Biology subjects

Wietz, M.

Publications and source records attributed to Wietz, M..

17 recordsLinked to original sources

bioRxiv2026

Benthic biodiversity hotspots in the Weddell Sea: Bridging geomorphology, biogeography, and oceanography across scales

Benthic ecosystems are shaped by seafloor structure, yet linking geomorphology and biology across environmental gradients remains challenging. Here, we integrate seafloor imagery, multiscale bathymetry, and predictive modelling to quantify benthic biodiversity and its environmental drivers along the Powell Basin flank of the Antarctic Peninsula. Steep geomorphological landforms (terraces and steep slopes) hosted maximal densities and distinct communities, with significant enrichment of corals, sponges, ophiuroids, and sea pens. The marked congruence of slope across bathymetric resolutions enabled regional upscaling, estimating a standing stock of [~]96 billion individuals across 7,400 km{superscript 2} of the basin flank. Decadal oceanographic models indicate that benthic densities peak in cold bottom water below -0.15 {degrees}C. We identified four biodiversity hotspots ([~]33 km2) with slopes >35{degrees} and depths >1,700 m, with up to threefold higher densities. Hotspots align with the pathway of Weddell Sea Deep Water, where thermal decoupling between bottom and overlying waters indicates dynamic hydrography along steep, biodiverse terrain. Furthermore, contrasting sea-ice cover and stratification regimes suggest distinct cryo-pelagic-benthic coupling around hotspots. The concentration of biodiversity through seafloor geomorphology and ocean circulation bridges Antarctic benthic ecology from habitat to biogeography, with implications for monitoring change and guiding conservation in the warming Weddell Sea.

ecology↗

bioRxiv2025

Seasonal connectivity of microbes and carbohydrates between ocean, atmosphere, and cryosphere in Kongsfjorden (Svalbard, Arctic Ocean)

The coupling between ocean and atmosphere across the strong seasonal gradients in the Arctic is poorly understood. Here, we explored the microbial and glycobiological connectivity between the sea surface microlayer (SML), the underlying seawater (ULW), snow, and aerosol particles in Kongsfjorden (Svalbard, 79{degrees}N) during autumn and spring. The marked overlap between marine and atmospheric microbiomes illustrates considerable sea-air transfer, linked to seasonally distinct environmental communities. For instance, Polaribacter and Formosa were aerosolized during the spring bloom, compared to Colwellia in autumn. Air-mass trajectories and microbial source tracking revealed a greater marine contribution in autumn, whereas spring aerosols were shaped by stronger winds and the cryosphere. Aerosol particles nonetheless contained numerous unique taxa, including Actinobacteria likely originating from terrestrial sources. Linking bacterial, microeukaryotic, carbohydrate, and meteorological dynamics established an overarching perspective across seasons and habitats, identifying four distinct ecosystem states. Genome-sequenced bacterial model isolates, representing key environmental populations, encode adaptive traits such as carotenoid and ectoine biosynthesis, supporting survival in the SML and atmospheric transfer. Comparison with time-series records from the nearby Fram Strait revealed that many aerosolized bacteria are consistent microbiome components; with implications for ecology and biogeochemistry across the wider Arctic.

microbiology↗

bioRxiv2025

Characterizing organisms from three domains of life with universal primers from throughout the global ocean

We introduce the Global rRNA Universal Metabarcoding Plankton database (GRUMP), which consists of 1194 samples that were collected from 2003-2020 and cover extensive latitudinal and longitudinal transects, as well as depth profiles in all major ocean basins. DNA from unfractionated (> 0.2{micro}m) seawater samples was amplified using the 515Y/926R universal three- domain rRNA gene primers, simultaneously quantifying the relative abundance of amplicon sequencing variants (ASVs) from bacteria, archaea, eukaryotic nuclear 18S, and eukaryotic plastid 16S. Thus, the ratio between taxa in one sample is directly comparable to the ratio in any other GRUMP sample, regardless of gene copy number differences. This obviates a problem in prior global studies that used size-fractionation and different rRNA gene primers for bacteria, archaea, and eukaryotes, precluding comparisons across size fractions or domains. On average, bacteria contributed 71%, eukaryotes 19%, and archaea 8% to rRNA gene abundance, though eukaryotes contributed 32% at latitudes > 40{degrees}. GRUMP is publicly available on the Simons Collaborative Marine Atlas Project (CMAP), promoting the global comparison of marine microbial dynamics.

ecology↗

bioRxiv2025

Genome restructuring and adaptation in Arctic marine bacteria

Arctic marine bacteria experience seasonal changes in temperature, salinity, and light caused by the formation and melting of sea-ice. Time-series studies have identified spatial and temporal patterns in microbial communities in the Arctic and environmental sequencing has provided insights into the genetic potential of key taxa. We cultured and sequenced the complete genomes of 34 Arctic marine bacteria to identify patterns of gene gain, loss, and rearrangement that structure genomes and underlie adaptations to Arctic conditions. We found that the most abundant lineage in the Arctic (SAR11) is comprised of diverse species and subspecies, each encoding 50-150 unique genes. Half of the SAR11 genomes (8/16) harbor a genomic island with the potential to enhance survival in the Arctic by utilizing the osmoprotectant and potential methyl donor glycine betaine. We also cultured and sequenced four species from a new family of Pseudomonadales, four subspecies of Pseudothioglobus (SUP05), a genus of high GC Puniceispirillaes (SAR116), and a family of low GC SAR116. Time-series data indicate that this collection represents up to 60% of the marine bacterial community in Arctic waters at peak abundance. Their complete genomes provide insights into the evolutionary processes that underlie diversity and adaptation to the Arctic Ocean.

microbiology↗

bioRxiv2024

Arctic Ocean virus communities: seasonality, bipolarity, and prokaryotic interactions

Viruses play important roles in ocean environments as agents of mortality and genetic transfer, influencing ecology, evolution and biogeochemical processes. However, we know little about the diversity, seasonality, and host interactions of viruses in polar waters. To address this, we studied dsDNA viruses in the Arctic Fram Strait across four years via 47 long-read metagenomes of the cellular size-fraction. Among 5,662 vOTUs, 69%, 30% and 1.4% were bacteriophages (Myoviridae, Podoviridae, and Siphoviridae), Unassigned, and Phycodnaviridae, respectively. Viral coverage was, on average, 5-fold higher than prokaryotic coverage, and 8-fold higher in summer. Viral community composition showed annual peaks in similarity and was strongly correlated with prokaryotic community composition. Using a Convergent Cross Mapping network, we identified putative virus-host interactions and six ecological modules, each associated with distinct environmental conditions. The network also revealed putative novel cyanophages with time-lagged correlations to their hosts (late summer) as well as diverse viruses correlated with Nitrososphaerales (winter). By comparison with global metagenomes, we found that 42% of Fram Strait vOTUs peaked in abundance in high latitude regions of both hemispheres (average 61{degrees}N and 51{degrees}S), and encoded proteins with biochemical signatures of cold adaptation. Our study reveals a rich diversity of polar viruses with pronounced seasonality, providing a foundation for understanding how they regulate and impact ecosystem functionality in changing polar oceans.

microbiology↗

bioRxiv2024

Seasonal recurrence and modular assembly of an Arctic pelagic marine microbiome

Deciphering how microbial communities are shaped by environmental variability is fundamental for understanding the structure and function of ocean ecosystems. Thus far, we know little about the structuring of community functionality and the coupling between taxonomy and function over seasonal environmental gradients. To address this, we employed autonomous sampling devices and in situ sensors to investigate the taxonomic and functional dynamics of a pelagic Arctic Ocean microbiome over a four-year period. We demonstrate that the dominant prokaryotic and microeukaryotic populations exhibit recurrent, unimodal fluctuations each year, with community gene content following the same trend. The recurrent dynamics within the prokaryotic microbiome are structured into five temporal modules that represent distinct ecological states, characterised by unique taxonomic and metabolic signatures and connections to specific microeukaryotic populations and oceanographic conditions. For instance, Cand. Nitrosopumilus and the machinery to oxidise ammonia and reduce nitrite are signatures of early polar night, along with Radiolarians. In contrast, late summer is characterised by Amylibacter, sulfur compound metabolism and diverse Haptophyta lineages. Exploring the composition of modules further along with their degree of functional redundancy and the structuring of genetic diversity within functions over time revealed seasonal heterogeneity in environmental selection processes. In particular, we observe strong selection pressure on a functional level in spring while late polar night features weaker selection pressure that likely acts on an organismal level. By integrating taxonomic, functional, and environmental information, our study provides fundamental insights into how microbiomes are structured under pronounced environmental variability in understudied, yet rapidly changing polar marine ecosystems.

microbiology↗

bioRxiv2024

Beyond blooms: A novel time series analysis framework predicts seasonal keystone species and sheds light on ecosystem stability in the Fram strait

A thorough understanding of ecosystem functioning in the Arctic Ocean, a region under severe threat by climate change, requires detailed studies on linkages between biodiversity and ecosystem stability. The identification of keystone species with special relevance for ecosystem stability is of great importance, yet difficult to achieve with established community assessments. In the case of microbes, metabarcoding and metagenomics offer fundamental insights into community structure and function, yet remain limited regarding the ecological relevance of individual taxa. To overcome this limitation, we have developed an analytical approach based on three different methods: Co-Occurrence Networks, Convergent Cross Mapping, and Energy Landscape Analysis. These methods enable the identification of seasonal communities in microbial ecosystems, elucidate their interactions, and predict potential stable community configurations under varying environmental conditions. Combining the outcomes of these three methods allowed us to define 38 keystone species in the Arctic Fram Strait that represent different trophic modes within the food web, and might signify indicator for ecosystem functionality under the impact of environmental change. Our research reveals a clear seasonal pattern in phytoplankton composition, with distinct assemblages characterizing the phases of carbon fixation (polar day) and consumption (polar night). Species interactions exhibited strong seasonality, with significant influence of summer communities on winter communities but not vice versa. Spring harbored two distinct groups: consumers (heterotrophs), strongly linked to polar night, and photoautotrophs (mainly Bacillariophyta). These groups are not causally related, suggesting a "winter reset" with selective effects that facilitates a new blooming period, allowing survivors of the dark phase to emerge. Energy Landscape Analysis showed that winter communities are more stable than summer communities. In summary, the ecological landscape of the Fram Strait can be categorized into two distinct phases: a production phase governed by specialized organisms that are highly responsive to environmental variability, and a heterotrophic phase dominated by generalist species with enhanced resilience.

bioinformatics↗

bioRxiv2023

Collaborative metabolic curation of an emerging model marine bacterium, Alteromonas macleodii ATCC 27126

Inferring the metabolic capabilities of an organism from its genome is a challenging process, relying on computationally-derived or manually curated metabolic networks. Manual curation can correct mistakes in the draft network and add missing reactions based on the literature, but requires significant expertise and is often the bottleneck for high-quality metabolic reconstructions. Here, we present a synopsis of a community curation workshop for the emerging model marine bacterium Alteromonas macleodii ATCC 27126 and its genome database in BioCyc, focusing on pathways for utilizing organic carbon and nitrogen sources. Due to the scarcity of biochemical information or gene knock-outs, the curation process relied primarily on published growth phenotypes and bioinformatic analyses, including comparisons with related Alteromonas strains. We report full pathways for the utilization of the algal polysaccharides alginate and pectin in contrast to inconclusive evidence for one carbon metabolism and mixed acid fermentation, in accordance with the lack of growth on methanol and formate. Pathways for amino acid degradation are ubiquitous across Alteromonas macleodii strains, yet enzymes in the pathways for the degradation of threonine, tryptophan and tyrosine were not identified. Nucleotide degradation pathways are also partial in ATCC 27126. We postulate that demonstrated growth on nitrate as sole N source proceeds via a nitrate reductase pathway that is a hybrid of known pathways. Our evidence highlights the value of joint and interactive curation efforts, but also shows major knowledge gaps regarding Alteromonas metabolism. The manually-curated metabolic reconstruction is available as a "Tier-2" database on BioCyc. ImportanceMetabolic reconstructions are vital for the systemic understanding of an organisms ecology. Here, we report the outcome of a collaborative, interactive curation workshop to build a curated "metabolic encyclopedia" for Alteromonas macleodii ATCC 27126, a marine heterotrophic bacterium with widespread occurrence. Curating pathways for polysaccharide degradation, one-carbon metabolism, and others closed major knowledge gaps, and identified further avenues of research. Our study highlights how the combination of bioinformatic, genomic and physiological evidence can be harvested into a detailed metabolic model, but also identifies challenges if little experimental data is available for support. Overall, we show how an interactive get-together by a diverse group of scientists can advance the ecological understanding of emerging model bacteria, with relevance for the entire scientific community.

microbiology↗

bioRxiv2023

Sea-ice melt determines seasonal phytoplankton dynamics and delimits the habitat of temperate Atlantic taxa as the Arctic Ocean atlantifies

The Arctic Ocean is one of the regions where anthropogenic environmental change is progressing most rapidly and drastically. The impact of rising temperatures and decreasing sea ice on Arctic marine microbial communities is yet not well understood. Microbes form the basis of food webs in the Arctic Ocean, providing energy for larger organisms. Previous studies have shown that Atlantic taxa associated with low light are robust to more polar conditions. In this study, we compared to which extent sea ice melt influences light-associated phytoplankton dynamics and biodiversity over two years at two mooring locations in the Fram Strait. One mooring is deployed in pure Atlantic water, and the second in the intermittently ice-covered Marginal Ice Zone. Time-series analysis of amplicon sequence variants abundance over a two-year period, allowed us to identify communities of co-occurring taxa that exhibit similar patterns throughout the annual cycle. We then examined how alterations in environmental conditions affect the prevalence of species. During high abundance periods of diatoms, polar phytoplankton populations dominated, while temperate taxa were weakly represented. Generally, polar pelagic and ice-associated taxa (such as Fragilariopsis cylindrus or Melosira arctica) were more prevalent in Atlantic conditions whereas temperate taxa (such as Odontella aurita or Proboscia alata) have limited potential to persist in colder ice-impacted waters. In contrast to previous assumptions, we think that sea-ice melt acts as a barrier to the horizontal extent of temperate diatoms by preventing their succession at places strongly influenced by polar conditions such as the melting sea ice.

ecology↗

bioRxiv2023

Ecogenomics reveals distinctive viral-bacterial communities in the surface microlayer of a natural surface slick

Visible surface films, termed slicks, can extensively cover the sea surface, particularly in coastal regions. The sea-surface microlayer (SML), the upper 1-mm at the air-water interface in slicks (slick SML) harbors a distinctive bacterial community, but little is known about SML viruses. Using flow cytometry, metagenomics, and cultivation, we investigated viruses and the bacterial community from a brackish slick SML in comparison to non-slick SML as well as the seawater below (SSW). We conducted size-fractionated filtration of all samples to distinguish viral attachment to hosts and particles. The slick SML contained higher abundances of virus-like particles, prokaryotic cells, and dissolved organic carbon compared to non-slick SML and SSW. The community of 428 viral operational taxonomic units (vOTUs), 426 predicted as lytic, distinctly differed across all size fractions in the slick SML compared to non-slick SML and SSW. The distinctness was underlined by specific metabolic profiles of bacterial metagenome assembled genomes and isolates, which revealed prevalence of motility genes and diversity of CAZymes in the slick SML. Despite overall lower diversity, several vOTUs were enriched in slick SML over slick SSW. Nine vOTUs were only found in slick SML and six of them were targeted by slick SML-specific CRISPR spacers likely originating from Gammaproteobacteria. Moreover, isolation of three previously unknown lytic phages for Alishewanella sp. and Pseudoalteromonas tunicata, representing abundant and actively replicating slick SML bacteria, suggests that viral activity in slicks can contribute to biogeochemical cycling in coastal ecosystems.

microbiology↗

bioRxiv2022

"Wissenschaft fürs Wohnzimmer" - two years of interactive, scientific livestreams weekly on YouTube

Science communication is becoming increasingly important to connect academia and society, and to counteract fake news among climate change deniers. Online video platforms, such as YouTube, offer great potential for low-threshold communication of scientific knowledge to the general public. In April 2020 a diverse group of researchers from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research launched the YouTube channel "Wissenschaft furs Wohnzimmer" (translated to "Sitting Room Science") to stream scientific talks about climate change and biodiversity every Thursday evening. Here we report on the numbers and diversity of content, viewers, and presenters from 2 years and 100 episodes of weekly livestreams. Presented topics encompass all areas of polar research, social issues related to climate change, and new technologies to deal with the changing world and climate ahead. We show that constant engagement by a group of co-hosts, and presenters from all topics, career stages, and genders enable a continuous growth of views and subscriptions, i.e. impact. After 783 days the channel gained 30,251 views and 828 subscribers and hosted well-known scientists while enabling especially early career researchers to improve their outreach and media skills. We show that interactive and science-related videos, both live and on-demand, within a pleasant atmosphere, can be produced voluntarily while maintaining high quality. We further discuss challenges and possible improvements for the future. Our experiences may help other researchers to conduct meaningful scientific outreach and to push borders of existing formats with the overall aim of developing a better understanding of climate change and our planet.

scientific communication and education↗

bioRxiv2022

Characterization of membrane vesicles in Alteromonas macleodii indicates potential roles in their copiotrophic lifestyle

Bacterial membrane vesicles (MVs) are likely abundant in the oceans. Based on observations from non-marine bacteria, MVs are involved in a range of physiological processes and play important roles in interactions between microbial cells. In this study we characterized MV production of six different strains of Alteromonas macleodii, a cosmopolitan marine bacterium. A. macleodii strains produced MVs at rates of up to 30 MVs cell-1 generation-1. The produced MVs had high morphological diversity that could potentially define their functional roles. Proteomic characterization revealed that MVs are rich in membrane proteins related to iron and phosphate uptake, as well as proteins with potential functions in biofilm formation. Furthermore, MVs were harboring hydrolytic enzymes. Taken together, our results suggest that in the largely oligotrophic oceans, A. macleodii MVs may support its growth through generation of extracellular "hotspots" that facilitate access to essential substrates. This study provides an important basis for further investigation of the ecological relevance of MVs in heterotrophic marine bacteria.

microbiology↗

bioRxiv2022

Variations in Atlantic water influx and sea-ice cover drive taxonomic and functional shifts in Arctic marine bacterial communities

The Arctic Ocean is experiencing unprecedented changes as a result of climate warming, necessitating detailed analyses on the ecology and dynamics of biological communities to understand current and future ecosystem shifts. Here we show the pronounced impact that variations in Atlantic water influx and sea-ice cover have on bacterial communities in the East Greenland Current (Fram Strait) using two, 2-year high-resolution amplicon datasets and an annual cycle of long-read metagenomes. Densely ice-covered polar waters harboured a temporally stable, resident microbiome. In contrast, low-ice cover and Atlantic water influx shifted community dominance to seasonally fluctuating populations enriched in genes for phytoplankton-derived organic matter degradation. We identified signature populations associated with distinct oceanographic conditions and predicted their ecological niches. Our study indicates progressing "Biological Atlantification" in the Arctic Ocean, where the niche space of Arctic bacterial populations will diminish, while communities that taxonomically and functionally resemble those in temperate oceans will become more widespread.

microbiology↗

bioRxiv2021

The Polar Night Shift: Annual Dynamics and Drivers of Microbial Community Structure in the Arctic Ocean

Change is a constant in the Arctic Ocean, with extreme seasonal differences in daylight, ice cover and temperature. The biodiversity and ecology of marine microbes across these extremes remain poorly understood. Here, using an array of autonomous samplers and sensors, we portray an annual cycle of microbial biodiversity, nutrient budgets and oceanography in the major biomes of the Fram Strait. In the ice-free West Spitsbergen Current, community turnover followed the solar cycle, with distinct separation of a productive summer state dominated by diatoms and carbohydrate-degrading bacteria, and a regenerative winter state dominated by heterotrophic Syndiniales, radiolarians, chemoautotrophic bacteria and archaea. Winter mixing of the water column replenishing nitrate, phosphate and silicate, and the onset of light were the major turning points. The summer succession of Phaeocystis, Grammonema and Thalassiosira coincided with ephemeral peaks of Formosa, Polaribacter and NS clades, indicating metabolic relationships between phytoplankton and bacteria. In the East Greenland Current, ice cover and greater sampling depth coincided with weaker seasonality, featuring weaker bloom/decay events and an ice-related winter microbiome. Low ice cover and advection of Atlantic Water coincided with diminished abundances of chemoautotrophic bacteria while Phaeocystis and Flavobacteriaceae increased, suggesting that Atlantification alters phytoplankton diversity and the biological carbon pump. Our findings promote the understanding of microbial seasonality in Arctic waters, illustrating the ecological importance of the polar night and providing an essential baseline of microbial dynamics in a region severely affected by climate change.

microbiology↗

bioRxiv2020

CAZymes in Maribacter dokdonensis 62-1 from the Patagonian shelf: Genomics and physiology compared to related flavobacteria and a co-occurring Alteromonas strain

Carbohydrate-active enzymes (CAZymes) are an important feature of bacteria in productive marine systems such as continental shelves, where phytoplankton and macroalgae produce diverse polysaccharides. We herein describe Maribacter dokdonensis 62-1, a novel strain of this flavobacterial species, isolated from alginate-supplemented seawater collected at the Patagonian continental shelf. M. dokdonensis 62-1 harbors a diverse array of CAZymes in multiple polysaccharide utilization loci (PUL). Two PUL encoding polysaccharide lyases from families 6, 7, 12 and 17 allow substantial growth with alginate as sole carbon source, with simultaneous utilization of mannuronate and guluronate as demonstrated by HPLC. Furthermore, strain 62-1 harbors a mixed-feature PUL encoding both ulvan- and fucoidan-targeting CAZymes. Core-genome phylogeny and pangenome analysis revealed variable occurrence of these PUL in related Maribacter and Zobellia strains, indicating specialization to certain "polysaccharide niches". Furthermore, lineage- and strain-specific genomic signatures for exopolysaccharide synthesis possibly mediate distinct strategies for surface attachment and host interaction. The wide detection of CAZyme homologs in algae-derived metagenomes suggests global occurrence in algal holobionts, supported by sharing multiple adaptive features with the hydrolytic model flavobacterium Zobellia galactanivorans. Comparison with Alteromonas sp. 76-1 isolated from the same seawater sample revealed that these co-occurring strains target similar polysaccharides but with different genomic repertoires, coincident with differing growth behavior on alginate that might mediate ecological specialization. Altogether, our study contributes to the perception of Maribacter as versatile flavobacterial polysaccharide degrader, with implications for biogeochemical cycles, niche specialization and bacteria-algae interactions in the oceans.

microbiology↗

bioRxiv2020

Sweet and magnetic: Succession and CAZyme expression of marine bacterial communities encountering a mix of alginate and pectin particles

Polysaccharide particles are an important nutrient source and microhabitat for marine bacteria. However, substrate-specific bacterial dynamics in a mixture of particle types with different polysaccharide composition, as likely occurring in natural habitats, are undescribed. Here, we studied the composition, functional diversity and gene expression of marine bacterial communities encountering a mix of alginate and pectin particles. Communities were collected above macroalgal forests near Helgoland Island - where polysaccharide-rich particles might regularly occur - and exposed to a mix of magnetic particles of each polysaccharide, allowing the targeted evaluation by particle type. Amplicon, metagenome and metatranscriptome sequencing revealed that particle-associated (PA) and free-living (FL) communities significantly differed in composition and metabolism, whereas dynamics on alginate and pectin particles were unexpectedly similar. Amplicon sequence variants (ASVs) from Tenacibaculum, Colwellia, Psychrobium and Psychromonas dominated the community on both particle types. Corresponding metagenome-assembled genomes (MAGs) expressed diverse alginate lyases, several co-localized in polysaccharide utilization loci. One low-abundance MAG related to Catenovulum showed pectin specialization through upregulated GH53 and GH105 genes. A single Glaciecola ASV dominated the FL fraction, likely persisting on particle-derived oligomers through different glycoside hydrolases. The bacterial preference for alginate, whereas pectin mainly served as colonization scaffold, illuminates substrate-driven microbial dynamics within mixed polysaccharide resources. Moreover, elevated ammonium metabolism signifies nitrogen availability as important factor on particles, whereas elevated methylcitrate and glyoxylate cycles illustrate nutrient-limited conditions in the surrounding water. These insights expand our understanding of bacterial microscale ecology, niche specialization and the biological carbon pump in macroalgae-rich habitats.

microbiology↗

bioRxiv2020

Submesoscale dynamics directly shape bacterioplankton community structure in space and time

Submesoscale eddies and fronts are recognized as important components of oceanic mixing and energy fluxes. These submesoscale phenomena occur in the surface ocean for a period of a few days on scales between several hundred meters and a few tens of kilometers. Remote sensing and modeling suggest that they may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0 - 400 m) revealed enhanced vertical mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical conditions. Compared to the surrounding waters the filament was characterized by a distinct phytoplankton bloom dominated by diatoms and two-fold higher bacterioplankton cell densities. High-throughput 16S rRNA gene sequencing of both bacterioplankton communities revealed 3-4 orders of magnitude higher sequence abundance of Synechococcus inside the filament, as well as tenfold higher sequence abundance of taxonomic groups typically found during summertime in aging phytoplankton blooms (e.g., Flavobacteriales). In contrast, the surrounding waters contained severalfold higher sequence abundance of winterly taxonomic groups that are also associated with polar water masses (e.g., SAR202 clade). Altogether, our results show that physical submesoscale processes in the ocean can shape distinct biogeochemical conditions and microbial communities within a few kilometers. Furthermore, our results underline the importance of such submesoscale features for our understanding of surface ocean diversity and biogeochemical processes.

ecology↗