L2 - The properties of water ; currents and tides

Question 1

What is the water molecule comprised of?

Answer 1

Oxygen atom which is weakly negatively charged. Hydrogen atom which are weakly positively charged. This makes water a polar molecule, but also creates electrical attractions (hydrogen bonds) between adjacent water molecules

Question 2

What are the three states of water?

Answer 2

Liquid, solid (ice), gas (water vapour). The only known substance on earth to exist naturally in three states

Question 3

Over what range is water a liquid?

Answer 3

A large temp range. Temperature reflects the average speed of molecules - the faster they move, the higher the temperature. Hydrogen bonds hold most of the molecules together in small groups, but these groups constantly break apart and re-form. When a molecule moves fast enough it breaks free of all the hydrogen bonds and escapes from the liquid phase into the gaseous phase (evaporation).

Question 4

What is Ices characteristics?

Answer 4

Ice is less dense than water, sinking of cold, dense seawater is a key part of global water circulation. Hydrogen bonds lock the water molecules in a fixed, 3D lattice (a crystal). This means water freezes at a higher temperature than would be predicted

Question 5

What is heat capacity in terms of water molecules?

Answer 5

These hydrogen bonds means water has one of the highest heat capacities of any known substance. Heat capacity is the amount of heat required to raise a substances temperature.

Question 6

Aside from heat capacity what other things does water also have very high?

Answer 6

Latent heat of fusion (melting/freezing ; 334 kJ kg-1). Latent heat of vapourisation (evaporation/condensation ; 2,260 kJ kg-1)

Question 7

What does the prevalence of Waters very high heat capacity, latent heat of fusion and evaporation mean?

Answer 7

Waters ability to absorb a lot of heat for a relatively small increase in temperature means the temperature of water is relatively stable compared with air temperature. Most marine animals are generally not subject to rapid changes in temperature. The global ocean absorbs huge amounts of solar energy and redistributes it around the planet.

Question 8

What is the prevalence of water being a universal solvent?

Answer 8

Water can dissolve more things than any other natural substance. Especially salts, which dissociate into their component ions (e.g. Na+, Cl-) in water

Question 9

What is the composition of water?

Answer 9

Cl-, Na+, SO42-, Mg2+, Ca2+, K+, HCO3-, Br-, H2BO3-, Sr2+, F-

Question 10

What is salinity?

Answer 10

Total amount of dissolved salt in water. Traditionally measured as the amount of salt left behind after seawater evaporated (ppt). Today, salinity is measured via the conductivity of seawater (ions increase the conductivity). Salinity determined from conductivity measurements are technically unitless, but sometimes the term practical salinity units (psu) is used. (psu and ppt are numerically the same, however)

Question 11

What is the rule of constant proportions?

Answer 11

Oceans are remarkably well mixed, salinity will change : oceanic water is generally ~35, salinity will change across estuaries, rockpools can experience fluctuations in salinity. But this is through the addition/removal of water, not ions

Question 12

What is the relationship between salinity, temperature and density?

Answer 12

The temp and salinity of seawater determine its density, it gets denser as it gets saltier and colder. Ocean temp varies between -2 and +30. Temperatures below 0 are possible because salt water freezes at a colder temperature than pure water. Temp is the main controller of seawater density.

Question 13

What are the most important gases in the ocean?

Answer 13

Oxgen, carbon dioxide, nitrogen. Ocean-atmosphere gas exchange

Question 14

What is the prevalence of oxygen in the ocean?

Answer 14

200ml O2 L-1 air, 0.04 - 12 ml O2 L-1 water (5,000 to 17-times less than in air). O2 decreases as temp or salinity increases. Amount of O2 is strongly affected by photosynthesis and respiration. Seawater is far more susceptible to oxygen depletion by respiration

Question 15

What is the prevalence of Carbon in the ocean?

Answer 15

CO2 is far more soluble than O2 because it reacts chemically when it dissolves (the carbonate/bicarbonate buffer system). CO2 is >80% of dissolved gas in the ocean. Ocean stores >50 times more CO2 than the atmosphere

Question 16

What is light transmission in oceans?

Answer 16

Light in water is attenuated through absorption and scattering. Intensity declines with depth, shorter wavelengths transmitted better so red light absorbed first, blue/green absorbed last. No sunlight at all below ~1000m

Question 17

What is water transparency?

Answer 17

Otherwise referred to as turbidity, strongly affected by suspended and dissolved material. Can be greatly affected by plankton. Coastal waters often contain a lot of terrestrially-derived material and appear greenish. Oceanic water is blue

Question 18

What increases with depth and in what way?

Answer 18

Hydrostatic pressure increases linearly with depth. 1atm at surface.

Question 19

Where do the strongest ocean currents occur?

Answer 19

At the surface, where they are caused by wind. Surface currents are, therefore, ultimately driven by heat energy from the sun. Surface currents and winds are also influenced by the coriolis effect.

Question 20

What is the Coriolis effect?

Answer 20

The Coriolis effect deflects large-scale motion like winds and currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Question 21

What is wind driven by?

Answer 21

The winds in our atmosphere are driven by heat energy from the sun. Trade winds (between 30 N/S and equator) are the steadiest winds on earth.

Question 22

What is the Ekman Transport?

Answer 22

Instead of moving in the same direction as the wind, water at the surface moves at an angle of 45 to the wind (Coriolis effect). Each layer down is deviated a little further (R in N hemisphere, L in S) = Elkman spiral. Effect decreases with depth ; dissapears after a few hundred of metres. Net water movement is 90 to the wind direction.

Question 23

What does the Coriolis effect mean for equatorial currents?

Answer 23

It means that equatorial currents move parallel to the equator. Water is very good at transporting heat

Question 24

What do wind-driven surface currents combine into?

Answer 24

They combine into huge, more or less circular systems called gyres. Warm western currents carry vast amounts of solar heat from the equator to higher latitudes. Cold currents flow in the opposite direction on the eastern sides. Ocean currents thus act like a giant thermostat, warming the poles, cooling the tropics, and regulating the climate of our planet

Question 25

What are currents?

Answer 25

Average patterns over large distances and a long time span. At a given place on a given day the current is often different. Currents shift with the season and the weather. On the continental shelf, currents are strongly affected by the sea bed, the shape of the coastline and the tides.

Question 26

Where do tropical organism extend into in the ocean?

Answer 26

Tropical organisms like corals extend into higher latitudes on the western sides of oceans.

Question 27

Where do cold-loving organisms extend into in the ocean?

Answer 27

Cold-loving organisms like kelps extend into lower latitudes on the eastern sides of oceans

Question 28

How is the ocean layered?

Answer 28

The major drive of seawater density is temp. The ocean is usually layered or stratified, with the densest water on the bottom and the least dense at the surface : Surface (mixed layer) : to 100-2--m ; mixed by wind, waves, and currents. Intermediate layer : to 1000-1500m ; site of permanent thermocline. Deep layer : >1500m ; not in contact with seabed, cold (<4 degrees), dense. Bottom layer : in contact with seabed, cold (<4 degrees), dense.

Question 29

What are thermoclines?

Answer 29

Permanent (main) thermocline : a transition zone between warm surface water and cold water below. A permanent feature of the open ocean that rarely breaks down. Waters over the continental shelf are not deep enough to have a main thermocline ; in shelf waters the mixed surface layer often extends all the way to the bottom

Question 30

What are seasonal thermoclines?

Answer 30

Form in temperate and polar latitudes in the spring and summer. Uppermost part of the surface layer gets heated by the sun, sharp transition to cooler water below. Disappear as weather becomes colder.

Question 31

What is thermohaline circulation?

Answer 31

After water masses leave the surface they sink to a depth determined by their density. Water of intermediate density descends only part way. To sink all the way to the bottom of the ocean, surface water must become very dense - that is, cold and relatively salty. This occurs at only a few locations, and only intermittently.

Question 32

Where does water become dense enough to reach the bottom?

Answer 32

Atlantic ocean, south of Greenland and just north of Antarctica. After sinking, the water spreads through the Atlantic and into the other ocean basins. The water eventually rises to the surface and flows back to the Atlantic, where the cycle begins again (a 'cycle' take 1000 yrs.)

Question 33

What impact does wind have on waves?

Answer 33

Not only drives surface currents but also causes waves

Question 34

When do waves begin to form?

Answer 34

As soon as the wind starts to blow. The faster and longer the wind blows, the larger the waves get. The size of waves generated by the wind also depends on the fetch, the span of open water over which the wind blows.

Question 35

What is the dynamic theory of tides?

Answer 35

Devised by Bernoulli, Euler & Laplace. Tides occur in a pinwheel-shaped, standing-wave pattern. In addition to lunar and solar gravity, this theory includes : imperfect shape of earth, land masses, seasons, bathymetry, coriolis effect.

Question 36

What do larger bodies of water have?

Answer 36

Higher ranges

Question 37

What can bathymetry act as?

Answer 37

A funnel amplifying or dispersing the tide.

Question 38

What bay has the highest tidal range in the world?

Answer 38

Bay of Fundy

Question 39

Safety in the intertidal?

Answer 39

Intertidal is a dangerous environment, always know tide times, follow a dropping tide, return when it turns, tide can come in very rapidly in big, shallow bays.

Question 40

What is the cause of tides?

Answer 40

Gravitational pull of the moon on the ocean.

Question 41

What effect does the sun have?

Answer 41

A smaller effect, it is too far away

Question 42

What are spring tides?

Answer 42

Big tides, sun and moons gravitational pull

Question 43

What are neap tides?

Answer 43

When gravitational pulls cancel out