A Milestone for Ocean Observation: International Argo Program Reaches One-Millionth Profile
On November 4th 2012, the international ocean observation program, Argo, passed a momentous milestone, collecting its one-millionth "profile" of ocean conditions in real-time since its launch in 2000. Over the years, Fisheries and Oceans Canada scientists have played key roles in making Argo what it is today - one of the most effective and comprehensive ocean observation systems in the world.
Argo takes the climatic pulse of the oceans using a global array of robotic floats equipped with sensors that mainly record data on ocean temperature, salinity, and pressure (a measure of depth) from the surface to a depth of two kilometres.
One-million profiles is an impressive achievement in 12 years in comparison to other sources of data. For example, since the start of deep sea oceanography in the late 19th century, ship-based observations have gathered just over half a million temperature and salinity profiles to a depth of one kilometre and only 200,000 to two kilometres.
Cost-effective ocean observation
"Argo is not only a more efficient way of collecting ocean data, it is also extremely cost-effective - about 25 times cheaper per profile than by ship," says Fisheries and Oceans Canada researcher Dr. Denis Gilbert, who is the national director of Argo Canada and a member of the international Argo steering team. "The program also covers far more ocean than is possible by ship."
Canada is one of 31 countries that have contributed floats to the global array since the beginning. The array reached its initial target of 3,000 in late 2007 and has been at or above that number since. As of November 29, 2012, there were 3,619 active floats, which are gathering profiles at an impressive rate of one approximately every four minutes - equal to 360 profiles a day or about 11,000 every month. At that rate it will take the program only eight years to collect its next million profiles.
Maintaining the Argo array
The floats - which are manufactured by several companies around the world, including MetOcean Data Systems in Dartmouth, Nova Scotia - have an average life expectancy of about five years. To maintain the network, 700 to 800 floats are launched every year. Participating countries coordinate their deployment missions in an effort to maintain an average distance between floats of 300 kilometers.
Argo Canada, which is coordinated by Fisheries and Oceans Canada, has launched 340 floats since 2001. About 100 of those are still active, of which four also measure oxygen in addition to the core measurements. Dr. Gilbert has been instrumental in having oxygen sensors added to some 25 floats since the discovery that deep, offshore ocean conditions in the northwest Atlantic are connected to hypoxia (low oxygen) in the Gulf of St. Lawrence, which can impact fish populations.
How the floats work
Deployed from ships or airplanes, the floats hitch a ride on slow-moving currents as they gather real-time data on evolving ocean conditions. They are programmed to perform 10-day cycles that include 9.5 days of drift at a depth of 1,000 metres, a dive to 2,000 metres depth from which the float begins its collection of data while ascending to the surface. To dive, fluid is mechanically pumped from a flexible external bladder to the interior of the float, reducing the float's buoyancy. Reversing the pumping action makes the float rise back to the surface where it transmits data to a satellite, which subsequently relays it to a land-based receiving station. After 30 minutes at the surface, the float is ready to dive again for another cycle.
Argo partners send the data to computer networks jointly run by the World Meteorological Organization and the Intergovernmental Oceanographic Commission within 24 hours of when the float transmitted the data.
Among the many Fisheries and Oceans Canada scientists who have contributed to the effort is Dr. Howard Freeland of the Institute of Ocean Sciences (IOS) in Sidney, B. C. Dr. Freeland helped write a 1998 prospectus outlining design and implementation of Argo, and he is also co-chair emeritus of Argo's 28-member international steering team.
Canada was also an early developer of software used to manage the flow of Argo data. Robert Keeley (now retired), formerly of the Department's Integrated Science Data Management (ISDM) branch, served as co-chair of Argo's international data-management team from 1999 to 2004.
Continuing Keeley's work at ISDM, Anh Tran handles all of the data in real-time and ensures timely transfers of data from ISDM to international Argo data servers. She also monitors delays between when Argo data are collected and when they are delivered to the international repository, providing annual summaries that can be used to assess where improvements in data delivery can be made. Mathieu Ouellet is responsible for the delayed mode quality control of Argo Canada data, which involves detecting and correcting changes in the calibration of conductivity and pressure sensors on the floats. Both sensors, as well as temperature measurements, are involved in the calculation of salinity.
Putting Argo Data to Use
Colourful computer graphics depict the annual temperature cycles (left) and salinity cycles (right) in the Labrador Sea. Dr. Igor Yashayaev of the Bedford Institute of Oceanography produces these profiles annually from Argo data as part of ongoing research into the role of the Labrador Sea in the world's climate patterns.
Argo data are free to anyone and can be accessed in real time through an internet connection. Their applications range from seasonal climate and short-term weather forecasting to ocean exploration, fisheries management, search and rescue and more.
Since the oceans are intricately connected to the Earth's climate system, Argo is providing valuable insights for those who study climate change. "The program has become, by and large, the dominant source of ocean climate data, and is now crucial for assessments carried out by the Intergovernmental Panel on Climate Change," says Dr. Gilbert. Using Argo data, researchers have shown that about 90 percent of the additional heat put into the climate system as a result of human activities is actually stored in the ocean.
Researchers are already using the data to develop more accurate seasonal climate forecasts. This would make it easier for anyone who depends on such forecasts, including farmers, to plan with more certainty.
"Meteorologists also anticipate that better knowledge of the oceans will help to improve the accuracy of four- and five-day weather forecasts," says Dr. Gilbert. "More precise data about ocean temperatures may also assist with forecasting the trajectory of hurricanes and whether they will intensify or not as they pass over certain parts of the ocean."
A collaborative effort underway between Fisheries and Oceans Canada and Environment Canada is using Argo data to develop computer models of the oceans, which are starting to be used to develop the equivalent of numerical weather predictions for the oceans.
"Argo is also making oceanography more like meteorology because it delivers data in real-time," says Dr. Gilbert. "This has enabled Dr. Howard Freeland of the IOS to map changing circulation in the northeast Pacific between seasons and from one year to the next. Atmospheric circulation has been tracked this way for decades, but it's revolutionary to be able to do it for the ocean."
Fisheries and Oceans Canada also uses Argo data for producing hindcasts - summaries of ocean conditions over the previous year or decade that can be used for fisheries applications. For example, at the Bedford Institute of Oceanography, Dr. Igor Yashayaev calculates detailed profiles of annual temperature and salinity cycles in the Labrador Sea, as well as other oceanic events with shorter than seasonal timescales. On the west coast, Dr. William Crawford of the IOS relies on Argo data to assess the state of Canada's Pacific waters.
Expanding Argo's mission
While continuing its core mission of monitoring ocean temperature and salinity, Argo is extending into ice-covered and shallower areas and partners are adding measurements of ocean biogeochemistry.
The symbolic one-millionth profile milestone is just one of Argo's many achievements that are contributing to a greater understanding of the oceans and their role in Earth's climate.
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