Tag Archives: Measure

Hydrometers: Measuring Oceans Salinity

Hydrometers are used to measure the oceans salinity, or how “salty” the ocean is. To use a hydrometer you must fill up the tool with saltwater and then observe how much the lever is raised by the salinity. We like to use the measurement PPT or Parts per Thousand. PPT is a measure of salinity in the units of thousands, for instance if we had 1000 buckets of freshwater and then added 1 bucket of salt water to it we would have 1 PPT. Here on Catalina Island our PPT ranges from around 32 and 34 PPT. To make more sense of these numbers we like to break them down into percentages. If we were to do that our PPT in percentages would range from about 3.2 to 3.4 percent salt!


There are many other tools we can use to study Oceanography. We will use Secchi Disks to measure the visibility of the ocean, lead lines to measure the depth and plankton tows to measure what exactly is in our water column! Plankton tows work by towing a net with a jar attached to the bottom. The net will siphon through the excess water not allowing the plankton to escape. At the end hopefully you will have a jar full of microscopic plankton!


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