bio 207 chapter 3: chemical and physical features of seawater and the world ocean

water in organisms

80% or more by weight
sea jellies almost 95%

water

consists of one larger oxygen atom and two smaller hydrogen atoms
oxygen has a great affinity for electrons and pulls strongly on hydrogen’s electrons producing a polar molecule, the only molecule that naturally exists in all 3 states

hydrogen bonds

exist between water molecules
negatively charged oxygens on water molecules are weakly attracted to positively charged hydrogens on other water molecules

liquid water

hydrogen bonds are weak and constantly breaking and reforming, makes molecules fluid

gaseous/vapor water

molecules are not held together by hydrogen bonds
as temperature rises so does the evaporation rate
water boils as water molecules simultaneously enter the state

liquid seawater cooling

the molecules move more slowly and are more densely compacted, causing the overall volume to decrease and causing cold seawater to sink

freshwater

gets denser but only to a temperature of about 4 degrees C
below 4 degrees C, gets less dense as it cools

solid water

freezes when molecules move so slowly that the hydrogen bonds lock molecules into a fixed, 3D pattern (crystals)
less dense than liquid
insulates water below

ice crystals

molecules are further apart than in liquid water so it expands as it freezes

latent heat of melting

the energy needed to absorb to change a substance from a solid to a liquid at a constant temperature

heat capacity

water can absorb a lot of heat without its temperature changing drastically

latent heat of evaporation

the amount of heat energy required to change a substance from a liquid to a gas at a constant temperature, must absorb a large amount of heat to evaporate

evaporative cooling

as molecules break away during evaporation, the remaining ones have a slower velocity and therefore a lower temperature, why perspiration cools the skin

water as a solvent

a universal solvent, good at dissolving salts (polar)

seawater

the nature is due to purewater and the minerals dissolved in it
some solids are produced by weathering of rocks on land (carried by rivers to the sea), released by hydrothermal floor vents, released by volcanoes and enter the ocean in rain and snow

salt composition

seawater contains 6 different ions that exist as solutes
sodium and chloride (85%), sulfate, magnesium, calcium, potassium

salinity

the total salt dissolved in seawater
used to be found by evaporating 1,000 grams of seawater and massing the resulting salts, now instruments are used
measure in parts per thousand or psu (practical salinity units)

average salinity of the ocean

35 ppt, varies between 33-37 ppt

salinity increases

as water evaporates or freezes

salinity decreases

during precipitation events

the Red Sea salt composition

40 ppt
hot, dry region
evaporation predominates over precipitation

the Baltic Sea salinity

7 ppt, due to runoff from rivers emptying into the sea

dense seawater

becomes denser as it gets saltier and colder

satellites

used to measure the surface water temperature and salinity

important gases in seawater

oxygen (O2), carbon dioxide (CO2), nitrogen (N2)
gases dissolve better in cold water

dissolved oxygen

the ocean contains between 0-8 mL per liter of seawater, amount is affected by photosynthesis and respiration, the ocean is more susceptible to depletion (if respiration rate is greater than photosynthetic)

carbon dioxide

more soluble than oxygen (reacts with water when dissolved)
makes up 80% of the dissolved gas in the ocean
does not diffuse to the atmosphere as easily as oxygen

transparency

allows sunlight to penetrate into the ocean, vital to photosynthetic organisms
blue light penetrates deeper
in coastal waters, blue light is absorbed by materials and green light penetrates deeper
affected by suspended material dissolved in the seawater

coastal waters

less transparent than deep blue waters of the ocean due to discharge from rivers and runoff from land

pressure

changes dramatically with depth
water is heavier than air
on land, 1 atmosphere or 14.7 pounds per square inch
with each 10 meters of increased depth, another atmosphere is added
gas-filled chambers in organisms (air bladders, floats, lungs) would collapse at excessive depths

ocean circulation

currents move and mix ocean waters, transport heat, nutrients, pollutants and organisms, affect organisms an their habitats, impact Earth’s climate and organisms on land

surface circulation

the wind drives the strongest ocean currents only at the surface
driven by the heat energy of the Sun

the Coriolis Effect

because the Earth is round and rotating, anything that moves over its surface tends to turn a little rather than moving in a straight line, impacts wind and ocean currents
things are tilted to the right in the Northern Hemisphere, to the left in the Southern Hemisphere

wind patterns

the equator is warmer than the poles because the Sun’s energy is absorbed there, air there becomes less dense and quickly rises, air from adjacent areas gets pulled in to replace it creating wind

trade winds

approach the equator at an 45 degree angle
steadiest over the ocean, more variable on land, northwest and southeast trades

westerlies

trade winds in the middle latitudes, more variable

polar easterlies

high latitude trade winds, most variable of all

surface currents

driven by wind on the open ocean, surface water moves off at a 45 degree angle to that of the wind due to the Coriolis effect, top layer used the second layer and continues with depth
Ekman spiral
winds only effect water to a certain depth (Ekman layer)

Ekman spiral

a spiraling pattern of ocean currents that forms due to the interplay of wind, friction, and the Coriolis effect

Ekman layer

a thin, frictional boundary layer at the bottom of rotating fluid

gyres

huge, circular systems of wind driven surface currents under the influence of the Coriolis effect, impacts surface water temperature

thermohaline circulation layers

the surface layer, intermediate layer, deep/bottom layer

the surface layer

usually 100-200 meters deep, mixed by wind, waves and currents (mixed layer)

thermoclines

sudden changes in temperature over small depth intervals

the intermediate layer

lies below the surface layer, 1000-1500 meters
transition zone between warm surface water and cold water below

deep/bottom layer

below 1500 meters, uniformly cold

stability and overturn

surface water is warmer and less dense, floats to the top of the denser water (stable water column)
the surface water cools, it sinks

downwelling

when water on the surface of the sea becomes denser than the water beneath it causing it to sink, displaces and mixed with deeper water leading to overrun, typical in temperature and polar waters

overturn

the circulation of the layers of water whereby surface water sinks and mixed with bottom water

waves

caused by winds that drive the surface currents

crest

the highest part of a wave

trough

the lowest part of a wave

wave height

the size of a wave

wavelength

the distance between 2 crests

period

the time it takes for a wave to pass a point

size of a wave

depends on the strength of the wind and the fetch

fetch

the distance of open water that the wind blows

steps of a wave

1. when the wind is blowing, it pushes the crests up into sharp peaks and stretches out the troughs
2. once away from the wind, the seas settle into swells
3. as waves approach the shore, the water gets shallower
4. they begin to move in long ellipses instead of circles and slows the wave
5. the next wave gets closer (decreasing wavelength)
6. the wave gets steeper, eventually falling forward and breaking creating surf

seas

short-period waves being created by winds

swells

waves that have moved out of the generating area

tides

rhythmic rising and falling of the sea surface and have very large effect over life in the ocean, especially near the shore
caused by the gravitational pull of the moon and sun and by rotations of the Earth, moon and Sun

why are there tides?

the moon and Earth rotate around the Sun (at their combined center of mass), producing a centrifugal force that opposes gravity

tide process

1. on the side of the Earth nearest the moon, the moons gravity pulls the water more than on the side farther away from the moon
2. makes 2 bulges, one near the moon and one father away (oval shaped)
3. process takes 24 hours

tide duration

24 hours to complete a rotation

number of tides per 24 hours

4 total, 2 high and 2 low

full tidal cycle

take 24 hr 50 min

tidal range

difference between high and low tides

spring tides

when the sun and moon are aligned, their pulls are combined and a great tidal range is experienced

neap tides

tidal range is small

when neap tides are experienced

when the sun and moon are at right angles, their effect cancel each other, occurs when move is in 1st and 3rd quarters

semidiurnal tides

2 high and 2 low tides

mixed semidiurnal tides

with successive high tides of different heights

diurnal tides

one high, one low, very rare