BioArgo: A global scale chemical sensor network to observe carbon, oxygen, and nitrogen cycles in the ocean

This talk will focus on the development and operation of a global scale, chemical sensor network that is distributed throughout the world's ocean. The daily, seasonal and interannual changes in the concentrations of inorganic carbon, pH, dissolved oxygen and nitrate that are driven by photosynthesis and respiration are basic tracers of ocean metabolism. This metabolism has a fundamental control on the earth's climate, as production of organic matter in the surface ocean acts to lower atmospheric carbon dioxide by about 200 ppm. It is possible that these rates of elemental cycling will change in the future as the surface ocean warms [1]. However, there are no existing observing systems that allow ocean metabolism to be observed directly at a global scale. In particular, sampling chemistry from ships does not work because of the expense and remoteness of most of the ocean. At the global scale, ocean productivity can only be sensed indirectly from satellite ocean color observations. Global scale sensor networks using robotic platforms equipped with chemical sensors are required to directly observe ocean metabolism [2]. The Argo network (http://www.argo.ucsd.edu), which is used to monitor the heat content of the ocean, is a model for such a system. There are >3000 Argo profiling floats throughout the ocean. They rise from 2000 m depth at 5 to 10 day intervals measuring temperature and salinity during the ascent and then transmit the data to low earth orbit communications networks. This cycle is repeated for the 5 year life of each float. The BioArgo system is now working to build a complementary network equipped with pH, oxygen, nitrate and biooptical sensors [3]. More than 200 profiling floats with oxygen and >40 floats with nitrate are now operating from the Arctic to the Antarctic in all of the major ocean basins (http://argo.jcommops.org/maps.html, scroll right to the Bio map). These sensors have demonstrated exceptional stability and precision over time periods now reaching four years [4-7]. Experimental pH sensors are now operating on profiling floats with a precision and stability near 0.001 pH over an annual cycle. These results demonstrate the feasibility of establishing a global chemical sensor network. This talk will review the methods used to develop chemical sensors with multi-year stability and the development of a global observing system.