Objectives

1. Understand the basic chemical and physical properties of water & seawater.

2. The origin of the seas

Global Water Distribution Estimate

(Scroll down to global water distribution table)

What percentage of the human body consists of water?

• Babies: 78%• One Year old: 65%• Adult men: 60%• Women: 55%• Why do women have less

water?– They have a higher

percentage of fat --> hold less water

What about marine organisms?• Most consist of about 80% of water• Jellyfish?

– Over 95%!!

Recently discovered species of sea anemone, Aleutian Islands

Nomura Jellyfish, Japan

Water is unique. Why?• Naturally occurs in all three states:

– Solid, liquid, and gas

• No other substance on earth does this

Element vs. Molecule• What’s the difference?• Element:

– Composed of a single type of atom (only about 118 of these in the world)

• Molecule: – Combination of two or more atoms

• What does water consist of?

Molecular Makeup: H2O

• Opposite charges• Oxygen is (-)

• Hydrogen is (+)

• Draw a water molecule• Forms weak hydrogen

bonds• Why is it important that

water has weak bonds??

Hydrogen bonds• This is what allows

water to go from state to state

• Molecules in constant motion

• What happens when they speed up?

• They get warmer and then . . . ?

Fast and Slow molecules

• The bonds break and water enters the vapor state

• What about when it cools?

• Movement slows down, becomes dense until is slows down so much that. . .

It freezes!• What temperature is

water at it’s most dense form?

• 4º C. Is it frozen at this temperature?

• Why is this important?• What if ice were

water’s densest state?

The Changing Molecular Structure of H2O

What do you notice about the structure of each state?

Bottom line

• Seawater becomes denser as it cools, until it freezes.

• Ice is less dense than liquid water

Heat and Water• Water has the highest latent

heats of melting and evaporation

• How does ice keep our drinks cold?– It takes a lot of heat to melt ice – Heat breaks hydrogen bonds in

ice instead of heating up your drink --> drink stays cold

– Why do we sweat?

• H2O has high heat capacity– Absorbs a lot of heat w/ a

relatively small increase in temp

• Why is this important for marine organisms?– Not subject to drastic temp

change

The Universal Solvent

• Why can water dissolve more things than any other substance?

• It’s both (-) and (+) charged!

• Pulls apart salt– Sodium (Na+)

Chloride (Cl-)

What Makes up Seawater?

Ions (charged particles) enter the sea from different places

Composition of Seawater• There’s a little bit of

everything• 6 ions compose over 99% of

dissolved solids in seawater• NaCl make up over 85%• This composition stays

relatively the same– Rule of constant proportions

• Why is this important?• Sea organisms rarely have to

deal with changes in the ratios of various ions --> easier to control their internal water/salt balance

How Salty is the Ocean?

• Seawater has a salinity of 35 parts per thousand (ppt)– For every 1000 g of

seawater --> 35 g of salt

That’s a lot of salt . . .• If salt were removed

from ocean and spread evenly over earth’s land surface, it would form a layer about 500 feet thick (the height of a 40-story office building)

• How do the seas get so salty?

• How did the seas get here in the first place?

Origin of the Oceans• 4 bya earth was large, hot

rock w/out a trace of water• Outgassing

– Releasing of gasses from mantle through volcanic activity

– Comets and meteorites brought gasses as well

– Methane, ammonia, water vapor, carbon dioxide

• 3.8 bya, earth’s surface cooled below 100°C --> water condensed into rain and poured onto land for centuries

• Water filled basins and gravity kept it there

The Water Cycle• Quick review of the water cycle.

• What does this mean?

Cleopatra

• Your drinking the same water Cleopatra bathed in over 2000 years ago!

SalinitySalinity, Temperature, and Density

• Halocline:– A layer of cold, salty water

that acts as a barrier• Sea ice forms --> releases salt

--> denser water sinks

• Keeps warmer water from melting ice

*Icicle of Death Clip

Salinity, TemperatureTemperature, and Density

• Thermocline:– Layer of water where the temp

changes rapidly

• What causes this?– Solar radiation absorbed and

mixed (waves and turbulence) evenly in the first 30-40 m

– 90% of total ocean volume is below thermocline

– Avgerage SST?• 62°F

– Average temp of the rest of ocean (below thermocline)?

• 32°-37° F

Salinity, Temperature, and DensityDensity

• Temp decreases --> ?– density increases

• Salinity increases -->?– density increases

• Pycnocline:– Layer where there is a

rapid change in density

*underwater lake clip

Bottom Line

• Temp and salinity of seawater determine it’s density: It gets denser as it gets saltier, colder, or both

• How do scientists get these measurements?

How do we get this data?• CTD:

– Conductivity-temp-depth meters

• Fig. 3.9 in text

• Red arrow for water samples

• Yellow arrow: electronic instruments (temp, salinity, light, clarity)

• CTD description

Dissolved Gases• How do fish breathe?• What are they filtering

out of the water?• Dissolved oxygen• Seawater has dissolved

gasses: O2, CO2 (80%!), N2

• How much O2 in seawater?– 4-6 ml/l (less than 1%)– In the air we breathe?– 210 ml/l of air or 21%

Transperency

• Seawater is relatively transparent. Why is this so important?

• So photosynthetic organisms can grow

• What colors are in sunlight?

• Do they all travel equal distances?

True colors• Fig 3.12 in text: at 30m (90ft) only blue light remains• With an electronic flash you see sea star’s true colors• Can a plant photosynthesize at this depth if only blue light is

present?

Pressure• At surface, how much

pressure?– Tin can demo– 1 ATM or 14.7 lbs/in2

• Every 10m (33ft) of increased depth --> 1 ATM

• How much pressure on a organisms that dives to 100m?– 14.7psi x 11 = 161 psi

• What happens if that organisms surfaces too quickly?

Fig 3.15 in text: swim bladder blows up like a balloon because of decreased pressure.