Biogeosciences

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 ICDC in 2013 is the 9th conference. The conference topics encompass the global carbon cycle, global and regional budgets, and processes with specialized sessions on the individual components of atmosphere, ocean and land, in the timeframes of past, present and future. It covers both fundamental science advancement and discovery, the generation of policy relevant information, and new technological observational platforms, datasets, and modeling approaches.

The three main themes of the conference are:

• Theme 1: Past and present changes and variability
• Theme 2: Carbon sources and sinks, their changes and trends
• Theme 3: Future of the carbon cycle: drivers, vulnerabilities, feedbacks and management options

Conference website: http://icdc9.lasg.ac.cn

Improving our understanding of terrestrial carbon and water cycle is of the highest scientific and socio-economic importance. The key to understanding both the processes and spatial scaling of estimates requires a careful fusion of observations from ground, airborne and satellite systems. At present, a full integration of aircraft and space-sensed information and ecosystem level observations has not been achieved.

The main objective of the COST Action ES0903 "EUROSPEC" is to develop common protocols and new instruments within a larger European network for optical measurements, bringing together scientists and industries in order to increase the reliability, value and cost-efficiency of the existing spectral observations within the European flux network. In the last 3 years, the Action has focused on proximal sensing, which can be considered a fundamental tool in monitoring Biophysical Parameters and which acts as a "bridge" between the flux tower and the remote sensing community. In fact, the EUROSPEC activities actively involved researchers from the FLUXNET, SPECNET, ICOS, ABBA networks.

Four Working Groups have been active within EUROSPEC, organizing meetings, field campaigns, experiments and summer schools:

• WG1 focused on the state of the art of the optical sampling network, database issues and building a common platform for storing, sharing, visualizing spectral data.
• WG2 on instrument intercomparison, characterisation, standardisation, intercalibration and measurement protocol issues.
• WG3 dealing with upgrading instruments for continuous measurements at the Eddy Covariance towers.
• WG4 focused on scaling Biophysical Parameters and fluxes from the ecosystem at upper levels.

The purpose of the cruise (June–July 2011) was to study the impact of ocean acidification on surface waters of the northwest European shelf, providing a glimpse into what may happen to the ocean as a whole as atmospheric CO2 concentrations continue to rise. The aim was to examine impacts on marine organisms and ecosystems, on the cycling of carbon and nutrients, and on the production of climatically important gases. These potential impacts were investigated in two main ways. Firstly, observational data was analysed to look at how organisms, ecosystems and processes vary between regions where the chemistry of seawater is naturally more acidic and those where it is more alkaline. This comparison of observational data gives insights into the effects of ocean acidification taking place over centuries, long enough for natural selection and adaptation to play out. The second approach was to conduct short-term CO2 bioassay perturbation experiments in bottles with natural communities collected in the surface layer and incubated in a controlled laboratory on deck. The natural communities were subjected to various levels of CO2 that may occur in the future and the responses were determined. This large experiment examined the effects of changing CO2 levels on real world samples whilst at sea, as opposed to monocultures in the laboratory.

Peatlands are ecosystems in which biological, chemical and physical processes are intimately interlinked drivers of greenhouse gas fluxes. Drained peatlands are hotspots of anthropogenic greenhouse gases. Recent national and international research projects have accumulated a wealth of new observational data, improved process understanding and new tools for empirical and process-based regionalization. The special issue aims to collect papers with a focus on understanding the human impact on the peatland carbon and greenhouse gas balance. Studies include experimental manipulations, gradient studies along land-use changes and management intensity, and studies of short-term and long-term dynamics of peatland restoration.

The special issue is solicited by the collaborative project "Organic soils" supported by the Thünen Institute and the European research project GHG-Europe – "Greenhouse gas management in European land use systems" supported by the European Commission in the 7th Framework Programme (grant agreement no. 244122). The special issue is open to for all submissions within the scope of the special issue.

This special issue will address the relations between climate extremes and biogeochemical cycling in terrestrial ecosystem. It will emerge from a global conference on this topic (www.bgc-extremes2013.org). Contributions regarding the following topics are welcome: ecosystem responses to climate variability and weather extremes, recovery of ecosystems after extreme events and climate related disturbance (e.g. wind-throws, fire), feedback mechanisms from the biosphere to the climate system. We welcome conceptual, observational, experimental and modeling approaches, and studies from the local to the global scale.

Anthropogenic impacts such as elevated pCO2 and eutrophication threaten the structure and functioning of marine ecosystems as well as the role of the ocean in the global carbon cycle. While sinking-particle-based carbon sequestration (the biological pump; BP) has been extensively studied, the biogeochemical behaviour of dissolved organic matter (DOM) and its role in carbon sequestration (the microbial carbon pump, MCP), is largely unexplored. The BP and the MCP operate simultaneously and interactively but their responses to environmental conditions may be regulated differently. These regulatory mechanisms have not been examined, and it is not known whether the BP and the MCP would interact to enhance or reduce their individual effects.

This special issue will bring together articles arising from discussions undertaken at IMBIZO III held in Goa in January 2013. Topics to be investigated include the organisms and microbial processes which produce and transform dissolved organic carbon in the ocean, organisms and processes which influence the interaction between the BP and the MCP, and the impact of anthropogenic perturbations such as nutrient addition and ocean acidification on oceanic carbon transformation, export and sequestration.

The Northern Indian Ocean is home to remarkable phenomena, including seasonally reversing monsoon winds and associated upwelling and productivity, as well as the planet’s largest expanses of oxygen-depleted waters. The upwelling, productivity and hypoxia (open-ocean and coastal) are associated with biogeochemical processes that are of exceptional importance to global bioelement cycles, ocean nutrient inventories, and future climate. Given the large human populations that inhabit the rim nations and depend on marine resources, processes affecting the region also have major societal relevance. However, the two main basins – the Bay of Bengal and the Arabian Sea - also represent striking contrasts, in terms of circulation, upwelling and degree of hypoxia, in riverine and terrestrial influence, and in the effects on associated biogeochemical processes. As a result, the Arabian Sea, and more recently the Bay of Bengal, have been sites of extensive biogeochemical and ecosystem research. With the advent of new methods and technology, and recognition of fundamental gaps in our understanding of both pelagic and benthic processes, a special issue focused on the Northern Indian Ocean region is timely.

The special issue will serve to highlight results of benthic and pelagic process studies in the Arabian Sea, and more recently the Bay of Bengal and Andaman Sea, including sediment trap deployments and moorings with biogeochemical sensors (etc). It will also be a venue for articles on coastal studies by scientists from Northern Indian Ocean rim nations, as well as diverse physical and biogeochemical modelling studies. Finally, the issue will serve to illustrate some of the key research areas that are relevant to the wider Indian Ocean, which have recently become the focus of the Sustained Indian Ocean Biogeochemistry and Ecosystem Research (SIBER) initiative.

How important are N2O and CH4 emissions in different ecosystems? How difficult is to measure and to model their emission? How do non-CO2 greenhouse gases contribute to the total global warming potential (GWP) of terrestrial and aquatic ecosystems?

The overall goal of this Special Issue is to gather contributions discussing the challenges and opportunities in measuring and modeling CH4 and N2O fluxes using the new available instrumentation. We encourage contributions that discuss the role of non-CO2 greenhouse gases to global biogeochemical cycles and planetary radiative forcing. This is a unique chance to cross compare the contribution of these non-CO2 gases to the carbon budget of the biosphere, and to quantify the full global warming potential (GWP) of terrestrial and aquatic ecosystems worldwide. This Special issue is linked to the goals of GHG-Europe and of the WP2 of the ABBA (COST Action ES0804), and to the Integrated Carbon Observation System (ICOS) aiming at harmonizing and integrating trace gas flux measurements around the globe.

This special issue intends to provide an outlet for the most recent results in ocean acidification research presented at the 3rd Symposium on the Ocean in a High-CO2 World in Monterey, September 24-27, 2012. All symposium participants are invited to submit their original scientific work presented at the symposium and within the scope of Biogeosciences to this special issue.

Background

The EU project SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) was initiated by a larger international consortium, in order to study the contribution of mostly naturally emitted halogenated very short-lived substances (VSLS) to the stratospheric inventory of ozone destroying halogens. Today the SHIVA consortium comprises about 120 full or associated partners coming from 19 institutions in 9 countries.

SHIVA’s scientific objectives infer from past research that mostly brominated and less likely iodinated VSLS, predominately emitted from biologically active surface waters of the global oceans, are eventually significantly contributing to the halogen load of the global stratosphere. Moreover, theoretical studies revealed that only the combination of sufficiently strong VSLS sources together with efficient vertical atmospheric transport would support a relevant contribution of VSLS to the stratospheric halogen burden. Both conditions are likely to be met in the western Pacific during the wet season (November to March). Since details of the relevant processes and their relevance for stratospheric ozone are yet largely unexplored, four major objectives of EU-SHIVA were identified, namely investigations of:

1. The oceanic emission strengths of a suite of halogenated VSLS
2. The atmospheric transport and transformation of the halogenated VSLS
3. The past, present and likely future trend of the total stratospheric halogen burden
4. The impact of long and short-lived halogenated trace gases and their inorganic product gases for past, present and future ozone within the upper troposphere, TTL and global stratosphere

Synopsis

The special ACP-BG-OS SI is intended to cover the research performed within the EU project SHIVA and related undertakings. Contributing manuscripts may cover investigations of halogenated VSLS emissions from marine micro- and macro algae, to their atmospheric transport and transformation as well as impacts of VSLS for global ozone studied in the laboratory, field and by theoretical models.

Extreme climate events (e.g., drought, heat and cold waves) and disturbances (e.g., fire, hurricane, and insect outbreaks) substantially affect carbon cycle processes. However, their impacts on terrestrial carbon dynamics over landscapes, regions, and continents are not well understood. We invite submissions that investigate and quantify the impacts of extreme climate events and disturbances on the terrestrial carbon dynamics over various spatial and temporal scales using observations (e.g., eddy covariance flux measurements, and national inventories), remote sensing, state-of-the-art modeling approaches (e.g., ecosystem models, upscaling methods), and model-data fusion techniques.

A special issue focusing on this topic will be timely and valuable to the research communities of carbon and global change. Collectively, we believe that this special issue will play a critical role in our understanding of how extreme climate events and disturbances influence the terrestrial carbon cycle and increase the visibility and influences of Biogeosciences in carbon cycle and climate change.

The main goal of DUNE (a DUst experiment in a low Nutrient, low chlorophyll Ecosystem) was to estimate by the mean of mesocosms experiments, the impact of atmospheric inputs on an oligotrophic ecosystem submitted to strong atmospheric inputs. Atmospheric deposition is currently recognized as a significant source of macro- and micro-nutrients for the surface ocean, but the quantification of its role on the biological carbon pump is still poorly determined. The main difficulty of such a quantification relies mainly on the diversity of the processes involved:

1. within atmospheric cycling of particles (from emission processes to deposition onto surface ocean, including physical-chemical transformations occurring during transport) and;
2. within the water column (uptake by bacteria and phytoplankton of particle-derived elements of biogeochemical interest, and carbon export resulting from fertilization induced by those inputs).

We proposed in DUNE to investigate the role of atmospheric inputs on the functioning of an oligotrophic system particularly well adapted to this kind of study: the Mediterranean Sea. The Mediterranean Sea – etymologically, sea surrounded by land, is submitted to atmospheric inputs that are very variable both in frequency and intensity. During the thermal stratification period, only atmospheric deposition is prone to fertilize surface waters which had become very oligotrophic due to the nutrient depletion (after the spring bloom). In order to quantify the impact of both natural and anthropogenic inputs on productivity and biogenic carbon sequestration, it is necessary to parameterize the processes affecting the ecosystem functioning.

During the DUNE project, large clean mesocosms (developed during the project) were successfully deployed twice (DUNE1 experiment in 2008 and DUNE2 experiment in 2010) in the oligotrophic waters of the preservation area of Scandola in Corsica. Dry, wet and successive wet depositions of Saharan dust were simulated. Chemical and biological changes, along with modification of the dynamic of particles following a dust event have been followed and the multidisciplinary results obtained are bringing new insights regarding the role of atmospheric deposition on oligotrophic ecosystem and carbon export. Those results are presented in this Special Issue.

The marginal seas of the western North Pacific Ocean are sensitive to climate variation, because they are adjacent to the western Pacific warm pool, and subject to the wind forcing of the East Asian monsoons, the buoyancy forcing of several large rivers, and the climate oscillation, such as ENSO. Continental margins in this region are bordered by the world’s most densely populated coastal communities and receive runoffs from highly populated large river basins. The intense anthropogenic pressure threatens diverse coastal marine ecosystems, as demonstrated by the four-fold increment of Changjiang nitrogen loading and rising atmospheric deposition of macro- and micronutrients in the past 30 years that possibly contribute to the increasing hypoxia in the East China Sea. Increasing frequencies of widespread flooding since the beginning of the 20th century, which is attributable to the accelerated hydrological cycle partly to changes in land-use, may also cause marked changes in coastal ecosystems. On the other hand, increasing impounding of freshwater for irrigation purposes may reduce riverine load of particles, dissolved silicate, altering discharge patterns, nutrient elemental ratios and phytoplankton community downstream. As continental margins sustain arguably the most productive ecosystems and most active biogeochemical processes in the earth system, the stressed ecosystems may threaten the livelihood of a large human population. Moreover, the altered biogeochemical cycles may cause unknown feedbacks that exacerbate the effects of climate change.

Considering the consequences of the world-wide degradation of mangrove forests for their unique biodiversity, for coastal protection, for the fisheries, for timber and non-timber forest products and for the human subsistence populations living within and beyond the mangrove, it is increasingly important to assess and to monitor these semi-terrestrial forests growing at the edge of land and sea. Mangroves in good conditions should be protected, whereas degraded forests should be restored. This Special Issue will focus on geomatic tools such as airborne and space-borne remote sensing, analyses in a GIS environment (change detection, assessment of sea-level-rise effects using digital terrain models, hydrodynamic modelling).

Observations have shown that the arctic climate system is shifting. As river discharge increases, the sea-ice-free season lengthens, and air, sea and permafrost warm, the arctic shelf ecosystem can be expected to be transformed. Given the importance of fluvial discharge to shelf sea dynamics, the Lena Delta and Laptev Sea region are used measure the trajectory of processes critical to these transformations for the Arctic as a whole. This special issue examines processes in transition, from the land surface, hydrological inputs to the region of freshwater influence, over coastal mass transfer, water column chemistry of terrestrially-derived suspended and dissolved material, to fluvial transport to resulting changes in shelf hydrography. As a group, the special issue contributions create a multidisciplinary focus on land-shelf fluxes and their influence on the arctic shelf seas.

Increasing concentrations of anthropogenic greenhouse gases (GHGs) are known to be causing changes in global climate patterns, and will continue to do so for the foreseeable future. Our ability to predict future climatic states is still limited for a variety of reasons. Key among these reasons is our understanding of the coupled behaviour of the components of the Earth system. A research training programme GREENCYLCEII has scientific focus on the evaluation, improvement, and application of a range of different Earth System models (ESMs). This special issue brings together manuscripts from a range of GREENCYLCEII projects, broadly classed into data and model benchmarking, marine processes, terrestrial processes, high latitude feedbacks, and coupled modelling.

The worldwide increase in coastal hypoxia and anoxia over the past decades is an alarming signal that underlines profound changes in and collapses of ("dead zones") ecosystem processes in shallow shelf seas. This special issue is largely based on experimentally induced small-scale anoxia in a benthic soft-bottom community at 24m depth (Northern Adriatic, Mediterranean). The approach combines plexiglas chambers with time-lapse photography, microsensors, core sampling and the DET technique (diffusive equilibrium in thin-films). This yielded detailed data on:

• macrofauna behavioral responses and tolerances;
• meiofauna (harpacticoid copepods and foraminiferans) responses;
• sediment geochemistry processes;
• post-anoxia scavenging and recovery.

Macrofauna behaviour links physiological functions and ecological processes and therefore depicts multi-level effects of oxygen deficiency. A detailed series of behavioral responses reveals more tolerant and more sensitive species and emphasizes the broad range of possible responses in a community setting. Among the meiofauna, the focus is on harpacticoid copepod and foraminiferan abundance and diversity. A fluorescent staining technique (CellTrackerGreen: CTG) is applied for the first time to copepods, improving the distinction between living and dead components. An accompanying pulse-chase lab experiment with pre-labeled diatoms reveals functional responses of primary consumers (copepods) to anoxia. The in situ sediment geochemistry processes (key pore water and solid phase parameters in response to migration of redox layers, mobility of trace elements) are documented (millimeter-scale resolution). Finally, post-anoxia time-lapse films examine the sequence of scavenger/predator arrivals and (the lack of) macroepifauna recolonization even after 2 years. Combined, these perspectives yield a more comprehensive picture of events during and after anoxia, improving on the information available from laboratory experiments and fragmentary in situ documentations. This is a step forward in interpreting post-hypoxia/anoxia community composition and recovery potential in the past and present.

Due to the high CO₂ solubility and low carbonate saturation states of its cold surface waters, the Arctic Ocean is considered particularly vulnerable to ocean acidification. If anthropogenic CO₂ emissions continue at current rates, large parts of the Arctic Ocean will be corrosive for calcium carbonate before 2050. While several Arctic calcifying species have been shown to respond negatively to ocean acidification, the effects of ocean acidification on pelagic communities and biogeochemical cycling is presently unknown. To close this gap, a mesocosm CO₂ enrichment experiment was conducted in the Kongsfjord off Svalbard (78°56’N, 11°56’E) in June-July 2010 in the framework of the European Project on Ocean Acidification (EPOCA). This study, which involved 35 scientists from 12 institutes, yielded a comprehensive data set on community level responses to ocean acidification and their impacts on nutrient cycling and air-sea exchange of climate relevant gases.

Monthly sampling at the Boknis Eck (BE) Time Series Station started on 30 April 1957 and, thus, BE represents one of the oldest continuously sampled marine time series sites worldwide. The long high-quality time series observations at BE are invaluable to decipher long-term trends in a representative coastal environment, which is locally (via eutrophication) and globally (via climate change) influenced by human activities. The location of BE at the entrance of the Eckernförde Bay (SW Baltic Sea) makes it an ideal site (i) to study a coastal ecosystem under the influence of pronounced changes of salinity and (ii) to study biogeochemical processes sensitive to pronounced changes of dissolved oxygen (i.e. hypoxia/anoxia). This special issue of Biogeosciences (BG) aims to bring together papers which cover different topics (eutrophication, deoxygenation, trace gas production, nitrogen cycling, marine microbiology) and approaches (incl. measurements and model studies) in order to investigate the biogeochemical processes in the water column and in the sediments at BE and the SW Baltic Sea. You are welcome to submit manuscripts on related topics to this special issue of BG.

The REgional Carbon Cycle Assessment and Processes (RECCAP) is an international effort to establish the mean carbon balance and change over the period 1990–2009 for all subcontinents and ocean basins. It is based on comparing and reconciling multiple bottom-up estimates, which include observations and model outputs, with the results of regional top-down atmospheric CO₂ inversions (and CH₄ and N₂O when possible).

This special issue presents the final synthesis papers for 14 RECCAP regional carbon budgets, 10 terrestrial regions (Africa, Arctic tundra, Australia, Europe, Russia, East Asia, South Asia, Southeast Asia, Central and South America, and North America) and 4 ocean regions (Atlantic and Arctic, Indian, Pacific, and Southern Ocean). In addition, 8 global synthesis support the regional budgets and their integration into the global picture.

RECCAP is an activity of the Global Carbon Project, with two major sponsors: E.U.-COCOS (Coordination Action on Carbon Observation Systems) and the U.S.-Carbon Cycle Science Program.

iLEAPS is the land-atmosphere core project of the International Geosphere-Biosphere Programme (IGBP). The scientific goal of iLEAPS is to provide understanding how interacting physical, chemical and biological processes transport and transform energy and matter through the land-atmosphere interface. Atmospheric Chemistry and Physics (ACP) and Biogeosciences (BG) have opened a joint special issue on iLEAPS-related science, and you are welcome to contribute by sending manuscripts on land-atmosphere interactions to this joint issue via either ACP or BG.

Human alteration of the nitrogen cycle represents a major driver of global environmental change. Since the invention, a century ago, of industrial methods to fix atmospheric di-nitrogen (N₂), the production of reactive nitrogen (N_r) has roughly doubled at the global scale and tripled in Europe (Erisman et al., 2008; Galloway et al., 2008; Sutton et al. 2011a). The main use of this deliberate anthropogenic N_r production has been to produce fertilizers to increase crop production, allowing the world’s human population to increase, as well as for people to eat richer diets, with a larger fraction of animal products.

In parallel, increased rates of fuel combustion have caused an additional inadvertent rise in anthropogenic N_r production and release to the atmosphere. This has especially been the result of greater use of high temperature combustion processes in vehicles, electricity generation and other industries, which oxidize atmospheric N₂ to nitrogen oxides (NO_x). In addition, low temperature combustion processes, from domestic burning of coal, wood, dung and burning of forests and other land, have led to an increase in both NO_x and ammonia (NH₃) emissions. Together with the emissions of N_r from agricultural systems in the form of NH₃, NO_x, nitrous oxide (N₂O), nitrates (NO₃) and many organic nitrogen forms, this human alteration of the nitrogen cycle is causing multiple effects on global change. The consequences include pollution of air, soil and water, alteration of the climate balance and threats to biodiversity. While some policies have already been enacted in Europe and elsewhere, N_r pollution represents a still largely unsolved problem. Many details of the science remain uncertain, while levels of N_r pollution are causing major threats across Europe and other industrialized and agricultural areas of the world. The complexity is illustrated by the way in which N_r emissions alter climate balance. The recent European Nitrogen Assessment (ENA) estimates that N_r emissions may be having a net cooling effect on climate, as aerosol N_r effects and forest fertilization from atmospheric N_r deposition tend to outweigh the warming effects of N₂O emissions and the N_r contribtion to O₃ formation (Butterbach-Bahl et al., 2011). However, the cooling components of N_r have even bigger estimated societal costs than their climate benefits, as aerosols affect human health and N_r deposition threatens biodiversity. Overall, the ENA estimates a societal damage cost of between €70 billion to €320 billion per year across the European Union (Brink et al., 2011; Sutton et al., 2011c). Even from this limited set of interactions, it is clear that human alteration of the nitrogen cycle is a highly complex issue, with major economic consequences. Advances in the underlying science are needed using new measurement methods and models, as a basis to inform policies that maximize the intended benefits of N_r, while minimizing its environmental threats.

These issues have been addressed by concerted efforts in Europe over the last 5 years, as a number of projects have contributed to the global ambitions of the International Nitrogen Initiative (INI), a joint project under the International Geosphere Biosphere Programme (IGBP) and the Scientific Committee on Problems of the Environment (SCOPE). The European collaboration has linked closely to the efforts of the NitroEurope Integrated Project, a consortium of 62 institutes funded by the European Union 6th Framework Programme to examine the effect of nitrogen on the European greenhouse gas balance (Sutton et al., 2007, 2011b). Several of the outcomes have already been reported in earlier special issues (Reis et al., 2009; Beier et al. 2010, Ambus et al. 2011). In order to increase the scientific scope, NitroEurope has worked closely with the Nitrogen in Europe (NinE) framework networking programme of the European Science Foundation (Bleeker et al., 2008), allowing an increased focus on interactions with biodiversity, water quality, policy and economic issues. In parallel, the COST Action 729, “Assessing nitrogen fluxes in the atmosphere biosphere system”, has added to the critical mass through workshops to stimulate collaborative activities, including a major focus on the interaction between nitrogen deposition and the Natura 2000 network, protected under the EU Habitats Directive (Hicks et al. 2011; Bleeker and Erisman 2011).

These combined efforts have come to fruition in the presentations and discussions at the international science conference Nitrogen & Global Change (NEU, 2011), held in Edinburgh from 11-15 April, 2011. The conference launched the European Nitrogen Assessment, including the key messages (Sutton et al., 2011a,b), with an emphasis on improving public awareness of the nitrogen (see NinE, 2011, plus numerous press reports).

This special issue now reports the detail of the scientific findings discussed at the Nitrogen and Global Change conference. The papers discuss key aspects of N_r in the environment, including – but not limited to – the relevance of nitrogen for climate change and air quality, for food and energy security and for biodiversity and ecosystem health. While the focus is on Europe and terrestrial ecosystems, papers addressing issues from other parts of the world are represented, as well as contributions discussing the role of nitrogen in freshwater and marine environments. The submitted papers under discussion here in Biogeosciences thus reflect the full breadth of societal challenges related to human perturbation of the nitrogen cycle. As will be seen, the contributions are also broad in nature, covering the full suite of approaches, from measurement and modelling techniques, process understanding, temporal and spatial upscaling, to analysis of policy options and N_r biogeochemistry-economic interactions.

Finally, in addition to this special issue and the other products, the conference agreed ‘The Edinburgh Declaration on Reactive Nitrogen’ (Nitrogen and Global Change Conference, 2011). This short statement highlights the need for further scientific efforts to understand the ways in which nitrogen is both causing global change and being impacted by it. At the same time, it illustrates how continued integration between disciplines - a key theme of this special issue - will be essential to develop future solutions at local, European and global scales. We take this opportunity to thank the European Comission, the European Science Foundation and national and international organizations for supporting the the underlying work reported here, and thank the many policy, industry, agricultural and conservation stakeholders for their active involvement in the process.

One of the most important aspects to understand marine organic carbon fluxes is to resolve the molecular mechanisms which convert fresh, labile biomolecules into semi-labile and refractory dissolved and particulate organic compounds in the ocean. In this interdisciplinary project, we carried out a detailed molecular characterisation of dissolved organic matter (DOM) during a North-South transect in the Atlantic surface ocean to relate the data to different biological, climatic, oceanographic, and meteorological regimes. Our goal was to achieve a high resolution data set for the biogeochemical characterisation of the sources and reactivity of DOM. We applied various biogeochemical analyses for 220 samples from the upper water column (0-200m) and eight deep profiles. Spectroscopic techniques were applied continuously for phytoplankton characterization in a constant sample water flow supplied by a fish system and the moon pool. Radiocarbon dating enabled assessing DOC residence time. Bacterial abundance and production provided a metabolic context for the DOM characterization work.