Y13 Oceans Flashcards
Reasons why oceans are important
Produces 70% atm oxygen (phytoplankton carrying out photosynthesis)
Absorbs CO2 from atm
Regulate earth temp
Distribute heat from equator to poles
Influences climate and weather
85% water added to the atmosphere comes from ocean evaporation, regulating temp
Formation of the ocean
Earth formed from dust and ice
GPE of dust and ice converted to KE, friction, hence molten surface to earth
Steam released into atm
Surface cooled, clouds formed, rain —> oceans
Comets and meteors entering earths atm add the other half of water
Properties of water
Absorb a lot of heat (high specific heat capacity)
Universal solvent - dissolves a lot of substances
Polar, so it forms a lattice when it freezes
So ice less dense than water
Strong intermolecular attraction - hydrogen bonding
Created surface tension
What is hydrogen bonding?
Strong intermolecular attraction between hydrogen and oxygen on another molecule
Define latent heat
The energy needed to change states
Latent heat of fusion - energy needed to change from solid to liquid
Latent head of vaporisation
Energy needed to change from liquid to gas
Define specific heat capacity
Amount of energy needed to raise the temperature of 1kg of water by 1C
Water has high heat capacity
So the ocean is slow to warm
Transports a huge amount of heat with only a small temperature change
Three main layers of the ocean
Mixed layer: surface
EUPHOTIC ZONE
Warmed by sunlight
Wind, waves, tides, convection currents mix this layer
Depth varies with seasons
Transition layer:
DISPHOTIC ZONE
Temp; salinity and density rapidly change
Deep layer:
APHOTIC ZONE
Fairly constant in temp and salinity
Parts of the transition layer
200m-1000m
Based on physical properties:
Thermocline - rapid temperature changes
Halocline - rapid salinity changes
Pycnocline - rapid density changes occur
Layers of the ocean in terms of light
Light is absorbed, reflected and scattered by the ocean
6% reflected at surface
65% absorbed in the first meter
Top 200m = euphotic or Protic zone = sunlight zone
200m-1000m = disphotic = twilight zone
Below 1000m = aphotic = midnight zone
Euphotic zone
Depth 50-200m, depending on turbulence and water clarity
The depth at which light drops to 1%
90% of all marine life lives here
Photosynthesis zone
Describe the temperature at different layers of the ocean
Mixed layer distributes heat, consistent
Transition layer
Thermocline, where heat energy is conducted slowly downwards, creating a temperature gradient
Temperature decreases rapidly
Deep layer: stays cold
How does the thermocline vary depending on latitude?
Upper seasonal thermocline and lower permanent thermocline
Seasonal thermocline depends on latitude
High latitude
No thermocline - low solar heating of surface layer
Mid latitudes - winter no thermocline
Summer strong thermocline. Direct sunlight and low winds so less mixing
Low latitudes - strong thermocline due to direct heating and low winds
Define salinity
The amount of dissolved salts in the ocean
Average salinity is 35ppt (parts per thousand)
How does salinity vary with layers of the ocean?
Mixed layer: similar due to mixing
Transition layer: the HALOCLINE
Deep: similar due to limited mixing
How is salinity reduced and increased
Reduced by rainfall (tropics and mid latitudes) and river runoff
Increased by evaporation (tropics) and ice formation (polar regions)
Seawater freezes, salt left behind, forming dense water which sinks
How does salinity vary with latitude
Poles: high rainfall, runoff and melting reducing salinity
Equator:
High evaporation, with rainfall reducing the effect
Tropics: Mid latitudes
Low rainfall with high evaporation, so high surface salinity
Low to high: poles, equator, tropics
What does density of the ocean depend on?
Temperature
Colder = denser
Salinity
Saltier = denser
Pressure
Deeper = denser
How does density vary with depth
Mixed layer: similar density due to mixing
Low density due to high temp
Varied with latitude due to temp and salinity
Transition: PYCNOCLINE
density increases rapidly with depth due to temp drop or salinity increase
Deep: density increases due to pressure
Cold dense water sinks
Four factors affecting ocean currents
Solar radiation
Gravity
Winds and wind friction
Coriolis
How does solar radiation cause ocean currents?
Uneven distribution of solar energy across globe results in uneven heating of ocean
Heating also causes evaporation and ppt, altering salinity and hence density
How does gravity affect current?
Heating of water at equator causes expansion - equatorial bulge
Gravity and slope of earth - water flows toward poles
Describe Ekman transport
Ocean surface waters influenced by friction force due to wind
Due to coriolis effect, ocean water moves at a 90 degree angle to the wind direction
Southern Hemisphere: 90 degrees to the LEFT
Northern Hemisphere: 90 degrees to the RIGHT
Coastal upwelling: Surface waters flow away from coast, replaced with UPWELLING of cold, nutrient rich water from below
How does coriolis effect affect currents
As water moves away from equator, subject to coriolis force, deflected
This currents tend to move in curves
What are surface currents and why are they important?
Top 10% of the ocean
Like rivers in the ocean, water flowing horizontally in the upper 400m
Transfer water and heat from tropical to polar regions
Influence weather and climate
Distribute nutrients, scatter organisms
Describe Western boundary currents, how they are formed and where they flow
Narrow, fast moving currents on western boundaries of ocean basins
Eg. Gulf Stream, eastern Australia current
Trade winds move water across ocean basin from the east, causing ‘build up’ on western boundary
Water flows towards poles due to gravity
Describe eastern boundary currents, how they work and where they go
Found on eastern boundaries of ocean basins
Broader and slower than western
Return the flow from western boundary currents, hence flow back toward equator
Powered by westerly winds
Name the Transverse currents, and the direction of flow
North and South Equatorial currents
flow from EAST to WEST
driven by easterly trade winds
Arctic circumpolar current WEST to EAST
driven by strong westerly winds
carry the largest volume of water of any current (because strong winds, no land masses to slow it down)
Counter currents
between North and South Equatorial currents, flowing in the opposite direction (west to east)
separates gyres
What are gyres caused by and where are they located
large rotating masses of water caused by wind action and Coriolis effect
Sides of gyres are land masses
top and bottom are transverse currents
Formation of the South Pacific Gyre
trade winds move water across the Pacific to the Western boundary, builds up.
Flows toward South Pole due to gravity.
Due to Coriolis, moves away from boundary. Carried by Westerlies to the East boundary.
Flows back toward equator, curving away from boundary due to Coriolis.
what is thermohaline circulation and how does it work
A convection current, ‘vertical’ in the ocean
thermo = heat, haline = salt
Cold, salty water = denser, sinks. from poles to equator.
replaced by warm surface water. from equator to poles.
three factors driving thermohaline circulation
temperature - cold winds cause surface temp to drop.
salinity - ocean ice formation causes increased salt concentration in the water.
evaporation - remaining water is saltier
what two regions drive the global ocean conveyor belt?
North Atlantic up to Arctic
Southern Ocean
(thermohaline circulation)
how tides work
bulge on two sides of earth, earth turns inside the bulge.
bulge due to sun and moon’s gravitational pull.
water is more responsive to this pull than earth, bulges
describe the process of upwelling
wind blows across ocean surface, pushes it away from an area. water rises up to replace the diverging surface water.
El Nino process
Normally - cell of circulation in Pacific, trade winds push warm surface water toward western boundary (Asia, Australia)
cold water replaces it at the Eastern boundary (Americas) - upwelling.
Temperature difference! warm in West (heats air, rising, unsettled weather), cool in East (descending air).
Sets up atmospheric circulation, reinforces Easterlies. Cycle.
El Nino: Weakened trade winds - less pushing and upwelling.
cancels normal temp difference, warm ocean spot moves east. `
changes rainfall and wind pattern over equatorial pacific.
Tropics - increase in floods/droughts
Role of ocean currents
Redistribute massive amounts of Solar heat energy from one part of the earth to another
waves vs tides vs currents
waves are usually created by wind, transport energy, NOT matter
measurable crest / trough
tides are a result of the interaction between the rotation of the earth and the gravitational pull of the moon
currents are large masses of water moving from one location to another
transports energy AND MATTER
how do wind waves form
the transfer of energy from the wind to the water
friction of wind on surface
three factors affecting the growth of wind waves
Wind strength: wind must move FASTER than wave crests to transfer energy to it
wind duration
Fetch: the uninterrupted distance over which the wind blows
a strong wind must blow in one direction for almost 3 days for the largest waves to develop
eg. in the Southern Ocean
Why and how do tides occur
grav pull from sun / moon stronger on one side of the earth
the longest of all waves – wavelength = half the circumference of earth
spring tides
New / Full moon (earth, moon and sun aligned).
Either the highest high or lowest low tides
neap tides
first-quarter and third-quarter moons
the highest low tide and the lowest high tide
lunar and solar tides partially cancel
unusually small tidal range
describe the ocean acidification process
CO2 reacts w/ H2O to form carbonic acid, H2CO3
dissociates to form bicarbonate ions,
HCO3-, and H+
some reacts to form CO3^2-, more H+
