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Redefinition Of 'Seawater' To Aid Climate Research; 'A More Accurate Calculation Of Salinity'

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CANBERRA, Australia -- A specialist in thermal fluid dynamics, CSIRO Wealth from Ocean Flagship's Dr Trevor McDougall, recently led an international science team which has – following its acceptance by the Intergovernmental Oceanographic Commission – now released a new thermodynamic definition of salinity, 'heat content' and other seawater properties.

Speaking today at the International Union of Geodesy and Geophysics (IUGG) conference in Melbourne as this year's Prince Albert I Medal winner, Dr McDougall said the new definition facilitates the more accurate representation of heat content and of heat uptake by the ocean.

"To date the ocean's role in the climate system has been handled only in an approximate manner, both because of a lack of theoretical understanding of the "heat content" of seawater, and also because of the inability to calculate the required thermodynamic quantities.

"The new definition of seawater gives a more accurate calculation of salinity in which, the flow velocities in the deep ocean below 1,000 meters will be more accurately calculated."

Seawater is a mixture of 96.5 per cent pure water and 3.5 per cent other material, such as salts, dissolved gases organic substances and un-dissolved particles. Salinity, comprising the salts washed from rocks, has been deduced to date solely using the conductivity of seawater. The new definition of seawater builds on this observational approach and additionally allows for the spatially variable composition of seawater which is not apparent in the conductivity measurements alone.

"The ocean we observe today could not have got that way without mixing of the ocean's many layers, and ocean models cannot simulate these mixing processes by themselves. Rather, the information about mixing intensity has to be put into these climate models by scientists," Dr McDougall said.

"Considerable scientific uncertainty surrounds global ocean mixing processes and there are in fact many different mixing processes at work in the ocean, some of which occur only because of the rather complicated dependence of seawater density on temperature, salinity and pressure."

Dr McDougall has discovered several of these complicated mixing processes and has shown that they are important for the ocean circulation and climate, particularly in the Southern Ocean.

Dr McDougall, with colleagues from Germany (Dr Rainer Feistel) and Canada (Dr Rich Pawlowicz) as well as Dr Paul Barker at CSIRO Marine and Atmospheric Research, Hobart, have generated a new, significantly more accurate international thermodynamic equation of seawater, producing a 'toolbox' for oceanographers and climate modellers.

The Prince Albert I Medal has been awarded to Dr McDougall for his fundamental advances in ocean mixing processes. He is the first Australian to receive the medal and deliver the biennial lecture to a meeting of the International Association for the Physical Sciences of the Oceans (IAPSO) being held in association with the IUGG conference.

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