Biogeosciences 

Ocean alkalinity enhancement is one of several ocean-based carbon dioxide removal (CDR) approaches that are currently under evaluation. By increasing alkalinity of the seawater, dissolved carbon dioxide is converted to bicarbonate and carbonate ions, thereby allowing alkalinity-enhanced seawater to absorb more carbon dioxide from the atmosphere.

There are several different methods by which ocean alkalinity can be enhanced. These include the spreading of fine-grained natural or manufactured minerals in coastal or open-ocean settings, electrochemical production of alkaline compounds, electrochemical removal of hydrochloric acid, and a combination of the aforementioned, among others. Following the alkalinity enhancement, either carbon dioxide is absorbed passively from the atmosphere through natural air–sea gas exchange dynamics or carbon dioxide sourced from the atmosphere may be added directly to treated water prior to its release into the ocean. While ocean alkalinity enhancement could be an effective, durable, and scalable CDR strategy, the environmental impacts, both intended and unintended, are not well understood.

This special issue explores a range of biological and ecological impacts associated with alkalinity enhancement and approaches for monitoring strategies in order to safely scale scientific research in the field. The target audience of this special issue includes not only the ocean alkalinity enhancement research community but also those involved in making decisions about the funding, permitting, and monitoring of potential field trials and pilot-scale studies. In keeping with our mission to publish all valid research, we consider negative and null results.

Submission is open to research within, but is not limited to, the following scope:

• biological and ecological impacts of ocean alkalinity enhancement, including those related to secondary abiotic changes (changes in trace metal concentrations, turbidity, etc.) as documented through manipulative lab, mesocosm, and field experiments; natural analogues; and computer models;
• mitigation of harmful biological or ecological impacts associated with ocean acidification;
• reversibility of harmful biological or ecological impacts;
• spatial differences in biological or ecological impacts across ocean regions or habitats;
• discussion and/or modelling of environmental monitoring strategies for field trials, pilot studies, or large-scale applications;
• review papers or meta-analyses on any of the above.

The following related topics are out of scope:

• research focused solely on abiotic processes (e.g. dissolution kinetics, estimates of CO₂ removal potential),
• techno-economic and life-cycle analyses,
• social impact studies.

To accelerate high-quality submissions, the first 10 accepted manuscripts (limited to two publications per research grant) will be offered financial support of up to  1800 Euro to offset either publication fees or costs for conference travel.

Financial support is provided the Ocean Alkalinity Enhancement (OAE) R&D Program, a multi-funder effort incubated by Additional Ventures and fiscally sponsored by the Windward Fund. The Program is partnering with CEA Consulting to support this Special Issue. Please direct all questions to Lydia Kapsenberg (lydia@ceaconsulting.com).

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.