Biogeosciences 

Over the last 2 decades, studies have shown that the sea-surface microlayer covers large areas of the global ocean and, under certain conditions, can even form biofilm-like (and thus unique) habitats between the ocean and the atmosphere. Due to its recurrent biofilm-like features and unique position at the atmosphere–ocean interface, the microlayer is central to a range of global biogeochemical and climate-related processes, including marine carbon cycling, air–sea gas exchange, physical surface processes, and aerosol production. Despite the fact that processes occurring in and across the microlayer have received increasing attention during recent years, our knowledge about the microlayer remains rudimentary. New approaches and technologies have been developed to understand the formation and function of the microlayer on a mechanistic level. For example, the BASS (Biogeochemical processes and Air–sea exchange in the Sea-Surface microlayer; https://uol.de/en/bass) group has been funded to explore the significance of the microlayer as a bio- and photochemical reactor in an unprecedented comprehensive and interdisciplinary approach, and BASS findings will contribute to this special issue (SI). The purpose of the SI is twofold: (1) to present outcomes of a BASS mesocosm study and (2) to present further contributions on the microlayer from the wider research community based on field, mesocosm, modelling, and laboratory studies. This SI will bring together the latest scientific studies to describe the microlayer as an interface between the ocean and atmosphere across different disciplines.

Mercury (Hg) is a chemical pollutant of human health concern worldwide; a consequence of anthropogenic activities; and the focus of the Minamata Convention on Mercury (MC; https://minamataconvention.org/en), an international treaty to protect human health and the environment from the adverse effects of mercury. The MC entered into force on 16 August 2017 and committed to limiting the use and environmental release of mercury. Also, the 1998 Protocol on Heavy Metals of the 1979 Convention on Long-Range Transboundary Air Pollution (LRTAP) commits parties to mitigating emissions of mercury (as well as cadmium and lead) from a variety of point sources and provides guidance on mitigating emissions associated with heavy metal use in manufactured products. The MC framework requires an evaluation of the effectiveness of its measures in meeting the objectives beginning no later than 6 years after the convention’s entry into force and periodically thereafter. The Protocol on Heavy Metals requires a periodic review of the progress towards meeting the obligations in the protocol and the sufficiency and effectiveness of those obligations and an evaluation of whether additional emission reductions are warranted.

This multi-journal special issue (SI) is intended to develop the required information that can be scientifically exploited to address key policy questions of the conventions: (1) what are the contributions of anthropogenic emissions and releases and other Hg sources to current Hg levels observed in air, biota, humans, and other media? (2) How have these contribution levels changed over time and over the timeline of the convention? (3) How do the contribution levels and their trends vary geographically at the global scale? (4) What are the contributions of anthropogenic emissions and releases and other drivers to the temporal trends in observed Hg levels across global regions? (5) How are observed Hg levels expected to change in the future?

The special issue aims at collecting relevant research advances arising from the design, implementation, and results of the Multi-Compartment Hg Modeling and Analysis Project (MCHgMAP) and from the scientific community on all aspects of biogeochemical mercury cycling, including primary and secondary emissions, observations, process studies, and single to multi-compartmental and statistical model development and application. A challenge of analysing the fate of emitted mercury is that it can recycle between the atmosphere, land, and ocean, and as a result, past and present emissions can continue to affect the environment on timescales of decades to centuries. MCHgMAP is an ensemble modelling initiative developed to inform the effectiveness of evaluations of the MC and LRTAP, utilizing a coordinated modelling approach between single-medium (atmosphere, land, and ocean) and multi-media mercury models to consistently simulate the changing global and regional environmental Hg cycling and analyse its drivers. The SI includes an overview paper on MCHgMAP, describing its scientific background and design (an important and crucial preparatory stage), which will be referenced by the individual papers on this project that follow.

SCOR (Scientific Committee on Oceanic Research) Working Group 167 (Reducing Uncertainty in Soluble aerosol Trace Element Deposition, RUSTED), appointed in October 2022, brings together experts from the atmospheric chemistry, ocean biogeochemistry, and modelling communities. Aiming to reduce uncertainties in soluble aerosol trace element deposition, RUSTED will quantitatively assess different aerosol leaching schemes; formulate standard operating procedures (SOPs) for frequently used aerosol leaching schemes; and develop a user-friendly, open-access database of aerosol trace element data which includes advice on the use of the data in Earth system models.

In this special issue, we propose to curate cutting-edge studies which advance our knowledge of the deposition of soluble aerosol trace elements and their impacts on marine ecosystems. We also encourage the submission of manuscripts which address challenges and/or report recent advances in the field of aerosol trace element deposition from researchers outside the working group.

The Tropospheric Ozone Assessment Report (TOAR-II) is an official activity of the International Global Atmospheric Chemistry Project (IGAC) (https://igacproject.org/activities/TOAR/TOAR-II). The goal of TOAR-II is to build on the success of TOAR-I (2014–2019) and produce an updated assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause. This effort will include an analysis of the impacts of ozone on human health, crop and ecosystem productivity, and climate. Original tropospheric ozone research conducted by the TOAR-II community may be submitted to one of six Copernicus journals (ACP/AMT/BG/GMD/ESSD/ASCMO), and the accepted papers will be linked through the TOAR-II Community Special Issue.

Drought is a complex phenomenon resulting from interactions between physical and social systems that impacts both societies and ecosystems around the world yearly. Drought risks are systemic and increasing (UNDRR, 2021). In 2019, scientists from African countries urged the world to end the drought in drought research and asked for more support to better identify and prepare for drought disasters (Padma, 2019). Preparing for future drought requires a thorough understanding of the complexities of systemic drought risk and adaptation feedbacks, effective drought risk management, and good communication of the risk and potential adaptation options. In the special issue on Drought, society, and ecosystems, we aim to showcase the diverse interdisciplinary research being done on the interactions between drought, ecosystems, and people (including human-induced climate change and management).

We solicit contributions (commentaries, review articles, original research articles) from different perspectives on this interdisciplinary topic from research scientists of different fields, students, practitioners, and stakeholders. It will be a unique opportunity to further our understanding of drought risk, adaptation, and feedbacks. The co-listing of this special issue under the Copernicus journals Natural Hazards and Earth System Sciences (NHESS), Hydrology and Earth System Sciences (HESS), Geoscience Communication (GC), and Biogeosciences (BG) allows for more diversity in perspectives.

Abstracts that fall under one of the following (or related) themes will be considered:

• drought risk analysis
• drought impact attribution
• water security in diverse contexts
• drought risk management and communication
• co-creation of drought information services
• drought in (socio-)ecological systems
• drought and the food–water–energy–environment nexus
• influence of human activities on drought hazard
• socio-hydrology of human–drought interactions
• drought and vulnerability (in ecological and/or social systems)
• drought adaptation (in ecological and/or social systems)
• climate change impacts on drought/water security.

Manuscripts with diverse authorships and with case studies in different geographic regions are especially welcomed. The special issue arises from the International Association of Hydrological Sciences (IAHS) Panta Rhei working group Drought in the Anthropocene and aims to showcase the research done on drought–society–ecosystem interactions during the IAHS Panta Rhei decade (2013–2023). However, unsolicited contributions are also highly encouraged. The guest editors aim for diversity and balance in contributions and authors, encouraging researchers from countries underrepresented in science, women, and minorities to contribute to this special issue.

References:

UNDRR: GAR Special Report on Drought 2021, United Nations Office for Disaster Risk Reduction, ISBN 9789212320274, 2021.

Padma, T.V.: African nations push UN to improve drought research, Nature, 573, 319-320, https://doi.org/10.1038/d41586-019-02760-9, 2019.