PASADENA, Calif. -- NASA says an international satellite studying the world's oceans has stopped working after four years.

The space agency said Wednesday that the Argentine-built satellite ceased operations last week after a hardware failure.

The satellite carried a NASA instrument called Aquarius that measured the concentration of dissolved salt at the sea surface. The amount of brine in the ocean remains fairly constant, but salt levels in the uppermost layer vary around the globe.

Scientists say the information gathered from the mission is helping to improve climate models.

The satellite launched in 2011 from Vandenberg Air Force Base along the California Central Coast.