Scheduled special issues
Effects of rising CO2 on a Baltic Sea plankton community: ecological and biogeochemical impacts
As one of the largest brackish-water seas, the Baltic Sea has a comparatively low alkalinity and carbonate saturation state, leading to a low carbonate system buffer capacity. As a result of this, Baltic Sea surface waters experience large seasonal changes in pH and pCO2 and show strong changes in carbonate chemistry in response to biologically mediated carbon turnover, such as primary production, respiration, remineralisation, and calcification. Over the past two decades the Baltic Sea has experienced acidification of its surface waters at a rate more than twice as high as mean ocean acidification. Thus, carbonate system perturbations – diurnally, seasonally, and as a result of CO2-induced acidification – are much more pronounced than in marine systems. Whether the Baltic Sea biota has adapted to stronger carbonate system variations and is therefore able to better cope with anthropogenic acidification or whether it is less resilient because acidification further amplifies the stress already caused by natural carbonate system perturbations is presently not well understood.
Hydrography, biogeochemistry, and biology of "dead-zone eddies" in the eastern tropical North Atlantic
The eastern tropical North Atlantic (ETNA) is characterized by a moderate O2 minimum zone (OMZ) with lowest O2 concentrations just under 40 μmol kg-1 (Stramma et al., GRL, 2009). Current understanding is that the ETNA OMZ has been expanding over the past decades both in terms of vertical extent and intensity (Stramma et al., Science, 2008). The recent discovery of isolated low-oxygen (O2) eddy-associated water bodies, ranging from hypoxic (<20 μmol kg-1) to even suboxic (<1 μmol kg-1) conditions, in the generally well ventilated open ocean region near the Cape Verde Archipelago changed our understanding of oceanic processes in this area (Karstensen et al., BGD, 2014, doi:10.5194/bgd-11-17391-2014). In order to better understand the origin and development of these extreme dead-zone eddies as well as their biogeochemical and biological properties, a multi-facetted, multi-platform, interdisciplinary field study in the eastern tropical North Atlantic was designed to investigate biogeochemical and ecological processes in these eddies. This so-called "Dead Zone Eddy Hunt Study" was carried out most successfully in 2013/2014 and yielded a wide range of excellent results featuring unique and surprising findings. The special issue will cover the whole range of concerted hydrographic, biogeochemical, and biological observations carried out in the interdisciplinary study.
Biogeochemical and biological response to a diazotroph bloom in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosms experiment
In the ocean, the availability of N is one of the most influential factors controlling primary productivity. Biological N2 fixation, i.e., the reduction of atmospheric N2 gas to biologically available ammonium (NH4+), constitutes the major source of new N for the surface ocean (140 ± 50 Tg N yr-1), significantly larger than riverine and atmospheric inputs. By maintaining a pool of bioavailable N, this process sustains oceanic productivity over broad time and space scales. However, a critical question that has been poorly studied is the transfer and fate of diazotroph-derived N (DDN) in the pelagic food webs. The actual flux of DDN that supports the growth of different groups of autotrophic and/or heterotrophic plankton and can be transferred up the trophic chain, remineralized and/or exported from the euphotic zone is unknown. To answer these questions, a triplicate mesocosm (55 000 L) experiment was conducted in the southwest Pacific (New Caledonia; 22°29.073 S, 166°26.905 E) in January–February 2013 within the framework of the ANR-INSU-IRD-GOPS-funded VAHINE project. This study, which involved 25 scientists from 7 institutes, yielded a comprehensive data set on community-level responses to a diazotroph bloom and its impact on community changes, biogeochemical cycles and export.
Integrated perspectives on biological and geological dynamics in ancient Lake Ohrid
Ancient Lake Ohrid on the Balkan Peninsula constitutes the oldest and most biodiverse lake in Europe. The processes generating this high biodiversity, however, are poorly understood. In order to unravel the geological and biological history of the lake and to study, among others, the influence of major geological and environmental events on the evolution of endemic taxa, an international research initiative was launched. This research project included a deep drilling campaign at Lake Ohrid. Drilling took place in spring 2013 with a maximum penetration of 569 m below lake floor. Almost 2 years after the drilling operation, core opening and processing as well as biological and geological analyses are still ongoing. Preliminary analyses of sediment core and borehole logging data indicate that Lake Ohrid is roughly 1.3 to 1.5 My old, which confirms the results of molecular dating analyses conducted prior to the drilling operation. This special issue brings together the results of the biological and geological studies back to the end of the Middle Pleistocene transition ca. 620 ka ago, and explores patterns and processes of biodiversity and biogeography and in relation to geological processes. These findings not only shed new light on long-term environmental change and short-term geological events in the northeastern Mediterranean region, but they also will contribute to a better understanding of the driving forces of biotic evolution.
Hotspots of greenhouse emissions from terrestrial ecosystems on global and regional scales
Identifying hotspots of greenhouse gas (GHG) emissions from terrestrial ecosystems on global and regional scales is pivotal to limiting the future increase of GHG concentrations in the atmosphere, and to assisting in the targeting of effective mitigation strategies. Hotspot identification, however, needs to be based on a multi-dimensional approach that considers realistic biophysical, agronomic, economic and social constraints. This special issue is open to contributions that relate to the general topic of terrestrial GHG hotspots, including but not restricted to improved GHG data sets that solve current data gaps, ii) improved estimations of GHG data uncertainties, iii) improved interoperability of databases on different scales (spatio–temporal) and streams (i.e. satellite remote sensing, ground measurements), iv) inclusion of socio-economic dimensions in GHG mitigation strategies, and vi) considerations of mitigation strategies. This analysis is supported by the CGIAR research programmes on Climate Change, Agriculture and Food Security (CCAFS) and Forests, Trees and Agroforestry (FTA), which have a focus on mitigation interventions from smallholder systems in the developing world.
Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) (ACP/BG Inter-Journal SI)
Catastrophic reduction of sea ice in the Arctic Ocean – its impact on the marine organisms and ecosystems in the polar region
The topical target areas are located in the Arctic Ocean and its marginal seas, including the Bering Sea. The marine ecosystem surrounding the Arctic Ocean is complicated, and it is difficult to predict the future because "disadvantage" phenomena such as ocean acidification and "advantage" phenomena such as improving light conditions for marine organisms, respectively, are simultaneously progressing. Investigations such as observations by research vessels and satellites, culture and breeding of plankton, and marine ecosystem models are necessary to understand not only the current status but also prediction of changes in Arctic environments and the impact on the ecosystem. In this special volume, the latest research findings are reported as follows: (1) description of recent environmental changes, physical and chemical properties associated with Arctic climate change; (2) temporal changes in primary production, secondary production and lower trophic level ecosystems; (3) recent changes in behavior and distribution of higher trophic level organisms including marine mammals; (4) the physiological response of marine phyto- and zooplankton having carbonate tests on warming or freshening associated with sea-ice melting; and (5) development of a new model for marine ecosystems in the Arctic Ocean, to reproduce the primary production by using the model and to understand the response of marine ecosystems on the catastrophic environmental changes caused by rapid sea-ice reduction. These reports can be valuable for not only for understanding the current environmental changes in the Arctic Ocean but also for obtaining new predictions of marine ecosystems of both low and high trophic level organisms including fish resources in this area. The prediction of fish resources in the Arctic Ocean would contribute to the planning of not only Japanese but also international policy for fisheries. This special issue is open to all submissions within the scope of this special issue.
Data assimilation in carbon/biogeochemical cycles: consistent assimilation of multiple data streams (BG/ACP/GMD Inter-Journal SI)
How changes in ice cover, permafrost and UV radiation impact on biodiversity and biogeochemical fluxes in the Arctic Ocean – The Malina project
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.
Biogeochemical processes, tropospheric chemistry and interactions across the ocean–atmosphere interface in the coastal upwelling off Peru (BG/OS/ACP/AMT Inter-Journal SI)
The R/V Meteor cruise M91 (Callao-Callao) took place off Peru from 01 December to 26 December 2012. The overall goal of M91 was to conduct an integrated biogeochemical study on the upwelling region off Peru and its adjacent oxygen minimum zone in order to assess its importance for the emissions of various climate-relevant atmospheric trace gases and tropospheric chemistry. The various work packages of M91 included measurements of (1) atmospheric and dissolved trace gases, (2) aerosols, (3) nitrogen processes and isotopes in the water column, (4) dissolved organic matter in the surface microlayer, (5) upwelling velocity, and (6) exchange fluxes across the ocean−atmosphere interface. M91 was funded by the German BMBF project SOPRAN (Surface Ocean Processes in the Anthropocene; http://www.sopran.pangaea.de), which is a contribution to the International SOLAS (Surface Ocean – Lower Atmosphere Study; http://www.solas-int.org).
Low oxygen environments in marine, fresh and estuarine waters
General Scope: Hypoxic to anoxic and even sulfidic conditions have already been reported for various aquatic systems, from lakes, estuaries and coastal areas to off-shore regions of the ocean, where oxygen supply does not compensate for its consumption in various redox processes, including respiration of organic matter. In the coastal ocean, oxygen minimum zones (OMZs) have spread exponentially since the 1960s with potential catastrophic biological losses for the benthic communities living on the bottom. In the open ocean, eastern boundary upwelling systems (EBUSs) are characterized by high primary and export production that, in combination with weak ventilation, cause oxygen depletion and the development of OMZs in sub-surface waters.
The Liege Colloquium: The purpose of the 46th International Liege colloquium organized in May 2014 on "Low Oxygen Environments in marine, fresh and estuarine waters" was to generate an overview of the current knowledge on deoxygenation, its monitoring, modelling, impact on ecosystems and biogeochemical cycles as well as the potential evolution of low oxygen conditions in a changing climate (http://modb.oce.ulg.ac.be/?page=colloquium&year=2014). Thematic sessions have been organized on:
Freshwater ecosystems in changing permafrost landscapes
Considerable attention is now focused on permafrost systems given the accelerated warming of the Arctic and the potential mobilization of its vast stocks of soil organic carbon, and the wide-ranging importance of permafrost for geosystem and ecosystem processes throughout the polar regions. Although many terrestrial studies have provided new information about permafrost degradation and its associated carbon dynamics, few have considered the role of aquatic ecosystems in these processes. There has been little consideration given to the strikingly diverse and changing limnology of these lake and river systems, including their geomorphology, hydrology, hydrodynamics, other physical and ecosystem properties, biogeochemistry, biodiversity and food webs, microbiology, photochemistry and regional differences. More knowledge about each of these aspects is needed for a full understanding of the global importance of thaw aquatic ecosystems as biogeochemical reactors; as elemental sources, sinks and conduits; as ecological oases in the Arctic and Antarctica; and as systems that may respond rapidly to climate change. This special issue brings together specialists from different disciplines to share their knowledge about these dynamic systems on permafrost landscapes, and to identify priorities for future research.
KEOPS2: Kerguelen Ocean and Plateau Study 2
The project KEOPS studies the impact of natural iron fertilization of the Southern Ocean on the functioning of the ecosystem and on the biogeochemical cycles. In this context the region around Kerguelen is an exceptional natural laboratory where in situ observations and experimentations could be conducted both in iron fertilized and non-fertilized regions. The main objectives are (i) to identify and quantify the sources and the pathways for iron fertilization, (ii) to study and quantify the impact of iron fertilization on the biogeochemical processes occurring in the water column and at the interfaces with air and sediment, (iii) to study the impact of iron fertilization on the structure of the ecosystem, from viruses to zooplankton, and to investigate how changes in biology affect biogeochemical fluxes. This special issue will gather publications of the results of the second oceanographic campaign (KEOPS2) that took place in October-November 2011. It will include comparisons with the results of the first campaign (January-February 2005) and with other previous natural or artificial iron fertilization experiments in the Southern Ocean.
EUROSPEC – spectral sampling tools for vegetation biophysical parameters and flux measurements
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:
The EU Project SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) (ACP/AMT/BG/OS Inter-Journal SI)
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:
The special ACP-AMT-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.
Interactions between climate change and the Cryosphere: SVALI, DEFROST, CRAICC (2012–2016) (TC/ACP/BG Inter-Journal SI)