The purpose of this special issue is to illustrate the role of a sustainable coastal research infrastructure in supporting monitoring, sciences, and management of the coastal marine areas. As such the JERICO-RI research infrastructure is most suitable, gathering 34 partners in Europe with the same overarching objective: to strengthen and enlarge a solid and transparent European network of coastal observatories and to provide an operational service for the timely, continuous, and sustainable delivery of high-quality environmental (physical, biogeochemical, and biological) data and services related to the marine environment in European coastal seas. Six scientific areas are targeted, from the sensor development to the data analysis and the scientific results. These are the following:

1. the pelagic biodiversity with phytoplankton and harmful algal blooms;
2. the benthic biodiversity and habitats;
3. the contaminant transports;
4. the coastal transport and hydrology;
5. the carbonate systems and C cycle; and
6. the coastal operational oceanography and modelling.

The special issue will present results from the MOSES/REEBUS Eddy Study on the mesoscale and sub-mesoscale dynamics associated with ocean eddies of West Africa which was carried out on the German R/V Meteor cruises M156 and M160 in 2019.

The scope of the study included physical, chemical, biological and geological research questions around the physical-chemical-biological coupling and the overall role of ocean eddies in an ocean area in the vicinity of the Canary Current System, a major eastern boundary upwelling system. The observational concept featured a wide range of platforms (research vessel, glider airplane, Saildrones, wave gliders, gliders, BGC Argo floats, drifters, moorings, AUVs, bottom landers, bottom crawler), observation and sampling approaches (towed, winched, free-falling and drifting instruments, multinet, rhodamine dye release experiment), instruments, and observed variables (in situ, underway, discrete samples) and specifically addressed the mesoscale and sub-mesoscale variability associated with ocean eddies.

Since its inception, data assimilation has proved to be enormously useful in the most varied fields throughout the Earth sciences. It is certainly essential in meteorology, where the short-range forecasts would otherwise be almost impossible. In oceanography, its development has been slower, partly due to the smaller number of continuous and stable observations and partly due to fewer studies that show the importance of ocean forecasts for societal benefit. However, recently, these techniques have been used more and more widely, both in operational oceanography and to produce climate reconstructions. Although the techniques are similar to those used in the atmospheric field, they have to deal with particularities due to the different environment, where the boundary conditions, open and closed, have greater importance and the sparsity of observations pose unique challenges. This special issue is open to contributions describing data assimilation techniques, both methodological and case studies, in the oceanographic field. We welcome original work describing new techniques or new types of observations that cover every aspect of data assimilation, including varied applications of data assimilation, both in coastal seas and in the open ocean. This issue was inspired by the session OS4.7 at EGU2022.

This special issue describes efforts establishing high-resolution regional ocean and biogeochemical modelling capabilities for Modular Ocean Model 6 (MOM6) and selected initial applications. MOM is amongst the most widely used ocean models for global climate and earth system applications, with a lineage of scientific contributions exceeding 50 years. MOM6 represents an ambitious evolution of previous MOM formulations, embracing numerous recent modelling advances and an open development approach. MOM6 and its associated biogeochemical components have been successfully deployed for the Sixth Coupled Model Intercomparison Project (CMIP6) and other international global climate and ocean prediction efforts. The resolution and regional optimality of global simulations, however, are inevitably limited by the computational, forcing, and parameterization demands of global climate-scale simulations. Ocean modelling frameworks capable of simulating and connecting physical, biogeochemical, and ecosystem processes from ocean basins to coasts and estuaries are needed to understand the role of oceans in global change and to anticipate global change impacts on marine ecosystems and coastal communities. Development of robust regional modelling capabilities for MOM6 (i.e. regional MOM6) creates such a framework, but the extension of MOM6 to high-resolution regional applications presents many challenges.

The papers in this collection present the overall design and implementation of regional MOM6, describe new parameterizations intended for regional applications, present a first generation of regional MOM6 configurations from across the global ocean, and offer select initial applications in ocean science. Advances in horizontal grid generation and boundary condition formulation are highlighted, including those enabling a more seamless transmission of physical and biogeochemical information from global to regional scales and those required to handle flexible Lagrangian vertical coordinates. The robustness of physical and biogeochemical configurations and parameterizations – many of which were developed for global applications – is explored in higher-resolution implementations spanning environments from the Arctic to equatorial waters. Analysis of tradeoffs between model skill and computational cost highlights algorithmic improvements critical for producing decision-relevant ensembles that span a range of ocean futures. The collected works provide a foundation for the expanded application of regional MOM6 to understand and predict ocean conditions across scales.

This is a traditional style special issue open to all papers within the topic. We anticipate that contributions will be primarily to GMD initially but that there will be a growing number of applications suitable for OS once the core development papers have been published. The indefinite ending date will allow for a greater number of initial applications to be published in OS and enable eventual documentation of generational updates planned for some configurations.

In this special issue papers resulting from the project “Marine biological production, organic aerosol particles and marine clouds: a Process Chain – MarParCloud” and closely related projects shall be aggregated. MarParCloud is a highly interdisciplinary project funded by the German Leibniz Society (https://www.leibniz-gemeinschaft.de/en/about-us/leibniz-competition/projekte-2016/funding-line-2/), which aims to improve our knowledge on the nature, formation, transfer and effects of organic matter (OM) in the marine environment. To this end the biological formation of OM in the ocean, its accumulation in the sea surface microlayer (SML), the export to marine aerosol particles and, finally, the importance of OM for the formation of cloud droplets and ice crystals are investigated. Within MarParCloud several field and tank studies were performed to investigate ambient seawater, the SML, aerosol particles and cloud water as well as water and air samples obtained during artificial bubble experiments. Closely related campaigns comprise the EU project MARSU (“Advanced analytical and mass spectrometric techniques to study ocean-atmosphere interactions”) and the MILAN study (“sea-surface MIcroLAyer at Night”), focusing on diel dynamics of the uppermost layer of the ocean, as well as the cruise EMB184 “Aerosol” performed with the R/V Elisabeth Mann Borgese. In addition to results from these projects and campaigns, this special issue is open for all submissions concerning the cycling of OM in the marine environment with potential atmospheric implications.

Clouds over the ocean and their radiative properties are partially influenced by the biology, biogeochemistry and physics of the surface ocean. For example, the production of sea spray via bubble bursting associated with breaking waves can be influenced by biogenic material present in surface seawater, and biogenic material carried in sea spray aerosol can also influence ice-nucleating properties in air overlying the ocean. Furthermore, phytoplankton produce a range of compounds, including gases and particles, which when emitted to the atmosphere participate in the atmospheric chemistry. Our recent ship campaign Sea2Cloud had a primary focus of investigating the link between marine particle emissions and the biogeochemical properties of the seawater in subantarctic and subtropical waters, examining new particle formation processes and the relationship between surface ocean biogeochemistry and sea spray aerosol in dedicated ship-borne experiments. In parallel, ambient air aerosol, gas and cloud properties were measured along the ship track, which will allow for testing of these relationships in modelling exercises. Along with the ship campaign, longer-term measurements of aerosol properties were monitored at the Baring Head GAW research station (NZ) as well as continuously ongoing onboard the R/V Marion Dufresne over the years 2021–2022. These measurements will be used for the inspection of the representativeness of the ship campaign's process-orientated results. The Sea2Cloud project is running from July 2018 to July 2023, with potential additional laboratory and ship-borne measurements in the Southern Ocean by January 2023.

The Weddell Sea and the ocean off Dronning Maud Land, constituting the Weddell Gyre, are representative of the high-latitude Southern Ocean due to its pronounced seasonality, circumpolar currents, deep-water formation and seasonal sea-ice cover. The Weddell Gyre connects water masses from the Antarctic Circumpolar Current with those shaped by the large ice shelves and sea-ice formation in the southern perimeter of the Weddell Gyre. Biological and biogeochemical processes are strongly influenced by these conditions and contribute to a unique Weddell Sea ecosystem.

A portion of the western Weddell Sea is already experiencing consequences of climate change, including the acceleration of mass loss from ice shelves, enhanced ocean warming and freshening, rising air temperatures, and changes in wind patterns. This likely has an emerging influence on the local biological and biogeochemical processes. The eastern part of the Weddell Gyre, off Dronning Maud Land, however, appears relatively stable but is expected to experience warming, sea-ice retreat and ice-shelf loss in the course of this century. The re-emergence of the Maud Rise Polynya, with a potentially significant impact on regional water masses and biogeochemistry, underscores the importance of observing and understanding this region. Establishing knowledge of the present biological and biogeochemical processes and coupling with physics prior to major changes in this region is essential.

This special issue emerged from an October 2020 workshop organized by the Southern Ocean Observing System (SOOS) Weddell Sea and Dronning Maud Land Regional Working Group that brought together numerous scientists across multiple disciplines. However, the issue is open to anyone and we welcome additional contributions.

This special issue describes efforts establishing high-resolution regional ocean and biogeochemical modelling capabilities for Modular Ocean Model 6 (MOM6) and selected initial applications. MOM is amongst the most widely used ocean models for global climate and earth system applications, with a lineage of scientific contributions exceeding 50 years. MOM6 represents an ambitious evolution of previous MOM formulations, embracing numerous recent modelling advances and an open development approach. MOM6 and its associated biogeochemical components have been successfully deployed for the Sixth Coupled Model Intercomparison Project (CMIP6) and other international global climate and ocean prediction efforts. The resolution and regional optimality of global simulations, however, are inevitably limited by the computational, forcing, and parameterization demands of global climate-scale simulations. Ocean modelling frameworks capable of simulating and connecting physical, biogeochemical, and ecosystem processes from ocean basins to coasts and estuaries are needed to understand the role of oceans in global change and to anticipate global change impacts on marine ecosystems and coastal communities. Development of robust regional modelling capabilities for MOM6 (i.e. regional MOM6) creates such a framework, but the extension of MOM6 to high-resolution regional applications presents many challenges.

The papers in this collection present the overall design and implementation of regional MOM6, describe new parameterizations intended for regional applications, present a first generation of regional MOM6 configurations from across the global ocean, and offer select initial applications in ocean science. Advances in horizontal grid generation and boundary condition formulation are highlighted, including those enabling a more seamless transmission of physical and biogeochemical information from global to regional scales and those required to handle flexible Lagrangian vertical coordinates. The robustness of physical and biogeochemical configurations and parameterizations – many of which were developed for global applications – is explored in higher-resolution implementations spanning environments from the Arctic to equatorial waters. Analysis of tradeoffs between model skill and computational cost highlights algorithmic improvements critical for producing decision-relevant ensembles that span a range of ocean futures. The collected works provide a foundation for the expanded application of regional MOM6 to understand and predict ocean conditions across scales.

This is a traditional style special issue open to all papers within the topic. We anticipate that contributions will be primarily to GMD initially but that there will be a growing number of applications suitable for OS once the core development papers have been published. The indefinite ending date will allow for a greater number of initial applications to be published in OS and enable eventual documentation of generational updates planned for some configurations.

Since its inception, data assimilation has proved to be enormously useful in the most varied fields throughout the Earth sciences. It is certainly essential in meteorology, where the short-range forecasts would otherwise be almost impossible. In oceanography, its development has been slower, partly due to the smaller number of continuous and stable observations and partly due to fewer studies that show the importance of ocean forecasts for societal benefit. However, recently, these techniques have been used more and more widely, both in operational oceanography and to produce climate reconstructions. Although the techniques are similar to those used in the atmospheric field, they have to deal with particularities due to the different environment, where the boundary conditions, open and closed, have greater importance and the sparsity of observations pose unique challenges. This special issue is open to contributions describing data assimilation techniques, both methodological and case studies, in the oceanographic field. We welcome original work describing new techniques or new types of observations that cover every aspect of data assimilation, including varied applications of data assimilation, both in coastal seas and in the open ocean. This issue was inspired by the session OS4.7 at EGU2022.

Clouds over the ocean and their radiative properties are partially influenced by the biology, biogeochemistry and physics of the surface ocean. For example, the production of sea spray via bubble bursting associated with breaking waves can be influenced by biogenic material present in surface seawater, and biogenic material carried in sea spray aerosol can also influence ice-nucleating properties in air overlying the ocean. Furthermore, phytoplankton produce a range of compounds, including gases and particles, which when emitted to the atmosphere participate in the atmospheric chemistry. Our recent ship campaign Sea2Cloud had a primary focus of investigating the link between marine particle emissions and the biogeochemical properties of the seawater in subantarctic and subtropical waters, examining new particle formation processes and the relationship between surface ocean biogeochemistry and sea spray aerosol in dedicated ship-borne experiments. In parallel, ambient air aerosol, gas and cloud properties were measured along the ship track, which will allow for testing of these relationships in modelling exercises. Along with the ship campaign, longer-term measurements of aerosol properties were monitored at the Baring Head GAW research station (NZ) as well as continuously ongoing onboard the R/V Marion Dufresne over the years 2021–2022. These measurements will be used for the inspection of the representativeness of the ship campaign's process-orientated results. The Sea2Cloud project is running from July 2018 to July 2023, with potential additional laboratory and ship-borne measurements in the Southern Ocean by January 2023.

The special issue will present results from the MOSES/REEBUS Eddy Study on the mesoscale and sub-mesoscale dynamics associated with ocean eddies of West Africa which was carried out on the German R/V Meteor cruises M156 and M160 in 2019.

The scope of the study included physical, chemical, biological and geological research questions around the physical-chemical-biological coupling and the overall role of ocean eddies in an ocean area in the vicinity of the Canary Current System, a major eastern boundary upwelling system. The observational concept featured a wide range of platforms (research vessel, glider airplane, Saildrones, wave gliders, gliders, BGC Argo floats, drifters, moorings, AUVs, bottom landers, bottom crawler), observation and sampling approaches (towed, winched, free-falling and drifting instruments, multinet, rhodamine dye release experiment), instruments, and observed variables (in situ, underway, discrete samples) and specifically addressed the mesoscale and sub-mesoscale variability associated with ocean eddies.

The Weddell Sea and the ocean off Dronning Maud Land, constituting the Weddell Gyre, are representative of the high-latitude Southern Ocean due to its pronounced seasonality, circumpolar currents, deep-water formation and seasonal sea-ice cover. The Weddell Gyre connects water masses from the Antarctic Circumpolar Current with those shaped by the large ice shelves and sea-ice formation in the southern perimeter of the Weddell Gyre. Biological and biogeochemical processes are strongly influenced by these conditions and contribute to a unique Weddell Sea ecosystem.

A portion of the western Weddell Sea is already experiencing consequences of climate change, including the acceleration of mass loss from ice shelves, enhanced ocean warming and freshening, rising air temperatures, and changes in wind patterns. This likely has an emerging influence on the local biological and biogeochemical processes. The eastern part of the Weddell Gyre, off Dronning Maud Land, however, appears relatively stable but is expected to experience warming, sea-ice retreat and ice-shelf loss in the course of this century. The re-emergence of the Maud Rise Polynya, with a potentially significant impact on regional water masses and biogeochemistry, underscores the importance of observing and understanding this region. Establishing knowledge of the present biological and biogeochemical processes and coupling with physics prior to major changes in this region is essential.

This special issue emerged from an October 2020 workshop organized by the Southern Ocean Observing System (SOOS) Weddell Sea and Dronning Maud Land Regional Working Group that brought together numerous scientists across multiple disciplines. However, the issue is open to anyone and we welcome additional contributions.

In this special issue papers resulting from the project “Marine biological production, organic aerosol particles and marine clouds: a Process Chain – MarParCloud” and closely related projects shall be aggregated. MarParCloud is a highly interdisciplinary project funded by the German Leibniz Society (https://www.leibniz-gemeinschaft.de/en/about-us/leibniz-competition/projekte-2016/funding-line-2/), which aims to improve our knowledge on the nature, formation, transfer and effects of organic matter (OM) in the marine environment. To this end the biological formation of OM in the ocean, its accumulation in the sea surface microlayer (SML), the export to marine aerosol particles and, finally, the importance of OM for the formation of cloud droplets and ice crystals are investigated. Within MarParCloud several field and tank studies were performed to investigate ambient seawater, the SML, aerosol particles and cloud water as well as water and air samples obtained during artificial bubble experiments. Closely related campaigns comprise the EU project MARSU (“Advanced analytical and mass spectrometric techniques to study ocean-atmosphere interactions”) and the MILAN study (“sea-surface MIcroLAyer at Night”), focusing on diel dynamics of the uppermost layer of the ocean, as well as the cruise EMB184 “Aerosol” performed with the R/V Elisabeth Mann Borgese. In addition to results from these projects and campaigns, this special issue is open for all submissions concerning the cycling of OM in the marine environment with potential atmospheric implications.

The purpose of this special issue is to illustrate the role of a sustainable coastal research infrastructure in supporting monitoring, sciences, and management of the coastal marine areas. As such the JERICO-RI research infrastructure is most suitable, gathering 34 partners in Europe with the same overarching objective: to strengthen and enlarge a solid and transparent European network of coastal observatories and to provide an operational service for the timely, continuous, and sustainable delivery of high-quality environmental (physical, biogeochemical, and biological) data and services related to the marine environment in European coastal seas. Six scientific areas are targeted, from the sensor development to the data analysis and the scientific results. These are the following:

1. the pelagic biodiversity with phytoplankton and harmful algal blooms;
2. the benthic biodiversity and habitats;
3. the contaminant transports;
4. the coastal transport and hydrology;
5. the carbonate systems and C cycle; and
6. the coastal operational oceanography and modelling.