water UNESCO adopts new definition of seawaterAt a meeting in Paris last month, the General Assembly of UNESCO’s Intergovernmental Oceanographic Commission (IOC) agreed to introduce a new thermodynamic description of seawater. The new description will be based on a new salinity variable called Absolute Salinity.

Scientists will now have an accurate measure of the heat content of seawater for inclusion in ocean models and climate projections,” said Hobart-based CSIRO Wealth from Oceans Flagship scientist Dr Trevor McDougall. “Variations in salinity and heat influence ocean currents and measuring those variations are central to quantifying the ocean’s role in climate change. The new values for salinity, density and heat content should be in widespread use within 18 months.”

Salinity is measured using the conductivity of seawater, a technique which assumes that the composition of salt in seawater is the same all over the world – which it isn’t. Salinity varies throughout the world’s oceans and for over one and a half century, scientists have been searching for the ‘magic formula’ for measuring salinity.

The new approach, involving Absolute Salinity, takes into account the changes in the composition of seasalt between different ocean basins which, while small, are a factor of about 10 larger than the accuracy with which scientists can measure salinity at sea,” Dr McDougall explained.