SEAWATER PROPERTIES: SALINITY

All water, even rain water, has dissolved

chemicals called “salts”

Salinity = the amount of dissolved salts in the

water

What Is Seawater Made of?

Where Do The Salts Come From?

1. Water on land (rivers & rainwater) erode the salts in the rock & carry them to the sea

2. Volcanoes - release salt into air & underwater

How Does It Stay Salty?

• Evaporation - freshwater leaves, salts stay behind

• Decomposition - as living things decay in the ocean they add to the salt content

The ocean is constantly fed freshwater, why does it remain salty?

FYI - if all the water were to evaporate enough salt would be left behind to build a 180 mile tall, one mile thick wall around the equator!

What Is The Salinity Of Seawater?

Salinity is measured in parts per thousand, the symbol = o/oo

Average salinity = 35 o/oo (meaning there are 35 grams of salt for every 1000 grams of water) (Or that the ocean is 3.5% salt)

Salinity varies depending on the amount of: rainfall, runoff, evaporation, ice formation, and current in a given area

Salinity Variations

• Ranges from 39-41 o/oo

• No rivers enter & hot/dry climate with high evaporation (6ft per year)!

FYI: Vast amount of deep water mineral deposits (from volcanic activity) - 30,000x more lead than normal as well as gold, silver & copper

A. The Highest:

Salinity Variations

• RangesRanges from 5-15 o/oo

• Huge amount of freshwater inflow (runoff supplies 1/40 of its volume each year)

B. The Lowest:

Salinity Variations

• ~ 38~ 38 o/oo

• Water trapped in by sargassum (sea weed) & caught in circular eddy current = warmer, more evap.

B. Highest in open ocean:

Salinity Variations

• Arctic ocean - 30 o/oo or Arctic ocean - 30 o/oo or lessless

• low evaporation & melting ice

B. Lowest in open ocean:

Salinity Variations

Salinity at Different Depths

• Halocline = layers of water where the water’s salinity changes rapidly with depth

• Salinity is closely tied to water temperature & density!

SEAWATER PROPERTIES: TEMPERATURE

• Most solar radiation (light & heat) is absorbed in the 1st 50-100 meters - this is the surface layer

• Waves & turbulence mix this heat evenly throughout the surface layer

• The temperature of the surface layer varies mainly with latitude

SEAWATER PROPERTIES: TEMPERATURE

Thermocline =

Boundary between surface & deep layers that are not mixed - where temp drops fast!

90% of ocean water is between 0-3ºC (seawater freezes at ~ -2ºC!)

SEAWATER PROPERTIES: DENSITY

Density = a mass/volume ratio

Density of seawater is controlled by salinity & temp

• Density increases as salinity increases

• Density increases as temp decreases

• Density increases as pressure increases

Let’s Watch a Density Demonstration!

How to Measure Salinity

1. Hydrometer= an instrument that measures

specific gravity (density relative to water)

= Use the density & temp graph to find salinity

http://www.aquatext.com/tables/hyd1.htm

How to Measure Salinity

2. CTD= an instrument that measures

conductivity, temperature & pressure at different depths & is the most accurate!

= conductivity tells amount of salt ions in the water

How to Measure Salinity

3. Refractometer= measures the angle of light

refraction, which changes with salt concentration!

THE RELATIONSHIP BETWEEN SEAWATER PROPERTIES

Temp, Salinity, Density & Circulation

Temperature affects density more than salinity because temp varies more in open ocean, but both drive circulation of the water!

Denser water sinks displacing less dense water

This heat & salt (thermohaline) circulation drives a global current (circulation of water) called the Global Conveyer Belt

The Global Conveyor Belt

The Global Conveyor Belt

• High Salinity, cold water sinks in North Atlantic & in Antarctica

• Deep water returns to surface in Indian & Pacific (upwelling)

• It takes ~200 years for water to circulate from N to S Atlantic & ~1000 years to complete the circuit

The Global Conveyor Belt

Why is it important?

• The Global Conveyor Belt is the main way oceans store and transport heat. The ocean stores more heat in the uppermost 3 meters than that of the entire atmosphere and acts as a "global heat engine."

• The ocean circulation helps drive the water cycle & climate!