Salinity matters

A press release from the European Space Agency: Measurements of salt held in surface seawater are becoming ever-more important for us to understand ocean circulation and Earth’s water cycle. ESA’s SMOS mission is proving essential to the quest.

The Soil Moisture and Ocean Salinity satellite, SMOS, is monitoring changes in the amount of water held in the surface layers of soil and concentrations of salt in the top layer of seawater – both of which are a consequence of the continuous exchange of water between the oceans, the atmosphere and the land. Launched in 2009, SMOS has provided the longest continuous record of sea-surface salinity measurements from space.

The salinity of surface seawater is controlled largely by the balance between evaporation and precipitation, but fresh water from rivers and the freezing and melting of ice also changes the concentrations. With a wealth of salinity data from SMOS now in hand complemented by measurements from the US–Argentinian Aquarius satellite, which uses a different technique, scientists gathered recently at the UK Met Office to review the benefits this has brought to science.

Speaking at the Ocean Salinity Science and Salinity Remote-Sensing Workshop, Prof. Dame Julia Slingo, Met Office Chief Scientist, said, “We need to understand the role of salinity in the closure of the hydrology cycle – arguably the weakest point in global climate modelling.

“Salinity, and particularly sea-surface salinity, is a challenging but important topic for ocean circulation and climate variability about which we need to know more, especially given the recent climate-warming hiatus. The SMOS mission, now celebrating five years in orbit, is providing detailed global measurements of ocean-surface salinity that are now used to address some of these challenges.”....

From the European Space Agency: Average sea-surface salinity values. Areas of red indicate regions of high salinity, and areas of green indicate regions of low salinity. The map is overlaid with the simplified global circulation pattern called the ‘thermohaline circulation’. The blue arrows indicate cool deeper currents and the red indicate warmer surface currents. Temperature (thermal) and salinity (haline) variations are key variables affecting ocean circulation.