1) Introduction: What is salinity?

Seawater is salty.  Minerals from weathering of rocks and soils are washed down rivers and eventually end up in the ocean.  Over time, waters are habitually evaporated from the surface of the ocean in one place and this water vapor moves through the atmosphere to eventually rain out over another area of the ocean or over land.  When this evaporation occurs, the various minerals and salts are left behind.  This process “distills” the salty water such that the freshwater is separated from the dissolved salts.  The freshwater moves away as vapor and the left over salts mix with the surrounding waters, making them more concentrated.  The salinity of the seawater, that is the concentration of total salts dissolved in the water, is increased during this process.  In contrast, rain falling over the ocean will add freshwater back to the surface and decrease the salinity.

Salinity is typically expressed in units of “parts per thousand”.  The term parts per thousand (abbreviated as ppt) is a fractional expression of concentration.  “Percent” is a similar concept.  For example, average seawater has a salinity of about 35 ppt.  This is the same as saying that average seawater is about 3.5 % salt and 96.5 % water.  By definition, freshwater has a salinity of zero.

Figure 1.  Bar graph showing the quantities of salt and water combining to form 1 kilogram of solution with varying salinities:  0, 10, 20, 25, 30, and 35 ppt (or grams per kilogram).  The solution with a zero salinity is comprised entirely of water and has no salt.  As the salt content increases, so does the salinity.

Figure 1. Bar graph showing the quantities of salt and water combining to form 1 kilogram of solution with varying salinities: 0, 10, 20, 25, 30, and 35 ppt (or grams per kilogram). The solution with a zero salinity is comprised entirely of water and has no salt. As the salt content increases, so does the salinity.

In the deep Arctic Ocean, the salinity of surface waters can range from values as low as 25 ppt to values as high as 35 ppt.  Differences in the salinity of these waters are caused by the addition (decreases salinity) or removal (increases salinity) of freshwater.  River runoff, precipitation (rain and snow), melting sea ice, and melting glaciers can all add freshwater to the ocean and decrease the salinity.  In contrast, evaporation and freezing (ice formation) can remove freshwater from the liquid ocean and increase the salinity.

This research project will help to determine how these different freshwater sources contribute to salinity changes in the nearshore regions of the Canadian Arctic Archipelago.