Chemical and Physical Features of Seawater and the World Ocean Shipley’s Marine Biology.

Chemical and Physical Features of Chemical and Physical Features of Seawater and the World OceanSeawater and the World Ocean

Shipley’s Marine BiologyShipley’s Marine Biology

Matter is defined as anything that has mass

and takes up space. So, everything you have ever seen or touched

on earth is matter (including you!) All matter is composed of elements of

different types.

Basic Chemistry 101

Each of the elements naturally occurs as small

units known as atoms. Atoms can be found solo (such as atoms of

helium) or atoms can bound to other atoms in molecules.

Molecules are the result of two or more atoms bonded chemically.

Basic Chemistry 101

One molecule that everyone on the planet has

encountered is H20. You should recognize this as a chemical

description of water. In the water molecule, there are two atoms of

hydrogen and one atom of oxygen bonded chemically together.

Basic Chemistry 101

Water molecules are unique in many ways. First of all, each water molecule has slight

positive and negative electrical charges. The positive charges are near the hydrogen

atoms and the negative charges exist around the oxygen atom.

Unique Nature of Water

Due to these slight electrical charges, water

molecules are attracted to one another. The negative charge of one molecule is

attracted to the positive charge of other molecules (remember: opposites attract!)

This attraction of one water molecule to another is known as hydrogen bonding.


Hydrogen bonds help keep water molecules as

a cohesive group at most temperatures found on earth.

This is the reason we have liquid water. The liquid form is just one of the three states

matter can have. The other two are gas and solid.


Everyone is very familiar with the liquid form

of water. Ice is the solid form of water that is caused by

subjecting water molecules to low temperatures.

The gas form is experienced as water vapor (we lovingly call the amount of water vapor in the air humidity).


Water vapor is formed when molecules of

water escape the hydrogen bonds holding them together and become airborne.

This process, called evaporation, increases with increasing temperatures (think of the steam you see rising from a pot of boiling water – this is water vapor).

Water is the only substance on earth that exists in all three states naturally – solid (ice), liquid and gas (water vapor).


With lower temperatures, water molecules

move closer to one another. Imagine a gallon bucket of seawater. At 75 degrees, the molecules are further apart

than when this same gallon of water is at 35 degrees.

When molecules are closer together, the substance is said to have more density.


Substances with more density are heavier

than those with less density when the same volume is present.

Now imagine you have two kitchen measuring cups (volume = one cup):

You fill one cup with bird feathers. You fill the other cup with lead pellets. Which cup weighs more?


Of course, the cup of lead pellets weighs more

because lead has a greater density than the feathers.

Now, how does this apply to marine biology? Cold water has more density than warm water

= which means it weighs more per volume of water. So…….


Cold water sinks underneath the warmer

water. You might have actually experienced this

yourself. Ever been in a pool, pond or ocean and

noticed that while the water close to the surface was warm, your legs are feeling cooler water?


Colder water also holds more oxygen than the

same volume of water. Great for all those organisms living at the

ocean floor. Now, even though colder water is more dense

than warmer water, this changes when the water gets cold enough to freeze.


Ice is less dense than liquid water due to all

the air trapped in it. This is why ice floats. This is fantastic for the organisms living in

areas where freezing temperatures are common.

What would happen if the ice stayed at the bottom?


If ice did not float, a body of water would

freeze from the bottom up and eventually the whole body of water would freeze.

This would not be great for all the organisms in that water.

Since ice floats, the floating ice creates a barrier between the air temperature and the water below the ice, keeping it from freezing.

Whew, the organisms under the ice are safe! (from freezing anyway!)


Water has other unique chemical properties. One is a high latent heat of melting.

Water has a higher latent heat of melting than any other commonly occurring substance.

This means that ice melts at relatively high temperatures and it absorbs a great deal of heat as it does melt.


Water also absorbs a great deal of heat before its

temperature rises. This property, know as heat capacity, is the

defined as the amount of heat required to raise a substance’s temperature by a given amount.

Water has one of the highest heat capacities of any naturally occurring substance.


This high heat capacity is great for marine

organisms because it means that they are not subject to the wide temperature ranges often seen on land (an exception to this rule occurs in shallow water; shallow bodies of water warm up quickly just due to the small volume of water. This will be important when estuaries are discussed.)


A great deal of heat is also required for

evaporation to occur. The amount of heat required for a substance

to evaporate is known as the latent heat of evaporation.

Water has the highest heat of evaporation of any naturally occurring substance.


Water also acts as a solvent, which means

that substances can dissolve in water. Think about the sugar that easily

dissolves in a coffee or tea (mostly water). Any substance dissolved in water is

known as a solute. Ocean water has solutes dissolved in the

water – we call the level of solutes salinity.


The main solutes dissolved in ocean water are

sodium and chloride (which gives it a salty taste).

Salinity is measured in parts per thousand (ppt). This means that for every 1000 grams of water, there are 35 grams of salt.


The Composition of Seawater at 35 ppt

Salinity

Salinity is normally around 35 ppt, however,

this can vary by location. Ocean water near a location where a river

meets the sea can be 15-25 ppt. Other areas can be higher if evaporation is

high and no rivers are bringing freshwater to that area.


Water is also relatively transparent (you

can see through it). This means that sunlight shining on the

surface can penetrate the surface (great for those photosynthetic organisms living under the sea)

This level of penetration varies greatly depending on the amount of solutes in the water.


To illustrate that point, imagine the

crystal clear waters of the Bahamas (or other tropical locations you may have visited or seen in photos).

Compare this with the less transparent water at the NC coast.

The difference is rivers. Several rivers in North Carolina empty

into the Atlantic. This means more solutes and less transparency (we sometimes also call this visibility).


Water comes from rivers and from

precipitation such as rain and snow. And, to a lesser extent, from melting of polar

ice. Solutes come from the weathering of rocks,

hydrothermal vents and solutes that were delivered in rivers from land run-off.

Adding Water and Solutes to the Oceans

Many gases are also dissolved in seawater

including:– Oxygen– Carbon dioxide– Nitrogen

Gases dissolve at the sea surface from the atmosphere. Occasionally, the reverse happens.

Like other aerobic organisms, many organisms in the ocean utilize oxygen and expel carbon dioxide.

Gases in Seawater

Conditions at the ocean floor, in the water

column and at the surface can vary greatly. Oxygen content, temperature, salinity and

other factors are often very different from one depth to another.

Pressure is also greater the deeper the depth. Water at the bottom has the weight of the water above it pushing down on it (which means that organisms living there also experience this pressure).

Conditions are not the Same at All Depths

Pressure Increases with Increasing Depth

Some of the differences seen in different

parts of the ocean are due to circulation patterns.

Circulation can occur as waves, tides, currents and gyres.

Circulation within the ocean is significantly driven by wind patterns.

Winds are ultimately driven by sunlight energy.

Ocean Circulation

As sunlight heats air, air rises. Cooler air rushes in to take the place of air

that has risen. This movement is the source of winds. Ever notice how the winds at the coast are

stronger during the day than at night?

Ocean Circulation

Winds created in this manner continuously at

the equator are known as the Trade Winds. The Westerly's in the mid latitude and the

Easterlies at the poles are less consistent than the Trade Winds.

Ocean Circulation

Major Surface Currents of the Ocean

Waves are the result of wind blowing over the

water’s surface. The size of waves depends on how long and

fast the wind blows; longer and faster equals a larger wave.

The size of waves is also larger when the fetch is larger. Fetch is the amount of open water a wind blows over.

Ocean Circulation

The highest point of a wave is the crest, the

lowest point is the trough. The distance between two crests (or two

troughs) is the wavelength. The time is takes for a wave to pass by a set

point is the wave period.

Ocean Circulation

As waves near the shore (shallower water), the bottom

of the wave “drags” the bottom. This forces the waves to slow and move closer together

(shorter wavelength). Eventually, the “drag” causes the wave crest to fall over

- we call this a wave break. The surf caused from breaking waves displaces lots of sand which affects the organisms living there.

Ocean Circulation

Currents are also a product of the wind. Current can be in surface layers of

deeper water layers Both winds and the currents they drive

are affected by the Coriolis Effect. Because the earth spins continuously,

anything that passes over the earth is deflected.

Ocean Circulation

In the northern hemisphere, winds and currents are deflected to the right.

In the southern hemisphere, winds and currents are deflected to the left.

This deflection termed the Coriolis Effect. Since the Earth is spinning, it causes this defection of winds and currents.

This deflection often causes currents to travel in circular patterns called gyres.

Ocean Circulation

Despite repeated mixing by winds and

currents at the ocean’s surface, the ocean is still stratified into three layers: Surface layer – from surface to about 200

meters; this layer stays well mixed most of the year.

Intermediate layer - from 200 – 1500 meters; major temperature change (thermocline) is located here. Less mixing occurs here.

Bottom layer – below 1500 meters; low mixing and normally uniformly cold.

Ocean Circulation

In some locations, large volumes of water may

sink or rise. Water sinks due to changes in temperature

and salinity – this is known as an area of down-welling.

Down-welling brings gases from the surface to deeper layers.

Ocean Circulation

Areas of upwelling come from currents that

push deeper waters toward the surface. Nutrients are much more plentiful in the

deeper layers, so these areas of upwelling are beneficial for organisms in an upwelling area.

Ocean Circulation

Circulation is also driven by tides. Tides are the rhythmic rising and falling of sea

surface levels. The tides are caused by the gravitational pull

of the moon on the ocean waters (and the sun to a lesser degree).

Waters on the side of the earth closer to the moon are pulled towards the moon, causing a high tide.

Waters on the far side of the earth are pushed away from the moon, causing a low tide.

Ocean Circulation

Most locations have two high tides and

two low tides each day, known as semidiurnal tides.

Normally, tides at night are higher and lower than day time tides.

Number and size of tides can be affected by bottom features, geographic features such as islands, canyons, reefs, etc.

The amount of difference between the high and low tide (tidal range) is also affected by the bottom features.

Ocean Circulation

When the sun and the moon, which both

affect tides, are both in line at times of the new and full moon, the tidal range is even greater.

These are called spring tides; despite the name, they happen each month.

Neap tides occur between the spring tides when the sun and moon are not in alignment.

Ocean Circulation

Organisms that live in areas exposed during a

low tide are especially affected during spring tides.

Movement of water during tidal changes results in significant mixing of water which also affects organisms.

Many organisms time their reproduction according to the tides.

Organisms are Affected by Tides

Chemical and Physical Features of Seawater and the World Ocean Shipley’s Marine Biology.

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Transcript of Chemical and Physical Features of Seawater and the World Ocean Shipley’s Marine Biology.