Ocean Life zones
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 (summer)
Davidson Current flows towards continental shelf (warm…short lived)
Which of these two would produce a strong upwelling?
Temperature variations
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
Ocean Exploration
HMS Challenger (Late 1800’s)
First expedition funded to exam deep ocean
Mission:
Physical conditions of deep sea (temp, salinity, depth, light)
Chemical composition of water and sediments at different depths
Distribution of life in oceans based on
temperature, dredges, depth, samples
1920’s….Echo Sounder
After WWI, how sound waves move through water were explored more fully
Discovered they behave similar to light waves
Refract, reflect and speed
Echo Sounders
Sold commercially to keep ships from running aground
Help to lay the first telegraph line underwater (1922)
1924 suggested could be used to find fish schools
By WWII used by subs in military
Reflection and refraction of sound creates shadow zones in ocean
After WWII
Glomar Challenger Phase I and II (1966 & 1967)
Deep sea drilling project
Drilled into ocean crust
Age of crust
Distribution of ocean crust
Oil reserves
Multibeam sonar, remote sensing and submersibles
New Ocean drilling project just getting underway
What did they find…
Large volcanic mountain chain in oceans
Age distribution of rocks along ridge….
Magnetic anomalies of rocks along ridge
All indicate ridges are spreading from center
Leads to the idea of seafloor spreading
Mid ocean Ridge systems
If floor is spreading, are the ocean basins getting bigger?
Theory of Plate tectonics is developed due to the ocean floor research in the 60’s and 70’
Fundamental theory for Geology…
Theory of plate tectonics
Earth’s crust or surface is broken into many plates that move and interact with each
other.
Three ways plates can interact
Pull away from each other
Divergent boundaries
Come together
Convergent boundaries
Slide by each other
Transform boundaries
Mid Ocean ridges are divergent boundaries
Two plates moving away from each other
Volcanic eruptions form new oceanic crust
Most divergent boundaries are found in the ocean
Transform boundaries
Mid ocean ridge does not erupt continuously and how much it erupts varies from
place to place
As one part of the ridge erupts an others don’t, fractures occur forming transform
boundaries
Two plates sliding by each other
Most transform boundaries are found in the ocean
Convergent boundaries
Two plates coming together…
Three different things can happen depending on what type of material or crust is
involved
Continental Crust:
Density: ~2.8 g/cm3 Thickness: ~30-70 km
Oceanic Crust:
Density: ~3 g/cm3 Thickness: ~5-15 km
Convergent boundaries often destroy (recycle) crust that is created at divergent
boundaries
Oceanic to Oceanic Convergence
One plate will push under the other in a process known as subduction
As plate subducts, volcanoes form on over-riding plate…volcanic island arc
Also creates deep ocean trenches where two come together
Deepest part of the ocean
35,838 ft or ~7 miles below surface of ocean
Video Clip (8min)
http://www.extremescience.com/zoom/index.php/videos/146-challenger-deep-video
Oceanic to Continental Convergence
Oceanic crust is more dense and thinner than continental so ocean crust is subducted
under continental
Creates volcanoes on over-riding plate and trenches but not deep trenches
Continental to Continental Convergence
Continents collide…neither subduct
Forms VERY large mountains
Other regions of the ocean….
Continental Shelf
Submerged part of the continent
Very gentle slope and wide
Economically important
Fisheries
Off shore drilling
Mineral resources
Submarine Canyons
Often cut into Continental shelves and slopes
Thought to be formed by landslides and rivers
Continental Slope
Represents edge of continent
boundary between continental crust and oceanic crust
slope between 5-25o
very narrow feature
Continental Rise
Found at the base of the slope
Accumulate of turbidity deposits
Ocean Sediments
Terrigenous: Derived from land
Found ocean wide with finer sediments away from shorelines
Biogenic: Derived from organisms
Shells and skeletons
Calcareous oozes--> shallow water deposit due to deep cold water being acid
Siliceous oozes--> deep water deposits
Phosphates--> teeth and bones of critters
Hydrogenous: precipitated from water
limestone
Manganese nodules (economical resource)
Abyssal Plain
Flat region that covers about 70% of ocean floor.
Fine sediments comprised of terrigenous mud and organic debris
Seamounts and Guyots
Volcanic structures/cones
Often created at ridges
Guyots are flat topped due to wave action