ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 26, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(8):1498-1503; doi:10.1093/icesjms/fsn110
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This article appears in the following ICES Journal of Marine Science issue: Marine Environmental Indicators: Utility in Meeting Regulatory Needs [View the issue table of contents]
An operational monitoring system to provide indicators of CO2-related variables in the ocean
1 Plymouth Marine Laboratory, Prospect Place, Plymouth, UK
2 School of Environmental Sciences, University of East Anglia, Norwich, UK
3 Met Office, Fitzroy Road, Exeter, UK
4 British Oceanographic Data Centre, Joseph Proudman Building, University of Liverpool, Liverpool, UK
5 Marine Climate Change Impacts Partnership, Centre for Environment, Fisheries and Aquaculture Science, Lowestoft, UK
6 Proudman Oceanographic Laboratory, Joseph Proudman Building, University of Liverpool, Liverpool, UK
7 National Oceanography Centre, Southampton, Empress Dock, Southampton, UK
Correspondence to N. J. Hardman-Mountford: tel: +44 01752 633429; fax: +44 01752 633101; e-mail: nhmo{at}pml.ac.uk
Hardman-Mountford, N. J., Moore, G., Bakker, D. C. E., Watson, A. J., Schuster, U., Barciela, R., Hines, A., Moncoiffé, G., Brown, J., Dye, S., Blackford, J., Somerfield, P. J., Holt, J., Hydes, D. J., and Aiken, J. 2008. An operational monitoring system to provide indicators of CO2-related variables in the ocean. – ICES Journal of Marine Science, 65: 1498–1503.Demand by governments and scientists is increasing for indicators of CO2-related variables for the ocean. We describe a recent project, CARBON-OPS, during which a "supply chain" was developed for automated measurement of pCO2 in the surface of the ocean, data processing, and its use in providing information for research and policy development. Data are gathered by new pCO2 measurement systems on five UK research ships in the Southern Ocean, Atlantic Ocean, and northwestern European shelf seas. These send data in near-real-time, via satellite communication systems, to the British Oceanographic Data Centre, where they are automatically processed, quality controlled, and archived. The data are then delivered to the UK Met Office and others for use in testing predictions from operational ocean models. These models will generate indicator products and assist government through the Marine Climate Change Impact Partnership, a partnership of scientists, government, its agencies, and NGOs, by providing information on ocean CO2 uptake, changes in ocean pH, and potential impacts on global climate and marine ecosystems.
Keywords: autonomous systems, carbon dioxide, CO2, forecast, indicators, models, ocean acidification, operational oceanography, pH
Received 23 November 2007; accepted 13 May 2008; advance access publication 26 June 2008.
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Introduction |
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 Top Introduction Towards an operational ocean...The carbon-OPS operational...Future developments and...References |
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The atmospheric concentration of carbon dioxide (CO2) has reached a level not exceeded during the past 650 000 years, and possibly not during the past 15–20 million years (Pearson and Palmer, 2000; Cicerone et al., 2004; Siegenthaler et al., 2005). The ocean is the largest natural reservoir of "free" carbon and has buffered the changes in atmospheric CO2 by absorbing about half of the CO2 released by human activities since 1800 (Sabine et al., 2004). Uptake of CO2 is determined by a number of interrelated variables and processes (e.g. temperature, salinity, primary production, mixing, pH, export of carbon from the surface ocean to depth). The difference in partial pressure (pCO2) between the ocean and the atmosphere is the driving force for oceanic uptake. As atmospheric concentrations continue to rise, pCO2 in the surface ocean is expected to increase to double its pre-industrial value by the middle of the century, depending on emissions. Coupled with rising temperatures, this is expected to lead to a decrease in the global rate of oceanic uptake, accelerating the rate of atmospheric CO2 increase (IOCCP, 2007). Recent studies from the Southern Ocean (Le Quéré et al., 2007), North Atlantic (Schuster and Watson, 2007), and globally (Canadell et al., 2007) suggest that this may already be happening.
A major consequence of increased CO2 concentration in the ocean is the disruption of the oceanic carbonate system and a decrease in surface pH. This is predicted to be three times greater and to occur 
100 times faster than pH changes experienced during the transition from glacial to interglacial periods (The Royal Society, 2005). CO2-related changes in the oceanic carbonate system have already been reported (Feely et al., 2004), and these could have profound impacts on marine organisms and ecosystems (Riebesell et al., 2000; Cicerone et al., 2004; Orr et al., 2005).
The Kyoto Protocol was introduced in 1997 and entered into force in 2005, with the aim of achieving "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system" [Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC)]. The protocol requires countries to reduce greenhouse gas emissions below specified levels, although some signatory nations are already setting more stringent targets (e.g. the UK has proposed legislation for 60% emission cuts by 2050, as part of a Climate Change Bill). Negotiations towards a future post-Kyoto agreement commenced at the UNFCCC meeting in Montreal, November 2005, and continued at the UN Climate Change Conference held in Bali, December 2007. Part of the post-Kyoto carbon accounting requires that changes in natural sinks of CO2 be tracked and if possible predicted, and these requirements are unlikely to change with future agreements.
Monitoring changes in surface–ocean pCO2 and ocean–atmosphere CO2 exchange can provide an early warning of changes in the ocean’s ability to absorb CO2 and consequent feedback to the global climate system, yet ocean pCO2 is grossly undersampled. This is especially true for the shelf seas, Southern Ocean, and southern-hemisphere subtropical gyres (IOCCP, 2007). Knowledge of CO2 fluxes is needed to assess the global importance of these regions in CO2 exchange.
An ocean-carbon monitoring system has been identified as an essential part of the Global Ocean Observing System and Global Climate Observing System, established to support the UNFCCC. The Integrated Global Observing Strategy (IGOS) proposed an integrated strategy for monitoring the global carbon cycle that combines in situ and remote sensing data with numerical models (Doney and Hood, 2002). A key part of this strategy, within its "Integrated Global Carbon Observation Theme", is the required development of a global-scale operational ocean-carbon observation network, using a coordinated combination of research vessels, ships of opportunity, and autonomous drifters (Ciais et al., 2004).
In the UK, the Evidence and Innovation (E&I) strategy of the Department for Environment, Food and Rural Affairs (Defra), requires the operational collection of CO2 data as part of its evidence base in support of global climate-change projections and process understanding of earth-system interactions. The strategy recognizes that innovation is required to improve environmental sensors, models, and modelling techniques to deliver the strategy. The development of pH-related indicators is required for marine ecosystem management and support of a sustainable marine environment, another part of the E&I strategy (Defra, 2005).
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Towards an operational ocean-carbon observation capability |
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TopIntroductionTowards an operational ocean...The carbon-OPS operational...Future developments and...References |
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A challenge central to the E&I strategy has been the lack of accurate, robust, and cost-effective autonomous sensors for ocean pCO2. To address this technological limitation and the global and regional paucity of pCO2 data, the Centre for Observation of Air-Sea Interactions and Fluxes (CASIX) commissioned autonomous pCO2 systems for permanent installation on five UK research vessels. These Live pCO2 systems were developed by Plymouth Marine Laboratory (PML) and Dartcom, and combine cost-effective technologies with a low-maintenance, autonomous design and satellite communications (for data transmission and remote instrument diagnostics). They were installed during 2006 on RRS "James Clark Ross", mainly for sampling in the Southern and Atlantic Oceans (occasionally in the Arctic Seas); RRS "Discovery" and RRS "James Cook", for sampling worldwide, predominantly in the Atlantic Ocean and European Shelf Seas; RV "Prince Madog" and RV "Plymouth Quest", for sampling in European shelf seas, predominantly the Irish Sea and western English Channel (Table 1).
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The new systems supplement UK data-collection efforts by voluntary observing ships (VOS). The MV "Santa Maria" has collected data between the UK and Caribbean over the past 5 years, supported by the University of East Anglia through the EU-funded CAVASSOO and CARBOOCEAN projects (Schuster and Watson, 2007). Since 2006, the National Oceanography Centre, Southampton, has added two new VOS routes for pCO2 measurement: on the P&O ferry MV "Pride of Bilbao" (UK to Spain, funded by NERC) and on the Swire Shipping MV "Pacific Celebes" (global circumnavigation, funded by the Swire Group Charitable Trust).
To support the monitoring effort and permit efficient processing of large data volumes, a system for automated data processing, quality control, archiving, and dissemination to user communities is required. Similar data-supply systems support weather forecasting, including ocean temperatures and salinity from the Argo programme (www.bodc.ac.uk/projects/international/argo).
In situ measurements alone are not sufficient to monitor changes in ocean CO2 adequately. Data need to be combined with ocean forecast models that are coupled to ecosystem and carbonate models, making it possible to assess and forecast ocean-carbon parameters and their impact on ecosystems. Measurements of surface ocean pCO2 are essential to validate and improve model predictions of ocean–atmosphere CO2 exchange and ocean–pH changes.
We describe the CARBON-OPS initiative, an operational pCO2-monitoring system that combines UK resources for under-way pCO2 observation with its operational ocean-forecasting capabilities to provide the UK government with products for monitoring changes in CO2 uptake by the oceans and associated feedback on global climate, ocean pH, and marine ecosystems. These will be evaluated for inclusion as indicators in a new government initiative, the Marine Climate Change Impacts Partnership (MCCIP), through their new Annual Report Card (ARC) scheme.
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The carbon-OPS operational "supply chain" |
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TopIntroductionTowards an operational ocean...The carbon-OPS operational...Future developments and...References |
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The operational supply chain is summarized in Figure 1.
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Autonomous under-way pCO2 measurement system
pCO2 in marine air and seawater is measured by the Live pCO2 autonomous measurement system (Figures 2 and 3), installed in laboratories of UK research vessels. Principles of measurement are the same as those described by Cooper et al. (1998). The system uses a combined glass-bead and showerhead equilibrator to sample gaseous CO2 from headspace air that is in equilibrium with seawater. Seawater is supplied to the equilibrator from the non-toxic seawater supply. Marine air is sampled from forward on the vessel. Both air streams are dried and the CO2 content measured using a non-dispersive infrared analyser. Three standard gases of known CO2 content (0, 250, and 450 ppm) are also sampled to calibrate against drift of the infrared analyser (model: LI-COR LI-840). The on-board standard gases are calibrated against international standards (supplied and certificated by the United States National Ocean Atmosphere Administration). The pCO2 system samples in the following sequence: equilibrator air, ancillary data, marine air, standard gases. Total cycle length is optimally selected for each vessel, based on factors such as operating environment, number of days at sea, distances to be covered, and method of data transmission. Currently, this varies between 30 min and 1 h, although a minimum cycle length of 15 min is possible. Dissolved oxygen is also measured alongside the equilibrator, using an Aanderaa oxygen optode (model 3835). The ancillary data streams necessary for post-processing of pCO2 data (hull-inlet temperature, conductivity, thermosalinograph temperature, calculated salinity, and atmospheric pressure) and for environmental diagnostics (chlorophyll fluorescence and turbidity) are integrated into the pCO2-system data file from the vessel’s own underway logging system. Near-real-time transmission of the data, or a subset, is via iridium-satellite short-burst data service or direct satellite Internet connection (VSAT; currently only available for RRS "James Clark Ross" and RRS "James Cook"). All data logged on board are also uploaded to the central database at the end of each cruise.
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Because of their low maintenance requirements, the Live pCO2 systems only require minimal on-board supervision (e.g. cleaning the equilibrator) by the existing technical support staff responsible for other underway systems. Additionally, a technical troubleshooter, based at PML, is responsible for monitoring all systems remotely and liaising with the ships, ensuring that any operational issues are identified and dealt with quickly.
Automated processing system
To ensure end users, such as the UK Met Office, have access to data on operational time-scales, an automated processing, quality-control, archiving, and dissemination system has been designed, with data delivery through an Internet interface (www.bodc.ac.uk/carbon-ops). Data received from the research vessels by the British Oceanographic Data Centre (BODC) are immediately transferred to and secured within their accession database. Receipt of the data triggers automated application of the atmospheric-pressure, temperature, salinity, and calibration corrections to the measured pCO2 data. Calibration offsets are applied for equilibrator temperature sensors. The data processing uses Weiss and Price (1980) for humidity corrections, Takahashi et al. (1993) for equilibrator temperature corrections, and Weiss (1974) for the virial coefficients when calculating fugacity. The process includes automated quality control of the data, according to a set of agreed standards and protocols taking account of internationally recognized procedures developed by the International Ocean Carbon Coordination Project (IOCCP) of the Intergovernmental Oceanographic Commission. Data are then added sequentially to the BODC database in conjunction with appropriate information describing the nature of the flagging procedures applied.
On completion of each cruise, delayed-mode quality control of the data is performed. This involves direct visual screening of the data, using BODC’s bespoke software.
Model validation and indicator products
The Met Office Forecasting Ocean Assimilation Model (FOAM; Hines et al., 2006) comprises nested ocean general-circulation models that are run operationally. The system includes a sea-ice model and assimilation of physical oceanographic and satellite measurements (sea surface temperature and sea surface height). For ecosystem simulations, it is coupled to the Hadley Centre Ocean Carbon Cycle model (HadOCC; Palmer and Totterdell, 2001), an NPZD (nutrient, phytoplankton, zooplankton, detritus) ecosystem model that also includes carbon and alkalinity. Assimilation of satellite-derived ocean chlorophyll data in HadOCC is being evaluated as part of the CASIX research programme. Model configurations are run as preoperational demonstrations at a range of resolutions, from a 1° global configuration to high-resolution, limited-area configurations at up to 1/27° resolution. Ten-year hindcasts (1997–2007) will be run for three configurations as part of ongoing research activities in CASIX: a 1° global model, a 1/3° North Atlantic and Arctic configuration, and a 1/9° North Atlantic configuration.
The coupled Proudman Oceanographic Laboratory (POL) Coastal Ocean Modelling System–European Regional Seas Model (POLCOMS–ERSEM), developed by the POL and PML, provides ecosystem predictions in shelf-sea waters using a more complex Plankton Functional Type model (Blackford et al., 2004; Siddorn et al., 2007), and includes a carbonate-model component (Blackford and Gilbert, 2007). This model system is used both operationally by the UK Met Office and as a principal research tool of the UK community. Boundary conditions are obtained from the FOAM–HadOCC North Atlantic configuration. A 17-year hindcast has been run as part of CASIX activities.
The pCO2 observational data are used to validate the hindcast and preoperational nowcast and forecast demonstrations (Figure 4). A particular advantage of the pCO2 observations for validation is that they are collected with co-located observations of other physical and biological variables, allowing exploration of the coupling of data and errors in the pCO2 model field and other variables.
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These models will generate diagnostic products targeted at policy objectives for ocean CO2. Preliminary products, such as seawater pCO2, air–sea CO2 flux, and seawater pH fields will be submitted to the Government’s evidence groups for evaluation as environmental indicators and baselines. Figure 5 shows an example model-output field of the current seawater pH annual range, which is important for consideration of marine-habitat vulnerability to decreasing pH.
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Future developments and applications |
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TopIntroductionTowards an operational ocean...The carbon-OPS operational...Future developments and...References |
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The policy requirement for CO2-based indicator products can be expected to grow as climate and carbon mitigation policies continue to gain acceptance and increase in priority. We identify four main areas where action is required to support future development: (i) autonomous sensor development: underway and moored; (ii) automated data-processing, quality-control, archiving, and dissemination systems; (iii) forecast capability; and (iv) sustained funding of long-term CO2 monitoring.
Development of pCO2 sensors for both moored and underway use is well established in the research community, and a few commercially available systems are being evaluated. Further improvements to the autonomy of systems, reductions in instrument size, and satellite telemetry will facilitate large-scale expansion of current monitoring efforts. Automated measurement of other ocean-carbon variables (pH, dissolved inorganic carbon, total alkalinity) is much less developed, and the current lack of commercially available autonomous sensors for these variables is a hindrance to monitoring requirements.
As the demand for automated measurement of the marine environment increases, so must the requirement for timely access to quality-controlled data in usable formats. The automated data-handling infrastructure described could be readily expanded to a wider range of monitoring systems.
The merits of modelling for assessment and prediction of ecological change have been well demonstrated. Nonetheless, recent, rapid development of marine ecological models for use in operational forecasts requires stringent, observational, data-hungry tests of their accuracy. Therefore, the demand for high-quality measurements is growing. pCO2 is an integrating variable dependent on a wide range of physical and biogeochemical processes, including atmospheric concentration, temperature change, and the net production–respiration balance of the marine ecosystem. As such, it is a highly useful measurement for testing ecological-model performance.
Assimilation of observations by physical models has demonstrated advantages for constraining errors and improving model estimates. Data assimilation of pCO2 observations can greatly improve ecological-model forecasts, but current feasibility is questionable, given the small number of measurements being taken.
These areas of development can increase the global capability for ocean carbon-cycle monitoring; however, improved capability will only be useful if a serious commitment is made to sustaining and increasing the volume of in situ observations of ocean-carbon variables.
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Acknowledgements |
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We gratefully acknowledge the help and support of many others with the work described, especially the crews and technical support of the research vessels (RRS "James Clark Ross", RRS "James Cook", RRS "Discovery", RV "Plymouth Quest", and RV "Prince Madog") and voluntary observing ships (MV "Santa Maria", MV "Pride of Bilbao", and MV "Pacific Celebes"). The CARBON-OPS project is funded by NERC through its Knowledge Transfer programme (NE/E002021/1). Development of pCO2 systems was funded by NERC grant (NE/C513277/1). NHM is funded through the Centre for observation of Air-Sea Interactions and fluXes (CASIX), a Centre of Excellence in Earth Observation. CAVASSOO was funded by the EC between 2000 and 2003 (EVK2-CT-2000-00088). FerryBox activities on MV "Pride of Bilbao" have been funded by the EC (FP5 EVK2-CT-2002-00144) and a NERC Capital grant (NE/C513418/1). Data collection on MV "Pacific Celebes" was funded by the Swire Group Charitable Trust. This paper represents CASIX publication No. 51.
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