By Kate Larkin and Richard Lampitt (on behalf of the EuroSITES Consortium)
National Oceanography Centre, Southampton, U.K.
In-Situ Ocean Observation: A Societal Need
In recent years the societal motivation and need to monitor and sustainably manage our oceans has become more apparent. The recent oil spill in the Gulf of Mexico, hurricane and tsunami disasters and ocean Û÷healthÛª issues including ocean acidification are all current issues at the forefront of science news. These issues pose as a constant reminder to understand how the oceans are changing as a result of climate change and the role the global ocean plays in mitigating and amplifying climatic and geologic phenomena.
It is only possible to understand the complex ocean processes and interactions can only be achieved through sustained sampling programs at the right temporal resolution. There is currently an international drive to observe and monitor our oceans from the coast to the open ocean and from the surface to the abyssal seafloor. Results from this global effort from remote sensing to in-situ observations and emerging technology were presented at the OceanObsÛª09 conference in Venice (September 2009) . Ocean observation from satellites has gained recognition as a key tool for ocean observation, providing a global view (at fine resolution) of the surface Û÷healthÛª of the oceans. In contrast, there is far less sustained funding commitment for in-situ ocean observation even though only in-situ datasets can reveal the deeper layers, resolve fine-scale ocean processes and provide real datasets for validating remote sensing and modeling.
This article reviews the current global effort for in-situ open ocean observatories and the key role these platforms play in understanding critical processes such as biogeochemical cycling and ocean circulation in the open ocean. Current European (EuroSITES) and international (OceanSITES) initiatives are presented as key contributions to an integrated, sustained observing system. The growing need for high quality, high resolution ocean datasets to feed models and produce products and services to society is also discussed alongside current research and development for innovative ocean observation of biogeochemical and biological variables. The fragility of current funding mechanisms and lack of longer-term commitments is also highlighted as an urgent issue which jeopardizes the vision for a sustained approach to open ocean observation as part of a global earth observation system.
A Matter of Time: Unique Strengths of Fixed Point Ocean Observatories
Crucially important ocean processes occur on time scales that often cannot be observed by ships and in the deep parts of the ocean that are outside the reach of satellites. Sustained in-situ observations at a high temporal resolution are therefore required to provide high quality data on climatically and ecologically relevant variables at a few key locations. Eulerian (fixed point) observatories are one key platform that can achieve this (Figure 1). Firstly they offer the perspective of time to ocean data, providing high resolution, high quality data at a few key locations (see review by Lampitt and Favali ). Ocean observatory infrastructure often spans the full ocean depth allowing it to support a multitude of larger, power hungry sensor payloads compared to other platforms such as gliders. This enables simultaneous multidisciplinary research linking surface and seafloor processes. It also allows samplers (e.g. water samplers for zooplankton, sediment traps for particle flux) and processors involving rate measurements or genetic monitoring (e.g. Environmental Sample Processor) to be deployed together with automated sensors for standard variables. Permanent telemetry links enable real time data delivery at a high temporal resolution. In some remote locations (e.g. North Atlantic) ocean observatories are the only platform to have produced sustained winter biogeochemical datasets at a fixed location e.g. nitrate  and pCO2 .
EuroSITES: The Multidisciplinary European Open Ocean Observatory Network
EuroSITES is a network funded by the European Commission (3.5M Euro) with the objective to integrate and enhance the nine existing open ocean fixed point observatories around Europe (Figure 2). These observatories are multidisciplinary and make in-situ observations within the full water column and seafloor of a wide range of physical, biogeochemical and geological variables. Key research themes range from biogeochemical cycling in the open ocean (e.g. carbon multi- and inter-disciplinary and nitrogen cycles) to ocean circulation, deep water formation and developing tsunami warning systems. However, all sites in the network share the same aim: to enhance the open ocean observing capability of European waters and move towards an integrated and sustained operational network for societal benefit.
EuroSITES is the European component of the OceanSITES international network of deep water reference stations. EuroSITESÛª contribution to the global ocean and climate observing system is therefore a regional implementation of the OceanSITES network, an essential component of the Global Ocean Observing system (GOOS) contributing to the Group on Earth Observation. Within the OceanSITES community ethos EuroSITES has developed a common data policy and promotes full and open access to all data. The network is also identifying a list of core ocean variables, aligning with the Global Climate Observing System and United Nations Framework Convention Climate Change list of Atmospheric, Oceanic and Terrestrial Essential Climate Variables (ECV) that would form the back-bone of any future open ocean observatory network.
Moving Ocean Observation beyond the Current State-Of-The-Art
EuroSITES promotes the development of innovative sensors and samplers to progress the ocean observing capability for key climate- and environment variables. For example, an oxygen consumption device, the IODA6000 (Figure 3) has been designed by partner Microbiology Laboratory of Marine Ecology and Geochemistry, which is a joint research unit of the Centre of Oceanology of Marseille (CNRS/LMGEM) and deployed successfully in situ in both coastal (ANTARES; Ligurian Sea) and open ocean (PAP; North Atlantic) environments. This device will revolutionize our understanding of the mesopelagic zone (100-1000m depth band), the biological carbon pump and the oceansÛª role in the carbon cycle. A key variable is mesozooplankton abundance and diversity. EuroSITES conducted trials and improved a commercially available device for long-term sampling both in the Atlantic in 2009 and in the Mediterranean in 2010 to achieve this. Measuring the pH is one key element for monitoring the ocean carbonate system and the levels and impacts of ocean acidification in the ocean. EuroSITES is supporting the development of a novel pH sensor (led by ULPGC) with high reproducibility and accuracy for long-term oceanic deployment. Having successfully demonstrated the instrument during trials, the sensor has recently been deployed at the ESTOC site in April 2010.
Although much of the focus of EuroSITES is on the water column, significant development of seafloor capabilities is also taking place. Two autonomous seafloor platforms have been deployed in the Mediterranean, one for tsunami detection (off Pylos, Greece) and one to monitor fluid flow and pore pressure (off Patras, Greece) to assess slope stability. Seafloor science missions in 2010 include monitoring benthic biological communities and associated biogeochemistry as indicators of climate change in both the Northeast Atlantic and Mediterranean.
EuroSITES has close collaboration with related projects both within Europe and elsewhere. One example is the ESONET project which has funded a demonstration mission at the EuroSITES PAP observatory in the North Atlantic. The demonstration mission, called MODOO (www.modoo.info) will enhance the seafloor monitoring at the site by deploying a lander system on the abyssal seafloor (4800 m depth) and using acoustic telemetry to send datasets from the abyssal depth (4800m) via the existing EuroSITES water column mooring.
Societal Benefit: The Need for Monitoring the Open Ocean
Ever since the emergence of humankind, the oceans have played a crucial role in shaping the prosperity and survival of our species. In recent years the commercial importance of the global ocean has become more apparent with, for example, ÛÏecosystem servicesÛ from ocean biogeochemical cycles are currently valued at trillions of US dollars .
Sustained, open ocean time-series are invaluable for assessing both short-term and longer-term change in ocean processes. Having a continuous monitoring program also ensures that less predictable or random events such as phytoplankton blooms and storm surges are captured and recorded in high resolution. As ocean and climate models become ever more sophisticated there is a growing demand for ocean time-series data. Historical datasets are required for reanalysis studies producing hind casts and for validating and constraining models.
The models are essential not only to provide the spatial context to in-situ ocean observations but also to enable predictions of future scenarios e.g. how biogeochemical cycles, primary production and gas flux may change with climate change. In-situ ocean datasets underpin such studies and are essential if we are to reduce the uncertainty in modeling outputs and successfully plan mitigation strategies against the effects of climate change and effectively manage our resources and environment. EuroSITES is a key provider of multidisciplinary open ocean datasets to the global ocean observing system. Data from across the network are openly accessible both in near real-time and as fully quality controlled datasets in a single data format (OceanSITES NetCDF) through the EuroSITES project website and through the CORIOLIS OceanSITES ftp site. Daily deliveries of temperature and salinity data are uploaded to the Global Telecommunications System (GTS), a global network supplying climate and ocean data for numerical modeling forecasts. Links are being developed with modeling initiatives e.g. MyOcean and Mercator-Ocean to maximize the use of EuroSITES datasets by society .
Over the course of the EuroSITES programme the European coverage and data accuracy of the open ocean fixed-point observing systems have been improved as well as the management and online access to the data and information. As a result, there have been an expansion in the numbers and types of queries from individuals interested in the ocean time-series data. EuroSITES is seen as a key data provider of in-situ ocean data to the global observing system. However, without sustained funding for ocean time-series such as the EuroSITES network, there is a high risk that there will be gaps in these valuable time-series. There urgently needs to be a more coordinated approach to link the upstream data providers (e.g. EuroSITES) and the downstream services and products (e.g. MyOcean). Only by ensuring that every link in the chain is sustained can the full societal benefit of in-situ ocean data be realized.
We would like to thank the EuroSITES Consortium (13 partners) for their significant contribution towards making the EuroSITES network a success. We are also pleased to acknowledge the support of the European Commission for financial support (Call FP7-ENV-2007-1, grant agreement Nå¡ 202955 Sub-Activity 6.4.1. Earth Observation; monitoring the ocean interior, seafloor, and subsea floor).
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