patterns of water movement

Question 1

what are 3 types of currents depending on the factor that powers the flow?

Answer 1

Tidal currents - small scale (e.g. Race Rocks)

Wind-driven currents - major surface currents
(e.g. Gulf Stream, EAC)

Density-driven currents - major subsurface
currents (e.g. Great Ocean Conveyor)

Question 2

what are the main gases that can be found in the atmosphere?

Answer 2

Nitrogen: 78.08% 
Oxygen: 20.94% 
Water vapor: 0-4% 
Argon: 0.93% 
Carbon dioxide: 0.035% 
Helium: 0.0005% 
Methane: 0.00015% 
Krypton: 0.00011% 
Hydrogen: 0.00005% 
Ozone: 0.000004%

Question 3

what is the atmosphere structure?

Answer 3

Five layers characterized by differences in
temperature, composition, movement and density: from down to up
- troposhere (8-8-16)
- stratosphere 8-16-50
- mesosphrere (50 to 80km)
- ionosphere (80-600)
- exosphere (+ionosphere=thermosphere) (600-1000km)

Question 4

troposphere

Answer 4

• Starts at earth’s surface
• Most dense layer - contains most of
  atmosphere’s mass, water vapour and dust
• Site and source of almost all weather
  -varies with season, highest in summer, lowest in winter
• Temperature decreases from 17oC to -75oC in troposphere as the distance from earth increases
• Contains most of water vapour and clouds in atmosphere
• Troposphere means “region of mixing”
• Wind speeds increase with height due to decreased friction

Question 5

stratosphere

Answer 5

• Less dense than troposphere
• Dry → very low water vapour
• Lacks dust, ash, pollen
• Little vertical mixing - movement by diffusion only
• Temperature remains constant up to 25 km then it increases to -3oC due to UV absorption by ozone layer (at 20-30 km)
• 90% of ozone in atmosphere is the
  stratosphere

Question 6

explain the global wind pattern

Answer 6

• Air near the equator is warmed and rises because it is less dense than the air around
• The rising air creates a circulation cell, called a Hadley Cell, in which the air rises and cools at high altitudes moves outward (towards the poles) and, eventually, descends back to the surface.
• The continual heating and rise of air at the equator create low pressure there, which causes air to move (wind) towards the equator to take the place of the air that rises.
• sinking air creates high pressure at the surface where it descends. A gradient of pressure (high to low) is formed that causes air to flow away from the high and towards the low pressure at the surface.
• the Coriolis effect causes winds (and all moving objects) to be deflected:
  
  • to the right in the Northern Hemisphere
  • to the left in the Southern Hemisphere
    The Coriolis effect causes winds to deflect as they travel within circulation cells and results in the two large hypothetical Hadley cells breaking into six smaller cells.

Question 7

explain the unequal heating of Earth’s surface by

the sun

Answer 7

High solar radiation at the equator produces hot
air which rises because of its low density

In contrast, air at the poles is cold because of
low solar radiation - the cold air sinks because of
its high density which results in a high pressure
zone near the poles

Due to unequal heating of the Earth by the sun and the Coriolis force

An area at the equator receives more solar radiation than an equal area at the poles because of:

• The angle of exposure
• The distance the radiation travels through the atmosphere is less at the equator (the atmosphere absorbs part of the energy)

Question 8

what’s coriolis force?

Answer 8

Objects that are moving relative to the ground are deflected to the right in the northern hemisphere and to the left in the southern hemisphere”
There is no Coriolis force at the equator AND

The amount of deflection increases with speed of the
moving object and with latitude

Question 9

what’s atmospheric circulation?

Answer 9

the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.

Question 10

hadley cell

Answer 10

wind flow pattern of air rising at the

equator and descending at 30oN and 30oS

Question 11

ferrel cell

Answer 11

at 30oN and 30oS some of the
descending air travels pole-ward - these surface
winds are deflected by the Coriolis force to
become the Westerlies of both hemispheres

Question 12

polar cell

Answer 12

upper air moving pole-ward cools,
becomes dense and sinks back to the surface at the
poles

Question 13

explain the global wind pattern

Answer 13

• Heating at equator causes air to warm, causing it to expand and results in a low pressure zone
• Warm air rises, expands and cools, losing moisture by precipitation and resulting in a high pressure zone
• Air flows toward low pressure zones, becoming cooler and drier which increases it’s density
• At 30 degrees N and S, the air sinks
• Much of this air returns to the equator along the surface, becoming warmer and picking up moisture along the way. The Coriolis force deflects the air, resulting in the Northeast Trade Winds and Southeast Trade Winds
• These trade winds converge at the equator resulting in light and variable winds (Doldrums) where wind is being convected upwards
• little wind at 30N/S (Horse Latitudes) because air is moving downwards

Question 14

where do surface currents blow

Answer 14

Surface winds blow in regular patterns (due to unequal heating of the Earth and the Coriolis
force)

Question 15

what causes the surface currents

Answer 15

by the drag of the wind on the water and the Coriolis force – water is set in motion by winds and affected by Coriolis force

Question 16

explain Ekman transport

Answer 16

• The Coriolis force causes a deflection of the water
  flow to the right (North) or left (South)
• Each layer of water is deflected about 45o
• An Ekman spiral (A) is a rotating column of water that forms when water moves at an angle to the wind direction due to the Coriolis Effect.
• The net effect of the rotating water is movement at a right angle to the wind direction. The water turns to the left in the Southern Hemisphere.

Question 17

what’s ekman transport?

Answer 17

Within each gyre, water piles up in the center and creates its own super intense Ekman spiral that intensifies the currents contributing to it

Question 18

explain the surface currents

Answer 18

At low altitudes, trade winds produce westward moving currents

Westerly winds produce eastward moving currents at mid latitudes in both hemispheres

Currents are deflected by the continents creating gyres

Question 19

how do surface currents vary? give examples

Answer 19

they vary in speed, depth and width:
Gulf stream and Kuroshio are the fasted (3-10 km/h), the deepest (1000-2000 m), and the narrowest (50-75 km)

Canary and California currents are slowest (~1 km/hr) and hundreds of kilometers wide

Question 20

what is the Gulf stream, how does it work?

Answer 20

Western boundary current in the North Atlantic Gyre
Northward flow of warm water from the equator
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida

Question 21

what is the importance of the gulf stream?

Answer 21

Helps regulate temperature through this process

Moderates the climate as heat moves onto land

North Atlantic Current also helps push the warmer water out

Together they aid climate regulation in Western Europe and the Eastern USA

San Francisco and Dublin have similar climates despite San Francisco being 1600 km further south than Dublin

Question 22

How to measure the wind-driven currents?

Answer 22

Current meter mounted on a mooring

ADCP: Acoustic Doppler Current Profiler: measure how fast water is moving across an entire water column.

Dyes, buoys, and drift cards

Davis drifter: A Davis drifter is an instrument designed to measure wind-driven surface currents. It has four major components: (1) body, (2) sails, (3) floats, and (4) a data collection/transmitter package.

Question 23

what is upwelling?

Answer 23

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface

Question 24

where does the upwelling occur?

Answer 24

Coastal upwelling occurs where Ekman transport moves water away from the coast

Surface waters are replaced by deep (cold and nutrient rich) water that comes up from below

Common on the west coasts of continents

Question 25

what is downwelling?

Answer 25

the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the sinking limb of a convection cell

Question 26

where does downwelling occur?

Answer 26

In contrast, downwelling occurs where Ekman transport moves water toward the coast

Also occurs as water becomes more dense and sinks which occurs at the poles

Question 27

what’s the el nino?

Answer 27

The periodic, irregular (every 2-7 years) disruption of trade winds due to the breakdown of the atmospheric pressure gradient

Without the wind, water is no longer pushed offshore from eastern Pacific and piled up in the western Pacific

Less upwelling, maybe some downwelling

Bad for plankton: No upwelling, no nutrients for plankton

Results in sea surface temperature anomalies

Very warm waters

Question 28

what are the impacts of el nino?

Answer 28

Warmer water expands north and south of the equator

Range extensions of warm water species (mola mola), Humboldt squid, great white sharks

Atypical weather patterns

Increased precipitation in Ecuador and NW Peru

Droughts in agricultural regions of Bolivia and Southern Peru

Severe droughts in Australia, southern India, Indonesia, and Southern Africa

Severe coastal storms along west coast of North America, mild winter in Eastern North America

Question 29

what is la nina?

Answer 29

Intensification of trade winds which results in more water being pushed toward the western Pacific

Colder water is pushed across from the eastern Pacific

Upwelling along west coast of South America is stronger

Question 30

explain the deep ocean currents (thermohaline circulation)

Answer 30

describes the movement of ocean currents due to differences in temperature and salinity in different regions of water.

Density is a function of temperature and salinity
- Cold, salty water sinks which is what drives the thermohaline circulation

Dense water masses sink and displace less dense water masses

Question 31

what is thermohaline circulation?

Answer 31

Dense water masses sink and displace less dense water masses

Question 32

how does sea ice form?

Answer 32

during the thermohaline circulation, When saltwater rises, the salt gets left behind

Question 33

what happens to the salt the is left behind during the thermohaline circulation?

Answer 33

Left behind salt gets cooled and then forms even more cold salty water

Question 34

what is the great ocean conveyor?

Answer 34

The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity.

Question 35

explain the great ocean conveyor belt

Answer 35

Driven by sinking in northern N. Atlantic

Warm salty surface water reaches the N. Atlantic (Gulf Stream) and cools and becomes more dense as salt is excluded during ice formation

This dense water sinks and flows south towards Antarctica (deep current)

There it is cooled further and continues to flow along the bottom of the ocean into Atlantic, Indian, and Pacific basins

Upwelling occurs in Pacific and Indian Oceans and water returns as surface flow to the North Atlantic

Question 36

what’s the significance of the great ocean conveyor?

Answer 36

Helps oxygenate the deep sea and maintain nutrition levels
redistributes heat from equator to poles

Oxygenates deep oceans

Returns nutrients and CO2 from deep water to surface

Question 37

how can you measure the great ocean conveyor?

Answer 37

Argo Floats (also used for measuring temp/salinity): Approximately every 10 days, an Argo float dives about 1.2 miles deep, drifts with the ocean currents, and then surfaces to transmit data in real-time via satellite

Moored buoys

Question 38

how fast does the goc move?

Answer 38

Ranges between 12-20 sverdrups

1 sv = 1 million cubic meters/second

Gulf Stream ranges between 30sv in the Florida Current to a maximum of 150sv

GOC is NOT fast