To explore key zones of the oceans using profiling floats, a new generation of undersea robots, in order to improve our understanding of carbon and nitrogen biogeochemical cycles: that is the goal of the remOcean project headed by Hervé Claustre, a researcher at the Observatoire Océanologique de Villefranche sur Mer (CNRS/UPMC).
Combining these findings with satellite observations of seawater color patterns will also help clarify the role of phytoplankton in the regulation of the oceanic carbon cycle. The five-year project (2010-2015) is funded by a €3.3 million grant from the European Research Council.
Deployment of a profiling float in the barren—and thus deep blue— waters of the South Pacific (off Easter Island).
Credit: © Antoine Poteau, Observatoire Océanologique de Villefranche CNRS/UPMC
The remOcean project ("remotely-sensed biogeochemical cycles in the Ocean") will explore five key zones: the North Atlantic, which represents only 1.4% of the world ocean's total surface but could account for more than 20% of its carbon sequestration, and four large subtropical central zones of the Pacific and Atlantic that are veritable biological deserts about which little is known, even though they represent more than 60% of the ocean surface.
To study the characteristics of these various regions, Hervé Claustre and his team will develop and deploy ultramodern profiling floats (see box) with enhanced capacities, remote-controlled and equipped with multiple sensors. A new iridium satellite communication system will enable the researchers to receive data from these submarine robots and send them new instructions (e.g. a change of observation frequency) each time they resurface before beginning a new observation cycle. In addition, an array of miniaturized sensors will enable the floats to carry out physical as well as chemical (oxygen, nitrates) and biological measurements (chlorophyll and particle counts, etc.).
This undersea robotics technology offers many advantages, such as "real time" continuous remote observation, even in zones that are difficult to reach or too costly to access regularly by ship. In addition, once deployed, the profiling floats remain independently operational for two to three years. Lastly, they offer the only solution for studying variations in the ocean's biological properties across a range of time scales (from diurnal to seasonal and even interannual).
However, the information gathered by remOcean will be fully significant only when it is cross-referenced with other observation techniques, such as the satellites monitoring the ocean's color. The color of the light "emitted" by the ocean, and remote-detected by satellite, is indicative of the quantity of phytoplankton (botanical plankton) in the water: zones rich in phytoplankton are greener and those with lower levels are bluer. Based on this information, researchers can map the concentrations of these tiny plants, the simplest marine organisms to transform CO2 into living matter, in the world's oceans.
But this mapping technique only concerns the ocean's surface layer, down to about one-fifth of the depth occupied by phytoplankton. The profiling floats will supplement these maps with information on deeper waters that the satellites cannot "see." The long-term goal of remOcean is to compile the first biological profile of the oceans in three dimensions. A 3D view will offer unique perspectives for the marine sciences, for example making it possible to estimate the quantity of carbon (CO2) trapped by phytoplankton through the photosynthesis process.
By providing a better understanding of aspects of certain biogeochemical cycles, the remOcean project constitutes a major new development in the current research on environmental changes.
The project is funded by an advanced grant from the European Research Council (ERC). Founded in 2007, the ERC backs basic research projects that meet two criteria: the innovative potential of the proposal and the scientific excellence of the submitting party. In 2009, 236 researchers were selected for funding throughout Europe. Hervé Claustre is the first French oceanographer to receive this distinction. The €3.3 million grant awarded to remOcean is close to the maximum allowed by the program, which allots a total of €515 million, all scientific disciplines combined.
The work cycle of "conventional" multi-cycle profiling floats A conventional multi-cycle profiling float carries out identical preset cycles: descent, immersion drift (to ~1,000 meters), descent to maximum depth (~2,000 meters), ascent while taking measurements, and data transmission upon resurfacing. A profiling float can "yoyo" between the surface and depths of about 2,000 meters by adjusting its buoyancy. The typical duration of such a cycle is 10 days, and the measurements conducted are physical—primarily salinity, temperature and depth. The data is transmitted using ARGOS, a simple, reliable and perennial system, but one that does not allow remote reprogramming of the float.