ALBERT

Description: The Black Sea has undergone several limnic and marine stages due to fluctuations in the global sea level. The exchange of saline water from the Mediterranean Sea to the Black Sea through the Bosporus Strait was interrupted when the sea level dropped below the Bosporus sill. This induced limnic conditions, while marine conditions were established after the reconnection to saline Mediterranean seawater. Extended river fan systems developed during sea level low-stands, providing large amounts of organic material being buried by rapid sedimentation on the slopes of the Black Sea margins. The biogenic degradation of this material produces most of the methane gas expelled into the anoxic water column today. This largely happens by ubiquitous cold vents at ~700 m water depth (i.e. at the stability boundary of methane hydrates) and by mud volcanoes in ~2000 m water depth. A significant amount of gas is expected to accumulate in the sediment within the methane hydrate stability zone. However, bottom-simulating reflectors, the seismic indicator for gas hydrates, are not found everywhere along the margin. Recent analyses of the Danube and Dniepr fans have revealed a discontinuous gas hydrate formation in an area with no active seeps, while areas of active seepage located in the vicinity of BSR reflections held no gas hydrates. In addition, the ongoing diffusion of salt into the uppermost Black Sea sediment pore space since the last glacial maximum further reduces the volume of the gas hydrate stability zone. Estimates of the total amount of gas stored in gas hydrates therefore require a detailed structural analysis prior to regional- or basin-scale modelling attempts.

Description: Marine electromagnetic methods provide useful and independent measures for the identification and quantification of submarine gas hydrates. The resistivity of seafloor sediments, drawn from area-wide electromagnetic data, mainly depends on the sediment porosity and the nature of the pore fluid. Gas hydrates and free gas are both electrically resistive. The replacement of saline water, thus conductive pore water with resistive gas hydrate or free gas, increases the sediment resistivity and can be used to provide accurate saturation estimates if the background lithology is known. While seismic methods are predominantly used to study the distribution of submarine gas hydrates, a growing number of global field studies have demonstrated that the joint interpretation of marine seismic and electromagnetic methods improves the evaluation of submarine gas hydrate targets. This article discusses the relationship between resistivity and free gas/gas hydrate saturation levels, how the resistivity of the sediment may be measured and summarizes the status and results of current and past field studies.

Description: Every year, vast quantities of plastic debris arrive at the ocean surface. Nevertheless, our understanding of plastic movements is largely incomplete and many of the processes involved with the horizontal and vertical displacement of plastics in the ocean are still basically unknown. In this chapter we review the dynamics associated with the transport of plastics and other pollutants at oceanic fronts. Fronts had been historically defined as simple barriers to exchange, but here we show that the role of these structures in influencing the transport of plastics is more complex. The tools used to investigate the occurrence of frontal structures at various spatial scales are reviewed in detail, with a particular focus on their potential applications to the study of plastic pollution. Three selected case studies are presented to better describe the role of fronts in favoring or preventing plastic exchanges: the large-scale Antarctic Circumpolar Current, a Mediterranean mesoscale front, and the submesoscale fronts in the Gulf of Mexico. Lastly, some aspects related to the vertical subduction of plastic particles at oceanic fronts are discussed as one of the most promising frontiers for future research. The accumulation of floating debris at the sea surface is mainly affected by the horizontal components of frontal dynamics. At the same time, vertical components can be relevant for the export of neutrally buoyant particles from the surface into the deep sea. Based on these evidences, we propose that submesoscale processes can provide a fast and efficient route of plastic transport within the mixed layer, while mesoscale instabilities and associated vertical velocities might be the dominant mechanism to penetrate the deeper ocean on slower but broader scales. We conclude that given the ubiquitous presence of fronts in the world’s ocean, their contribution to the global plastic cycle is probably not negligible and the role of these processes in vertically displacing neutrally buoyant microplastics should be investigated in more detail.

Description: The Barents Sea, located close to the Arctic Ocean, is a petroleum province featuring an extensive occurrence of gas hydrates and shallow gas in compacted sediments. Glacial erosion and uplift have contributed to the migration of gas originating from deeper rocks to the shallow sediments of this region, resulting in hydrates with higher-order hydrocarbons in addition to methane. This article documents reported gas hydrate indications and major controls on hydrate stability in the Barents Sea.

Description: Since global navigation satellite systems (GNSS) for determining the absolute geolocation do not reach into the ocean, underwater robots typically obtain a GNSS position at the water surface and then use a combination of different sensors for estimating their pose while diving, including inertial navigation, acoustic doppler velocity logs, ultra short baseline localization systems and pressure sensors. When re-navigating to the same seafloor location after several days, months or years, e.g. for coastal monitoring, the absolute uncertainty of such systems can be in the range of meters for shallow water, and tens of meters for deeper waters in practice. To enable absolute relocalization in marine data science applications that require absolute seafloor positions in the range of centimeter precision, in this contribution we suggest to equip the monitoring area with visual markers that can be detected reliably even in case they are partially overgrown or partially buried by sediment, which can happen quickly in coastal waters. Inspired by patterns successful in camera calibration, we create robust markers that exhibit features at different scales, in order to allow detection, identification and pose estimation from different cameras and various altitudes as visibility (and therefore the maximum possible survey altitude) in coastal waters can vary significantly across seasons, tides and weather. The low frequency content of the marker resembles a human-readable digit, in order to allow easy identification by scientists. We present early results including promising initial tests in coastal waters.

Description: While offshore groundwater has been utilized by coastal communities as far back as 1000 BC, only in the past 10 years has the global volume of fresh-to-brackish water hosted in offshore aquifers been truly appreciated. There are vast quantities (~300–500 × 103 km3) of offshore freshened groundwater sequestered in continental shelf sediments under water depths of less than 60 m within 110 km of the coastline. New marine geophysical methods now make it possible to map and quantify low salinity offshore groundwater bodies. To date, these offshore resources have not been developed. Offshore freshened groundwater could be produced if wells are located close to the shoreline and coastal desalination plants.

Description: Underwater images are challenging for correspondence search algorithms, which are traditionally designed based on images captured in air and under uniform illumination. In water however, medium interactions have a much higher impact on the light propagation. Absorption and scattering cause wavelength- and distance-dependent color distortion, blurring and contrast reductions. For deeper or turbid waters, artificial illumination is required that usually moves rigidly with the camera and thus increases the appearance differences of the same seafloor spot in different images. Correspondence search, e.g. using image features, is however a core task in underwater visual navigation employed in seafloor surveys and is also required for 3D reconstruction, image retrieval and object detection. For underwater images, it has to be robust against the challenging imaging conditions to avoid decreased accuracy or even failure of computer vision algorithms. However, explicitly taking underwater nuisances into account during the feature extraction and matching process is challenging. On the other hand, learned feature extraction models achieved high performance in many in-air problems in recent years. Hence we investigate, how such a learned robust feature model, D2Net, can be applied to the underwater environment and particularly look into the issue of cross domain transfer learning as a strategy to deal with the lack of annotated underwater training data.

Description: Fish food is an inevitable item in human consumption with healthy sourceof good quality proteins and fat. Aqua industry can help to improve food security,livelihoods for the poorest and to meet the world’s food demands. But producingmore seafood that is at affordable cost with rich nutrition is challenging for aquaindustry. Many factors affect the productivity of aqua industry; one such an impor-tant constraint is bacterial diseases. Hence, Aqua industry, a booming businesssector, immensely requires continued research with scientific and technical devel-opments, and innovations. Study of bacterialfish disease is one such thrust areawhich requires intense research to understand the causes and control bacterialdiseases infish. The appearance and development of afish disease is the result ofthe interaction among pathogen, host and environment. An insight into bacterialfishdiseases, clinical symptoms and treatment may help to manage the bacterial diseasesand so can make aqua industry a more profitablefield. This chapter deals withdifferent aspects of the most threatening bacterial diseases, occurring in farmedfishes and also in wildfishes, which are results infish loss and economic lossworldwide. A wide range of gram positive and gram-negative bacteria causingbacterial diseases, clinical symptoms, diagnosis, treatment, vaccines and the natureof water habitat are also discussed in this chapter.

Description: The Digital Earth project aimed for the integration of data science and Earth science. Here, we reflect on the main lessons learned that include the need for interdisciplinary collaboration, thinking out of the box, the concept of ‘thinking in workflows’ and models for the sustainable implementation of scientific software, data infrastructure and policies.

Description: Digital Earth is a project funded by the German Helmholtz Association with all centers of the research field Earth and Environment involved. The main goal of the Digital Earth project is to develop and bundle data science methods in extendable and maintainable scientific workflows that enable natural scientists in collaboration with data scientists to achieve a deeper understanding of the Earth system. This has been achieved by developing solutions for data analysis and exploration with visual and computational approaches with data obtained in a SMART monitoring approach and modeling studies, accompanied by a continuous evaluation of the collaboration processes. In this chapter, the history, setup, and focus of the Digital Earth project are described.

Description: The Digital Earth project aims at a strong interrelation between Data and Earth Science and a step-change in implementing data science methods within Earth science research. During the project, the progress of interdisciplinary collaboration and adoption of data science methods has been measured and assessed with the goal to trace the success of the project. This chapter provides the set-up of this evaluation and the results from two online questionnaires that were held after the start and before the end of the project.

Description: Diversity within marine microbiomes spans the three domains of life: microbial eukaryotes (i.e., protists), bacteria, and archaea. Although protists were the first microbes observed by microscopy, it took the advent of molecular techniques to begin to resolve their complex and reticulate evolutionary history. Symbioses between microbial entities have been key in this journey, and such interactions continue to shape the ecology of marine microbiomes. Nowadays, photosynthetic marine protists are appreciated for their activities as primary producers, rivalling land plant contributions in the global carbon cycle. Predatory protists are known for consuming prokaryotes and other protists, with some combining metabolisms into a mixotrophic lifestyle. Still, much must be learned about specific interactions and lifestyles, especially for uncultured groups recognized just by environmental sequences. With respect to the fate of protists in food webs, there are many paths to consider. Despite being in early stages of identifying interactions, whether mutualistic or death-inducing infections by parasites and viruses, knowledge is advancing rapidly via methods for interrogation in nature without culturing. Here, we review marine protists, their evolutionary histories, diversity, ecological roles, and lifestyles in all layers of the ocean, with reference to how views have shifted over time through extensive investigation.

Description: Data-driven science has turned into a fourth fundamental paradigm of performing research. Earth System Science, following a holistic approach in unraveling the complex network of processes and interactions shaping system Earth, particularly profits from embracing data-driven approaches next to observation and modeling. At the end, increasing digitalization of Earth sciences will lead to cultural transformation towards a Digital Earth Culture.

Description: A comprehensive study of the Earth system and its related processes requires a holistic examination and understanding of multidimensional data acquired with a large number of different sensors or produced by various models. To this end, the Digital Earth project developed a set of software solutions to study environmental data sets using visual approaches. In the following chapter, we present three data visualization products developed to deal with the challenges of the analysis and exploration of environmental data.

Description: Reliable data are the base of all scientific analyses, interpretations and conclusions. Evaluating data in a smart way speeds up the process of interpretation and conclusion and highlights where, when and how additionally acquired data in the field will support knowledge gain. An extended SMART monitoring concept is introduced which includes SMART sensors, DataFlows, MetaData and Sampling approaches and tools. In the course of the Digital Earth project, the meaning of SMART monitoring has significantly evolved. It stands for a combination of hard- and software tools enhancing the traditional monitoring approach where a SMART monitoring DataFlow is processed and analyzed sequentially on the way from the sensor to a repository into an integrated analysis approach. The measured values itself, its metadata, and the status of the sensor, and additional auxiliary data can be made available in real time and analyzed to enhance the sensor output concerning accuracy and precision. Although several parts of the four tools are known, technically feasible and sometimes applied in Earth science studies, there is a large discrepancy between knowledge and our derived ambitions and what is feasible and commonly done in the reality and in the field.

Description: Global population projections foresee the biggest increase to occur in Africa with most of the available uncultivated land to ensure food security remaining on the continent. Simultaneously, greenhouse gas emissions are expected to rise due to ongoing land use change, industrialisation, and transport amongst other reasons with Africa becoming a major emitter of greenhouse gases globally. However, distinct knowledge on greenhouse gas emissions sources and sinks as well as their variability remains largely unknown caused by its vast size and diversity and an according lack of observations across the continent. Thus, an environmental research infrastructure—as being setup in other regions—is more needed than ever. Here, we present the results of a design study that developed a blueprint for establishing such an environmental research infrastructure in Africa. The blueprint comprises an inventory of already existing observations, the spatial disaggregation of locations that will enable to reduce the uncertainty in climate forcing’s in Africa and globally as well as an overall estimated cost for such an endeavour of about 550 M€ over the next 30 years. We further highlight the importance of the development of an e-infrastructure, the necessity for capacity development and the inclusion of all stakeholders to ensure African ownership.

Description: The present study investigates the response of the high-latitude carbon cycle to changes in atmospheric greenhouse gas (GHG) concentrations in idealized climate change scenarios. To this end we use an adapted version of JSBACH – the land surface component of the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) – that accounts for the organic matter stored in the permafrost-affected soils of the high northern latitudes. The model is run under different climate scenarios that assume an increase in GHG concentrations, based on the Shared Socioeconomic Pathway 5 and the Representative Concentration Pathway 8.5, which peaks in the years 2025, 2050, 2075 or 2100, respectively. The peaks are followed by a decrease in atmospheric GHGs that returns the concentrations to the levels at the beginning of the 21st century, reversing the imposed climate change. We show that the soil CO2 emissions exhibit an almost linear dependence on the global mean surface temperatures that are simulated for the different climate scenarios. Here, each degree of warming increases the fluxes by, very roughly, 50 % of their initial value, while each degree of cooling decreases them correspondingly. However, the linear dependence does not mean that the processes governing the soil CO2 emissions are fully reversible on short timescales but rather that two strongly hysteretic factors offset each other – namely the net primary productivity and the availability of formerly frozen soil organic matter. In contrast, the soil methane emissions show a less pronounced increase with rising temperatures, and they are consistently lower after the peak in the GHG concentrations than prior to it. Here, the net fluxes could even become negative, and we find that methane emissions will play only a minor role in the northern high-latitude contribution to global warming, even when considering the high global warming potential of the gas. Finally, we find that at a global mean temperature of roughly 1.75 K (±0.5 K) above pre-industrial levels the high-latitude ecosystem turns from a CO2 sink into a source of atmospheric carbon, with the net fluxes into the atmosphere increasing substantially with rising atmospheric GHG concentrations. This is very different from scenario simulations with the standard version of the MPI-ESM, in which the region continues to take up atmospheric CO2 throughout the entire 21st century, confirming that the omission of permafrost-related processes and the organic matter stored in the frozen soils leads to a fundamental misrepresentation of the carbon dynamics in the Arctic.

Description: A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere.

Description: Variability of surface water masses of the Laptev and the East Siberian seas in August–September 2018 is studied using in situ and satellite data. In situ data were collected during the ARKTIKA-2018 expedition and then complemented with satellite-derived sea surface temperature (SST), salinity (SSS), sea surface height, wind speed, and sea ice concentration. The estimation of SSS fields is challenging in high-latitude regions, and the precision of soil moisture and ocean salinity (SMOS) SSS retrieval is improved by applying a threshold on SSS weekly error. For the first time in this region, the validity of DMI (Danish Meteorological Institute) SST and SMOS SSS products is thoroughly studied using ARKTIKA-2018 expedition continuous thermosalinograph measurements and conductivity–temperature–depth (CTD) casts. They are found to be adequate to describe large surface gradients in this region. Surface gradients and mixing of the river and the sea water in the ice-free and ice-covered areas are described with a special attention to the marginal ice zone at a synoptic scale. We suggest that the freshwater is pushed northward, close to the marginal ice zone (MIZ) and under the sea ice, which is confirmed by the oxygen isotope analysis. The SST-SSS diagram based on satellite estimates shows the possibility of investigating the surface water mass transformation at a synoptic scale and reveals the presence of river water on the shelf of the East Siberian Sea. The Ekman transport is calculated to better understand the pathway of surface water displacement on the shelf and beyond.

Description: Although numerous pollen records are available worldwide in various databases, their use for synthesis works is limited as the chronologies are, as yet, not harmonized globally, and temporal uncertainties are unknown. We present a chronology framework named LegacyAge 1.0 that includes harmonized chronologies of 2831 palynological records (out of 3471 available records), downloaded from the Neotoma Paleoecology Database (last access: April 2021) and 324 additional Asian records. All chronologies use the Bayesian framework implemented in Bacon version 2.5.3. Optimal parameter settings of priors (accumulation.shape, memory.strength, memory.mean, accumulation.rate, thickness) were identified based on previous experiences or iteratively after preliminary model inspection. The most common control points for the chronologies are radiocarbon dates (86.1 %), calibrated by the latest calibration curves (IntCal20 and SHcal20 for the terrestrial radiocarbon dates in the northern and southern hemispheres; Marine20 for marine materials). The original literature was consulted when dealing with obvious outliers and inconsistencies. Several major challenges when setting up the chronologies included the waterline issue (18.8 % of records), reservoir effect (4.9 %), and sediment deposition discontinuity (4.4 %). Finally, we numerically compare the LegacyAge 1.0 chronologies to the original ones and show that the chronologies of 95.4 % of records could be improved according to our assessment. Our chronology framework and revised chronologies provide the opportunity to make use of the ages and age uncertainties in synthesis studies of, for example, pollen-based vegetation and climate change. The LegacyAge 1.0 dataset and R code used are open-access and available at PANGAEA (https://doi.pangaea.de/10.1594/PANGAEA.933132) and Github (https://github.com/LongtermEcology/LegacyAge-1.0), respectively.

Description: The current geochronological state of the art for applying the radiocarbon (14C) method to deep-sea sediment archives lacks key information on sediment bioturbation. Here, we apply a sediment accumulation model that simulates the sedimentation and bioturbation of millions of foraminifera, whereby realistic 14C activities (i.e. from a 14C calibration curve) are assigned to each single foraminifera based on its simulation time step. We find that the normal distribution of 14C age typically used to represent discrete-depth sediment intervals (based on the reported laboratory 14C age and measurement error) is unlikely to be a faithful reflection of the actual 14C age distribution for a specific depth interval. We also find that this deviation from the actual 14C age distribution is greatly amplified during the calibration process. Specifically, we find a systematic underestimation of total geochronological error in many cases (by up to thousands of years), as well as the generation of age–depth artefacts in downcore calibrated median age. Even in the case of “perfect” simulated sediment archive scenarios, whereby sediment accumulation rate (SAR), bioturbation depth, reservoir age and species abundance are all kept constant, the 14C measurement and calibration processes generate temporally dynamic median age–depth artefacts on the order of hundreds of years – whereby even high SAR scenarios (40 and 60 cm kyr−1) are susceptible. Such age–depth artefacts can be especially pronounced during periods corresponding to dynamic changes in the Earth's Δ14C history, when single foraminifera of varying 14C activity can be incorporated into single discrete-depth sediment intervals. For certain lower-SAR scenarios, we find that downcore discrete-depth true median age can systematically fall outside the calibrated age range predicted by the 14C measurement and calibration processes, thus leading to systematically inaccurate age estimations. In short, our findings suggest the possibility of 14C-derived age–depth artefacts in the literature. Furthermore, since such age–depth artefacts are likely to coincide with large-scale changes in global Δ14C, which themselves can coincide with large-scale changes in global climate (such as the last deglaciation), 14C-derived age–depth artefacts may have been previously incorrectly attributed to changes in SAR coinciding with global climate. Our study highlights the need for the development of improved deep-sea sediment 14C calibration techniques that include an a priori representation of bioturbation for multi-specimen samples.

Description: It is a good method to utilize the grain size distribution curves and cumulative frequency curves of marine or river sediments to estimate the hydrodynamic conditions, transportation processes and sedimentary environment. However, researchers can only rely on Excel or Grapher to plot the curves one by one at the present day. The manual plotting procedures are complicated, and calculating the truncation points is time-consuming. To solve the aforementioned problems, we have developed a software tool to plot cumulative frequency curves and calculate the values of truncation points automatically. The software has the ability to plot curves of hundreds of samples accurately and rapidly, promoting researchers to analyze transport mechanisms and hydrodynamic environments. And it is convenient to apply the software to compare the processes of transportation and deposition between different samples.

Description: Geological records show that vast proglacial lakes existed along the land terminating margins of palaeo ice sheets in Europe and North America. Proglacial lakes impact ice sheet dynamics by imposing marine-like boundary conditions at the ice margin. These lacustrine boundary conditions include changes in the ice sheet’s geometry, stress balance and frontal ablation and therefore affect the entire ice sheet’s mass balance. This interaction, however, has not been rigorously implemented in ice sheet models. In this study, the implementation of an adaptive lake boundary into the Parallel Ice Sheet Model (PISM) is described and applied to the glacial retreat of the Laurentide Ice Sheet (LIS). The results show that the presence of proglacial lakes locally enhances the ice flow. Along the continental ice margin, ice streams and ice lobes can be observed. Lacustrine terminating ice streams cause immense thinning of the ice sheet’s interior and thus play a significant role in the demise of the LIS. Due to the presence of lakes, a process similar to the marine ice sheet instability causes the collapse of the ice saddle over Hudson Bay, which blocked drainage via the Hudson Strait. In control experiments without a lake model, Hudson Bay is still glaciated at the end of the simulation. Future studies should target the development of parametrizations that better describe the glacial-lacustrine interactions.

Description: In times of accelerating climate change, species are challenged to respond to rapidly shifting environmental settings. Yet, faunal distribution and composition are still scarcely known for remote and little explored seas, where observations are limited in number and mostly refer to local scales. Here, we present the first comprehensive study on Eurasian-Arctic macrobenthos that aims to unravel the relative influence of distinct spatial scales and environmental factors in determining their large-scale distribution and composition patterns. To consider the spatial structure of benthic distribution patterns in response to environmental forcing, we applied Moran’s eigenvector mapping (MEM) on a large dataset of 341 samples from the Barents, Kara and Laptev Seas taken between 1991 and 2014, with a total of 403 macrobenthic taxa (species or genera) that were present in ≥ 10 samples. MEM analysis revealed three spatial scales describing patterns within or beyond single seas (broad: ≥ 400 km, meso: 100–400 km, and small: ≤ 100 km). Each scale is associated with a characteristic benthic fauna and environmental drivers (broad: apparent oxygen utilization and phosphate, meso: distance-to-shoreline and temperature, small: organic carbon flux and distance-to-shoreline). Our results suggest that different environmental factors determine the variation of Eurasian-Arctic benthic community composition within the spatial scales considered and highlight the importance of considering the diverse spatial structure of species communities in marine ecosystems. This multiple-scale approach facilitates an enhanced understanding of the impact of climate-driven environmental changes that is necessary for developing appropriate management strategies for the conservation and sustainable utilization of Arctic marine systems.

Description: Nitrogen fixers, or diazotrophs, play a key role in the carbon and nitrogen cycle of the world oceans, but the controlling mechanisms are not comprehensively understood yet. The present study compares two paradigms on the ecological niche of diazotrophs in an Earth System Model (ESM). In our standard model configuration, which is representative for most of the state-of-the-art pelagic ecosystem models, diazotrophs take advantage of zooplankton featuring a lower food preference for diazotrophs than for ordinary phytoplankton. We compare this paradigm with the idea that diazotrophs are more competitive under oligotrophic conditions, characterized by low (dissolved, particulate, organic and inorganic) phosphorous availability. Both paradigms are supported by observational evidence and lead to a similar good agreement to the most recent and advanced observation-based nitrogen fixation estimate in our ESM framework. Further, we illustrate that the similarity between the two paradigms breaks in a RCP 8.5 anthropogenic emission scenario. We conclude that a more advanced understanding of the ecological niche of diazotrophs is mandatory for assessing the cycling of essential nutrients, especially under changing environmental conditions. Our results call for more in-situ measurements of cyanobacteria biomass if major controls of nitrogen fixation in the oceans are to be dissected.