General Oceanography: Salinity

Dissolved substances in rivers water are ________

Bicarbonate, Ca, SiO2, SO4, Cl, Na, Mg, K, NO3, and Iron aluminium oxide

If rivers continuously flow to the sea carrying solutes, why is the average salinity of the global ocean not increasing?

Salinity in the ocean is in a steady-state condition. The amount of salt added to the ocean equals amount removed

Salt sources include:

1. weathering of rocks on land

2. wind blown spray carries minute droplets of saltwater inland

3. absorption of ions onto clays and some hydrogenous minerals

4. shell formation by organisms

_____ are chemicals essentials for life

nutrients

Major nutrients in the sea are compounds of:

• nitrogen

• phosphorus

• silicon

nutrients are ____ at the surface (in photic zone)

scarce

Concentration of nutrients vary greatly over time and because of this they are considered a _________ of the sea.

nonconservative property

Many nutrients are considered _______ — vital for life, in small quantities (i.e. Fe)

micronutrients

What is the Principle of Constant Proportion?

The absolute amount of salt in seawater varies, but the relative proportions of ions is constant

Because of the principle of constant proportion it is necessary to test for ____ salt ion (concentration), usually ____, to determines the _____ of salt present (e.g. S (ppt) = 1.80655 x chlorinity (ppt))

one, chloride, total amount

Salinity sources must equal ____ for the ocean to be in a steady state and for salinity to not change through time

sinks

In order for the principle of constant proportions to be true, then the _____ of the oceans (<1000 yr) must be much shorter than the _____ of major solutes.

mixing time, residence time

What is residence time?

the average length of time that an ion remains in a solution in the ocean

Ions with ____ residence times tend to accumulate in the sea. Ions with ____ residence times are removed

long, short

What is salinity?

the total mass of all substances dissolved in 1 kg of seawater

Average ocean salinity is ____, the typical range is ____

35 ppt, ~33-37 ppt

Extreme values of salinity are only found in ______

1. marginal environments (near land)

2. near ice freezing/melting processes

3. river discharge (estuaries)

4. semi-enclosed seas (e.g. Mediterranean)

What is surface salinity controlled by?

the balance between precipitation and evaporation

Open ocean surface salinity is ____ at mid-latitudes where E>P. ____ in tropics and polar regions where P>E

highest, lower

What is a halocline?

salinity gradient with depth (sharp increase or decrease in salinity with depth)

What are the methods of measuring salinity?

1. Evaporate seawater and weigh remaining salts

2. Titration

3. Salinometer

4. Refractometer

How does titration work?

measures chlorinity and convert ( x 1.8065) to salinity utilizing the principle of constant proportions

How does a salinometer works?

measures how well an electrical current passes through the water and converts conductivity to salinity (more solutes = greater conductivity) e.g. YSI, CTD, flow-through system.

How does a refractometer work?

light waves refract (bend) depending on concentration of the solution (refractive index varies with the medium the light is passing through)

What is chlorinity?

the amount of halogens in seawater and is expressed as grams/kilograms or o/oo

Example of halogens:

• chlorine

• bromine

• iodine

• fluorine