Early white paper draft version- October 2013
This preliminary draft is intended as a consultation document.
Comments/edits welcome. Please do not use or cite.
Theme 1: Greenhouse gases and the oceans
Author: Christoph Heinze
1. Brief statement defining the theme:
The major driving forces for on-going climatic change are large additions of greenhouse gas to the Earth system
resulting from human activities. The natural cycles of these greenhouse gases in the oceans and troposphere
interact with these unprecedented direct inputs and lead to climatic feedbacks as well as environmental impacts,
which need to be identified, quantified, and predicted on local to global scale and on a variety of different time
scales.
2. The scientific and societal basis justifying research on this issue. Why is it critical and why does it
need to be done now? What is the end goal? Why is international coordination required?
Scientific basis: For the present increase in greenhouse gases - notably CO2, N2O, and CH4 - no adequate
paleo-analogue exists. While for the inorganic carbon cycling a well-developed fundamental research framework
has been established, still oceanic and atmospheric measurements are lacking in specific key regions - and
especially the Southern Ocean. For the modulation of the carbon cycle through biologically induced changes our
process-based knowledge is very poor. This applies as well for the increasing ocean acidification and associated
impacts/feedbacks. The N2O and CH4 cycles are still less well understood than the carbon cycle, especially in
view of changing physical as well as chemical boundary conditions. Global databases for N 2O and CH4 are only
slowly emerging. The potential vulnerabilities of ocean carbon uptake as well as potentially further strongly
increasing ocean based greenhouse gas sources must be identified and taken into account in estimating future
greenhouse gas budgets for the Earth system. Societal basis: A firm understanding and quantification (past,
present, future) of greenhouse gas sources and sinks is key to predict climatic change and environmental
change appropriately within the on-going Anthropocene. Energy production, food production, redistribution of
goods, access to natural resources and local societal infrastructures are dependent on a best possible
understanding and governance of related biogeochemical cycles. Why is it critical and why does it need to be
done now? We are currently at the beginning of an accelerating climatic and environmental change due to
increasing population and emergent greenhouse gas emissions on the pessimistic/high side of potential
alternatives. There are two major reasons why research on ocean-atmosphere interaction of greenhouse gases
is essential: 1. We need to provide a description of the present state of greenhouse gas budgets and related
Earth system variables now, in order to have a reference point for calibrating predictive models better once
climatic/environmental change will have progressed more strongly in the coming decades. 2. We need to set up
a complete as possible spectrum of processes and greenhouse gas interactions to determine whether
postulated and emergent feedbacks, impacts, as well as vulnerabilities are occurring as predicted or whether
new surprises become evident. What is the end goal? The end goal of the theme is to provide integrated
predictive capabilities of the distribution of key greenhouse gases - primarily CO2, N2O, and CH4 – in the oceanatmosphere system including impacts, feedbacks, and vulnerabilities for optimal design of mitigation/adaptation
measures concerning management of the carbon and nutrient cycles worldwide. Why is international
coordination required? Observations on greenhouse gases - data collection (ships, aircraft, satellites, automated
devices) as well as in-situ, laboratory, and mesocosm experiments - and Earth system modelling including
dynamical interactive greenhouse gas cycles are expensive undertakings and cannot be carried out in national
isolation. Data sets on measurements and modelling have to be merged from different originators in a sound
way in order to achieve calibrated, homogeneous, and quality checked data synthesis products. Earth system
models need to be developed within the context of international discussion, as hardly at every modelling centre
key expertise on all critical aspects is present.
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3. Background – major scientific concepts, key prior work defining the issues:
Coupled cycles: CO2 is still the major anthropogenic greenhouse gas directly emitted into the atmosphere and
then partially taken up by the ocean and land. In recent years, increasing focus has emerged also on other
important greenhouse gases whose cycle is influenced by human behaviour and climate/environmental change.
After all, the cycles of CO2, CH4, and N2O are interlinked, e.g. after release of CH4 from gas hydrates it becomes
relatively quickly oxidised to CO2, N2O production is highest near production of biogenic organic matter (N2
fixation) or its degradation at low oxygen levels (denitrification). Though considerable knowledge gaps
concerning the CO2 related carbon cycle still exist, uncertainties with respect to CH4 and N2O are presumably
even higher. The cycling of CH4 is critically linked to warming (destabilisation threshold) and tectonics, the N 2O
cycle is linked to a multitude of other factors influenced by human beings (de-oxygenation, nutrient inputs from
continents and artificial fertiliser production/use, increased water column stratification and slowing ocean
circulation as consequence of warming). Vulnerable greenhouse gas sources/sinks: Oceanic cycling of
greenhouse gases may undergo potential critical changes for the different long-lived gases CO2, N2O, and CH4.
For CO2 buffering it is critical that water saturated already with respect to CO 2 is mixed downward in the water
column and replaced by water masses carrying still lower CO 2 loads. In the recent past, transient decreases in
CO2 sink strengths have occurred in regions, which so far are hot spots of anthropogenic carbon storage
(northern North Atlantic, Southern Ocean; Watson et al., 2009; Le Quéré et al., 2007). On the other hand until
the end of this century, the Southern Ocean is projected to become one of the strongest sink regions for
anthropogenic carbon. Do these predictions hold? Will evidence from observations support this? For modulation
of anthropogenic CO2 uptake rates through the biological pump, a change in size spectra of marine particle flux
under warming/increased stratification and less CaCO 3 ballasting could lead to shallowing of the organic carbon
remineralisation depth interval with a corresponding increase in outgassing (e.g., Laws et al., 2000; Klaas and
Archer, 2002). On the other hand, carbon overconsumption in response to ocean acidification has been
suggested as a potential negative feedback (Riebesell et al., 2007). O 2/N2 measurements in the atmosphere so
far do not directly indicate such changes but do not exclude them for the future as yet. For N 2O, decreased
upwelling and de-oxygenation in conjunction with eutrophication and slowing overturning increase production,
especially close to continents (Naqvi et al., 2010). Further increases in marine levels N 2O could occur through a
potential stimulation of N2 fixation if dust deposition and additional iron supply would happen, though the change
of atmospheric dust mobilisation, transport, and deposition is not yet conclusively quantified (Mahowald and Luo,
2003). For the open ocean, N2 fixation has been proposed to be the key source of N2O (Freing et al, 2012).
Potential marine CH4 sources could occur due to accelerating deoxygenation and respective methanogenesis in
very low oxygen regimes (water column, sediment) especially in shallow seas and at the continental margins, but
also especially due to large scale destabilisation of methane gas hydrates once the stabilisation point
(temperature, pressure) has been reached under global warming. Arctic Ocean shallow shelves (sub-sea
permafrost areas) and continental margin areas may be susceptible (Biastoch et al., 2011), as they are areas of
higher tectonic activity. Critical oceanic GHG domains are marked in Figure 1. Observational systems and
related data sets: A suite of recent data syntheses and data collections concerning the marine carbon and
nitrogen cycles has emerged (GLODAP, CARINA, PACIFICA, SOCAT, MEMENTO). Still some oceanic areas
are highly under sampled in space and time. Modelling efforts, MIPs and related data sets: For climate
projections on timescales of several centuries, coupled Earth system models (ESMs) have been developed
which include detailed chemical and biogeochemical interactions as far as relevant process knowledge is
available. Output data sets are available through large international model intercomparison projects (MIPs) such
as CMIP5. Combining observations and models: Data assimilation of biogeochemical ocean models is still in its
infancy but progress has been made in implementing sequential as well as variational methods for ocean
biogeochemical models. The emergent constraint approach (e.g. Cox et al., 2013) can provide a short cut for
identifying the potentially most reliable models for future projections.
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Figure 1: Overview on critical areas for modifications of atmospheric greenhouse gases through the ocean.
4. Approaches – what will it take to make substantive progress on the issue? What will be achieved in
the 10 years of Future SOLAS?
APPROACHES:
Dynamical process formulations and firmer knowledge about impacts: The various drivers for modifications of
greenhouse gas fluxes such as changes in ice cover, reactive nitrogen input into the ocean, warming, ocean
acidification, and increasing stratification need to be linked in a dynamical way to the respective impacts and
feedbacks. This can be achieved to some degree by laboratory and mesocosm experiments. In addition, a
biogeographical approach is needed, where case studies in selected key regions along physical and
biogeochemical gradients are carried out in order to ground truth findings from artificially forced experiments.
Bridging the spatial scales: In order to quantify and predict oceanic greenhouse gas budgets and related air-sea
fluxes correctly, the highly heterogeneous continental margins have to be included in global budgets (as well as
for national greenhouse gas budgets to close budgets across national borders). This is a particular challenge as
outlined by Regnier et al. (2013). Respective higher resolution coupled ocean-atmosphere models including
biogeochemical cycles need to be developed, which allow for a proper representation of continental margins and
shallow seas in greenhouse gas budgets. This is of particular importance to upwelling systems and areas of
large N2O production. Better observational coverage in space and time through automated systems: In order to
assess variations in greenhouse gas fluxes within the ocean and across the air-sea interface still a far denser
observing system is needed. Automated systems need not only be installed on ships, but also on floats. Some
progress has been made to install O2 sensors on ARGO floats. Calibration problems still need resolving. With
high priority also pH sensors and highest-accuracy alkalinity sensors are needed in order to monitor changes in
ocean acidification and their impacts. Remotely sensed atmospheric greenhouse gas concentrations need to be
linked to oceanic measurements. Combining models and observations: The combination of observations and
models through systematic performance assessment and data assimilation will improve the models through
optimisation of free parameters in process descriptions and also elucidate the reason for regional variations in
marine greenhouse gas sources and sinks. Both sequential and variational methods are being implemented
currently and may come to full operational state within the next pentad.
ACHIEVEMENTS:
● Combined Observing-modelling capabilities will be created in order to monitor expected and potentially unexpected changes in GHG budgets and allow a better check on emission reductions.
● Transformations of biogeochemical cycles and ecosystems under multiple stressor forcing will be assessed
and predicted including the effects of ocean acidification, de-oxygenation, and reactive nitrogen deposition to the
ocean.
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● Internationally coordinated data syntheses actions will provide legacy data sets as reference for future
generations when climate as well as environmental change will have progressed more severely than now. This
includes also high accuracy CaCO3 and BSi (biogenic silica hard parts) production maps for the world ocean.
● An improved estimate of the varying land carbon sink through better ocean/atmosphere assessment including
O2 budgets will be achieved. This is important especially in view of the current discussion about nutrient
limitation of the terrestrial carbon fertilisation effect.
● Standardised procedures, formats, models, observations will be made open access to a wide user community
working on climate mitigation/adaptation.
5. Community readiness – is there an existing community engaged on this issue? Are there institutional
or other barriers to progress? Is infrastructure or human capacity building required in order to achieve
the goals?
Community readiness – is there an existing community engaged on this issue? Worldwide projects such as
SOLAS, IMBER, IOCCP, and GCP have essentially contributed to recent achievements in quantifying marine
greenhouse gas fluxes. The recently established international ocean acidification coordination centre (OA-ICC)
is underpinning this collaboration. Continent-/basin-wide projects have provided actual resources to carry out
respective research work such as OCB (US), the EU framework programmes 6 and 7 (with CARBOOCEAN,
CARBOCHANGE, EPOCA, and more), PICES and others. Linking the South American and in particular African
communities needs still a lot of improvement though progress could be made (e.g. cooperation with CSIR South
Africa, and Morocco). Ocean carbon cycle research is also supported through CLIVAR (repeat hydrography
programme). The community is linked to GEO and GOOS/FOO through a number of projects. Are there
institutional or other barriers to progress? An increasing number of joint projects between the terrestrial,
atmospheric, and oceanic greenhouse gas communities have emerged over the past decade, but still the
disciplinary groups work quite separately. Specifically targeted projects and collaboration networks may help to
enhance the communication and joint research work between these communities further. A better link to LOICZ
for incorporating the coastal oceans in worldwide greenhouse gas budgets would be welcomed. With respect to
oceanic greenhouse gas cycling, the spatial discrimination between SOLAS (upper ocean) and IMBER (deep
ocean) is somewhat artificial from an oceanographic point of view. Therefore, the SOLAS-IMBER carbon groups
(SIC, WG1-3) have been implemented. Concerning the coordination of international research, IOCCP and OAICC are encouraged to collaborate closely with each other in order to avoid fragmentation of the research
coordination worldwide. Is infrastructure or human capacity building required in order to achieve the goals?
Ocean observations as well as Earth system modelling are both expensive undertakings. Optimal international
coordination and use of research vessels as well as supercomputers is essential for greenhouse gas research.
Tracer measurements should be done as multi-tracer data sets in order to correlate as many as possible
different variables from the same casts. A particular problem is the storage of large model data sets as computer
power progresses faster than storage technology. Transdisciplinary collaboration is needed to take into account
for and implement dynamics of human behaviour (economics, energy, matter flow/waste handling, etc.) also in
the Earth system models through interactive modules. Personnel for professional data management have to be
trained and sustained, in particular also to facilitate data extraction from the substantial data archives.
6. External connections – what partnerships are required in order to achieve the goals? What
mechanisms will be used to accomplish the interactions?
As outlined in section 5, the ocean greenhouse gas communities are already based on established projects,
which are linked through coordination mechanisms (IOCCP, OA-ICC). Therefore, a firm framework for
collaboration and communication is already in place. Concerning the collaboration between modellers and
observing scientists, one may envisage a task team – possibly as part of the already well functioning SIC groups
– on greenhouse gas data assimilation and Earth system modelling (with links to their respective programmes
and networks such as WCRP and ENES). Further the SIC groups may open up to also include research on
nitrogen cycling and N2O.
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7. Sustainability – articulate relationship (if any) between this project and the FE goals of Global
Development and Transformation Towards Sustainability.
Optimal information and knowledge concerning greenhouse gas fluxes are the foundation for informed policy
decisions on measures for climate mitigation and adaptation. Integration of ocean-atmosphere greenhouse gas
cycling is therefore a condition sine qua non for any development towards sustainability (impacts of greenhouse
gases – also through ocean acidification, sources/sinks of greenhouse gases, optimal pathways for emission
reductions etc.). Because greenhouse gas emissions and greenhouse gas levels in the atmosphere and ocean
are tightly coupled to energy production, food supply, land use (including fertiliser applications), traffic, and also
health, the research topic is at the heart of FE.
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