18.12.2018 - Intergovernmental Oceanographic Commission

“Silent sentinels” deliver their 2 millionth snapshot of our changing oceans

Last month a team of international scientists achieved a major milestone when the Argo program delivered its two millionth profile of physical and chemical data from the world’s oceans, quadrupling the number collected by ships over the previous 100 years. Across the globe, about 4,000 Argo floats continuously collect data on the physical state of the ocean. The project has been revolutionizing physical oceanography and climate science for nearly 20 years.

The Intergovernmental Oceanographic Commission of UNESCO, and its Member States, have been supporting the development of the Argo program, the star of the Global Ocean Observing System (GOOS) in the last two decades.

Click to watch a video on the Argo program

Argo floats are cylindrical free-floating devices that stand 5 feet tall on end. Once deployed, the floats dive 1,000 meters (1.2 miles) deep, drift with the ocean currents for several days, then sink an additional 1,000 meters before slowly rising to the surface while collecting temperature and salinity data. This vertical series of measurements is known as a “profile”. At the sea surface, they transmit the data via satellite before diving down again. Argo floats continuously cycle through these data dives every 10 days, operating autonomously for four to five years on battery power. Since the first float was deployed in 1999, the Argo Program has produced nearly four times as many profiles as every other ocean observing tool combined.

The oceans cover 71 percent of the Earth’s surface and moderate the climate, impacting us greatly by influencing weather events such as hurricanes, floods, and droughts. Argo sheds light on very remote ocean regions where past ship-based and moored observations have been few, such as the vast oceans in the Southern Hemisphere. Temperature and salinity data from the global Argo array is helping scientists understand oceanic and atmospheric conditions as well as long-term climate trends. Two decades of Argo salinity data reveal that the wet (high rainfall) regions of the world are becoming wetter and the dry regions drier. The warming of subsurface layers of the ocean causes expansion of the water column that accounts for about one-third of global sea level rise. Argo data is also helping scientists describe the inter-annual El Niño Southern Oscillation global phenomenon, centered in the equatorial Pacific but with global impacts, and decadal variability including the North Atlantic and Pacific Decadal Oscillations.

“Argo floats have been out there for nearly two decades, quietly exploring our oceans’ changing temperature and salinity patterns,” said Susan Wijffels, Senior Scientist at the Woods Hole Oceanographic Institution. “They are our ‘silent sentinels’ – letting us peer into the mysteries of our remote and hostile deep oceans, which are so important to our daily lives.”

Argo is one of the central elements of the Global Ocean Observing System, the development of which is one of the priority areas for the UN Decade of Ocean Science for Sustainable Development. Ocean observations and marine technologies are at the center of a sustainable ocean-based economy and together with science can deliver actionable information for decision makers. “We need to rethink the concept of Blue Economy as a virtuous circle where the ocean provides services and resources, and economic actors in turn invest in marine observations, exploration and research,” says Vladimir Ryabinin, Executive Secretary of the Intergovernmental Oceanographic Commission of UNESCO.

Argo also exemplifies international collaboration on a scale rarely seen in the scientific community, with around 800 Argo floats are deployed each year by 26 countries. Many other nations contribute logistical support and ship access. “Strong international cooperation is the hallmark of Argo’s success. No nation could implement the global coverage of Argo on its own, and even the smallest of nations make critical contributions to the program,” stated Dean Roemmich, Professor at the Scripps Institution of Oceanography, University of California, San Diego.

The data that Argo provides make it possible for scientists to track changes occurring in the ocean across large distances and long periods of time. It is also helping improve operational weather forecasts, climate predictions, and is fueling a revolution in ocean research.

“Argo’s most important influence on our country occurs mainly in the field of supporting operational forecasts for predicting typhoon paths, for ocean fishery production, and to provide commercial ships and ocean survey ships a route forecast,” says Professor Jianping Xu, from the Second Institution of Oceanography, China. “The research community studying ocean change heavily relies on Argo data.”

All Argo data are freely available to anyone, and have been used for broad applications including aquaculture, pollution monitoring, ocean education, and national defense. Major ocean and climate assessments, such as the Intergovernmental Panel on Climate Change, rely on Argo. On average, a scientific paper using Argo data is published every day. Argo is now the key tool we use to track how fast the Earth’s climate system is warming, and can track marine heat waves as they form and dissipate.

Even as it achieves its two millionth profile, Argo is on the cusp of a major expansion into new dimensions of the ocean. Large-scale projects are underway to test floats that can descend to a depth of 6,000 meters (3.7 miles), to add sensors that measure biogeochemical (BGC) variables like oxygen, pH, and nitrate, and to expand further into seasonally ice-covered seas. Ocean acidification, deoxygenation, and ecosystem health will come into Argo’s gaze through BGC Argo. Deep-diving floats will track changes in ocean properties between 2,000 meters and the sea floor, revealing, for example, the influence of abyssal ocean circulation in climate variability. Float operating in sea-ice zones will help us understand the fast-changing Arctic and detect ocean shifts around the Antarctic. The promise of the new Argo Program is limitless as a global multidisciplinary ocean observing system serving science, education, and society.

“Argo is entering in a new era that will need an increased financial and political support from the international community. The 2020 vision for a global full-depth and multidisciplinary array will enable a new range of forecasting capabilities, fundamental ocean research, climate assessments, and blue economy benefits. To implement that vision, national Argo budget will have to triple and, deployments into Member States Exclusive Economic Zones be facilitated,” says Mathieu Belbéoch from the Intergovernmental Oceanographic Commission/World Meteorological Organization monitoring centre JCOMMOPS.

Discover the Argo story map to celebrate the 2 millionth Argo profile

For more information on the Argo program, visit: http://www.argo.ucsd.edu/About_Argo.html and http://www.jcommops.org/board?t=Argo

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