23 September 2011

After its successful launching on June 10th, the SAC-D/Aquarius satellite – designed and constructed by INVAP for the Argentine Space Agency (CONAE) and NASA – yielded its first global map of ocean surface salinity, providing a first glimpse of this satellite mission’s future discoveries. In the next months, Aquarius will complete the first NASA’s space observations of ocean surface salinity variations – a key component of Earth’s climate change.  Ocean salinity is related to the cycling of freshwater around the planet, to ocean circulation and its influence on climate.


“Aquarius’ salinity data are showing much higher quality than we expected to see this early in the mission,” said Aquarius Principal Investigator Gary Lagerloef of Seattle. “Aquarius will soon allow scientists to explore the connections between global rainfall, ocean currents and climate variations”.

The new map, which shows a tapestry of the current salinity patterns, demonstrates Aquarius’ ability to detect large-scale salinity distribution clearly and with sharp contrast.

“Aquarius/SAC-D is already advancing in our understanding of ocean surface salinity and Earth’s water cycle,” remarked Michael Freilich, director of NASA’s Earth Science Division at agency headquarters in Washington. “Aquarius is making continuous, consistent, global measurements of ocean salinity, including measurements from places that have been never sampled before”.

To produce the map, Aquarius scientists compared the early data with ocean surface salinity reference data. Although the early data contain some uncertainties, and months of additional calibration and validation work remain, scientists are impressed by the data’s quality.

“Aquarius has exposed a pattern of ocean surface salinity that is rich in variability across a wide range of scales,” said Arnold Gordon, professor of oceanography at Columbia University in Palisades, N.Y., and at the university’s Lamont-Doherty Earth Observatory. “This is a great moment in the history of oceanography. The first image raises many questions that oceanographers will be challenged to explain.

The map also confirms several well-known ocean salinity features such as higher salinity in the subtropics; higher average salinity in the Atlantic Ocean compared to the Pacific and Indian oceans; and lower salinity in rainy belts near the equator, in the northernmost Pacific Ocean and elsewhere. These features are related to large-scale patterns of rainfall and evaporation over the ocean, river outflow and ocean circulation. SAC-D/Aquarius will monitor how these features change and study their link to climate and weather variations.

Other important regional features are evident, including a sharp contrast between the arid, high-salinity Arabian Sea west of the Indian subcontinent, and the low-salinity Bay of Bengal to the east, which is dominated by the Ganges River and south Asia monsoon rains. The data also show important smaller details, such as a larger-than-expected extent of low-salinity water associated with outflow from the Amazon River.