NASA-sponsored scientists will use a dream team of instruments to analyze salinity of the saltiest spot in the Atlantic, which is a model for extreme shifts in ocean salinity seen in the past few years.
The official mission of the Salinity Processes in the Upper Ocean Regional Study is to collect data for calibration of NASA’s Aquarius salinity monitoring satellite.
Scientists speaking at a press conference acknowledged the importance of the satellite, but they have another goal in mind. “Our real motivation is trying to understand how salinity is related to the global water cycle,” said Raymond Schmitt, a Woods Hole Oceanographic Institution senior scientist and chief scientist of this SPURS expedition.
The scientists postulate that extreme weather patterns seen in the last few years are due to climate change. “What we think is going on is, with the increasing air temperature, the atmosphere can hold more humidity and that causes more evaporation in dry regions and more precipitation in wet regions,” Schmitt said.
Ocean salinity is the best lens through which oceanographers can view these trends. Salt content in water fluctuates with evaporation and precipitation. “(It) turns out that 90 percent of evaporation comes from the ocean,” Schmitt said. “So the ocean is really the source of the global water cycle.”
Recent aggregated data shows that salty areas are getting saltier and fresh areas are getting fresher with an intensity at least four times greater than what models predicted, Schmitt said.
Salinity is important because it essentially dictates water density in the ocean. Density dictates ocean mixing, and mixing dictates water temperature.
SPURS scientists are studying the saltiest spot in the Atlantic, which sits between the Bahamas and the West Coast of North Africa. The area, known as the surface salinity maximum, keeps getting saltier. This summer was one of the saltiest on record for the area, Schmitt said.
An array of instruments will be used to monitor the area. The research vessel Knorr, on which the SPURS crew travels, houses a weather-monitoring station and CTD (conductivity, temperature and depth) sensors said Dave Fratantoni, WHOI associate scientist. The ship has a traditional CTD rosette for site sampling. An Underway CTD will also profile salinity while the ship travels. A microstructure profiler will record small-scale salinity observations.
Once at the site, three mooring devices, developed by WHOI and the National Oceanic and Atmospheric Administration, will be deployed to track surface weather and deep water salinity conditions.
Fratantoni said several surface-drifting instruments will record data in the upper region of the ocean. Twenty-six modified Argo floats will measure surface salinity, wind speed and rainfall. Lagrangian drifters, named because of their ability to maintain neutral buoyancy, will ride currents to monitor how water mixes in the Atlantic.
Autonomous gliders and submersibles will also be deployed. Two IVER2 vehicles will conduct small scale salinity surveys. Two Slocum Gliders will observe the intensity of ocean mixing. Three Sea Gliders will measure temperature, salinity and microstructure in the area. Three wave- and solar-powered Wave Gliders will also measure surface chemistry conditions.
Some of the monitoring equipment will return to shore after the three-week voyage, but much will remain collecting data for the next year. The moorings, Wave Gliders, drifters and floats will all stay in the Atlantic collecting data. The Sea Gliders will remain in the Atlantic for six months and then will be replaced with three new units.
The array of instruments should give a multidimensional picture of the ocean that will greatly help scientist understand salinity patterns. “All this information is fed back to shore where it’s integrated into sort of a coherent picture of what the ocean is doing on scales from the entire Atlantic down to centimeter scales,” Fratantoni said.
Scientists hope the study will give them a better model of ocean mixing. They also hope that research will support theoretical climate change arguments which seem to continually make headlines and hypotheses.
Researchers emphasized that this study will mainly be used for a tune up of the Aquarius Satellite. Eric Lindstrom, NASA physical oceanography program scientist, said Aquarius has more precision and reach than any other salinity monitoring system, but it is still limited.
The satellite maps salinity across the entire surface of Earth’s oceans each week. Data from the expedition should tune up satellite modeling to make it even more precise.
Since data will only come from one year of sampling, no findings on climate change will be considered fully conclusive. Still, the information collected should give scientists a more complete picture of salinity and ocean mixing than ever before seen.
There will be a second SPURS mission in an oceanic area that has very low salinity, though that location has not yet been chosen.
Image: Steve Faluotico, senior engineer, adjusts the SPURS buoy (Credit: Bill Ingalls/NASA)