Biogeosciences

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.

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.

Lake Malawi in south-eastern Africa is a major ancient lake with an estimated age of over 4.5 million years. It is known as a global hotspot of biodiversity and, for example, harbours arguably the highest number of endemic freshwater fish species.
Lake Malawi has attracted major research activities including a deep drilling campaign. However, no comprehensive work summarizing new results from both geological and biological disciplines dealing with the lake exists to date. The planned special issue aims at publishing the state of the art of biological, paleobiological, limnological and geological research on Lake Malawi focusing on its evolution in a broad sense. You are welcome to contribute to this inter-disciplinary special issue.

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.

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.

We currently witness in the Arctic:

1. a decrease in summer ice cover that exposes sea surface to solar radiation and physical forcings;
2. permafrost thawing and increased river runoff, both leading to an increase in the export to the ocean of organic carbon previously sequestered in the Tundra;
3. an increase in ultraviolet radiation.

These three phenomena favour a growing mineralization of organic carbon through photo-oxidation and bacterial activity, amplifying the increase in atmospheric CO₂. At the same time, the exposure of a larger fraction of ocean surface to sun light and the increase in nutrients brought by rivers lead to larger autotrophic production and sequestration of organic carbon. To predict the balance of these processes, we conducted an extensive study in the Mackenzie River / Beaufort Sea system in July, August and September 2009 onboard the Canadian research ice-breaker CCGS Amundsen. The spatial distribution of organic carbon stocks (living and detrital) in the water column and sediments was determined on the shelf and beyond. The magnitude and variability of organic carbon mineralization through photo-oxidation and bacterial activity, and production through photosynthesis was measured. These targeted studies allows the monitoring of these processes using remote sensing in the coming years and decades. A detailed study of microbial biodiversity was conducted to describe the different biocenoses and biotopes and to anticipate their response to climate change. Diagnostic models of the studied processes (primary production, bacterial activity and light-driven mineralization of organic matter) are combined with a coupled physical-biological ecosystem model, and applied using outputs from global climate models to assess the fate of the associated carbon fluxes in the Arctic Ocean during the next decades under different climate change scenarios. Additionally, a retrospective approach was followed to partly answer the Malina questions, based on the analysis of geochemical proxies in the past 1000-y sediments.

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.

Low oxygen conditions (hypoxia) are becoming increasingly common in aquatic systems worldwide. While hypoxia can occur naturally due to stratification, eutrophication and limited bottom water renewal, there is strong evidence for a world-wide increase in hypoxia linked to human-activities and climate-change. This is of major concern because oxygen depletion leads to mortality of benthic fauna and major changes in ecosystem functioning. While true anoxia in the modern ocean is rare, wide-spread anoxia occurred episodically in the oceans during so-called oceanic anoxic events (OAEs) in Earth's past.

Numerous questions remain regarding the mechanisms driving hypoxia and anoxia in coastal and open ocean systems in the present and past, the role of natural processes versus human activities, the impacts on biota and the potential and timeline for (eco-) system recovery. This special issue of BG and CP aims to bring together papers on a broad range of aspects linked to oxygen depletion in modern and ancient settings addressing such questions.

Since the adoption of the 1978 Practical Salinity Scale (PSS-78) and the 1980 International Equation of State of Seawater about three decades ago, only slow scientific progress was made on understanding the thermophysical properties of IAPSO Standard Seawater, handling regional seawater composition anomalies, or characterizing the thermodynamic properties of seawater in contact with ice or humid air. Meanwhile, the subsequent introduction of new international standards such as the temperature scale ITS-90 or the pure-water description IAPWS-95 had not been incorporated into official oceanographic standards.

Recognising the need for a revised international standard on seawater properties, the Scientific Committee on Oceanic Research (SCOR) and the International Association for the Physical Sciences of the Oceans (IAPSO) established Working Group 127. This SCOR/IAPSO Working Group soon started a close cooperation with the International Association for the Properties of Water and Steam (IAPWS). On the occasion of the IAPWS 2008 International Conference in Berlin, the Special Issue "Thermophysical Properties of Seawater" of Ocean Science was established as a peer-reviewed and open-access resource for the wide range of scientific results produced by the work of WG 127, as well as by the IAPWS Subcommittee on Seawater.

The Special Issue now offers a comprehensive collection of background papers covering the new seawater standard, the "International Thermodynamic Equation of Seawater - 2010", TEOS-10, as well as new seawater experiments and observations, new equations of state, TEOS-10 source code, new description methods for oceanic salinity and a metrological assessment of the long-term stability of state-of-the-art salinity measurements. Additional material, including updates of equations or code published in this Special Issue, is freely available from the web pages www.TEOS-10.org and www.iapws.org and should be also consulted by interested readers of the Special Issue.