Transcript 1 Introduction to Marine Ecology jh part 2 2009

Basic Oceanography
• 4 main basins
• “Super Ocean” – interconnected
• physico-chem differences = different envts
= different communities of organisms
• Gulfs and seas – enclosed, strong
terrestrial influence
Bathymetry – Ocean floor features
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Shelf
Slope
Rise
Abyssal plain
Mid-ocean ridge
Seamount
Trench
Island arc
www.noc.soton.ac.uk/obe/PROJECTS/pap/images/largemap1.jpg
Basin cross section
stloe.most.go.th/.../LOcanada6/604/9_en.htm
Continental margins
•Shelf – to 250 m, 0.1° slope, 50-1000 km width, terrigenous
or oolotic sediment, sand – silt, highly productive
http://www.neseabirds.com/graphics/figure1.jpg
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Shelf
Slope
Rise
Submarine canyons
• Slope – cont. boundary, 1500-4000 m, 4° slope,
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sand to silt-clay, terrigenous and biogenic
Submarine canyons – Glacial or river cut @ lower
sea levels, carry shelf sediments via turbidity flows
Rise – 4000-6000m, 0.1-1° slope, alluvial fans
spread by deep currents
Abyssal plain
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3.5-5.5 km,
<0.1° slope,
“marine snow”
biogenic
– Calcareous
– Siliceous
• Terrigenous
– Red clay
http://www.ga.gov.au/image_cache/GA1705.jpg
• Red clay – vol. dust, marine
debris, zeolite, iron oxides
• Calcareous
tropical-temperate, high prod., max.
4500-5000 m
• Siliceous - silica available,
http://www.noc.soton.ac.uk/gg/BOSCORF/curatorial/pacific.html
moderate prod., low calcium
carbonate; polar and deep
tropical/subtropical
• Mid-ocean ridge
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Global network
Plate boundary
Sea floor spreading
2-3 km, emerge
Iceland, Azores
• Trenches
– Subduction
– Equilibrium
w/spreading
– 10 km melt zone
– Volcanic arcs
– PR- 8400m deep
– Mariana – > 11 km
Temperature
• Extremely important in regulating
distribution and abundance of organisms
• Latitude, depth
• Seawater range
-1.9 C  40 C
Surface Temperature
• Homeotherms (endotherms) and
Poilkiotherms (ectotherms) – metabolism
increase 2x for each 10° increase
• Temperature based biogeographic zones
Thermocline
• Warm surface water,
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tropics, summer
Declines w/depth
Rapid decline:
thermocline
Persistent in tropics,
summer
Deeper: isothermal
Depth
Thermocline
Temperature
Density and Ocean Circulation
• Temperature, salinity
• Themocline and pycnocline separate water
masses
• Upper or surface and deep
– surface T & S vary with latitude, season
– deep constant
Wind and Ocean Circulation
Surface water mass in constant motion via
waves and currents
• Waves – Energy transport, not molecules
– no horizontal transport
•Currents transport huge volumes of water
across vast distances
- result of from major wind bands and
Coriolis Force
Waves
• Movement of energy only
• Function of wind speed, fetch duration
• Propagate away from origin
• Wave length – distance between crests
• Period – time for 2 crests to pass
• Wave passage generates motion to depth
of ~ ½ WL (“wave base”)
• Each 1/9 of WL, orbit diameters drop by
½, so by ½ depth motion imperceptible
Waves
• Bottom slows energy passage
• WL declines, height increases
• At 1.3x wave height wave breaks, releases
energy
Wind systems and currents
• Temperature differences tropics to poles
generate winds
• Unequal heating
– Sun angle: oblique at poles
– Albedo (reflectiveness): high at poles
– Both reduce light absorption and heat build
up
• Atmosphere and ocean move heat from
tropics
Coreolis effect
Coriolis Force
• The effect of earth rotation on the
direction of the wind.
• two reasons,
• 1- system of latitude and longitude fixed
to a rotating earth, so our frame of
reference for a free-moving object above
the Earth is constantly changing.
• 2 - the amount of turning about a vertical
axis varies from a maximum at the poles
and minimum at the equator.
Deflection: a missile from the North Pole to
Equator; Earth, and the target, has rotated,
so it appears that the missile has changed
direction.
The deflection works the same way for an
east-west wind, the path will curve to the
right as it moves across the surface.
Coreolis effect - wind
• Speed of rotation – movement away from
poles decreases rotational speed
• Deflection due to earth’s rotation –
northward moving deflects wind eastward
• No Hemisphere – deflect to right,
Southern, to left
Three-cell circulation model
•considers effects of coriolis force due to the
Earth’s rotation.
•Northern and Southern Hemisphere are
each divided into three cells of circulation,
each spanning 30 degrees of latitude.
•Equator, 30° North and South, and 60°
North and South.
•Hadley, Ferrel, polar cells
•Heat transfer away form equator by
atmosphere
Hadley Circulation
• Tropical air rises, creates low pressure
system below
• Low level cool air moves in from higher
latitudes to replace it
• Warm air travels to poles, cools, becomes
more dense, sinks
• Hadley cell
Primary circulation cells and prevailing
wind belts of Earth
Surface currents
• a large mass of continuously moving oceanic
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water
~40 named currents
Do not move in direction of wind
Interaction of Coriolis effect, wind and land
masses
– wind friction on water – uneven sea surface, starts
water moving
– Coriolis effect deflection
– contact with the continents deflect currents, creating
giant oceanic current circles or gyres.
Gyres
– Direction – counterclockwise northern
Hemisphere
– Indian Ocean exception
– West, east sides of gyres
– Temperature transfer N-S profound
impact
– Spiral gyres “pile up” water in center
– Antarctic circumpolar current –
westerlies blow uninterrupted
– Narrow weak counter currents separate
gyres - Equatorial countercurrent
Subsurface flows
• 90% of water mass movement
• Density driven
• Arctic and Antarctic model
– Deep and bottom water, ice melt
Eckman Spiral
– each sheet of
water drags on
the one below
– net transport is
90o to right
(northern
hemisphere) of
the wind direction