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or collective redistirbution other or collective or means this reposting, of machine, is by photocopy article only anypermitted of with portion the approval The O of This article has been published in published been This has article NOPP SPECIAL ISSUE » Excellence in Partnering Award Winners

The Program , Volume 2, a quarterly 22, Number The O journal of Observing the Global with Profiling Floats

By Dean Roemmich, Gregory C. Johnson, ceanography S Stephen Riser, Russ Davis, John Gilson,

W. Brechner Owens, Silvia L. Garzoli, ociety.

Claudia Schmid, and Mark Ignaszewski © 2009 by The O ceanography S ceanography S ociety. All rights reserved. Permissionociety. is Allreserved. rights granted to in teaching copy this and research. for use article Republication, systemmatic reproduction, ociety. S end all correspondence to: [email protected] Th e O or

R/V Kaharoa 1st Mate Simon Wadsworth (left) and 2nd Mate John Hunt (right) practice a US Argo float deployment ceanography S with New Zealand Minister of Research, Science and Technology, the Hon. Steve

Maharey (center), in Wellington, New ociety, P Zealand, at the outset of an Argo deployment cruise in October 2007. M D 20849-1931, US 1931, Rockville, O Box This 28-m vessel has deployed more than 600 Argo floats.Photo by Alan Blacklock, NIWA, NZ 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 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 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 , 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 , 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 //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 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 . 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. 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 , 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., 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 . 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 (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 late 1999. All of the and gained valuable ocean deployment experience. Argo was also building its Dean Roemmich ([email protected]) is Professor, Scripps Institution of Oceanography, data system, including Data Assembly University of California, San Diego (UCSD), La Jolla, CA, USA. Gregory C. Johnson Centers (DACs) that acquire the raw is Oceanographer, Ocean Climate Research Division, Pacific Marine Environmental data, subject it to automated quality Laboratory, National Oceanic and Atmospheric Administration (NOAA), Seattle, WA, USA. checks, distribute it on the Global Stephen Riser is Professor, University of Washington, School of Oceanography, Seattle, WA, Telecommunications System (GTS), and USA. Russ Davis is Research Oceanographer and Director, Instrument Development Group, forward it to the two Argo Global DACs Scripps Institution of Oceanography, UCSD, La Jolla, CA, USA. John Gilson is Specialist, (GDACs) for Internet access. Scripps Institution of Oceanography, UCSD, La Jolla, CA, USA. W. Brechner Owens is Senior Scientist, Woods Hole Oceanographic Institution, Woods Hole, MA, USA. Global Deployment Silvia L. Garzoli is Director, Division, Atlantic Oceanographic and Global deployments began in 2004 Meteorological Laboratory, NOAA, Miami, FL, USA. Claudia Schmid is Oceanographer, (Figure 1, middle), and the 869 floats Physical Oceanography Division, Atlantic Oceanographic and Meteorological Laboratory, deployed that year exceeded the target of NOAA, Miami, FL, USA. Mark Ignaszewski is Oceanographer, US Navy Fleet Numerical 800 required annually to seed and sustain Meteorological and Oceanography Center, Monterey, CA. the array. To achieve cost-effective global

36 Oceanography Vol.22, No.2 coverage, Argo’s strategy has been to use all kinds of ships opportunistically. Assistance from commercial ships, Antarctic supply vessels, research vessels, training vessels, school vessels, and others keeps deployment costs manage- able. In western boundary regions, in the tropics, and at high southern latitudes, floats drift thousands of kilometers from their deployment positions. This drift 294 Floats 2001 helps disperse the array. However, the combination of ships-of-opportunity and float is not sufficient to popu- late the remotest regions of the globe. Where there is no inexpensive means for deployments, several Argo nations (e.g., Argentina, Brazil, New Zealand, South Africa, and the United States) have staged deployment cruises and aircraft drops. A partnership between the United States and New Zealand Argo programs has deployed more than 600 floats in 864 Floats 2004 the Pacific and Indian Oceans by New Zealand’s R/V Kaharoa (p. 34 photo and Figure 3). This cost-effective vessel has been critical in seeding the remote and infrequently visited South Pacific Ocean, thus achieving global Argo coverage. International deployment rates reached 1003 floats in 2005, and the global array increased rapidly from 1500 active floats in late 2004, reaching the 3000-float target in November 2007 3291 Argo Floats January 2009 and maintaining it since then (Figure 1, ARGENTINA (11) CHILE (11) FRANCE (157) JAPAN (365) NEW ZEALAND (7) UNITED KINGDOM (106) AUSTRALIA (214) CHINA (22) GERMANY (184) SOUTH KOREA (112) NORWAY (5) UNITED STATES (1847) BRAZIL (7) ECUADOR (3) INDIA (79) MAURITIUS (3) RUSSIAN FEDERATION (1) bottom). In spite of this celebrated CANADA (108) EUROPEAN UNION (19) IRELAND (4) (25) (1) accomplishment, the Argo array is not Figure 1. Progression of Argo implementation, from regional pilot arrays to global deployment, yet complete. About 200 floats are not illustrated by yearly deployment maps from 2001 (top) and 2004 (middle), plus a recent map transmitting useful profile data due to showing presently active Argo floats (bottom).Source: Argo Information Center malfunctions. Other instruments are located in marginal or in high- oceans under seasonal ice cover. Although these instruments are collecting valuable data, the Argo design of 3000 floats was based on the open

Oceanography June 2009 37 Figure 2. Float survival versus number of 10-day cycles for different deployment years for US Argo instruments (solid lines) and all other programs (dashed lines). Source: Argo Information Center

Figure 3. Pre-cruise diagnostic testing of a US Argo SOLO float in Wellington, New Zealand. Photo by Alan Blacklock, NIWA, NZ

ocean between 60°N and 60°S. A recent profiles being available via the GTS and developed a system that is now used study (Roemmich and Gilson, 2009) Internet within 24 hours of collection. internationally for validating salinity found that by late 2008, approximately US Argo has played a large role in this sensor calibrations, and for correcting 2600 active open-ocean floats in this success, with the US DAC processing sensor calibration drift when needed. latitude range provided about 7800 high- more than half of the total volume of This semi-automated system enables quality profiles per month. During 2004– international Argo data (Schmid et al., expert examination of large volumes of 2008, there were about 350,000 high- 2007). The US DAC has provided profile data. To further improve data quality open-ocean profiles. In the leadership in the development of data- quality, Johnson et al. (2007b) quanti- coming years, technical improvements processing guidelines and real-time fied sensor response corrections for the will increase the number of fully func- quality control procedures, and in Sea-Bird Electronics Inc. conductivity- tional floats through correction of training and assistance for international temperature-depth (CTD) sensors used problems and longer float lifetimes, if the partners. In addition, the United States on most Argo floats. Periodic Argo deployment rate is sustained. However, hosts one of the Argo Regional Centers workshops on delayed-mode processing to complete and maintain the global (ARCs) and one of two Argo GDACs. aid uniform and prompt produc- array, the Argo Program will require ARCs are involved in quality control, tion of research-quality data by all increased and long-term commitments education, outreach, and deployment national programs. from the international Argo partnership. planning. GDACs serve data and develop interfaces for easy data access. Argo Data Uses Data Management Argo’s delayed-mode system for Argo’s most valuable contribution will Argo’s data management system is processing research-quality data from be its observations of climate-related operating as planned, with over 90% of Argo floats is unique. Wong et al. (2003) ocean variability on seasonal to decadal

38 Oceanography Vol.22, No.2 time scales and beyond. To realize this mesoscale eddies, , and of Argo data (Figure 4) by students and goal, Argo’s global coverage must be seasonal-to-decadal variability. Argo’s other non-experts. maintained for decades. Heat and water open data policy has resulted in the Argo floats are also deployed by are the fundamental elements of climate, global data set being at the fingertips of students and scientists from developing and the ocean is by far the largest reser- researchers around the world. The rapid nations from educational and training voir of both on Earth. Argo observes the acceleration in the use of Argo data for vessels, involving them directly in storage and large-scale transport of heat research attests to the high demand for building an ocean observing system for and freshwater in the ocean, comple- climate-relevant ocean data. climate. For example, the US-sponsored menting other parts of the climate Argo data also find valuable applica- South Atlantic ARC has conducted observing system. tions in tertiary and secondary educa- training activities in South America Over 15 operational agencies around tion. Ocean, atmosphere, and climate and Africa targeting float deployment, the world ingest Argo data into models science must be an integral part of data acquisition, and use of the Argo for ocean state estimation, short-term educational curricula so that tomorrow’s float data. The latest activity, onboard forecasting, and seasonal-to-decadal adults have a better understanding of the the US Navy’s HSV-2 Swift in the Gulf prediction. (See http://www-argo. world and its changing climate. Argo and of Guinea, gave 24 participants from ucsd.edu for links to all operational other ocean data sets now afford students West Africa hands-on experience with centers known to be using Argo desktop explorations of the planet. Early floats, data processing, and interpreta- data.) In the United States, ocean data in Argo’s development, Pacific island tion in a historically undersampled assimilation modelers using Argo data nations, via a regional intergovern- region (Figure 5). include the NOAA/National Center mental body (the Pacific Islands Applied Despite Argo’s brief history, major for Environmental Prediction (NCEP), Geoscience Commission, or SOPAC), findings are emerging from the data. the National Aeronautics and Space named education as their highest priority Comparison of Argo with historical Administration (NASA), and the among Argo applications. SOPAC, New data reveals a global Navy, in addition to academic institu- tions. Because Argo is the first global subsurface ocean observing system, this work entails model development and testing as well as experimentation with Argo’s most valuable contribution will different approaches to maximize the be its observations of climate-related ocean information from Argo and other data variability on seasonal to decadal time scales sources. Already, operational centers, and beyond. including NCEP, the European Centre “ for Medium-Range Weather Forecasts, and the UK Met Office, are reporting improvement in their products due to the impact of Argo data. Zealand’s National Institute of Water pattern of multidecadal ocean warming The research community has & Atmospheric Research” (NIWA), the (Roemmich and Gilson, 2009) as well as rapidly adopted Argo and is using the United Nations Educational, Scientific, continuing surface (Johnson and Lyman, data widely. In 2007 and 2008, over and Cultural Organization, and US Argo 2008) and subsurface salinity changes 100 Argo-relevant research papers are collaborating on development of that are consistent with an accelera- were published each year. This work curricular units using ocean data for tion of the hydrological cycle. Argo’s includes a broad range of studies of regionally relevant examples in the unprecedented coverage of the Southern water-mass properties and formation, study of climate and . US Argo Ocean is showing large globe-circling air-sea interaction, ocean circulation, created display tools for easy viewing increases in heat content and changes

Oceanography June 2009 39 Figure 5. Participants of the training organized by the South Atlantic Argo Regional Center onboard the US Navy vessel HSV-2 Swift listen for pump sounds during predeployment testing of an Argo float.Photo by Augustus Vogel, US Navy

float technology through a partnership between the University of Washington and Teledyne Webb Research to improve design and performance of APEX (Autonomous Profiling Explorer) floats, and similarly through improvements in the SOLO (Sounding Oceanographic Figure 4. Temperature along 170°W (top) and sea surface salinity in the southwest Pacific (bottom), both averaged over January–March 2008, generated from Argo data Lagrangian Observer) float designed by employing an easy-to-use Argo data display tool, the Global Marine Atlas, that provides Scripps Institution of Oceanography. students and researchers with PC-based maps, vertical sections, and time-series plots This leadership is evident in US Argo from Argo and other data sets. The Global Marine Atlas uses Ferret plotting software. float performance (Figure 2). As of mid 2008, 68% of the US Argo floats deployed in 2004 remained active, compared to only 29% for all other in ocean circulation there (Roemmich Profiling Float programs. The manufacturer passes et al., 2007; Gille, 2008). A five-year Technology Advances Argo-developed APEX float improve- analysis of Argo, satellite altimetry, and Profiling float technology development ments to all APEX users, leading to satellite measurements (Willis made Argo possible, and continued subsequent increases in worldwide et al., 2008) shows little change in global technological evolution is central to survival rates (Figure 2). during 2003–2007, Argo’s future. Because floats and deploy- US Argo also provides its floats an but it cannot yet close the global sea ments are expensive, float lifetimes extra level of technical care and attention level budget in that period. must be maximized. US Argo leads in usually found only in research programs.

40 Oceanography Vol.22, No.2 This pays substantial dividends in longer float compressibility, has solved this regions of the sea with seasonal ice cover lifetimes of these mechanically complex problem in the APEX floats (Figure 6). (Klatt et al., 2007), and to store profiles instruments. Value-added steps are New, optional APEX carbon-fiber collected during extended periods under different for each US partner, but include composite cases also increase the wintertime ice for later transmis- in-house production and/or assembly, float compressibility. A recent SOLO sion. These changes expand the potential and careful quality checking and testing float redesign is increasing its domain of Argo sampling into these of instruments. Additional care taken control for 2000-m profiling worldwide, high-latitude regions, where measure- in shipping, field testing, and deploying with simplified assembly, reduced weight, ments of climate-related changes in floats led to sharp reductions in early volume, and energy consumption, and temperature and salinity are especially float mortality. International partners eliminating the problematic air bladder. valuable. Floats that sample additional take a wide range of approaches. Some Argo floats have been improved variables, such as dissolved oxygen programs have adopted US practices in a number of other ways. Use of (Riser and Johnson, 2008) or bio-optical through international exchanges and the Iridium satellite network for float properties (e.g., Bishop et al., 2002), float technology workshops. When communications is one example. Floats are also available. Although these new greater care is taken with float prepara- using Argos communications spend sensors are not part of Argo, their speci- tion and checkout, the long-term surviv- about 10 hours on the sea surface, fications, sampling protocols, quality ability of floats is greatly improved. while those using Iridium spend just a control, and usefulness are under discus- Argo floats are valuable only while few minutes. This change saves energy, sion both inside and outside of the Argo their CTDs collect useful data. Sea-Bird limits biofouling, decreases risks of community. Such developments will Electronics, working in partnership drifting into shallow water, and affords provide new scientific understanding with Argo, has made great strides in greatly increased vertical resolution. of both physical and biogeochemical providing low-power CTDs that are Also, modifications in float software and processes in the ocean, and they may highly accurate and stable over multiyear hardware now enable floats to survive in lead to an expanded Argo. deployments. As a result, Argo data are more accurate and uniform than was imagined possible ten years ago. Most Argo CTDs continue to have no detect- able salinity drift after several years at sea, and when drift does occur, it is usually slow and steady enough to allow accurate adjustment in the delayed- mode, quality-control process. In addition to float lifetime, efforts also have succeeded in increasing the capabilities of floats in several important ways. Early floats did not have sufficient buoyancy adjustment capacity to ascend from 2000 m through highly stratified tropical surface . As a result, until recently, most low-latitude floats cycled only to about 1000 m. The addition Figure 6. Schematic diagram of the main piston and nitrogen gas canister arrangement on a Webb of an optional canister of compressed N2 APEX profiling float. Normal EXAP floats have only the main piston and oil reservoir. For N2 floats, the additional oil and piston connected to the gas canister provide a means to store energy nitrogen gas in parallel with the instru- as the gas is compressed during the float descent, recover this energy, and use it to increase the ment’s single-cylinder pump, to increase float’s buoyancy during the ascent phase.

Oceanography June 2009 41 Although Argo floats generally do not be added to Argo floats? Should Argo’s for long-term CTD profiling. Continued sample at depths shallower than about domain be expanded to include the encouragement for instrument devel- 5 m, there is strong interest in measure- seasonal ice zones? Should deep-ocean opment is essential to improve float ments of temperature and salinity near floats be deployed, and if so, how many capabilities, efficiency, ruggedness, and the air-sea interface. As a result, new are needed to observe decadal signals? lifetime. Technical support is equally secondary CTD units able to collect Should systematic high-resolution essential to get the most value out of high-resolution temperature and salinity profiles between 5 m and the sea surface have been developed by Sea-Bird and are Argo has achieved more than anyone imag- now being tested. Finally, the below 2000 m is ined it would ten years ago, but the hardest a new frontier for future development work lies ahead… of profiling float technology. Climate- related changes on decadal time scales, “ including warming of abyssal waters (e.g., Johnson et al., 2007a) that in turn sampling of boundary currents by gliders these complex devices. contribute to (Domingues be added to complement Argo’s ”broad- Data quality is another key to Argo’s et al., 2008) are present in the deep scale observations? Each of these exciting future. Sensor performance and stability ocean. Profiling floats may be the most options would add both value and cost to need continued attention to make the feasible technology for observing these the array, so they must be weighed care- task of data quality control manageable. signals on a global basis. Deep-ocean fully, with new resources found for any Many problems in floats and sensors have floats will require stronger pressure extensions to the original mission. occurred during Argo and will inevi- cases and greater buoyancy control. Just as float technology has been the tably occur from time to time, so Argo Temperature and salinity signals are key to Argo implementation, continuing must improve its procedures for rapid smaller in the deep ocean than in the technological development is the key detection of systematic problems. It is ill upper kilometers. Thus, deep-ocean to Argo’s future. Argo is operational affordable, financially and scientifically, floats may need to be recovered for in the sense of providing a sustained to discover serious flaws in large batches post-mission CTD calibrations. All of data set that meets requirements for of deployed instruments. Promising these factors will raise the cost of deep data coverage, quality, and timeliness developments include the use of satel- profiles relative to the present mid-depth of delivery. This achievement does not lite altimetry to detect bias in profile ones. The global requirements for deep mean the technology should cease to sequences (Guinehut et al., 2006), and observations need to be studied, with evolve. Indeed, float technology is pres- the use of Argo climatologies (Gaillard deep profiling floats compared to other ently evolving along two lines. Larger et al., in press) in quality control. options such as repeat shipboard hydro- floats, such as the existing APEX and A key strategy of the NOPP US Argo graphic surveys or moorings, to deter- SOLO models, wherein buoyancy partnership is the multi-institutional mine the optimum mix of observations. changes occur by extending a piston distribution of effort and the diversifica- to fill a bladder with oil, have sufficient tion of hardware. The benefits of this Argo’s Future payload to carry additional sensors and approach, while building Argo’s largest As profiling float capabilities grow, batteries. Newer, smaller floats (SOLO-II national program through combining of Argo’s original mission of broad-scale and ARVOR, developed by the French efforts, are to ensure that the continuity observations of temperature, salinity, Research Institute for Exploitation of of US Argo is not contingent on any and circulation in the upper 2000 m of the Sea), with reciprocating pumps individual scientist, institution, or float the ice-free ocean could be extended. employed for buoyancy control, could manufacturer, and to maximize the rate Should oxygen and biological sensors prove more efficient and cost-effective of progress in ongoing instrumentation

42 Oceanography Vol.22, No.2 development. There are also costs, by US Argo via the National Ocean Johnson, G.C., J.M. Toole, and N.G. Larson. 2007b. Sensor corrections for Sea-Bird SBE-41CP and as each of the partners has suffered Partnership Program, including NOAA SBE-41 CTDs. Journal of Atmospheric and Oceanic losses from problems that might have Grants NA17RJ1231 (SIO–JIMO), Technology 24:1,117–1,130. been avoided through standardization. NA17RJ1232 (UW–JISAO), and Klatt, O., O. Boebel, and E. Fahrbach. 2007. A profiling float’s sense of ice. Journal of Atmospheric and When such problems are not imme- NA17RJ1223 (WHOI-CICOR). The Oceanic Technology 24:1,301–1,308. diately evident, they are discovered statements, findings, conclusions, and Nerem, R.S., B.J. Haines, J. Hendricks, J.F. Minster, G.T. Mitchum, and W.B. White. 1997. Improved through comparative examination of recommendations herein are those determination of global mean sea level varia- data, which is a strength of both the of the authors and do not necessarily tions using TOPEX/POSEIDON altimeter data. Geophysical Research Letters 24:1,331–1,334. international and national Argo part- reflect the views of the National Oceanic Riser, S.C., and K.S. Johnson. 2008. Net produc- nerships. We continue to believe the and Atmospheric Administration or tion of oxygen in the subtropical ocean. Nature multi-institutional approach is a healthy the Department of Commerce, and the 451:323–326, doi:10.1038/nature06441. Roemmich, D., O. Boebel, H. Freeland, B. King, P.-Y. one, and essential until such time as the mention of commercial products herein LeTraon, R. Molinari, W.B. Owens, S. Riser, U. technology is sufficiently mature and does not constitute endorsement by Send, K. Takeuchi, S. Wijffels, and others. 1999. On the Design and Implementation of Argo: An robust for a standardized and uniform these entities. Graphics in the Global Initial Plan for a Global Array of Profiling Floats. implementation. Marine Atlas are produced using Ferret International CLIVAR Project Office Report 21, Finally, while the Argo array and software, a product of NOAA’s Pacific GODAE Report 5. GODAE International Project Office, Melbourne, Australia, 32 pp. Available data set continue to improve, the Marine Environmental Laboratory. online at: http://w3.jcommops.org/FTPRoot/Argo/ Argo Program will continue only if PMEL contribution Number 3244. Doc/Argo_Design.pdf (accessed April 10, 2009). Roemmich, D., J. Gilson, R. Davis, P. Sutton, S. the high value of the array is convinc- Wijffels, and S. Riser. 2007. Decadal spin-up of the ingly demonstrated. Argo is now at an References South Pacific subtropical gyre. Journal of Physical Oceanography 37(2):162–173. awkward age. The array is deployed Bishop, J.K.B., R.E. Davis, and J.T. Sherman. 2002. Robotic observations of dust storm enhancement Roemmich, D., and J. Gilson. 2009. The 2004–2007 and must be maintained. It will take of carbon biomass in the North Pacific. Science mean and annual cycle of temperature, salinity and ten years and more to realize the full 298(5594):817–821. steric height in the global ocean from the Argo Davis, R.E., J.T. Sherman, and J. Dufour. 2001. Program. Progress in Oceanography, doi:10.1016/ benefits of measuring global patterns Profiling ALACEs and other advances in autono- j.pocean.2009.03.004. of interannual-to-decadal variability. mous subsurface floats. Journal of Atmospheric and Schmid, C., R.L. Molinari, R. Sabina, Y.-H. Daneshzadeh, X. Xia, E. Forteza, and H. Meanwhile, the cost must be borne by Oceanic Technology 18:982–993. Domingues C.M., J.A. Church, N.J. White, P.J. Yang. 2007. The real-time data management many national programs, and all nations Gleckler, S.E. Wijffels, P.M. Barker, and J.R. system for Argo profiling float observations. must concur on the need to collect this Dunn. 2008. Improved estimates of upper-ocean Journal of Atmospheric and Oceanic Technology warming and multi-decadal sea-level rise. Nature 24(9):1,608–1,628 data set, for societal benefit, throughout 453:1,090–1,093. Willis, J.K., D.P. Chambers, and R.S. Nerem. the world’s ocean. Argo has achieved Gaillard, F., E. Autret, V. Thierry, and P. Galaup. In 2008. Assessing the globally averaged sea level press. Quality control of large Argo data sets. budget on seasonal to interannual timescales. more than anyone imagined it would Journal of Atmospheric and Oceanic Technology. Journal of Geophysical Research 113, C06015, ten years ago, but the hardest work lies Gille, S. 2008. Decadal-scale temperature trends in doi:10.1029/2007JC004517. ahead—sustaining the program, broad- the southern hemisphere ocean. Journal of Climate Wong, A.P.S., G.C. Johnson, and W.B. Owens. 2003. 21:4,749–4,765. Delayed-mode calibration of autonomous CTD ening its applications and user base, and Gould, J. 2005. From Swallow floats to Argo: The profiling float salinity data by theta-S . ensuring that its global observations development of neutrally buoyant floats. Deep-Sea Journal of Atmospheric and Oceanic Technology Research II 52/3–4:529–543. 20:308–318. benefit people in all nations. Guinehut, S., P. Le Traon, and G. Larnicol. 2006. What can we learn from global altimetry/ Acknowledgements comparisons? Geophysics Research Letters 33, L10604, doi:10.1029/2005GL025551. Argo data are collected and made freely Johnson, G.C., and J.M. Lyman. 2008. Global Oceans: available by the international Argo Sea Surface Salinity. In State of the Climate in 2007, D.H. Levinson and J.H. Lawrimore, eds., Bulletin of Program and by the national programs the American Meteorological Society 89(7):S45–S47. that contribute to it (http://www.argo. Johnson, G.C., S. Mecking, B.M. Sloyan, and S.E. Wijffels. 2007a. Recent bottom water warming net). The authors and their part of in the Pacific Ocean. Journal of Climate the Argo Program were supported 20:5,365–5,375.

Oceanography June 2009 43