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Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater

Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater. Hannes Schmidt Henning Wolf Egon Hassel. Content. Introduction Importance of thermo physical properties of seawater Simplifications in calculation of thermo physical properties of seawater

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Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater

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  1. Realisation of a Substitution Method to Perform High Precision Density Measurements of Seawater Hannes Schmidt Henning Wolf Egon Hassel

  2. Content • Introduction • Importance of thermo physical properties of seawater • Simplifications in calculation of thermo physical properties of seawater • Motivation • Practical salinity and conductivity • Possible inconsistency • Approach • Traceability of salinity to density • Substitution method • Technical realisation • Demands on equipment • Density at atmospheric pressure • Density at high pressure • Results • Measurement results • Summary

  3. Importance of thermo physical properties of seawater http://www.drroyspencer.com/wp-content/uploads/climate-model-2.jpg http://www.drroyspencer.com/wp-content/uploads /2000-years-of-global-temperatures-small.gif http://www.oocities.org/marie.mitchell@rogers.com /climate_files/ClimateSimulation_1900-2100_IPCC2007.JPG Measurement data is used for understanding and prediction of climate on long term scales.

  4. Importance of thermo physical properties of seawater http://www.nasa.gov/images/content/436189main_atlantic20100325a-full.jpg Thermohaline circulation Conveyor belt Deviations in density – meaning salinity and temperature – are driving forces of subsurface currents (below 400 m). Surface currents are mainly driven by wind.

  5. Simplification in calculation ofthermo physical properties of seawater Conductivity replaces information on amounts of substances in calculations.

  6. Possible inconsistency Especially a change in salt composition can cause inconsistency.

  7. Substitution Method 1 bottle (200 ml) = 1 temperature = 8 h Ultrapure water Seawater Substitution methoddecreasesmeasurementuncertaintyaboutfactor 10.

  8. Density at atmospheric pressure 1,01325 0,1 MPa VAISALA REAR FRONT 0,1 MPa S-BUS USB S-BUS VGA 998,205 M FAN RS232 ETH AIRIN A. Paar DMA 5000M CAN AIRIN SEC ON SSW H2O SSW Standard Sea Water H2O Ultrapure Water M

  9. DHI RPM4Pressure measuring unit DMA HPDensitometer DMA 5000Mmaster device TeledyneISCO 100DMSyringe pump and controller Density at high pressure (2)

  10. Measurement results 1.2 ppm Ultrapure water Seawater Substitution result Density (Seawater) in kg/m3 Density (Water) in kg/m3 0.4 ppm Time in s Seawater measurement values were corrected by appr. 0.006 kg/m3.

  11. Summary • Calibrationandmeasurementroutinesforseawaterhave a riskofdatainconsistencywhendataiscollectedoverdecades. • The solutionistracing back salinitytodensitydirectlyby highprecisiondensitymeasurementsandelectrolyticconductivitymeasurements. • Afullyautomateddensitymeasurementdevice was builtandmeasurementuncertaintiesof 2 ppm at 1 bar (20 ppm at > 1 bar) werereached. • Atmosphericdensitymeasurementsarefinishedand high pressuredensitymeasurements will startsoon.

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