An artist's concept of Aquarius/SAC-D in orbit
Credit: NASA
WASHINGTON: NASA launched a satellite to observe levels of salt on the surface of the world's oceans and measure how changes in salinity may be linked to future climate.
The US$400 million Aquarius/SAC-D spacecraft, a partnership with Argentina, launched from Vandenberg Air Force Base in California.
The orbiting science instrument will aim to map the entire open ocean every seven days from its position 657 km above Earth, producing monthly estimates that show how salt levels change over time and location.
"Data from this mission will advance our understanding of the ocean," said Michael Freilich, director of NASA's Earth Science Division in Washington. NASA said the mission will survey salinity at the ocean's surface in "the most detailed summary of conditions ever undertaken”.
Salinity is increasing
Salinity is increasing in some ocean regions, like the subtropical Atlantic, which means more fresh water is being lost through evaporation at the sea surface.
But no one knows why this is happening; nor can anyone pinpoint why other areas are experiencing more rainfall and lower salinity. To solve these mysteries, scientists need a comprehensive look at global salinity.
Within a few months, Aquarius will collect as many sea surface salinity measurements as the entire 125-year historical record from ships and buoys.
Missing key element
"Salinity, along with temperature, governs the density of seawater," said Aquarius principal investigator Gary Lagerloef. "The saltier the water, the denser it is, and density drives the currents that determine how the ocean moves heat around the planet. For example, the Gulf Stream carries heat to higher latitudes and moderates the climate. When these currents are diverted by density variations, weather patterns such as rainfall and temperature change."
Scientists have gathered an ensemble of measurements over the ocean - for example wind speed and direction, sea surface heights and temperatures, and rainfall. But these data do not provide a complete picture.
"We've been missing a key element – salinity," said Lagerloef. "A better understanding of ocean salinity will give us a clearer picture of how the sea is tied to the water cycle and help us improve the accuracy of models predicting future climate."
