The Mediterranean Sea has recently shown clear signs of climate change, including an increase in sea surface temperature, salinization of the intermediate and deep waters, and a rise in sea level over the last century that makes it a very vulnerable environment given its particularities of semi-enclosed densely populated basin.

Urgent social and economic drivers need targeted improvements in weather, climate, water, oceans, and relevant environmental information and services. Risks associated with climate variability and extreme environmental events may create social and economic stress which would require new meteorological, hydrological, oceanographic, and climate services in order to ensure the safety and security of populations and the development of adaptive economic strategies.

This special issue is devoted to scientific advances in multidisciplinary studies at several spatial and temporal scales in the Mediterranean Sea. We seek for new approaches and methods in physical and biogeochemical observations and models as well as in developments in operational oceanography (e.g. the fusion of observations and modelling products as well as downstream product development).

Fostering the establishment of a global ocean observing system, Walter Munk defined the 20th century as the “century of undersampling”, and this is especially true for marine biogeochemical observations. Biogeochemical Argo is bringing us into a new era that is characterized by an unprecedented availability of high-resolution biogeochemical profiles, delivered throughout the year and globally distributed. Thanks to these observations, the dynamics of ocean carbon, oxygen, nutrients, primary producers, pH, and bio-optical properties can be examined in all three spatial dimensions. The increased availability of these observations allows us to unravel biogeochemical processes and to develop and validate hypotheses across a range of spatial and temporal scales. These new observations will also substantially improve the quality of biogeochemical models by allowing vigorous validation, improved parameterizations, and formal data assimilation.

In this special issue, we welcome contributions leveraging the high data availability provided by BGC-Argo floats combined with theoretical or numerical models, data assimilation, machine learning, multi-platform sensors, or other novel interpretative methodologies that expand the surface view of ocean ecosystem dynamics into the vertical dimension.

The purpose of the special issue is to collect the high-quality contributions presented at the oral and poster sessions entitled “Biogeochemistry in the BGC-Argo Era: From Process Studies to Ecosystem Forecasts” held at Ocean Sciences Meeting 2020 in San Diego. Moreover, the special issue is open to other relevant contributions.

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 Hydrological cycle in the Mediterranean Experiment (HyMeX, https://www.hymex.org/) programme is a 10-year concerted effort at the international level started in 2010 with aims to advance the understanding of the water cycle, and with emphases on the predictability and evolution of high-impact weather events, as well as on evaluating social vulnerability to these extreme events. The special issue is jointly organized between the Atmospheric Chemistry and Physics, Hydrology and Earth System Sciences, Ocean Science, Natural Hazards and Earth System Sciences, Atmospheric Measurement Techniques, and Geoscientific Model Development journals. It aims at gathering contributions to the areas of understanding, modelling, and predicting at various timescales and spatial scales of the Mediterranean water cycle and its related extreme events, including cyclones, heavy precipitation, flash floods and impacts, drought and water resources, strong winds, and dense water formation. The special issue is not limited to studies conducted within HyMeX: any multiscale or multidisciplinary approaches related to the Mediterranean water cycle are encouraged.

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.

Fostering the establishment of a global ocean observing system, Walter Munk defined the 20th century as the “century of undersampling”, and this is especially true for marine biogeochemical observations. Biogeochemical Argo is bringing us into a new era that is characterized by an unprecedented availability of high-resolution biogeochemical profiles, delivered throughout the year and globally distributed. Thanks to these observations, the dynamics of ocean carbon, oxygen, nutrients, primary producers, pH, and bio-optical properties can be examined in all three spatial dimensions. The increased availability of these observations allows us to unravel biogeochemical processes and to develop and validate hypotheses across a range of spatial and temporal scales. These new observations will also substantially improve the quality of biogeochemical models by allowing vigorous validation, improved parameterizations, and formal data assimilation.

In this special issue, we welcome contributions leveraging the high data availability provided by BGC-Argo floats combined with theoretical or numerical models, data assimilation, machine learning, multi-platform sensors, or other novel interpretative methodologies that expand the surface view of ocean ecosystem dynamics into the vertical dimension.

The purpose of the special issue is to collect the high-quality contributions presented at the oral and poster sessions entitled “Biogeochemistry in the BGC-Argo Era: From Process Studies to Ecosystem Forecasts” held at Ocean Sciences Meeting 2020 in San Diego. Moreover, the special issue is open to other relevant contributions.

The Mediterranean Sea has recently shown clear signs of climate change, including an increase in sea surface temperature, salinization of the intermediate and deep waters, and a rise in sea level over the last century that makes it a very vulnerable environment given its particularities of semi-enclosed densely populated basin.

Urgent social and economic drivers need targeted improvements in weather, climate, water, oceans, and relevant environmental information and services. Risks associated with climate variability and extreme environmental events may create social and economic stress which would require new meteorological, hydrological, oceanographic, and climate services in order to ensure the safety and security of populations and the development of adaptive economic strategies.

This special issue is devoted to scientific advances in multidisciplinary studies at several spatial and temporal scales in the Mediterranean Sea. We seek for new approaches and methods in physical and biogeochemical observations and models as well as in developments in operational oceanography (e.g. the fusion of observations and modelling products as well as downstream product development).

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 Hydrological cycle in the Mediterranean Experiment (HyMeX, https://www.hymex.org/) programme is a 10-year concerted effort at the international level started in 2010 with aims to advance the understanding of the water cycle, and with emphases on the predictability and evolution of high-impact weather events, as well as on evaluating social vulnerability to these extreme events. The special issue is jointly organized between the Atmospheric Chemistry and Physics, Hydrology and Earth System Sciences, Ocean Science, Natural Hazards and Earth System Sciences, Atmospheric Measurement Techniques, and Geoscientific Model Development journals. It aims at gathering contributions to the areas of understanding, modelling, and predicting at various timescales and spatial scales of the Mediterranean water cycle and its related extreme events, including cyclones, heavy precipitation, flash floods and impacts, drought and water resources, strong winds, and dense water formation. The special issue is not limited to studies conducted within HyMeX: any multiscale or multidisciplinary approaches related to the Mediterranean water cycle are encouraged.

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.