Seawater Redefined

Hobart-based CSIRO Wealth from Oceans Flagship scientist, Dr Trevor McDougall, made the case during his presentation of the Bruun Memorial Lecture to the Paris meeting. Marine scientists have been searching for the 'magic formula' for measuring salinity - which varies from ocean to ocean and between tropical, temperate and polar regions - for more than 150 years.

Unchanged since the last assessment 30 years ago, the case to review ocean thermodynamic measurements began in 2005 when the Scientific Committee on Oceanic Research (SCOR) established a working group, chaired by Dr McDougall. Supporting him were Dr Rainer Feistel from the Leibniz-Institut für Ostseeforschung in Warnemünde (Germany), Dr Frank Millero, from the Rosenstiel School of Marine and Atmospheric Science at the University of Miami in Florida, Dr Dan Wright of the Bedford Institute of Oceanography, Canada and Dr David Jackett of CSIRO (Australia).

Salinity, comprising the salts washed from rocks, is measured using the conductivity of seawater - a technique which assumes that the composition of salt in seawater is the same in all the world's oceans. 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 says. Until the new description of seawater is widely adopted, ocean models will continue to assume that the heat content of seawater is proportional to a particular temperature variable called "potential temperature".