIZ to the Labrador Sea convection region could have been important for SPG dynamics. In addition, the presence of sea ice at the transitions into and out of MIS 5e could point to its important role in modulating and enhancing the magnitude and coherence of climate signals at major climatic transitions.publishedVersio

Last Interglacial biomarker, dinoflagellate cyst, and stable oxygen isotope data from sediment core GS16-204-22CC-B

The dataset contains measurements of organic biomarkers and sterols, dinoflagellate cyst census counts, and benthic and planktonic stable oxygen isotope data from core GS16-204-22CC-B on the Eirik Drift (58°02.83′N, 47°02.36′W; 3160 m water depth) for Marine Isotope Stage 6, 5e and 5d. Total Organic Carbon (TOC), the Highly Branched Isoprenoids (HBIs) IP25, HBI II, HBI III (Z), and HBI III (E), and the sterols brassicasterol, dinosterol, campesterol and sitosterol were measured in the organic geochemistry lab at the Alfred Wegener Institute, Bremerhaven, Germany. Biomarker values are presented as biomarker/g dry sediment and biomarker/g TOC. Dinoflagellate cysts were counted along non overlapping traverses at x40 magnification using a transmitted light microscope and classified to species level as much as possible. The dataset consists of raw counts, relative abundances and dinocyst concentrations (cysts/g dry sediment). Stable oxygen isotopes (δ18O) were measured on the planktic foraminifera Neogloboquadrina pachyderma (sinistral) and benthic foraminifera Cibicidoides wuellestorfi. Values are reported relative to Vienna Pee Dee Belemnite. The measurements were carried out at FARLAB, University of Bergen, Norway. The age model for core GS16-204-22CC-B was obtained by correlation of benthic and planktic δ18O measured in this core with previously published isotope records in Irvali et al. (2012; 2016) and a 14C age from Griem et al. (2019)