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Friday, March 1, 2013

Salinity Levels In Atlantic Ocean Are Off The Chart, According To NASA Instrument

The salinity level of the world’s rivers, lakes and oceans has been a growing topic in response to global climate change. As NASA’s Aquarius instrument has shown previously, seasonal salinity has been on the rise in oceans all around the world. This year, the picture is no less striking, with deep shades of oranges and reds, at least in the image above, filling a large swath of the Atlantic Ocean both to the north and to the south of the equator.

Launched on June 10, 2011 aboard the Argentine spacecraft SAC-D, Aquarius was specifically developed to study the salt content of the oceans’ surface waters. Variations in ocean salinity, one of the main drivers of ocean circulation, are closely associated with the cycling of freshwater around the world. The data collected from these measurements provide scientists with valuable information on how global climate change is affecting rainfall patterns around the globe.

“With a bit more than a year of data, we are seeing some surprising patterns, especially in the tropics,” said Aquarius’ principal investigator Gary Lagerloef, of Earth & Space Research in Seattle, Washington. “We see features evolve rapidly over time.”

Aquarius was designed to cover the Earth from an orbit that takes it over all the world’s ice-free oceans, taking a complete measurement of salinity levels every seven days. The detector on the instrument measures the top 1 inch of ocean water in 240-mile-wide swaths as it sweeps across the world overhead.

NASA has now received its first full year worth of data from Aquarius showing the varying salinity patterns around the globe.

By studying the data, the research team has revealed some key findings. The Arabian Sea, which sits against the Middle East, is much saltier than the Bay of Bengal, which is diluted by intense monsoons and freshwater discharges from the Ganges River, as well as others.

The Amazon, which releases large amounts of freshwater into the southern Atlantic, will either send a plume of freshwater toward Africa or bend up toward the Caribbean, depending on the seasonal currents. Freshwater also builds up against Panama’s coast, carried down from the central Pacific.

Some of the most saline-rich regions highlighted by Aquarius would be the Mediterranean Sea and the North Atlantic Ocean. As for the North Atlantic, it is the saltiest stretch of water anywhere in the open sea. This region becomes synonymous with the arid regions of the world’s deserts, which receive little to no rain and evaporation occurs rapidly.

An expedition launched by NASA, the Salinity Processes in the Upper Ocean Regional Study (SPURS), sent researchers to the North Atlantic last fall to investigate these salt-rich waters and analyze the cause behind the high concentration levels. The expedition was also seen as a move to validate the measurements taken by Aquarius.

“My conclusion after five weeks out at sea and analyzing five weekly maps of salinity from Aquarius while we were there was that indeed, the patterns of salinity variation seen from Aquarius and by the ship were similar,” said Eric Lindstrom, NASA’s physical oceanography program scientist, NASA Headquarters, Washington, and a participant of the SPURS expedition.

Aquarius was designed to operate for three years, measuring the salinity of Earth’s precious oceans. But Aquarius project manager Gene Carl Feldman, from Goddard Space Flight Center in Greenbelt, Maryland, said “there is no reason to think that the instrument could not be able to provide valuable data for much longer than that.”

He said the salinity measuring tool has been “performing flawlessly and our colleagues in Argentina are doing a fantastic job running the spacecraft, providing us a nice, stable ride.”

Researchers plan to continue to use Aquarius for measuring the salinity of the world’s oceans but wish to fine-tune the readings and retrieve more data even closer to coasts and at the poles. Currently, land and ice emit very bright microwave emissions that block the satellite signal. And at the poles, an added complication is that cold polar waters require much larger changes in salt concentration to modify microwaves signals.

Still, Aquarius has been able to garner close coastal readings, producing valuable data for the NASA researchers, who are surprised to see how close to land those readings actually are.

“The fact that we’re getting areas, particularly around islands in the Pacific, that are not obviously badly contaminated is pretty remarkable. It says that our ability to screen out land contamination seems to be working quite well,” Feldman said in a statement.

Salinity readings can be further affected by intense rainfall. It does this by attenuating the microwave signal Aquarius reads off the ocean surface as it travels through a damp atmosphere. Rainfall also creates roughness and shallow pools of freshwater on the ocean surface, which can construe actual readings.

The team hopes to use another instrument aboard SAC-D in the future, the Argentine-built Microwave Radiometer, to gauge the presence of intense rain simultaneously to salinity readings. This could help scientists flag data collected during heavy rainfalls.

Ultimately, the team wants to combine the Aquarius measurements with those of the Soil Moisture and Ocean Salinity (SMOS) satellite operated by the European Space Agency (ESA). This combination could produce a more accurate and finer-detailed map of ocean salinity.

The team is also set to release its first global soil moisture dataset, which will further complement measurements made by SMOS. This dataset release will be in collaboration with the US Department of Agriculture (USDA).

“The first year of the Aquarius mission has mostly been about understanding how the instruments and algorithms are performing,” Feldman said. “Now that we have overcome the major hurdles, we can really begin to focus on understanding what the data are telling us about how the ocean works, how it affects weather and climate, and what new insights we can gain by having these remarkable salinity measurements.”


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