Tides: A Closer Look

The marine science point of view tides, salinity and temperature in the ocean.

If you have a bottle with 1kg of seawater the average salt which is dissolved in the water would be around 35g which is 3,5% or 35 psu (practical salinity unit). When we are talking about salt in seawater we are calling it the salinity. The salt comes from inorganic salts, a mix of organic material form living (or dead) organisms and dissolved gasses.

The inputs of salt are:

o Rocks and soil carried by freshwater from the main land to the ocean.

o Magma from undersea volcanoes.

o Gasses from the atmosphere.

The outputs of salt are:

o Evaporation from the ocean to the atmosphere.

o It can settle on the ocean floor as sediments.

o The ocean can dry out or/and leave land behind, where the salt is stored.

55% of the ions in seawater is Chloride, sodium is 30,6%, sulphate is 7,7% and magnesium is 3,7% which adds up to 97% of all the ions in the seawater. The salinity can vary along the coasts, but in the pacific it is usually between 34psu and 37psu. The temperature gets lower and lower the further you are moving away from equator (as the air temperature). Salinity and temperature also depends on the currents, out puts of freshwater from the main land, isolated areas, amount of rainfall and so on.

Tides are the alternate rising and falling of the water level in the ocean and big lakes caused by two forces:

· The gravity force of mostly the moon, but the suns gravity force also has an impact on the tides.

· The centrifugal force caused because the moon and the Earth in spinning around a common axis.

The two forces results in two tidal bulges on each side of the earth, which is almost equally big. The fact that we have to tidal bulges results in semi-diurnal tides, which mean that we mostly have two low tides and two hide tides in a day; but because of the landmasses on the earth, we sometimes only have on high tide and one low tide in a day. Another factor to remember is that the Earth has an inclination of 23.5degrees that results in mixed hides of the tides. There are other factors that can effect tides like; wind, large inputs of water from rain and rivers, atmospheric pressure and the coriolis effect.