21.01.2013 - Natural Sciences Sector

Argo collects its one millionth observation

Argo monthly map: density (SIO), detail

Today the mean sea level is rising, Arctic sea ice cover is shrinking and high latitude areas are warming rapidly. These effects are caused by a mixture of long-term climate change and natural variability. An improved understanding of global changes in both the atmosphere and ocean is needed to project regional impacts and guide international actions. But until recently, very little data was available on the ocean.

Before Argo, the temperature and salinity of the subsurface oceans could only be measured from ships or fixed point moorings. Today Argo provides the first-ever global-scale, all-weather subsurface observations of the oceans, an unprecedented dataset for researchers studying the temperature, salinity, and circulation of the global oceans and how these change over periods ranging from days to decades. This data is also crucial for weather forecasts!

The first Argo floats were deployed in late 1999, and by November 2012, Argo had collected its millionth profile of temperature and salinity, twice the number obtained by research vessels during all of the 20th century. 120,000 new profiles are collected every year, at the impressive rate of 1 profile approximately every 4 minutes. Each profile consists of up to 1,000 measurements of temperature and salinity at varying depths.

What can we learn from Argo?
Argo makes visible large-scale ocean and climate features and processes that were once hidden to scientists. The network has enabled new revelations about ocean dynamics that are helping society understand and forecast global climate.

The ocean moderates the planet’s climate by storing heat and moving it from the tropics to mid-latitudes. More than 90% of the heat absorbed by the Earth over the past 50 years is stored in the oceans. Argo data, along with satellite and other ocean data, feed into regional and global forecast models used for ocean and climate prediction over seasons, years, and decades.

Changes in ocean salinity observed by Argo reveal variations in the hydrological cycle – the oceans become fresher where rainfall increases relative to evaporation, and saltier where it decreases. Observed trends could have global-scale consequences for rainfall and drought patterns.

Argo data is also used to study ocean circulation, water mass characteristics, and ocean variability ranging from mesoscale eddies, to the seasonal cycle, to interannual variability (e.g. El Niño), and decadal oscillations (e.g. Pacific Decadal Oscillation, Southern Annular Mode).

As a novel, global data source Argo has also become a central element in operational oceanography and in basic research and has great value in education. High school students, university undergraduates, graduate students, and postdoctoral investigators all can use Argo from their desktops to explore the global ocean and its evolution. All Argo data are freely and publically available in near real-time via the Global Data Assembly Centres (GDACs) in Brest, France and Monterey, California.

How does Argo work?
It is a collaborative partnership of more than 30 nations from all continents, all working together to provide a seamless global array of over 3,000 profiling floats moving up and down in the water column from the sea surface to 2,000 meters and measuring temperature, salinity, and depth during every ascent to the sea surface. National contributions to Argo include building, deploying, and operating floats, data management and quality control, and communications.

Argo is a key component of the Global Ocean Observing System, led by UNESCO’s Intergovernmental Oceanographic Commission (IOC/UNESCO). The Joint WMO - IOC Commission for Oceanography and Marine Meteorlogy (JCOMM) office in Toulouse manages deployments to maintain an array of over 3400 Argo floats and 1250 surface drifters throughout the ocean, with IOC/UNESCO’s support. More than 2000 deployments per year are required to maintain the two global arrays. Argo sampling is global and year-round.

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