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Nitrogen (N 2 ) fixation in oligotrophic surface waters is the main source of new nitrogen to the ocean 1 and has a key role in fuelling the biological carbon pump 2 . Oceanic N 2 fixation has been attributed almost exclusively to cyanobacteria, even though genes encoding nitrogenase, the enzyme that fixes N 2 into ammonia, are widespread among marine bacteria and archaea 3 – 5 . Little is known about these non-cyanobacterial N 2 fixers, and direct proof that they can fix nitrogen in the ocean has so far been lacking. Here we report the discovery of a non-cyanobacterial N 2 -fixing symbiont, ‘ Candidatus Tectiglobus diatomicola’, which provides its diatom host with fixed nitrogen in return for photosynthetic carbon. The N 2 -fixing symbiont belongs to the order Rhizobiales and its association with a unicellular diatom expands the known hosts for this order beyond the well-known N 2 -fixing rhizobia–legume symbioses on land 6 . Our results show that the rhizobia–diatom symbioses can contribute as much fixed nitrogen as can cyanobacterial N 2 fixers in the tropical North Atlantic, and that they might be responsible for N 2 fixation in the vast regions of the ocean in which cyanobacteria are too rare to account for the measured rates. A symbiosis between a diatom and a newly discovered species of alphaproteobacteria, ‘ Candidatus Tectiglobus diatomicola’, can fix nitrogen in the ocean, providing evidence that nitrogen fixers other than cyanobacteria have a key role in the marine environment.

Photosynthesis is one of the most important biological processes on Earth, providing the main source of bioavailable energy, carbon, and oxygen via the use of sunlight. Despite this importance, the minimum light level sustaining photosynthesis and net growth of primary producers in the global ocean is still unknown. Here, we present measurements from the MOSAiC field campaign in the central Arctic Ocean that reveal the resumption of photosynthetic growth and algal biomass buildup under the ice pack at a daily average irradiance of not more than 0.04 ± 0.02 µmol photons m −2  s −1 in late March. This is at least one order of magnitude lower than previous estimates (0.3–5 µmol photons m −2  s −1 ) and near the theoretical minimum light requirement of photosynthesis (0.01 µmol photons m −2  s −1 ). Our findings are based on measurements of the temporal development of the under-ice light field and concurrent measurements of both chlorophyll a concentrations and potential net primary production underneath the sea ice at 86 °N. Such low light requirements suggest that euphotic zones where photosynthesis can occur in the world’s oceans may extend further in depth and time, with major implications for global productivity estimates. This study shows that photosynthesis in the Arctic Ocean can occur at lower light levels than previously thought. This finding is based on unique measurements made on microalgae underneath sea ice in the high Arctic at the end of the polar night.

In May 2016, the remote-controlled Automated Filtration System for Marine Microbes (AUTOFIM) was implemented in parallel to the Long Term Ecological Research (LTER) observatory Helgoland Roads in the German Bight. We collected samples for characterization of dynamics within the eukaryotic microbial communities at the end of a phytoplankton bloom via 18S meta-barcoding. Understanding consequences of environmental change for key marine ecosystem processes, such as phytoplankton bloom dynamics requires information on biodiversity and species occurrences with adequate temporal and taxonomic resolution via time series observations. Sampling automation and molecular high throughput methods can serve these needs by improving the resolution of current conventional marine time series observations. A technical evaluation based on an investigation of eukaryotic microbes using the partial 18S rRNA gene suggests that automated filtration with the AUTOFIM device and preservation of the plankton samples leads to highly similar 18S community profiles, compared to manual filtration and snap freezing. The molecular data were correlated with conventional microscopic counts. Overall, we observed substantial change in the eukaryotic microbial community structure during the observation period. A simultaneous decline of diatom and ciliate sequences succeeded a peak of Miracula helgolandica, suggesting a potential impact of these oomycete parasites on diatom bloom dynamics and phenology in the North Sea. As oomycetes are not routinely counted at Helgoland Roads LTER, our findings illustrate the benefits of combining automated filtration with metabarcodingto augment classical time series observations, particularly for taxa currently neglected due to methodological constraints.

Global warming affects the Earth system in complex ways, often preventing a functional understanding of the underlying processes. Disentangling these processes between abiotic drivers and single species or entire communities is, however, essential for an in-depth understanding of the impacts of climate change on the ecosystem. Using a high-resolution time series on heat waves and cold spells in an Arctic fjord system, we demonstrate that AI-supported digital data processing, which is based on state-of-the-art observatory technology, has the potential to provide new insights into the effects of abiotic factors on biotic communities, which would not be possible with traditional expedition-based sampling methods. Furthermore, our study shows that short-term, event-driven anomalies in key ocean variables not only alter a system’s hydrography but also have the potential to impact the entire community across the trophic chain from benthos and zooplankton to fish. We found a significant positive correlation between hydrographic temperature anomalies and biota abundance, with high biota abundances linked to ‘Atlantic’ phases with frequent heat waves and low biota abundances correlated with ‘Arctic’ phases dominated by cold spells. The study also revealed that hydrographic anomalies can not only influence overall biota abundance in an area but also trigger complex shifts in species composition. This leads to fluctuating interannual abundance peaks in specific biotic groups, such as jellyfish, fish, or chaetognaths, depending on trigger factors that are not yet fully understood.

In this study, we created a dataset of a continuous three-year 18S metabarcoding survey to identify eukaryotic parasitoids, and potential connections to hosts at the Long-Term Ecological Research station Helgoland Roads. The importance of parasites and parasitoids for food web dynamics has previously been recognized mostly in terrestrial and freshwater systems, while marine planktonic parasitoids have been understudied in comparison to those. Therefore, the occurrence and role of parasites and parasitoids remains mostly unconsidered in the marine environment. We observed high abundances and diversity of parasitoid operational taxonomic units in our dataset all year round. While some parasitoid groups were present throughout the year and merely fluctuated in abundances, we also detected a succession of parasitoid groups with peaks of individual species only during certain seasons. Using co-occurrence and patterns of seasonal occurrence, we were able to identify known host-parasitoid dynamics, however identification of new potential host-parasitoid interactions was not possible due to their high dynamics and variability in the dataset.

In the next decade the pressures on ocean systems and the communities that rely on them will increase as multiple stressors of climate change, food security and human activities start to impact. Our ability to manage and sustain our oceans will depend on the data we collect and the information and knowledge generated. Much of the uptake of this knowledge will be outside the ocean domain, for example by policy makers, local Governments, custodians and other organizations, so it is imperative that we democratize or open the access and use of ocean data. This paper looks at how technologies, scoped by standards, best practice and communities of practice, can be deployed to change the way that ocean data is accessed, utilized, value added and transformed into information and knowledge. The current portal-download model which requires the user to know what data exists, where it is stored, in what format and with what processing, limits the uptake and use of ocean data. Using examples from a range of disciplines, a web services model of data and information flows is presented. A framework is described, including the systems, processes and human components, which delivers a radical rethink about the delivery of knowledge from ocean data. A series of vision statements describe parts of the future vision along with a series of recommendations about how this may be achieved. The paper recommends the development of virtual test-beds for end to end development of new data workflows and knowledge pathways. This supports the continued development, rationalization and uptake of standards, creates a platform around which a community of practice can be developed, promotes cross discipline engagement from ocean science through to ocean policy, allows for the commercial sector, including the informatics sector, to partner in delivering outcomes and provides a focus to leverage long term sustained funding. The next ten years will be ‘make or break’ for many ocean systems. The decadal challenge is to develop the governance and co-operative mechanisms to harness emerging information technology to deliver on the goal of generating the information and knowledge required to sustain oceans into the future.

The Helgoland Roads time series is one of the richest temporal marine data sets available. Running since 1962, it documents changes for phytoplankton, salinity, Secchi disc depths and macronutrients. Uniquely, the data have been carefully quality controlled and linked to relevant meta-data, and the pelagic time series is further augmented by zooplankton, intertidal macroalgae, macrozoobenthos and bacterioplankton data. Data analyses have shown changes in hydrography and biota around Helgoland. In the late 1970s, water inflows from the south-west to the German Bight increased with a corresponding increase in flushing rates. Salinity and annual mean temperature have also increased since 1962 and the latter by an average of 1.67°C. This has influenced seasonal phytoplankton growth causing significant shifts in diatom densities and the numbers of large diatoms (e. g. Coscinodiscus wailesii). Changes in zooplankton diversity have included the appearance of the ctenophore Mnemiopsis leidyi. The macroalgal community also showed an increase in green algal and a decrease in brown algal species after 1959. Over 30 benthic macrofaunal species have been newly recorded at Helgoland over the last 20 years, with a distinct shift towards southern species. These detailed data provide the basis for long-term analyses of changes on many trophic levels at Helgoland Roads.

Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation.

Cabled coastal observatories are often seen as future-oriented marine technology that enables science to conduct observational and experimental studies under water year round, independent of physical accessibility to the target area. Additionally, the availability of (unrestricted) electricity and an Internet connection under water allows the operation of complex experimental setups and sensor systems for longer periods of time, thus creating a kind of laboratory beneath the water. After successful operation for several decades in the terrestrial and atmospheric research field, remote controlled observatory technology finally also enables marine scientists to take advantage of the rapidly growing communication technology. The continuous operation of two cabled observatories in the southern North Sea and off the Svalbard coast since 2012 shows that even highly complex sensor systems, such as stereo-optical cameras, video plankton recorders or systems for measuring the marine carbonate system, can be successfully operated remotely year-round facilitating continuous scientific access to areas that are difficult to access, such as the polar seas or the North Sea. Experience also shows, however, that the challenges of operating a cabled coastal observatory go far beyond the provision of electricity and network connection under water. In this manuscript, the essential developmental stages of the \"COSYNA Shallow Water Underwater Node\" system are presented, and the difficulties and solutions that have arisen in the course of operation since 2012 are addressed with regard to technical, organizational and scientific aspects.

Understanding the threats to global biodiversity and ecosystem services posed by human impacts on coastal and marine environments requires the establishment and maintenance of ecological observatories that integrate the biological, physical, geological and biogeochemical aspects of ecosystems. This is crucial to provide scientists and stakeholders with the support and knowledge necessary to quantify environmental change and its impact on the sustainable use of the seas and coasts. In this paper, we explore the potential for the coastal and marine components of the International Long-Term Ecological Research Network (ILTER) to fill this need for integrated global observation, and highlight how ecological observations are necessary to address the challenges posed by climate change and evolving human needs and stressors within the coastal zone. The ILTER is a global network encompassing 44 countries and 700 research sites in a variety of ecosystems across the planet, more than 100 of which are located in coastal and marine environments (ILTER-CMS). While most (50%) of the ILTER-CMS were established after the year 2000, in some cases they date back to the early 1900s. At ILTER sites a broad variety of abiotic and biotic variables are measured, which may feed into other global initiatives. The ILTER community has produced tools to harmonize and compare measurements and methods, allowing for data integration workflows and analyses between and within individual ILTER sites. After a brief historical overview of ILTER, with emphasis on the marine component, we analyze the potential contribution of the ILTER-CMS to global coastal and ocean observation, adopting the “Strength, Weakness, Opportunity and Threats (SWOT)” approach. We also identify ways in which the in situ parameters collected at ILTER sites currently fit within the Essential Ocean Variables framework (as proposed by the Framework for Ocean Observation recommendations) and provide insights on the use of new technology in long-term studies. Final recommendations point at the need to further develop observational activities at LTER sites and improve coordination among them and with external related initiatives in order to maximise their exploitation and address present and future challenges in ocean observations.