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.

This special issue investigates the fascinating interactions between the geosphere and biosphere that are active near the Earth’s surface and within the critical zone. The special issue focuses on modelling and observational studies conducted along the extreme climate and ecological gradient of the Chilean Coastal Cordillera. We welcome submissions that address the physical or chemical processes whereby micro-organisms, animals, and plants influence the shape and development of the Earth’s surface over timescales ranging from the present day to the distant geologic past. As this topic is highly interdisciplinary in scope, we encourage submissions from diverse disciplines including geology, geography, geochemistry, surface geophysics, ecology, microbiology, soil sciences, hydrogeology, geomorphology, and climatology. Integrative studies that bridge between disciplines are particularly welcome. Two types of manuscript submissions are possible. These include either original and/or new scientific full-length research articles presenting new data and interpretations or review and synthesis papers that are invited by the editors and integrate data from different studies and disciplines to address state-of-the-science questions related to Earth surface shaping by biota.

The Peruvian upwelling system is one of the most productive ecosystems in the ocean. Continuous upwelling of nutrient-rich water generates high primary production, supporting an efficient food web and leading to high fishery yields. An extensive oxygen minimum zone underlying the productive surface waters gives rise to high losses of fixed nitrogen via denitrification and anaerobic ammonium oxidation. This results in nutrient ratios of upwelled waters deviating strongly from Redfield stoichiometry, with a high N deficit and excess P. How this unusual nutrient stoichiometry affects plankton community production and succession and how this feeds back on biogeochemical cycling are still not well understood. To address these questions, an in situ mesocosm experiment was conducted in the coastal upwelling system off Peru in the framework of the Collaborative Research Center 754 "Climate-Biogeochemistry Interactions in the Tropical Ocean". The field experiment took place from January to April 2017 during a coastal El Niño, a rare event of El Niño conditions confined to Peruvian coastal waters. Key objectives of this mesocosm study, which involved 57 researchers from 10 nations, were to unravel the interplay of pelagic ecology and biogeochemistry under the unique environmental conditions of the Peruvian upwelling system. This special issue in Biogeosciences is intended as a collective outlet for publications resulting from this study, covering the broad range of research topics from seawater chemistry to plankton ecology and pelagic biogeochemistry.

This special issue brings together a collection of articles on ecosystem manipulation experiments, which have the potential to inform mechanistic ecosystem models on the effects of global changes. Terrestrial ecosystem dynamics and the interplay of multiple biogeochemical cycles are responsible for unresolved uncertainties in Earth system change projections. The advancement of ecosystem experiments and mechanistic modelling has great potential for addressing this research challenge. However, finding answers requires diverse theoretical and empirical research to be integrated. Ecosystem manipulation experiments allow for empirical testing of theoretical hypotheses, model predictions, and their assumptions. However, results from manipulation experiments can only contribute to advance our ability to improve ecosystem–climate feedback if these are informed by and integrated into mechanistic models.

The scope of this special issue is centred around terrestrial ecosystem experiments. Papers contain an explicit theoretical component for evaluating results or generating hypotheses, address identified open challenges in modelling ecosystem responses to various experimental treatments, or are centred around a model–data synthesis, using results from ecosystem manipulation experiments. Manipulation experiments is to be understood in a broad sense, including (but not restricted to) nutrient, CO₂, and/or water manipulation; isotope labelling studies; and natural perturbations, ranging from ecosystem to planetary scale.

Climate change is exposing terrestrial ecosystems to warmer temperatures, increased CO₂ levels, and more frequent and intense drought and rainfall events. How different ecosystems respond to changing climatic conditions depends on a multitude of biological and geochemical processes which interact at different temporal and spatial scales.

On the one hand, plants assimilate carbon from the atmosphere and control carbon inputs into soil via plant detritus and rhizodeposition. On the other hand, soil fauna and microorganisms govern the decomposition of plant detritus and soil organic matter, which determines the cycling of carbon and of the nutrients necessary for plant growth. These interactions are further shaped by local environmental properties, such as vegetation type, relief, soil mineralogy, and physical structure, as well as the composition of plants and soil biota. Since soils represent the largest stock of organic carbon in terrestrial ecosystems and regulate carbon fluxes for about 10 times the current anthropogenic emissions, changes in the above-mentioned processes can have strong implications for global carbon cycling. Furthermore, the understanding of soil functioning is critical for improving predictions on the resistance and resilience of terrestrial ecosystems to climate change.

In this special issue, we seek to highlight research on biotic and abiotic interactions underlying terrestrial biogeochemical responses to climate, with a specific emphasis on elevated atmospheric CO₂, warming, drought, and drying–rewetting events. We invite contributions covering field and laboratory experiments, conceptual development, and modelling studies.

Oxygen (O₂) is considered an effective indicator of ocean health and climate change. Its level, distribution and variability from sub-seasonal to multidecadal scales provide relevant information on the physical and biogeochemical functioning of the ocean and often act to constrain life in the ocean.

Current evidence indicates that the coastal (i.e., most directly influenced by land) and open-ocean areas have been losing O₂ since the middle of the last century, with consequences for living organisms and biogeochemical cycles that are not yet fully understood. In the open ocean the O₂ inventory has decreased by a few percent (i.e., 0.5–3%), and oxygen minimum zones (OMZs) are expanding, which is primarily attributed to global warming, although a quantitative understanding is still lacking. The number of hypoxic coastal sites has increased, predominantly in response to worldwide eutrophication, yet trends in deoxygenation in the global coastal zone remain ill-defined.

The development and extension of low-O₂ concentration areas degrade the living conditions and contract the metabolically viable habitat for a large number of pelagic, mesopelagic, and benthic organisms. The effects on individuals exposed to low O₂ can result in altered foodweb structures.

Deoxygenation affects many aspects of the ecosystem services provided by the ocean and coastal waters. For example, deoxygenation effects on fisheries include low oxygen affecting populations through reduced recruitment and population abundance and also through altered spatial distributions of the harvested species causing changes in fishing activity. This can lead to changes in the profitability of the fisheries and can affect the interpretation of the monitoring data, leading to misinformed management advice.

Model simulations for this century project a decrease in oxygen under both high- and low-CO₂ emission scenarios, while the projections of the coastal ocean at the land–ocean interface indicate that eutrophication will likely continue in many regions of the world. Warming is expected to further amplify deoxygenation in coastal areas influenced by eutrophication by strengthening and extending stratification.

This special issue will investigate new developments and insights related to low-oxygen environments and deoxygenation in open and coastal waters.

Due to a transitional zone between marine and terrestrial systems, coastal wetlands and seashores are dynamic and highly vulnerable ecosystems. The multi-scale and cross-scale spatio-temporal dynamicity of such systems in terms of various biophysical fluxes is currently poorly understood. A multi-sensor approach, including various active and passive remote-sensing and in situ sensor installations, can help in continuous monitoring and gaining a better understanding of these coastal ecosystems. A multi-sensor approach can account for long-term and cross-scale trends of the biophysical fluxes and their dynamics, providing a better understanding of how biotic and abiotic factors can influence such changes.

In this special issue, we encourage submissions that present innovative ways to implement multi-sensor approaches to monitor coastal wetlands and seashores, with particular interest in applications that integrate in situ with proximal and/or remote-sensing methods. Contributions including new modelling approaches for multi- and cross-scale data integration are also highly encouraged.

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.

Fire is an essential feature of terrestrial ecosystems and plays an important role in the Earth system. Fires are regulated by climate, vegetation characteristics, and human activity and also feedback to them in multiple ways. For example, fires can shape vegetation composition and structure; adjust land carbon, nutrient, water, and energy cycles; change atmospheric composition, chemistry, and physics; and affect air quality and human health. Elevated fire activity in 2019 across the arctic, Amazon, and other regions underscores the urgency of a quantitative understanding of fire as an Earth system process that interacts with vegetation, climate, and humans. The EGU2020 B3.17 session on the role of fire in the Earth system received the most abstracts in the Biogeosciences division this year and was highly attended during the live chat. The abstracts cover several aspects of interactions between fire and the biosphere, atmosphere, and humans across various temporal and spatial scales using modelling, field and laboratory observations, and remote sensing. Given that the topic is highly interdisciplinary and overarching, we propose an inter-journal (ESD/BG/ACP/GMD/NHESS) special issue for this session with ESD as the lead journal, and we also encourage the submission of topic-related studies outside the EGU fire session. The special issue will bring together new advances in understanding the feedbacks and interactions between fire and other components of the Earth system at all temporal and spatial scales using various methods, including (1) impacts of fire on weather, climate, and atmospheric chemistry; (2) interactions between fire, the biogeochemical cycle, vegetation composition and structure, and land water and energy budgets; (3) influence of humans on fire and vice versa; (4) fire characteristics (e.g., fire duration, emission factor, emission height, smoke transport); (5) spatial and temporal changes of fires in the past, present, and future; (6) fire products and models, their validation, and error/bias assessment; and (7) analytical tools designed to enhance situational awareness among fire practitioners and early warning systems, addressing specific needs of operational fire behaviour modelling.

Due to a transitional zone between marine and terrestrial systems, coastal wetlands and seashores are dynamic and highly vulnerable ecosystems. The multi-scale and cross-scale spatio-temporal dynamicity of such systems in terms of various biophysical fluxes is currently poorly understood. A multi-sensor approach, including various active and passive remote-sensing and in situ sensor installations, can help in continuous monitoring and gaining a better understanding of these coastal ecosystems. A multi-sensor approach can account for long-term and cross-scale trends of the biophysical fluxes and their dynamics, providing a better understanding of how biotic and abiotic factors can influence such changes.

In this special issue, we encourage submissions that present innovative ways to implement multi-sensor approaches to monitor coastal wetlands and seashores, with particular interest in applications that integrate in situ with proximal and/or remote-sensing methods. Contributions including new modelling approaches for multi- and cross-scale data integration are also highly encouraged.

This special issue investigates the fascinating interactions between the geosphere and biosphere that are active near the Earth’s surface and within the critical zone. The special issue focuses on modelling and observational studies conducted along the extreme climate and ecological gradient of the Chilean Coastal Cordillera. We welcome submissions that address the physical or chemical processes whereby micro-organisms, animals, and plants influence the shape and development of the Earth’s surface over timescales ranging from the present day to the distant geologic past. As this topic is highly interdisciplinary in scope, we encourage submissions from diverse disciplines including geology, geography, geochemistry, surface geophysics, ecology, microbiology, soil sciences, hydrogeology, geomorphology, and climatology. Integrative studies that bridge between disciplines are particularly welcome. Two types of manuscript submissions are possible. These include either original and/or new scientific full-length research articles presenting new data and interpretations or review and synthesis papers that are invited by the editors and integrate data from different studies and disciplines to address state-of-the-science questions related to Earth surface shaping by biota.

Oxygen (O₂) is considered an effective indicator of ocean health and climate change. Its level, distribution and variability from sub-seasonal to multidecadal scales provide relevant information on the physical and biogeochemical functioning of the ocean and often act to constrain life in the ocean.

Current evidence indicates that the coastal (i.e., most directly influenced by land) and open-ocean areas have been losing O₂ since the middle of the last century, with consequences for living organisms and biogeochemical cycles that are not yet fully understood. In the open ocean the O₂ inventory has decreased by a few percent (i.e., 0.5–3%), and oxygen minimum zones (OMZs) are expanding, which is primarily attributed to global warming, although a quantitative understanding is still lacking. The number of hypoxic coastal sites has increased, predominantly in response to worldwide eutrophication, yet trends in deoxygenation in the global coastal zone remain ill-defined.

The development and extension of low-O₂ concentration areas degrade the living conditions and contract the metabolically viable habitat for a large number of pelagic, mesopelagic, and benthic organisms. The effects on individuals exposed to low O₂ can result in altered foodweb structures.

Deoxygenation affects many aspects of the ecosystem services provided by the ocean and coastal waters. For example, deoxygenation effects on fisheries include low oxygen affecting populations through reduced recruitment and population abundance and also through altered spatial distributions of the harvested species causing changes in fishing activity. This can lead to changes in the profitability of the fisheries and can affect the interpretation of the monitoring data, leading to misinformed management advice.

Model simulations for this century project a decrease in oxygen under both high- and low-CO₂ emission scenarios, while the projections of the coastal ocean at the land–ocean interface indicate that eutrophication will likely continue in many regions of the world. Warming is expected to further amplify deoxygenation in coastal areas influenced by eutrophication by strengthening and extending stratification.

This special issue will investigate new developments and insights related to low-oxygen environments and deoxygenation in open and coastal waters.

This special issue brings together a collection of articles on ecosystem manipulation experiments, which have the potential to inform mechanistic ecosystem models on the effects of global changes. Terrestrial ecosystem dynamics and the interplay of multiple biogeochemical cycles are responsible for unresolved uncertainties in Earth system change projections. The advancement of ecosystem experiments and mechanistic modelling has great potential for addressing this research challenge. However, finding answers requires diverse theoretical and empirical research to be integrated. Ecosystem manipulation experiments allow for empirical testing of theoretical hypotheses, model predictions, and their assumptions. However, results from manipulation experiments can only contribute to advance our ability to improve ecosystem–climate feedback if these are informed by and integrated into mechanistic models.

The scope of this special issue is centred around terrestrial ecosystem experiments. Papers contain an explicit theoretical component for evaluating results or generating hypotheses, address identified open challenges in modelling ecosystem responses to various experimental treatments, or are centred around a model–data synthesis, using results from ecosystem manipulation experiments. Manipulation experiments is to be understood in a broad sense, including (but not restricted to) nutrient, CO₂, and/or water manipulation; isotope labelling studies; and natural perturbations, ranging from ecosystem to planetary scale.

Climate change is exposing terrestrial ecosystems to warmer temperatures, increased CO₂ levels, and more frequent and intense drought and rainfall events. How different ecosystems respond to changing climatic conditions depends on a multitude of biological and geochemical processes which interact at different temporal and spatial scales.

On the one hand, plants assimilate carbon from the atmosphere and control carbon inputs into soil via plant detritus and rhizodeposition. On the other hand, soil fauna and microorganisms govern the decomposition of plant detritus and soil organic matter, which determines the cycling of carbon and of the nutrients necessary for plant growth. These interactions are further shaped by local environmental properties, such as vegetation type, relief, soil mineralogy, and physical structure, as well as the composition of plants and soil biota. Since soils represent the largest stock of organic carbon in terrestrial ecosystems and regulate carbon fluxes for about 10 times the current anthropogenic emissions, changes in the above-mentioned processes can have strong implications for global carbon cycling. Furthermore, the understanding of soil functioning is critical for improving predictions on the resistance and resilience of terrestrial ecosystems to climate change.

In this special issue, we seek to highlight research on biotic and abiotic interactions underlying terrestrial biogeochemical responses to climate, with a specific emphasis on elevated atmospheric CO₂, warming, drought, and drying–rewetting events. We invite contributions covering field and laboratory experiments, conceptual development, and modelling studies.

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.

Fire is an essential feature of terrestrial ecosystems and plays an important role in the Earth system. Fires are regulated by climate, vegetation characteristics, and human activity and also feedback to them in multiple ways. For example, fires can shape vegetation composition and structure; adjust land carbon, nutrient, water, and energy cycles; change atmospheric composition, chemistry, and physics; and affect air quality and human health. Elevated fire activity in 2019 across the arctic, Amazon, and other regions underscores the urgency of a quantitative understanding of fire as an Earth system process that interacts with vegetation, climate, and humans. The EGU2020 B3.17 session on the role of fire in the Earth system received the most abstracts in the Biogeosciences division this year and was highly attended during the live chat. The abstracts cover several aspects of interactions between fire and the biosphere, atmosphere, and humans across various temporal and spatial scales using modelling, field and laboratory observations, and remote sensing. Given that the topic is highly interdisciplinary and overarching, we propose an inter-journal (ESD/BG/ACP/GMD/NHESS) special issue for this session with ESD as the lead journal, and we also encourage the submission of topic-related studies outside the EGU fire session. The special issue will bring together new advances in understanding the feedbacks and interactions between fire and other components of the Earth system at all temporal and spatial scales using various methods, including (1) impacts of fire on weather, climate, and atmospheric chemistry; (2) interactions between fire, the biogeochemical cycle, vegetation composition and structure, and land water and energy budgets; (3) influence of humans on fire and vice versa; (4) fire characteristics (e.g., fire duration, emission factor, emission height, smoke transport); (5) spatial and temporal changes of fires in the past, present, and future; (6) fire products and models, their validation, and error/bias assessment; and (7) analytical tools designed to enhance situational awareness among fire practitioners and early warning systems, addressing specific needs of operational fire behaviour modelling.

The Peruvian upwelling system is one of the most productive ecosystems in the ocean. Continuous upwelling of nutrient-rich water generates high primary production, supporting an efficient food web and leading to high fishery yields. An extensive oxygen minimum zone underlying the productive surface waters gives rise to high losses of fixed nitrogen via denitrification and anaerobic ammonium oxidation. This results in nutrient ratios of upwelled waters deviating strongly from Redfield stoichiometry, with a high N deficit and excess P. How this unusual nutrient stoichiometry affects plankton community production and succession and how this feeds back on biogeochemical cycling are still not well understood. To address these questions, an in situ mesocosm experiment was conducted in the coastal upwelling system off Peru in the framework of the Collaborative Research Center 754 "Climate-Biogeochemistry Interactions in the Tropical Ocean". The field experiment took place from January to April 2017 during a coastal El Niño, a rare event of El Niño conditions confined to Peruvian coastal waters. Key objectives of this mesocosm study, which involved 57 researchers from 10 nations, were to unravel the interplay of pelagic ecology and biogeochemistry under the unique environmental conditions of the Peruvian upwelling system. This special issue in Biogeosciences is intended as a collective outlet for publications resulting from this study, covering the broad range of research topics from seawater chemistry to plankton ecology and pelagic biogeochemistry.