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Salinity

Salinity. “In one drop of water are found all the secrets of all the oceans”. What is it?. Salinity is the total amount of dissolved material in grams in one kilogram of sea water. The variability of dissolved salt is very small Dimensionless quantity. It has no units.

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Salinity

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  1. Salinity “In one drop of water are found all the secrets of all the oceans”

  2. What is it? • Salinity is the total amount of dissolved material in grams in one kilogram of sea water. • The variability of dissolved salt is very small • Dimensionless quantity. • It has no units Notice that the range of salinity for most of the ocean's water is from 34.60 to 34.80 parts per thousand, which is 200 parts per million. Histogram of temperature and salinity of cold water in the oceans. Height is proportional to volume.

  3. Global Ocean Salinity

  4. Measurement • Never measured directly • Relative proportions of the major constituents of sea water are constant.

  5. Chemical method for determining salinity. Chloride is the most common dissolved ion Easiest to determine precisely Can be used to calculate the total concentration of dissolved constituents Used exclusively until the 1960’s Chlorinity • Salinity = 0.03 + 1.80655 x chlorinity • Or • S= 1.80655 CL

  6. Conductivity • Ability of a substance to conduct electric current • Proportional to salinity - a salty solution, because it is full of charged particles, will conduct electricity. • Reciprocal of resistivity (ohms) • mostly reported in microSiemens per centimeter (mS/cm) or milliSiemens per meter (mS/m) at a standard reference temperature of 25 degrees Celsius. • Affected by temperature (25ºC reference temp) • Widely used in the 80’s • Meters are expensive

  7. Refractometer When light passes from a medium of one refractive index to one with a different refractive index, the light bends (refracts) at the interface. The amount it bends or, the angle of refraction, depends on the difference in the two media's refractive indices. • Refractive index –the ratio of the speed of light traveling through a vacuum to the speed of light in the material being tested. • Affected only significantly by temperature. Many refractometers are automatically temperature compensated.

  8. Hydrometer • Measures density of liquids • Expressed in terms of specific gravity – describes the weight of dissolved material in the water • ratio of the density of the substance being measured to the density of water at the same temperature (1.00) • Specific gravity less than 1 are lighter than water, greater than 1 is heavier • HOW DOES IT WORK? The hydrometer floats in the liquid. The level where the surface of the liquid touches the scale indicates the specific gravity. Also, floating arm versions.

  9. YSI 85: Salinity, Conductivity, Dissolved Oxygen & Temperature Meter • Multi-parameter probe provides simultaneous measurement of: • Temperature • Dissolved oxygen (DO) • Conductivity • Salinity • For advanced users, an adjustable conductivity reference temperature and compensation factor can be used, as well as user defined equations for determining salinity.

  10. Practical Take Home • More than one way to skin a cat • Understand your instrument, it’s limitations and the principles behind how it works • Something other than the parameter you are measuring make affect your measurement • You may need a different instrument to measure the same parameter under different circumstances • All instruments have a range of effectiveness

  11. Quality ControlUsers of your data need to know how accurate and reproducible those data are! • Quality Assurance (QA) – broad plan for maintaining quality in all aspects of a program • Selection of parameters and procedures • Data management and analysis • Steps taken to determine validity of specific sampling or analysis procedures

  12. Quality Control (QC) Steps you take while running your analysis or taking measurements to insure accuracy and precision. Immediate Response Quality Asessment After the fact assessment. Blind Samples.

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