or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in NOPP SPECIAL ISSUE » EXCELLENCE IN ParTNERIng Award WInnERS Oceanography The Argo Program journal of The 22, Number 2, a quarterly , Volume Observing the Global Ocean with Profiling Floats O BY DEan ROEMMICH, GREGORY C. JOHNSON, ceanography STEPHEN RISER, RUSS DavIS, JOHN GILSON, S W. BRECHNER OwENS, SILVIA L. GarZOLI, ociety. CLAUDIA SCHMID, and MarK IgnaSZEWSKI © 2009 by The 2009 by O ceanography ceanography O ceanography ceanography S ociety. All rights reserved. Permission is granted to copy this article for use in teaching and research. Republication, systemmatic reproduction, reproduction, systemmatic Republication, article use for research. and this copy in teaching to granted rights All reserved. is ociety. Permission S ociety. ociety. S end all correspondence to: [email protected] or Th e [email protected] to: correspondence all end R/V Kaharoa 1st Mate Simon Wadsworth nd (left) and 2 Mate John Hunt (right) O practice a US Argo float deployment ceanography with New Zealand Minister of Research, Science and Technology, the Hon. Steve S Maharey (center), in Wellington, New P ociety, Zealand, at the outset of an Argo deployment cruise in October 2007. O Box 1931, Rockville, This 28-m vessel has deployed more than 600 Argo floats.Photo by Alan Blacklock, NIWA, NZ M D 20849-1931, US A. 34 Oceanography Vol.22, No.2 ABSTraCT. The Argo Program has created the first global array for observing the achieving initial targets for global subsurface ocean. Argo arose from a compelling scientific need for climate-relevant sampling and data management. The ocean data; it was made possible by technology development and implemented array’s value is being recognized, along through international collaboration. The float program and its data management with the need to sustain Argo into the system began with regional arrays in 1999, scaled up to global deployments by 2004, future. Nevertheless, Argo faces a chal- and achieved its target of 3000 active instruments in 2007. US Argo, supported lenging road ahead. Further improve- by the National Oceanic and Atmospheric Administration and the Navy through ments in data quality, uniformity, and the National Oceanographic Partnership Program, provides half of the floats in delivery of delayed-mode data are the international array, plus leadership in float technology, data management, data of highest importance. Float deploy- quality control, international coordination, and outreach. All Argo data are freely ments in the remotest ocean regions are available without restriction, in real time and in research-quality forms. Uses of increasingly costly. Finally, the expansion Argo data range from oceanographic research, climate research, and education, of the Argo Program into new domains, to operational applications in ocean data assimilation and seasonal-to-decadal disciplines, and applications requires a prediction. Argo’s value grows as its data accumulate and their applications are better review of the consensus on design and understood. Continuing advances in profiling float and sensor technologies open objectives, and also a matching multina- many exciting possibilities for Argo’s future, including expanding sampling into tional commitment to continue building high latitudes and the deep ocean, improving near-surface sampling, and adding Argo toward its potential. biogeochemical parameters. The Argo Program is perhaps the most internationally collaborative effort in the history of oceanography. The InTRODUCTION the international target of 3000 active array could not have been implemented Autonomous profiling floats are a trans- floats with a data system providing open and cannot be sustained without broad formative technology for oceanography, access to the complete data set. About multinational participation. However, for enabling continuous, real-time subsur- 90% of Argo profiles are available within this NOPP special issue, the focus will face observations of the global ocean and 24 hours of collection. be on US Argo’s unique contributions complementing satellite observations Argo’s user community includes and the NOPP US Argo partnership. of the sea surface. The implementation operational centers engaged in ocean We gratefully acknowledge the large and of a global float array, named Argo to state estimation and seasonal-to-decadal essential contributions of our interna- emphasize its synergy with the Jason prediction, plus diverse ocean and tional partners while describing Argo’s satellite altimeter, began in 1999. The climate researchers. As the only global brief history, its present status, and its National Oceanic and Atmospheric subsurface ocean network, and because future evolution from a US perspective. Administration (NOAA) and the it strongly complements satellite and Navy, via the National Oceanographic regional in situ ocean observations, Argo ArgO IMPLEMENTATION Partnership Program (NOPP), forged is a key element of the Global Ocean Beginnings the multi-institutional US Argo Observing System (GOOS), the World Argo’s first key ingredient was new consortium. US Argo joined with over Climate Research Program (WCRP) enabling technology. By 1997, the 20 international partners to deploy the Climate Variability and Predictability autonomous profiling float’s capability global Argo array and implement its (CLIVAR) project, and the Global for global temperature/salinity/velocity data management and quality control Ocean Data Assimilation Experiment measurements (Davis et al., 2001) systems. The US consortium’s focus on (GODAE). In 2007, Argo was recognized had been demonstrated during World technology development has produced as a major success of the Global Earth Ocean Circulation Experiment (WOCE) increasingly rugged and long-lived Observation System of Systems (GEOSS). deployments. This instrument was built profiling floats with greater capabili- Argo has progressed greatly in on earlier float technology (Gould, ties. In November 2007, Argo achieved the decade between conception and 2005) but was a revolutionary advance Oceanography June 2009 35 because it made collection and real-time national Argo partnership, including national Argo programs were initially reporting of high-quality ocean data both the scientific community and the modest in size, gaining experience with possible anywhere and anytime, without government agencies needed to support float technology and data by deploying the presence of a ship or mooring. Argo implementation. NOAA played a regional arrays totaling a few hundred The second key ingredient was a central role by engaging partner agencies floats. During 2001, 294 floats were scientific requirement for global obser- in Europe, North America, Asia, and deployed (Figure 1), with arrays taking vations of the physical state of the ocean. Australia to join the international effort shape in the tropics, the North Atlantic The WOCE and Tropical Ocean Global and by supporting US Argo through and Pacific oceans, and elsewhere. Atmosphere (TOGA) experiments, NOPP. The international Argo Science In 2002, Argo floats were failing as well as other already established Team (AST, later renamed the Argo earlier than their estimated four- to five- observing systems (e.g., tide gauge, Steering Team) held its initial meeting year battery life. Most floats deployed in expendable bathythermograph, and in March 1999 to begin planning Argo 2001 failed during their first two years surface drifter networks) demonstrated implementation. The AST decided that in the water. With short float lifetimes, that the ocean plays important roles in all Argo data would be publicly available Argo would not be practical. Major the climate system and its variability. By without restriction, a policy that has efforts were devoted to identifying 1998, satellite altimetry was revolution- aided Argo’s international growth and problems and correcting them in all float izing the study of climate variability acceptance enormously. models and sensors. These engineering patterns in sea surface height (SSH), Although the scientific benefits of a efforts were dramatically successful such as that of El Niño, and a spatially global Argo array were clear from the (Figure 2). Float lifetimes increased resolved global trend of increasing SSH outset, no one knew whether the effort every year. For the years of global Argo was emerging (Nerem et al., 1997). to create it would succeed. Enormous deployments, 2004 and later, over 85% Systematic subsurface ocean measure- hurdles existed, including the cost, the of the instruments have remained active ments were needed to complement and scalability of float technology, and the after two years. It now appears certain interpret satellite observations. To meet feasibility of global deployment. that Argo will meet its target of four-year this need, an initial plan for a 3000-float mean float lifetimes. global Argo array (Roemmich et al., Pilot Arrays Early technical difficulties took about 1999) was endorsed by the CLIVAR The first regional Argo deployments two years to resolve. Meanwhile, national project and by GODAE. were carried out by Argo Australia in Argo programs scaled up their capacity The final ingredient was the inter- the Indian Ocean in