World’s Oceans
Formed ~3.8 billion years ago
primarily by volcanic out gassing and comets
Largest to smallest: Pacific, Atlantic, Indian
Covers ~ 70% of earth’s surface
Circulation of water…
Two primary current circulation for ocean water
Surface currents
Deep water currents
Surface Currents
Driven Primarily by wind
Moves surface water around
Warm water and cold water currents
Surface currents of the Atlantic
Gulfstream flows along the coast of N. America
Warm water current
Keeps Europe from icing over
Turns into Canaries current along Africa
Current Oil spill in Gulf of Mexico (2010).
Problems with size of spill and potential fouling of Mississippi, Alabama and
Florida
Florida current could take it into the Gulf Stream
Pacific Ocean Currents
California current is cold water current found in the NW during the Summer
Davidson current is a warm water current that dominates coast in winter
What are Gyres and what is the cause of them?
Caused by continental land masses and coriolis effect
Coriolis Effect
Apparent turning of large bodies of fluid on earth due to the rotation of the earth.
Fluids in N. Hemisphere turn to the right
Fluids in S. Hemisphere turn to the left.
Air masses and oceans are deflected by the effect
Deep Ocean Currents
Circulation of water vertically due to density differences
What two properties could change the density of water?
What are some places on earth we could see these changes occurring?
Temperature
How does temperature affect water density?
Warmest areas?
Coldest areas?
Thermocline: change of temperature with depth
Salinity
Where is the salinity the greatest?
Where is it the lowest?
Why?
Halocline: change of salinity with depth
Pycnocline: change of density with depth
Why is there layering in the arctic
Which is more dense fresh water or salt water?
Thermohaline circulation
Deep ocean circulation
Mixes ocean waters
End
of Lecture Thursday 5/6/10
Review:
Deep water currents
Move vertically due to density differences
Salinity and temperature
Cold/salt water sinks in polar regions (high Latitudes) and “pulls” surface water
Rises back to surface in Pacific as it warms
Surface Currents
move primarily due wind
Create gyres in ocean
Warm and cold water currents
Affected by Coriolis effect
More details about currents and gyres
Why do surface currents actually move.
Wind is only one factor (more on how winds develop later)
Coriolis effect is another factor
Causes Ekman Spiral
Wind moves surface water fastest
Water below surface receives energy from layer above and only some of the energy is
transmitted so slower motion
Less energy/motion each layer effectively turns the water and net motion is 90o from
wind direction
Gyres form “hills” of water due to spiral
Creates geostrophic currents
A current or flow that is balanced between the Coriolis force and gravitational
pull
Boundary Currents
Rotation of the earth pushes gyres to the west of the ocean basins and creates a
faster flow on the western edge.
Eastern boundary currents: Move slower
Western Boundary currents move faster
In regions of the eastern boundary currents, upwelling often occurs
Vertical movement of water due to surface currents
Provides nutrient rich areas with high biodiversity
Ocean Life Zones
Upwelling is important as it provides nutrients to many of the upper life zones we
find in the oceans
What controls life in the ocean?
Light: (photic = light)
Euphotic zone:
near suface--> photosynthesis can occur
Dysphoric zone
Very low level light
Aphotic zone:
no light at all--> is there life?
Temperature
Waves and currents mix water
Layer of uniform temperature ~200m thick
below zone of mixing temperature drops quickly
Thermocline--> change from warm to cold
Salinity
proportion of dissolved salts to pure water
Why is the ocean salty?
Varies for different regions
Salinity based on evaporation rate or freshwater input
near surface higher salinity--> creates halocline
glacier formation/melting, rain, rivers, evaporation
These parameters control life zones in the ocean and the organisms that exist.
Intertidal zones
Well mixed water
Light and warm temperatures
Pelagic regions
Open ocean where organisms swim or float
Different organisms and regions based on temp, light and salinity
Benthic zones
Benthic zone: ocean bottom
Deep ocean floor
Very cold, low oxygen, & few nutrients
Primarily filter feeders
…and Mid-ocean ridges
Quick overview of Plate tectonics
Earth surface/crust is divided into sections or plates
Plates move around and interact with each other
Ocean contains Most of the earth’s plate boundaries
2 plates move apartà divergent boundary à mid-ocean ridges
2 plate slide by each otherà transform boundaries
2 plates convergeà can push one plate under another in a process known as
subduction
How are life zones affected by variations in ocean?
California Current vs Davidson Current
Ca. Current is eastern boundary current that flows away from continental shelf
Davidson Current flows towards continental shelf
Which of these two would produce a strong upwelling?
Temperature variations
Normal temperature ranges for oceans in pacific
Surface winds (trade winds) push warm water to the western pacific and create
upwelling along N. America and S. American coastline
El Nino Year…
Trade winds lessens and allow warm water to migrate to the east side of the
pacific.
Upwelling dies down
Storm tract follows warming current.
West Coast Dead Zones
Low oxygen zones
Creates areas where organisms suffocate
What causes Dead Zones
Possible Ideas
Extreme upwelling
Deep low oxygen ocean water pulled to surface by stronger than normal
winds
Possible caused due to global climate change
Bacterial and Algae mats due to high nitrates
Lowering oxygen