Chemical and Physical Features of Seawater and the World Ocean

The Waters of the Ocean• All matter is made of atoms• Elements are made from one kind of atom• A molecule is two or more different atoms

combined

The Unique Nature of Pure Water

• Water is a polar molecule• One end is positively charged and the

other is negatively charged

The attraction between the negative end of a water molecule and the positive end of another water molecule give rise to a “weak” attractive force known as hydrogen bonds.

The Three States of Water• Only substance on Earth to naturally exist in

three states!• Solid water molecules pack close together &

locked in fixed three dimensional pattern• Becomes more dense until about 4°C (get less

dense) & expands

• When water freezes in fresh and marine water the ice forms on top allowing organisms to live underneath the ice

• When marine water freezes it acts like an insulator to stop freezing all the water

Water as a Solvent

• Dissolve more things than any other natural substance (universal solvent) especially salts

• In water, strong ion charges attract water molecule, water molecules surround the ions and pull them apart (dissociation)

Seawater• Characteristics due to nature of pure water &

materials dissolved in it• Dissolved solids due to chemical weathering of

rocks on land & hydrothermal vents

Wieliczka Salt Mine in southern Poland

Salt Composition

• Salinity is the total mass, expressed in grams, of all inorganic substances dissolved in one kilogram of sea water

(with additional stipulations, we’ll ignore)

• Sodium chloride account for 85% of all solids dissolved

Salinity Measurement

• Often measured in parts per thousand• Abbreviated ppt or o/oo• Average salinity of the ocean is about 35 o/oo.•

Example:1000g of sea water is evaporated. 35g of salts remain behind. Salinity of the sample would be said to be 35 parts per thousand

Red Sea salinity is about 40 ‰ Baltic Sea salinity is about 6 to 8 ‰

Why is Red Sea salinity so high and the Baltic Sea so low?

Salinity, Temperature, and Density

• Get denser as it gets saltier, colder, or both -2° to 30°C

• temps. below zero possible because saltwater freezes a colder temps.

• Density controlled more by temperature than salinity

• There are exceptions therefore salinity & temp need to be measured to determine density

Dissolved Gases• O2, CO2 and N2 in atmosphere & sea

surface• 80% of gasses is carbon dioxide• Gas exchange happens between the surface

& atmosphere• Dissolved gas concentration higher in cold

water, lower in warm water

Dissolved Gases

• Amount of oxygen in water is affected by photosynthesis & respiration

• Most oxygen is released into the atmosphere• More susceptible to oxygen depletion than

atmosphere

Transparency• Sunlight can penetrate, but it’s affected by the

material suspended in the water• Important to the photosynthetic organisms• Runoff makes coastal waters less transparent

than deep blue waters of open ocean

Pressure

• On land, organisms are under 1 atm at sea level

• Marine organism have the pressure of the atmosphere & water

• With every 10m increase depth another atm is added

• Submarines & housing must be specially engineered to withstand pressure

• As atms increase gases are compressed • Organism have air bladders, floats and

lungs that shrink and collapse• Limits depth range, some organism are

injured when brought to the surface.

Barotrauma- physical damage due to significant changes in ambient pressure

-Uncontrolled assent from an extended deep dive can cause a condition known as decompression sickness or “the bends”

A Yelloweye rockfish having a bad day.

PRESSURE DEMO!• What a difference an atmosphere can make!

END