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.

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.

The Arctic is undergoing the most rapid changes in the climate system globally, as shown by the thinning and reduction of sea ice, the melting of ice sheets and glaciers, thawing permafrost, and the potential for more extreme weather events. Given the complexity of Arctic ecosystems, reducing uncertainties in the long-term response of Arctic ecosystems to climate change requires an interdisciplinary study of the relationships among physical, chemical, biological, and human processes with an emphasis on the interactions among system components. This special issue collects contributions from a wide range of fields supported by the Horizon 2020 project INTAROS (Integrated Arctic Observation System), including ocean and sea ice, atmosphere, the terrestrial sphere (e.g. patterns and controls of greenhouse gas emissions and their response to climate change particularly during the cold season), and the cryosphere. The ocean studies will be complemented by a wide range of other studies across the cryosphere, the atmosphere, and the terrestrial Arctic systems. The goal is to produce an integration of multi-disciplinary observations in the Arctic and report on innovative analysis and methods which can stimulate new products and improved services and to demonstrate the benefit of a continuous long-term effort in these observations to assess the temporal changes across the Arctic.

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.

The Arctic is undergoing the most rapid changes in the climate system globally, as shown by the thinning and reduction of sea ice, the melting of ice sheets and glaciers, thawing permafrost, and the potential for more extreme weather events. Given the complexity of Arctic ecosystems, reducing uncertainties in the long-term response of Arctic ecosystems to climate change requires an interdisciplinary study of the relationships among physical, chemical, biological, and human processes with an emphasis on the interactions among system components. This special issue collects contributions from a wide range of fields supported by the Horizon 2020 project INTAROS (Integrated Arctic Observation System), including ocean and sea ice, atmosphere, the terrestrial sphere (e.g. patterns and controls of greenhouse gas emissions and their response to climate change particularly during the cold season), and the cryosphere. The ocean studies will be complemented by a wide range of other studies across the cryosphere, the atmosphere, and the terrestrial Arctic systems. The goal is to produce an integration of multi-disciplinary observations in the Arctic and report on innovative analysis and methods which can stimulate new products and improved services and to demonstrate the benefit of a continuous long-term effort in these observations to assess the temporal changes across the Arctic.

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.