The ocean is made up of salt water, which is a combination of fresh water, plus minerals collectively called "salts." These salts aren't just sodium and chloride (the elements that make up our table salt), but other minerals such as calcium, magnesium, and potassium, among others. These salts get into the ocean through several complex processes, including coming from rocks on land, volcanic eruptions, wind and hydrothermal vents. How much of these salts are in the ocean?
The salinity (saltiness) of the ocean is about 35 parts per thousand. This means that in every liter of water, there are 35 grams of salt, or about 3.5% of the weight of sea water comes from salts. The salinity in the ocean remains fairly constant over time. It does differ slightly in different areas, though.
The average ocean salinity is 35 parts per thousand, but can vary from about 30 to 37 parts per thousand. In some areas near shore, fresh water from rivers and streams may cause the ocean to be less salty. The same may happen in polar areas where there is a lot of ice - as weather warms and the ice melts, the ocean will have less salinity. In the Antarctic, the salinity can be around 34 ppt in some places.
The Mediterranean Sea is an area with more salinity, because it is relatively closed-off from the rest of the ocean, and has warm temperatures leading to lots of evaporation. When water evaporates, the salt is left behind.
Slight changes in salinity can change the density of ocean water. More saline water is more dense than water with less salts. Changes in temperature can affect the ocean as well. Cold, salty water is denser than warmer, fresher water, and can sink beneath it, which can influence the movement of ocean water (currents).
How Much Salt Is in the Ocean?
According to the USGS, there is enough salt in the ocean so that if you removed it and spread it evenly over the Earth's surface, it would be a layer about 500 feet thick.
Resources and Further Information
- Helmenstine, A.M. Why Is the Ocean Salty?. About.com. Accessed March 18, 2013.
- Office of Naval Research. Ocean Water: Salinity. Accessed March 31, 2013.
- NASA. Salinity. Accessed March 31, 2013.
- National Earth Science Teachers Association: Windows to the Universe. Density of Ocean Water. Accessed March 31, 2013.
- NOAA. Salinity Data. NOAA National Oceanographic Data Center. Accessed March 18, 2013.
- Rice, T. 2009. "Why Is the Sea Salty." In Do Whales Get the Bends?. Sheridan House: New York.