Introduces Oceanography: oceanic plates, continental shelf, abyssal plain, trenches, hydrothermal vents, black smoke, temperature stratification, water masses and circulation, coriolis effect, el nino, larvae and larval ecology.

1. Semester 1
Aug – Dec 2012

2. • Study of all the aspect of the physics,
chemistry, geology and biology of the sea.
• 5 major oceans: Arctic (smlst), Pacific
(lgst), Atlantic, Indian and the Antarctic
Oceans.
• Oceans cover more than 80% of the
Southern Hemisphere and only 61% of the
Northern Hemisphere.
• Oceans also have several seas including
Caribbean, Bering, Mediterranean, Baltic,

4. • At the end of the landmasses, the ocean is
very shallow due to the extension of the
continent – continental shelf
• The continental shelf slopes from shore to
depths of 100-200meters and can extend
offshore for up to 400km.
• At the far end of the shelf, there is an
abrupt steepening of the bottom called the
continental slope.
• Descending lower to about 2-3km is the
continental rise.

6. • At 4-5km, the bottom becomes flat,
extensive, sediment-covered now called
the abyssal plain. This is what covers most
of the oceans at depths between 3 & 5km.
• Abyssal plains are broken in several
places by various submarine ridges. These
have been found in all oceans and is a
contiguous chain.
• Example: Mid-Atlantic ridge (separates the
Atl ocean i/o east & west)

7. • Occasionally, the ridges break the surface
& form islands.
• They also mark the boundaries of the
various crustal plates of the Earth and are
sites of volcanic activity.
• In certain areas, the abyssal plains are cut
by deep, narrow troughs called trenches
that lie in an arc bordering the islands &
continents in the Pacific ocean.
• Trenches- depths from 7000 to more than
11000m.

9. 1 – Geothermal fields producing electricity
2 – mid-ocean ridges crossed by transform faults (transversal fractures)
3 – subduction zones (subdecting plate bends downwards

10. • Lge divisions in the Earth’s crust bounded
by ridges and trenches – plates
• Sizes of the plates vary; 7 plates cover the
Earth.
• Plates are ridged and float on the mantle
covering continental and oceanic crust.
• b/c of the slow, continuous mov’t of the
plates over geologic time, the continents
may take up different positions over time –
continental drift.

11. • Plates move b/c the oceanic ridges are
centres of volcanic activity where new
material is formed & added to the crust.
• As volcanism takes place, the plates move in
opposite directions causing seafloor
spreading.
• The opposite would happen in trench systems
where the margin of 1 plate dives beneath the
other – subduction. The subducting crust
melts i/o the mantle once again.
• Oceanic ridge sys & subduction zones of the
trenches are sites of volcanic & seismic

13. 1 – Cold seawater seeps down thru cracks i/o the
ocean floor
2 – The water seeps further down & the T raises to
350-400 degrees C & reacts w/ the rocks as it is
heated.
3 – Hot liquids are less dense & thus, more buoyant
than cold liquids. Hydrothermal fluids rise up thru
the ocean’s crust carrying dissolved metals &
hydrogen sulfide w/ them.
4 – The hydrothermal fluid pushes up thru the
chimney & mixes w/ the cold seawater.
HYDROTHERMAL VENT

14. • The chemical rxns in #2 (prev slide) change the
water in the following ways:
• Removal of oxygen
• Becomes acidic
• Picks up dissolved metals including iron, copper & zinc
• Picks up hydrogen sulfide
• The metals carried in the hydrothermal fluids mix
with sulphur to form metal sulfides (black
minerals) & give the hydrothermal fluid the
appearance of smoke.
http://www.divediscover.whoi.edu/vents/vent-infomod.html#

15. •

16. • Based on the surface ocean Ts & the overall
distribution of organisms, 4 major biogeographical
zones can be established:
• Polar
• Cold temperate
• Warm temperate (subtropical)
• Tropical (equatorial)
• The zones are not absolute since their boundaries may
vary with season
• Surface waters in Tropical regions are warm (20-30°C)
thruout the yr, while the surface water in temperate
zones are warm only in the summer

17. • The T begins to fall below the surface water &
rapidly decreases as 50-300m is passed
(thermocline – depth zone of the most rapid T
decline)
• T also has an effect on the density of sea water:
• Warm sea water is less dense than cold sea water of
the same salinity
• Increase in salinity causes an increase also in density
• The rapid change in T that produces the
thermocline suggests that the seawater changes
rapidly over the same depth range producing
then a zone of rapid density change called the
pycnocline

19. • Upper water mass – surface water mass; all well-
mixed water above the thermocline
• In constant motion due to winds blowing across the
surface of the water, earthquakes, volcanic explosions &
underwater landslides
• The winds produce 2 kinds of motions: waves &
currents
• Waves range in size from ripples only a few centimetres
in height to storm waves 30m high
• Wavelength is the horizontal distance btw the tops of
crests of successive waves
• Earthquakes, volcanic explosions & underwater
landslides create tsunamis
• The attraction of the moon and the sun create the waves

20. • Wave height in the open ocean is dependent on:
1. Wind speed
2. The distance, or fetch, over which the wind blows
3. The duration that the wind blows
• Currents are water movts that result in the horizontal
transport of water
• The major shallow ocean currents are produced by wind belts
in which the winds are steady & persistent in direction
• These winds are caused by differential heating of the
atmospheric air masses, aided by the Coriolis Effect
• Northeast trade winds blow from northeast to southwest btw
the equator, while southeast trade winds move air from the
southeast to the northwest
• Westerlies blow from the southwest to the northeast in the
Northern hemisphere & to the southeast in the Southern
hemisphere, while the easterlies blow cold air towards the
equator (diagram of wind belts)

23. • A phenomenon having to do with the sea-air
interaction on a global scale
• Occur several times each decade & begin in the
tropical Pacific
• Warm water builds up in the western pacific &
moves eastward across the Pacific bringing
warm water to the coasts of South America
which are normally cool due to upwelling
• The influx of warm water is related to the
weakening of the winds @ the equator

24. • Now the higher Ts all across the Pacific in turn
changes the atmospheric circulation so that the
terrestrial areas that normally receive little rain
are rainy & rainy areas undergo droughts
• In the marine envt, the increased Ts change
shallow-water marine communities & the
distribution of spp
• Is also destructive on coral reefs due to an
increase in T

25. • Deep water masses – below thermocline
extending to the bottom
• Are not dependent on the wind; when seawater
increases in density, it sinks
• To move water into the deep basin of the oceans,
the density must be increased at the surface
• This is accomplished in 2 ways:
1. Losing heat:
• Warm water from the tropics or subtropics is high in salinity due
to evaporation; this warm saline water is transported out of the
Tropics by the Gulf Stream where it meets cold water in
Greenland & Iceland’s Labrador Current that is moving south
• Cooling at the surface increases the density of this highly
saline water & so it sinks to form the North Atlantic deep water
• Warm water moving south in the Atlantic loses heat to the
atmosphere causing the water masses to sink

26. 2. Becoming more saline
• Very high density water mass produced in the Weddell Sea in
Antarctica became more saline when winter freezing occur
• The water sinks to become the bottom water of most ocean
basins
• Since these waters are cold & produced @ the surface,
they contain large amounts of oxygen which is then
transported to the depths. W/o this oxygen deep water
would be anoxic
• The ocean conveyer belt is due to the temperature &
salinity differences in the ocean water that produce
vertical & horizontal surface & subsurface ocean
currents
(See page 17 for diagram in Figure 1.15)

27. • A lge # of marine organisms produce larvae in their
lifecycles
• Larvae are independent, morphologically different stages
that develop from fertilized eggs that must undergo a
profound change before assuming adult features
• They are almost always smaller than the adult stages
• These are important b/c they establish and maintain
many marine communities & associations
• In any given marine habitat, the distribution & abundance
of benthic invertebrates are maintained by 4 factors:
• Larval recruitment
• Migration
• Asexual reproduction
• mortality

28. • Many benthic communities are composed of spp that
reproduce by producing various larval types that undergo a
free-swimming, drifting or crawling stage in the water
column or on the bottom before metamorphosing in benthic
adults
Larval types & Strategies
• There are 3 paths that a benthic invertebrate may take for
development:
• To produce very many small eggs which hatch quickly i/o larvae that
are free swimming in the plankton. They depend on food sources in
the water column for nutrition & are called planktotrophic larvae
• To produce fewer eggs & give each more nrg in the form of yolk. This
allows the larvae to become settled quickly & are called
lecithotrophic larvae
• To produce few eggs with a large amount of yolk. This involves long
dev’t w/o additional nrg sources. The young passes thru the larval
stages in the egg & hatch as juveniles. These are called nonpelagic
larvae or juveniles

29. • Adv of planktotrophic larvae:
- a lge amt of young can be produced w/ the given
nrg
- wide dispersal is assured thru the long time spent in
the plankton
• Disadv of planktotrophic larvae:
- larvae depend on the plankton for nutrition, thus
allowing the larvae to be exposed to predators
• Adv of lecithotrophic larvae:
- spends less time in the plankton, thus less chance
of being consumed
- do not depend on the plankton for nutrition
• Disadv of lecithotrophic larvae:
- b/c of the amt of nrg that must be placed i/o each
egg, fewer eggs & larvae are produced
- is a larger target for predators
- short time in the plankton = less time to disperse

30. • Adv of the nonpelagic larvae:
- reduces the planktonic mortality to zero
• Disadv of the nonpelagic larvae:
- only a few eggs can be produced
- there is no dispersal
• In polar waters, nonpelagic devt is common
although productivity & confined to a narrow
summer peak
• Lecithotrophic are also common in conditions
similar to those in polar waters
• Planktotrophic larvae are common in tropical
waters bec planktons are high in abundance

31. • Larvae have the ability to “test” the substrate that they land
on
• If it is not suitable then they find 1 that is suitable
• They prefer substrates that already have adults living there
• They are attracted to the pheromones released by the
adults & so they find substrates that are in close proximity
to the adults
• Some larvae can even delay their metamorphosis if they
do not find a suitable substrate, but at some point, they will
metamorphose whether or not they find a suitable
substrate to land on
• They also respond to light, pressure & salinity….. Some
larvae prefer certain pressure & light & so live in certain

32. • Most marine communities are comprised of species
having a free swimming larval stage with the exception of
polar waters.
• Organisms here depend on the settlement of larvae,
while adults only live a short time – how do organisms
survive?
• Wilson [1952] concluded that larval settlement and
metamorphosis is dependent on environmental stimuli such as
light, gravity, and fluid movement.
• Larvae are able to ‘test’ the substrate before settling down to
metamorphose. This means certain substrate will always be
suitable while others will not.

33. • Larvae also respond to the presence or absence of adults
of their own species. They are attracted by the adults’
pheromone [presence of adults suggests suitability of
habitat].
• Larvae of many invertebrates are able to delay their
metamorphosis for a certain period until they find suitable
substrates.
• After certain time, the larvae will metamorphose whether
it finds suitable substrate or not.
• Larvae also respond to other physicochemical factors
such as light, pressure, and salinity.
• Many free floating organisms are positively phototactic in
their early stages of their larval life, making the upper,
faster moving waters more suitable for living.

34. • Later, they become phototactic and migrate toward the
bottom.
• Some, however, are highly sensitive to light and pressure
and inhabit only certain levels in the water column.
• Most studies favour the hypothesis that larvae select their
habitat, however, most of these studies have been done in
the lab where there is still water.
• Along with the still water limitation, there is also the
different timing for reproduction making the time in the
plankton different.

35. • Physical and chemical
differences -