Tropical ecosystems are epicentres of biodiversity and play key roles in global biogeochemical cycles, for example in the sequestration of terrestrial and coastal carbon. Tropical coasts are characterised by large river systems delivering huge amounts of material into the coastal ocean, with fluvial inputs of nutrients, carbon, and sediment from tropical rivers playing a globally significant role. The majority of the population in tropical regions lives along these rivers and coasts and depends economically on aquatic resources. Yet rapid development in many tropical regions, such as Borneo, is causing large-scale impacts on riverine and coastal ecosystems, the biogeochemical consequences of which remain poorly known. Interestingly, it has been suggested that coastal systems in tropical regions react differently to anthropogenic stresses compared to coasts in temperate and subtropical regions. However, our understanding of tropical rivers, estuaries, and coasts is still too basic to predict the impacts of increasing anthropogenic pressures. An improved understanding of these ecosystems and their biogeochemistry is therefore urgently needed. This special issue calls for work that examines biogeochemical processes of tropical rivers, estuaries, and coasts as well as their response to environmental change and the interplay of natural and anthropogenic control factors.

Increased harvest of forest biomass has the potential for mitigating climate change as well as reducing dependency on fossil fuels across much of the boreal zone. For forestry to be sustainable in the long term, the supply of weathering (chemical dissolution of minerals) needs to be sufficient to compensate for what is harvested and washed out by acid deposition. There are indications that current levels of forest harvest in boreal regions are not sustainable because soils are already being depleted of key elements in large areas, and increased harvest rates will be even less sustainable. This weathering deficit threatens both trees and aquatic ecosystems. But there is also a concern that weathering estimates are uncertain relative to the accuracy needed to guide forest policy. This special issue brings together key results and syntheses from a 5-year research programme involving six universities and two research institutes to improve weathering estimates at the spatial and temporal scales relevant to sustainable forest management, including how climate and forest management can affect weathering rates.

The articles in this issue do the following:

• present improvements made in soil mineral weathering models via improved descriptions of tree physiology, forest ecology, and aqueous geochemistry;
• advance our understanding of the biological controls upon and responses to changes in soil mineral weathering rates;
• demonstrate the sensitivity of base cation weathering rates to small changes in mineralogy;
• use improved understanding to project weathering in the coming century across a broad section of the boreal region for multiple climate scenarios;
discuss weathering rates and their importance for sustainable forestry and aquatic ecosystems in the context of other nutrient pools in the soil.

After more than 20 years, mining of mineral resources, such as polymetallic nodules and massive sulfides, in the deep sea is back on the agenda of many countries and companies in their search for high-tech raw metals. In this course, the past 10 years have seen an immense increase of exploration licences issued by the International Seabed Authority (ISA), which organizes and controls activities at the ocean floor beyond national jurisdiction, generally termed the "area". The seven pilot investors are renewing their exploration licences for another five years, after which they will need to apply for an exploitation licence (or lose their contracted claim). Thus, ISA is currently developing the regulatory framework for the exploitation of seafloor mineral resources, which includes legislation to "ensure effective protection of the marine environment from harmful effects" according to UNCLOS article 145. In order to support decision-making for ISA's regulations, several benthic impact experiments were conducted more than 20 years ago. However, the impacts have only been studied over the following 5–7 years. Until now, no information has been available for the expected longer-term impacts induced by mining operations, i.e. in case of nodule mining the removal of the surface sediments and dispersal of the suspended particle plume and subsequent seafloor blanketing. Therefore, in 2015 the European project MiningImpact, funded through the Joint Programming Initiative Healthy Seas and Oceans (JPIO), revisited several impact scars at the seafloor in the nodule exploration licence areas of the Clarion–Clipperton Fracture Zone (CCZ) as well as the benthic impact experiment DISCOL (DIsturbance and reCOLonization) in the Peru Basin. Our scientific study provides the first results of environmental consequences on the deep-sea ecosystem that prevail for up to 40 years after a disturbance was created. Also, the impacted areas vary in size from single 1–2 nm long dredge or sled tracks to the 78 criss-crossing, 4 m wide plough harrow marks in the 11 km² large DISCOL experimental area. This special issue presents the scientific results of the biological, biogeochemical, geological, and oceanographic investigations carried out in the MiningImpact project (consisting of 25 institutes from 11 European countries) that is used to provide recommendations for the exploitation mining code of ISA (e.g. improved methods for the management and monitoring of mining operations) and to improve our understanding of the ecological functions of the deep seafloor.

Paleoclimate data provide unique insights into climate dynamics across a range of timescales. Importantly, paleoclimate data are the only means of evaluating and constraining climate models under boundary conditions different from today and the recent past. However, most paleoclimate data are presently archived in a fragmented and non-standardized way, necessitating synthesis efforts in order to allow meaningful analysis of spatio-temporal climate dynamics and data-model comparison. Moreover, paleoclimate data are inherently uncertain since they are based on indirect evidence (proxies) and associated with chronological error, requiring rigorous uncertainty analysis to separate signal from noise and to make full use of paleoclimate data syntheses.

This special issue provides a platform to present paleoclimate synthesis products, to review the current state of proxy uncertainty analysis, as well as to present new developments. The issue is organized within the paleoclimate data synthesis working group of the PALMOD (http://www.palmod.de/ ) project, which focuses on the past 130,000 years. However, this is an open submission issue and we explicitly invite contributions from across the paleoclimate community describing synthesis methods and results from any kind of archive and/or parameter. We welcome contributions presenting paleoclimate synthesis products and their analysis across timescales, with regional or global focus and both time slice and transient approaches as well as conceptual contributions to proxy data uncertainty analysis (theoretical, empirical, Bayesian).

The International Carbon Dioxide Conference (ICDC) is the single largest conference organized by the global research community every four years to present the latest scientific findings on the science of the carbon cycle and its perturbation by human activities. The ICDC10 in 2017 is the 10th anniversary conference. It covers fundamental science advancement and discovery, the generation of policy relevant information, and observational and modeling approaches. ICDC10 brings together scientists from different disciplines to work towards an integrated view on the global cycle of carbon in the Earth system.

The main themes of the conference are as follows:

1. The contemporary carbon cycle
   • Trends, variability, and time of emergence of human impacts
   • Emerging approaches and novel techniques in observations
2. The paleo-perspective: patterns, processes, and planetary bounds
3. Biogeochemical processes
   • Process understanding and human impacts
   • Coping with complexity: from process understanding to robust models
4. Scenarios of the future Earth and steps toward long-term Earth system stability

GGMT-2017 is a key conference on measurement techniques for accurate observation of long- lived greenhouse and related gases, their isotopic composition in the atmosphere relevant for climate change, and global warming research findings. The biannual meeting, known as the WMO/IAEA Meeting of Experts on Carbon Dioxide, Other Greenhouse Gases and Related Tracer Measurement Techniques, is to be held for the 19th time in 2017.

Main topics:

• Developments of the GHG networks
• CO2 observations (measurement techniques and calibration)
• Non-CO2 observations (measurement techniques and calibration)
• Isotope measurement and calibration
• Emerging techniques
• GHG standards and comparison activities
• Integration of observations, data products and policy

The special issue is open for papers that emerged from ICDC10 and GGMT -2017 conference contributions.