Oceanography Flashcards
(98 cards)
1
Q
what are some statistics about the global ocean?
A
> 97.5% of water on or near the Earth lies in ocean
- southern hemisphere = 81% ocean
- northern hemisphere = 61% ocean
- the largest feature is the pacific ocean
average depth - 4,000 - 5,000 m
average temp = 3.9degrees C
average salinity = 34,48 %o (parts per 1000)
2
Q
what is phytoplankton?
A
> the first link between the physicl and the biological in the ocean
play a key role in the marine ecosystem
just like plants on land phytoplankton require
- light, water, carbon dioxide and nutrients to grow
Diameter concentration - 1000s to 1,000,000 per millilitre
global biomass -
3
Q
how do we map and study the ocean floor?
A
> the mapping and study of ocean floor contours is called bathymetry
4
Q
how did early scientists study the ocean floor?
A
> early bathymetric studies used a weighted line to measure the depth of the ocean floor
5
Q
what are some advancements in Bathymetry study?
A
> echo sounding
multibeam systems
satellite Altimetry
LIDAR ( light detection and ranging)
6
Q
What is echo sounding?
A
> method to measure seafloor depth using powerful sound pulses
- pulses of sound energy, or “pings”, spread out in a narrow cone as they travel from the ship
when depth is great, the sounds reflects from a large area of seabed
- measures over deep depressions often inaccurate
- because the first sound of the returning echo is used to sense depth
7
Q
what is the multibeam system?
A
> provide more accurate measurements
collect data from as many as 121 beams to measure contours of ocean floor
cover 120 deg arc @ right angles to direction of travel, ping sent every 10 secs
measure swath at bottom ~ 3.4x as wide as water is deep
8
Q
What is satellite altimetry?
A
> measures the sea surface height from orbit
- bounce 1,000 pulses of radar energy off ocean surface every second
measures sea surface levels accurately (~2.5cm)
shows sea surface disortions
9
Q
how does satellite altimetry measure sea surface distortions?
A
> distortion above a seabed feature occurs when extra gravitational attraction “pulls” water toward it from the sides, forming a mound over the water itself
2m or so mound
other influences are wind, currents , tides
10
Q
what is the bathymetry of the ocean floor?
A
> varies with location
1/2 of the Earth’s solid surface is at least 3,000 meters below sea level
average depth of the ocean is 3800m greater than the average elevation of the continents 840m
11
Q
how is the ocean floor classified?
A
Continental Margins
- the submerged outer edge of a continent
Ocean Basin
- the deep seafloor beyond the continental margin
12
Q
what are the two types of continental margins?
A
> passive margins
- face the edges of diverging tectonic plates
- little volcanic or earthquake activity associated
- atlantic-type
active margins
- located near the edges of converging tectonic plates
- sites of volcanic and earthquake activity
- pacific-type
13
Q
continental margins - are they passive or active?
A
> facing edges of diverging plates are PASSIVE MARGINS
> near edges of converging plates (or where plates are spilling past eachother) are ACTIVE MARGINS
14
Q
what can earthquakes cause?
A
Tsunamis
15
Q
What is a tsunami?
A
> generated by vertical movement of earth along faults
- are seismic waves
caused by water displacement
are long-wavelength, progressive waves caused by the rapid displacement of ocean water
move at high speed - due to extremely long wavelengths
200m between the peaks of each wave.
16
Q
what are the distinct components of the continental margins?
A
1) With a vertical exaggeration 50:1
>continental shelf = shallow, submerged edge of continent
> continental slope = transition between continental shelf and deep-ocean floor
> shelf break = abrupt transition from continental shelf to continental slope (200m)
> continental rise = accumulated sediment at base of continental slope
2) no vertical exaggeration
> depth steadily decreases to mean of 4000m
17
Q
what are the components of a x-section from a typical ocean basin flanked by PASSIVE continental margins? (atlantic)
A
> Continental margin
- submerged outer edge of a continent
Ocean basin
- deep-sea floor beyond the continental margin
oceanic ridges
- where new sea floor develops e.g., mid atlantic ridge
*note transition between thick, less dense granite rock of continents and thinner, denser basalt of deep-sea floor
18
Q
how is the continental shelf impacted by changing sea levels? ON GRAPH
A
> rise and fall of sea level due largely to periods of increased and decreased glaciation
- currently: rapid change due to climate change.
a) a low stand of -125m @ climax of last ice age ~18,000 yrs ago
b) a high stand of +6m during last interglacial period ~120,000 yrs ago
c) shows present sea level in accelerating period of global warming - these changes in sea level over last 250,00 years as traced by data from ocean-floor cores
19
Q
discuss continental shelves in relation to the sea levels of the past and the future
A
> SE coast of USA 18,000 years ago, during the last ice age, florida is much greater in size in the western edge
the position of sloping SE coast has been as much as 200km seaward from the present shoreline, leaving much of the continental shelf exposed
as the ocean expands and polar ice caps melt due to global warming, sea level could easily rise 6m, driving the coast inland as much as 250km
20
Q
what is the topology of deep-ocean basins ?
A
> it differs from that of the continental margin
some features are:
- Oceanic Ridges
- Trenches
- hydrothermal Vents
- Abyssal plains
- Seamounts - important, birds focus around these
21
Q
what is an oceanic ridge? refer to map
A
> a mountainous chain of young, basaltic rock at an actively-spreading centre of the ocean
the oceanic ridge system stretches 65,000km around Earth
East pacific rise typically spreads ~6x faster than mid-Atlantic rise
22
Q
What are trenches? refer to map
A
> form in subduction zones
are arc-shaped depressions in the ocean floor caused by the subduction of a converging ocean plate
mostly around the edges of the active Pacific
are the deepest places in the Earth’s crust - 3-6km deeper than adjacent basin floor
the Mariana Trench is 11,022m deep
23
Q
describe the hydrologic cycle
A
> water circulates in a continuous cycle between the ocean, the atmosphere and reservoirs of freshwater
24
Q
what is the difference between heat and temperature
A
> heat is energy produced by the random vibrations of atoms or molecules
temperature is the object’s response
25
what is heat capacity?
> heat capacity is a measure of heat (calories) required to raise the temperature of 1g of a substance by 1 degrees celsius
> not all substances have the same heat capacity
> water has a high heat capacity
> it resists changing temp when heat is added or removed
> due to the strength of H bonds between water molecules, water can gain or lose large amount of heat with little change in temperature
> this thermal inertia moderates temperatures globally
26
how does temperature affect density?
> the relationship between temperature and density for pure water is unusual
> refer to diagram
27
what are the implications of water's heat capacity?
> this along with the ability of ice to float are vital to maintaining Earths moderate surface temperature
> water also has the highest latent heat of vapourisation of any known substance (540cal/gram)
28
describe the cycle of temperature versus heat?
> must add 80 calories of energy to change a gram of ice to liquid water
> once melted, 1 calorie of heat is needed to raise each gram of water by 1 degree celsius
> but 540 calories must be added to each g of water to vaporise it!
> approx. 1m of water evaporates from ocean surface/ yr (334,00km3)
> when 1 g of ocean vapour condenses, it releases 540 calories
> these calories power thunder, storms, currents, wind and waves
29
describe the average surface temp and salinity for the world
> as expected, temperatures lowest in polar regions and highest near the equator
> heavy rainfall in the equatorial regions "freshens" the ocean near the equator
> hot and dry conditions near the tropic lines, salinity in the equatorial regions vs near the tropic lines: heavy rainfall vs hot and dry conditions
30
what allows for massive amounts of heat to be moved very efficiently?
>lots of latent heat is used to evaporate water in the tropics and is released when vapour is carried towards the poles and reprecipitated.
> oceans currents carry heat from the tropical to polar regions
> there is a much larger variation in the latent heat and specific heat capacity of land than in water, i.e, water is a moderator
31
what are the constituents of seawater?
> by weight, seawater = 96.5% water and 3.5% dissolved substances
> if oceans evaporated completely, a salt layer of 45m thick would result
32
what is salinity?
> the measure of total dissolved inorganic solids in 1kg of seawater
> by mass, salinity varies from 3.3-3.7% in the ocean (33-37ppt)
33
what are the most abundent components of sea water?
```
>chloride
> sodium
> sulfate
> magnesium
> bicarbonate
> calcium
> potassium
> other
```
34
where do salts come from?
> processes that regulate major constituents in seawater
- ions added: rivers, volcanic activity, hydrothermal vents, decay of once living organisms
- ions removed: mid-ocean ridge systems, uptake by livign organisms, incorporation into sediments, and ultimately subduction
> components of ocean salinity are modified by Earth's crust
35
how do scientists determine the salinity of seawter?
by measuring the chlorinity of the sample
> salinity in%o = 1.80655 x chlorinity in %o
> ratio of major salts in ocean is constant but salinity might vary in seawater from different locations
> ocean is in chemical equilibrium
36
what is residence time?
the average length of time an element spends in the ocean
> residence time of ocean water is 4,100 years
> residence for water in atmosphere is 9 days
> ocean mixing occurs over a period of 1,600yrs by currents
37
wht are the percentages of gases in surface seawater?
```
> nitrogen - 48%
> oxygen - 36%
- vital for many animals
- source from photosynthesis and dissolved from atmosphere
> carbon dioxide - 15%
- used in photosynthesis
- 60x more in ocean than in atmosphere
```
38
what are the different gas concentrations at different depths?
> refer to diagram
- O2 concentration is higher near the surface because photosynthesis of plants occurs here
> below sunlight layer [O2] decreases because of respiration and oxygen consumed by decay as organisms slowly sink
> as it gets even deeper, the [CO2] increases
> at the surface plants use CO2, but at depth, CO2 builds up as photosynthesis cannot occur in the dark
> CO2 also increases with depth because its solubility increases as pressure increases and temperature decreases
39
what is the pH of seawater?
> mildly alkaline with a natural pH of about 8
> however, the ocean is becoming more acidic as it absorbs additional carbon dioxide from the atmosphere
> a less alkaline environment is making it difficult for organisms to build hard structures containing calcium (shells, coral, etc)
> warmer
> viruses are evolving rapidly
40
describe accretion and erosion
> to produce a net growth, the rate of accretion (construction) has to be greater than the rate of erosion (destruction)
> however at high levels of CO2, the rate of erosion is higher than the rate of accretion so there will be a overall net loss.
41
what is density of water?
> a function of water's temperature and salinity and pressure (at greater depths)
- cold salty water is denser than warm, less salty water
> two samples of water could have the same density at different combinations of temperature and salinity
42
what are the different density zones?
> surface zone:
- the upper layer of the ocean, containing the least dense water
- majority of the biology occurs here because of the light
- 2%
> pycnocline
- zone in which density rapidly increases with depth
- blocks whats happening on the surface
- in the tropics the pycnocline is very strong because of the large change in temp an salinity
- 18%
> deep zone
- little change in density throughout this layer
43
what is the density stratification of the ocean?
> surface zone - (mixed layer) relatively warm, low-density water
> pycnocline - density increases rapidly with depth
> deep zone - of cold, dense water - about 80% of total ocean volume
44
what are the two variations on the pycnocline?
Thermocline
> rapid density increase due to rapid temp decrease
Halocline
> vertical variations in salinity result in a halocline
> occurs in the north pole where fresh water is released due to ice caps melting
45
describe light in the ocean
> light: a form of electromagnetic radiation, or radient energy
- travels as waves through space, air and water
> sunlight does not travel far in the ocean
- scattering: occurs primarily when light is bounced between air and water molecules
- absorption: occurs when light's electromagnetic energy is converted to heat in the molecules of seawater
> photic zone: thin film of lighted water at the top of the surface zone that recieves sufficient sunlight for photosynthesis
>uphotic zone: depth to which 1% of light remains
46
describe wavelength transmission in water
> light transmits blue light more efficiently than red
> thats why the ocean appears blue
> red light is absorbed in the surface layer by photosynthetic organisms
> the EAC is low in nutrients, that is why light penetrates further in the water column,
(refer to satellite data)
47
describe sounds transmission in water
> sound travels much further in water than in air
> average speed of sound in ocean is
- 1500m/s at surface (5x speed in air)
- increases as T and P incease
- decreases with depth
- minimum speed at 1000m where:
- the effect of increasing pressure offsets the decrease in temperature
- so > 1000m again increases with depth
> at the bottom of the ocean basin, speed may be higher than at surface
48
what oes refraction in the ocean cause?
the Sofar layer
> sound waves travel at minimum speed
> sound transmission is particularly efficient
> heard for great distances -> refraction tends to keep sound waves within the layer
>refer to diagram
49
what are sonar systems?
> used to detect underwater objects
> active sonar:
> pulses of high-frequency sound radiated from sonar array
> energy reflects from submerged submarine and returns to sending vessel
> analysis to plot position
> used to combat underwater threats
50
how do sonar systems harm marine mammals?
> whales and other marine mammals rely on their hearing for life's most basic functions, such as orientation and communication
> when a sound 1000x more powerful than a jet engine fills their ears, the results can be devastating and even deadly
> this is the reality that whales and other marine mammals face due to human-caused noise in the ocean, from sound of airguns used in oil exploration to subs and ships emitting sonar
> manmade sound waves can drown out the noises that marine mammals rely on for their very survival.
51
what are some of the effects of cyclones? specifically cyclone yasi?
```
> tropical cyclone
> occurs over the continental shelf
> decreases visibility
> therefore decreases productivity
> core was 930hPa
> winds 285
> 5m storm surge
```
52
what are the two factors that govern tthe global circulation of air?
1) uneven solar heating
2) earth's rotation
> lower atmosphere = homogenous mixture of gas
> water vapour = 4% of volume
> density of air is influenced
- by temp + water vapour/content
53
describe uneven solar heating
> varies with latitude
- equal amounts of sunlight - spread over greater surface area near poles than in the tropics
- ice near the poles
> earth is in thermal equilibrium, but different latitudes are not
- polar latitudes lose more heat to space than they gain
- tropical latitudes gain more heat than they lose
- only at ~30 degrees north an 30 degrees south: amount of radiation received = amount lost
> to keep long term temperatures stable -> must be efficient transfer of heat from regions with surplus heat to regions with deficit
> the ocean does not boil away at the equator or freeze solid near the poles because:
- the heat is transferred by winds and ocean currents from equatorial to polar regions
- winds = high latent heat of vaporization
- ocean currents = high specific heat capacity
54
what does solar heating also vary with?
> the seasons
- seasons casued by variations in ampunt of incoming solar energy as Earth makes its annual rotation around the sun on axis tilted by 23 1/2 degrees
- during NH winter, SH istilted toward the sun and NH receives less light and heat
- during the NH summer, situation is reversed.
55
what does earth's uneven heating result in?
> large-scale atmospheric circulation
56
what is the coriolis effect?
> coriolis effect is the observed deflection of a moving object, caused by the moving frame of reference on the spinning earth
- the effect only take place when the body is moving
> how does this apply to the atmosphere?
- as air warms, expands and rises at the equator, it moves toward the poles, but
- instead of travelling in a straight path, the air is deflected eastward
- in the NH the air turns to the RIGHT
- in the SH the air turns to the LEFT
57
how can the coriolis effect be observed from space in comparison to on earth?
>observed from space
- cannonball 1( shot northward) and cannonball 2 (shot southward) move as expected -> travel straight from the cannons and fall to earth
> observed from earth
- cannonball veers slightly east and cannonball two veers west of intended targets
EACH CANNONBALL CARRIES WITH IT THE EASTWARD VELOCITY IT HAD BEFORE IT WAS FIRED
> observed deflection is caused by the observer's moving frame of reference on the spinning Earth
58
How does the coriolis effects influence the movement of air in atmospheric circulation cells?
> air rises at the equator and falls at poles, but instead of on great circuit:
- there are 3 in each hemisphere
- note the influence of the Coriolis effect on wind direction
> global air circulation as described in the six-cell circulation model
59
describe the atmospheric circulation cells?
```
three cells exist in each hemisphere
> Hadley cells
- tropical cells found on each side of the equator
> ferrel cells
- found at the mid-latitudes
> polar cells
- found near the poles
```
60
What are the wind patterns found between and within cells
> doldrums - the equatorial low
- calm equatorial areas where two Hadley cells converge
- intertropical convergence, the ITCZ
> horse latitudes - subtropical high
- calm areas between Hadley and ferrel cells
> trade winds - surface winds of Hadley cells
> westerlies - surface winds of Ferrel cells
61
What are the cell circulation centres on the meterological (not geographical) equator?
> NH contains less ocean than the SH
> landmasses have lower specific heat capacity than the oceans
> seasonal differenced in temperature and atmospheric cell circulation more extreme in the NH because there is less ocean
> seasonal N-S movement of ITCZ is generally less over ocean than over land because of the greater heat capacity of water
62
what are monsoons?
> a monsoon is a pattern of wind circulation that changes with the season
> linked to
1) differing specific heats of land and water
2) seasonal movement of the ITCZ
> locations where monsoons occur generally have wet summers and dry winters
63
what are the patterns of monsoons?
> during monsoon circulations of
- a) january (ITCZ most Southern)
- b) July (ITCZ most northern)
> surface winds are delected to the right in NH and Left in SH
- c) summer asian monsoon, showing location of Cherrapunji, india, one of the wolrd's wettest places
- rainfall amounts exceed 10m/year!
64
what are storms?
> variations in large-scale atmospheric circulation
- have high winds and precipitation
- are rotating masses of low-pressure air
> tropical cyclones occur in tropical regions
> extra-tropical cyclones occur in Ferrel cells - are winter weather disturbances
65
how do tropical cyclones form?
> form in one humid air mass
> low pressure centre and high pressure edges
> air starts moving toward a zone of low pressure and veers off course to the right
> core of tropical cyclone rotating to left, or counter clockwise in the NH
> stirs up lots of sediments making the photic depth a lot shallower
> brings up colder water from the depths as well
66
what are the tracks of tropical cyclones?
> the breeding grounds of tropical cyclones are centred either side of the equator and fan down from there, excluding Africa's west coast and south america
> storms follow curving paths: first move westward with tradwinds
> die over land or turn eastward until lose power over cooler mid-latitudes ocean
> are not spawned over South Atlantic and southeast Pacific because the water is too cold
> nor in still air within a few degrees of the equator - the doldrums because coriolis is non existent there, and coriolis is needed to cause cyclones.
67
how do extra-tropical cyclones form?
>between two air masses (refer to diagrams)
a) genesis and early development of an extra tropical cyclone in the NH
b) how precipitation develops
> these relationships between two contrasting air masses are responsible for:
- storms generates in polar frontal zone
- high rainfall within these belts
- decreases salinities of waters below
68
why are there phytoplankton deserts and rainforests?
> higher biomass in the polar waters
69
what are surface currents?
```
> ~10% of water in world oceans
> flow horizontally in top ~400m
> driven mainly by wind friction
> prime movers:
- powerful westerlies
- persistent trade winds
> earth's surface wind energy is concentrated in easterlies and westerlies
> winds driven by
1) uneven solar heating
2) earth's spin (coriolis)
```
70
what drives surface currents?
1) surface winds
2) solar energy
3) Coriolis effect
4) gravity
> large ocean currents move in a circular pattern around the periphery of an ocean basin
- called an ocean gyre
71
descirbe the velocities at differnt points on earth (coriolis)
> given by the equation f = 2 omega sin(phi):
| - where omega is
72
what forms ocean gyres?
> in ocean basins, the combination of the 4 forces circulate the ocean surface, forming gyres
> surface currents flow around the periphery of ocean basins because coriolis deflects the current to the right or left, forming a circle like movement
73
describe the Ekman spiral
> body of water as a set of layers: top layer driven forward by the wind
- each layer below moved by friction
- each succeeding layer moves with a slower speed and at an angle to layer immediately above it
- to the right in the NH and to the left in SH until water motion becomes negligible
> though direction of movement varies for each layer, NET fLOW of water in NH (SH) is 90 degrees to the right (or left) of the prevailing wind forces
> speed of currents in reduced the further down the current you go
74
what is the movement of water away from a current moving with the trade winds influenced by? (diagram)
> rightward (NH) tendency of Coriolis effect
| > gravity-powered movement of water down pressure gradient
75
how are hills formed in the ocean?
> the surface of the north atlantic is raised through wind motion (elkman spiral) to form a low hill
- water from a point at the bottom of the hill turns westward and flows along the side of this hill
> the now westward-moving water is balanced between
- Coriolis effect
- flow down pressure gradient, driven by gravity (to the left/ down pressure gradient)
> thus balance of a) wind energy and friction( Ekman spiraling) and b) Coriolis effect and pressure gradient, propels currents of gyre and moves them along outside edges of the ocean basin
> so, the hill is formed by Ekman transport
- water turns clockwise (inward) to form the dome
- then descends, depressing the thermocline
in the centre of the ocean gyre, a high pressure system, water descends
76
how do ocean gyres effect the phytoplankton deserts?
> because the centre of the gyre, water is descending via the Ekman spiral, no water is being brought to the surface,
> therefore, no nutrients are being brought up
> no ascending water
77
what are the six great surface circuits?
Geostrophic gyres:
- in balance between the pressure gradient and the Coriolis effect (note directions - refer to diagram)
> of the six great currents, five are geostrophic gyres
> powerful western boundary currents flow along the western boundaries of ocean basins in both hemispheres
> current along the bottom near the south pole is blown by westerlies
78
What are Western boundary currents?
```
Western Boundary currents
- narrow ( Gulf Stream
> Kuroshio Current
> Brazil Current
> Agulhas Current
> Eastern Australian Current
```
79
Describe westward intensification
> without eh Coriolis effect: currents would form a regular and symmetrical gyre BUT:
- because Coriolis effect is strongest near the poles, water flowing eastward at high latitudes turns sooner to the right "short-circulating" gyres
- because Coriolis effect is zero at the equator, water flowing westwards near the equator tends to not turn until it encounters a blocking current
> net result - western boundary currents are faster and deeper than eastern boundary currents and the geostrophic hill is offset to the west.
80
what does ENSO stand for?
El nino - southern oscillation
81
describe the normal wind and current flow
> trade winds usually drag huge amounts of water eastwards along the ocean's surface on either side of the equator
> across the tropical pacific
- in a non-El nino yeat, normally the trade winds and surface water flow westward
- the thermocline is deeper in the west, rises in the east
- upwelling of cold water occurs along the west coast of central and South America
82
Describe what happens in a El nino year
> when the southern oscillation develops:
- trade winds diminish and then reverse
- they are the primary forcing object
- this leads to an eastward movement of warm water along the equator
- surface waters of central and eastern pacific become warmer and storms over land may increase
83
what happens in an La nina event?
> normal circulation returning with vigour
| > strong currents and powerful upwelling
84
describe the Southern oscillation index (SOI)
> an indication of development and intensity of El nino or la nina events in the pacific ocean
> sustained negative values -> El Nino episodes (ENSO)
> sustained positive values -> La Nina
85
what happens to the sea surface height in El nino and La nina events?
> in El nino events, sea surface height decreases in the central america area and increases in the Australian east and west coast
86
describe the vertical motions of water
> wind can cause vertical movement of ocean water
> wind-induced vertical circulation is vertical movement induced by wind-driven horizontal movement of water
> upwelling is the upward motion of water - brings cole, nutrient rich water towards the surface from beneath the pycnocline
> downwelling is downward motion of water - supplies the deeper ocean with dissolved gases
87
Describe equatorial upwelling
> south equatorial current straddles geographical equator
> water north of the equator veers to the right
> water south of the equator veers to the left
> surface water therefore diverges causing upwelling
> is replaced by water from the depths
> most upwelled water comes from area at depths of 100m or less (above equatorial undercurrent)
> upwelling brings cold nutrient rich water towards the surface
> impact of wind does not reach thermocline, occurs primarily in the east shallower pycnocline
88
describe coastal upwelling
Northern hemisphere example
> wind can induce upwelling near coasts
> winds from the north travel along the west coast of a NH continent
> water moved offshore by Ekman transport replaced by cold, deep, nutrient-laden water
> refer to diagram
89
describe upwelling in the southern hemisphere
> southeast wind travels along coast
> surface water is moved offshore by Ekman transport
> cold upwelling of nutrient rich water
4 major sites of upwelling (all 4 account for 90% of global ocean productivity:
> West Coast of Southern Africa - most productive
> Along Peru and Chile
> Californian Coast
> North Africa - Canary current
90
Describe coasteal downwelling
> wind can also induce downwelling near the coasts
> wind form south along NH west coast for prolonged period can result in downwelling
> in SH: wind from north along west coast for prolonged periods result in downwelling
> areas of downwelling are low in nutrients
> low in biological productivity
> refer to diagram
91
describe eddies in the northern hemisphere
> rotation in a clockwise direction
> result in downwelling
> high pressure in the middle
> much more dynamic than the massive oceanic gyres which are constant
92
describe Anticyclonic eddies
> as eddy spins up:
- inward coriolis force increases
- overbalances the outwards pressure force
- letting water flow inward at the surface (convergence)
- in turn causing water to be pumped downward at the eddy's centre
> no productivity
>clockwise in NH
>anticlockwise in SH
> warm water currents form eddy, spinning off it
> westerlies and trade winds emit there constantly
> warm core
93
describe cyclonic eddies
as eddy spins up:
> outward Coriolis force increases
> inward pressure force (H to L) now unbalanced
> causes water to flow outward at the surface (divergence)
> in turn, causing water to be pumped upward in the eddy's centre
> upwelling of cold, nutrient rich water
> productivity!
> high concentration of phytoplankton -> zooplankton -> fish -> birds
> cold core
> anticlockwise in the NH and clockwise in the SH
94
how does this eddy variability impact the ecosystem?
> shallow water near the coast have a lower heat capacity due to a lower volume
> change in temp from winter to summer much greater close to shore
> EAC speeds up in september
> clockwise, cyclonic, capricorn eddy with high nutrients is produced
> pronounced eddy affects the EAC
95
what are eddies' effect on higher trophic levels?
```
Wedge-tailed shearwaters
> pan-tropical species
> long-lived: 30+ years
> nest in burrows, so limited locations
> heron island and lady elliot island
> dual foraging mode
- daily short tripping (50-100km)
- distance self-foraging (7-10days)
- foraging strongly linked to eddy dynamics
- one parents for each method then switch
- dependent on nutrient rich eddy
Manta rays and whale sharks also use the eddies
```
96
what is project manta?
> to identify main drivers of high manta abundances
- seasonal peak mid-May to mid-August
- temperature peak: 21-23 degrees
-strong relationship with eddy dynamics
> focus around capricorn eddy
> affinity to: shelf- edge and frontal areas
97
what are eddies' effect on whale sharks?
> they have oceanographic influences
| > the largest congregation of whale sharks is at Mozambique near where there is a seasonal eddy
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What are Eastern Boundary Currents?
- Cold
- shallow (Canary Current
> Benguela Current
> California Current
> West Australian Current
> Peru Current
