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  • Salinity

    my head is spinning with all the different ways to record salinity!
    I have collected Sp Cond data recorded in mS/cm, but am having difficulty trying to compare my data to values recorded in journals (and various places) in g/L, EC, ppt, ppm and practical salinity scale.....HELP!

    Are g/L and ppt similar to practical salinity scale?? I hope they are...

    How do I convert mS/cm to pss? I found the 'salinity to conductivity conversion' thread in this forum and have used that, but how accurate is that, and how can that be the only way on the whole www??

    If there is a salinity expert out there - please help!

  • #2
    Re: Salinity

    I know that the milliSiemens is often used to measure the salinity of seawater, as salt makes water more conductive to electricity. But I could not find any way to convert units of conductivity to anything else.

    My guess would be that it is different for every substance. The other post you found here may only be accurate for those specific circumstances and may not be accurate for yours.

    I do know a couple things that will help you.

    PSU and ppt of salt ion concetrations are the same. Also g/L and ppt are the same.

    Comment


    • #3
      Re: Salinity

      If specific conductance values have been compensated to 25 C and water depths are sufficiently shallow making pressure corrections unnecessary, salinity can be calculated from specific conductance values using standard equations. Schemel (2001), following principles of the 1978 Practical Salinity Scale, simplified the general equation for salinity described by Lewis (1980) for the case of a single temperature (25 C) and atmospheric pressure (760 mm):

      Salinity=0.012+(-0.2174*((SC/1000)/53.087)^0.5)+(25.3283*((SC/1000)/53.087)^1)+(13.7714*((SC/1000)/53.087)^1.5)+(-6.4788*((SC/1000)/53.087)^2)+(2.5842*((SC/1000)/53.087)^2.5)

      SC is the specific conductivity in microsiemens/cm. The salinity is unitless (practical salinity units), and approximately equal to parts per thousand.

      Only use this equation if you have SPECIFIC conductivity compensated to 25 degrees C. For a complete reference see page 36 of:

      (no www) pubs.usgs.gov/tm/2006/tm1D3/pdf/TM1D3.pdf

      Comment


      • #4
        Re: Salinity

        Conductivity-Temperature-Pressure to Practical Salinity Converter (Calculator) can be find on:
        salinometry dot com

        (sorry, not allowed to post the link)

        Comment


        • #5
          Re: Salinity

          Originally posted by Unregistered View Post
          Conductivity-Temperature-Pressure to Practical Salinity Converter (Calculator) can be find on:
          http://www.salinometry.com/ctd-calculator/

          Comment


          • #6
            Re: Salinity

            This calculator is not necessarily one to use if your conductivity is in Specific Conductivity.

            Comment


            • #7
              Re: Salinity

              Originally posted by Unregistered View Post
              This calculator is not necessarily one to use if your conductivity is in Specific Conductivity.
              Hi there, what is Specific Conductivity? -I've never heard of it, it would be great if you could define it.

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              • #8
                Re: Salinity

                The Schemel equation can be used when the conductivity measurement (EC, electrical conductivity) is already at or compensated to 25 Celsius and at atmospheric pressure. Otherwise the Unesco practical salinity scale 1978 conversions can be used to provide the more accurate calculation of salinity. The formulas are available at some locations as an online calculator, e.g. fermi dot jhuapl dot edu / denscalc.html. These salinity calculations based on conductivity measurement are based on dilutions of seawater.

                Comment


                • #9
                  Re: Salinity

                  Originally posted by rock94 View Post
                  The Schemel equation can be used when the conductivity measurement (EC, electrical conductivity) is already at or compensated to 25 Celsius and at atmospheric pressure. Otherwise the Unesco practical salinity scale 1978 conversions can be used to provide the more accurate calculation of salinity. The formulas are available at some locations as an online calculator, e.g. fermi dot jhuapl dot edu / denscalc.html. These salinity calculations based on conductivity measurement are based on dilutions of seawater.
                  http://fermi.jhuapl.edu/denscalc.html

                  This a really useful document, thanks. - Just a note, practical salinity units (PSU) use weight of seawater - not volume - in the calculations.

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