Download Ocean Floor

Exploring the inner and
outer shells of earth
Earth consists of a
series of concentric
layers or spheres
which differ in
chemistry and
physical properties.
Chemical
Layers
Physical
Layers
Physical state is determined
by the combined effects of
pressure and temperature.
• Increasing pressure raises the melting
point of a material.
• Increasing temperature provides additional
energy to the atoms and molecules of
matter allowing them to move farther
apart, eventually causing the material to
melt.
• Both pressure and temperature increase
toward the center of the Earth, but at
variable rates.
How do we learn about the inner
structure of the planet?
Seismology is the study of elastic waves
that travel through the earth
Two main wave types:
Compression waves (Pwaves): travel by
squeezing and
expanding medium they
travel through. They can
travel through both
solids and liquids (e.g.,
sound waves).
Shear waves (S-waves):
travel by shearing
medium they pass
through. S-waves can
travel only through solids
since particles need to be
bonded to each other to
propagate wave (similar
to a bull whip)
Earthquake are an incredible
source of seismic waves
•
Seismic waves
travel along there
quickest route,
generally
through, the
planetary interior
to the seismic
stations, changing
speed every time
material
properties
change.
Reconstructing the internal
structure of the planet
•
Combining information
from many seismic
waves we can get a
detailed internal
structure of the earth.
•
Crust & upper mantle:
large increases in
seismic velocities and
density
•
Mantle: Gradual velocity
and density increase
•
Outer core: dramatic
density increase and no
S-waves
•
Inner core: Jump in
density and P-wave
velocity, S-waves return
Other planets?
Seismic Velocity and Density
solid
solid,
more dense
Liquid Iron
solid Iron
Earthquakes produce waves in the
ocean
Sea level:
RISE
FALL
Courtesy: K. Satake, unpublished
World Seismicity
(1898-2003)
Mw ≥ 6.0
Mw ≥ 7.7
Many
large earthquakes
along subduction
zonesevents
Most “Great”
earthquakesoccur
are subduction
mega-thrust
The Physiography of the North Atlantic Ocean Floor
continental
margins
deep ocean
basins
midoceanic
ridges
Type of continental margins
Continental margins are the submerged edges of the
continents and consist of massive wedges of sediment
eroded from the land and deposited along the continental
edge. The Continental Margin can be divided into three
parts: the Continental shelf, the Continental slope, and the
Continental rise.
Passive
Continental Margin
Transport of sediments from the shelf to the
continental rise
• Deep Ocean Province is between the
continental margins and the midoceanic
ridge and includes a variety of features
from mountainous to flat plains: Abyssal
plains, Abyssal hills, Seamounts, and
Deep sea trenches.
Deep Ocean Basin
• Midoceanic Ridge Province consists of a
continuous submarine mountain range
that covers about one third of the ocean
floor and extends for about 60,000 km
around the Earth.
Midocean Ridge
Hydrothermal Vents
03_13a
WHY DO LAND AND OCEAN EXIST?
Geologic Differences between
2-3
Continents and Ocean Basins
Continents and ocean basins differ in
composition, elevation and physiographic
features.
• Elevation of Earth’s surface displays a bimodal
distribution with about 29% above sea level and
much of the remainder at a depth of 4 to 5 kilometers
below sea level.
• Continental crust is mainly composed of granite, a
light colored, lower density, igneous rock rich in
aluminum, silicon and oxygen.
• Oceanic crust is composed of basalt, a dark colored,
higher density, volcanic rock rich in silicon, oxygen
and magnesium.
Geologic Differences between
Continents and Ocean Basins
WHY DO LAND AND OCEAN EXIST?
OCEANIC CRUST = THIN AND DENSER
CONTINENTAL CRUST = THICK AND LITHER
• Continents are thick (30 to 40 km), have
low density and rise high above the
supporting mantle rocks.
• Sea floor is thin (4 to 10 km), has greater
density and does not rise as high above the
mantle.
Oceanic Crust Versus Continental Crust
altimetry
Satellites in orbit around the planet use radar altimetry to measure
the height of the sea level (accuracy of 2 cm).
http://www.ecco-group.org/animations_iter21/TP_ps21.mpeg
Model of the shape of the Earth
geoid: The equipotential surface of the Earth's gravity field which best fits, in a
least squares sense, global mean sea level (MSL)
http://www.esri.com/news/arcuser/0703/geoid1of3.html
Why ocean bathymetry?
Ocean Circulation and Climate
Heat Transport affected by topography!
Ocean Circulation and Climate
Ocean Currents take different paths!
Ocean Circulation and Climate
Deep ocean mixing and pathways
Ocean Circulation and Climate
Mixing energy and dissipation of tides!
Social impacts:
Tsunami
Social impacts:
Gas and oil extraction
Evidence of Global Warming in
the Climate System:
Glacier melting
• Kilimanjaro: ice caps are 80% gone since early
1900’s
• All glaciers in tropics are melting rapidly
• Impacts: water supply, power generation,
tourism, local climate and ecology
Arctic - the most sensitive ecosystem?
• Arctic sea ice has shrunk by 1 million sq km and thinned from
3.1m to 1.8m average
– More freshwater, reduced ability to travel over ice
– All summer ice gone in this century
• Ecological consequences huge!
Arctic warming
• Sea ice melting
– Key feedback! (animation)
Reduces albedo (reflectivity) of earth,
allowing more radiation to be absorbed
http://www.gsfc.nasa.gov/topstory/2003/1023esuice.html
• Warming temperature
– Melts permafrost
– Ice sheet stability? Key sea level
question!
• Rate of warming 8x faster in last 20
years than in last 100
1979
2003
Arctic ecosystems impacts
• Reduced ice: less algal production
under ice = undermines base of food
chain
• Seal pups emerge just when ice is
melting - earlier melt means they
are exposed before ready to thrive
• Caribou need ice to island-hop;
they are falling through as ice thins
• Polar bears hunt on ice in winter,
retreat to land in summer. Less ice
forces them onto land earlier
Higher sea level…
•
As water warms, it expands (“thermal expansion”).
• Glaciers are melting
• Observation: 3mm/yr in past few decades
• Prediction: ~0.5m rise by the end of this century, 2-4m in 500 years
This will have a major impact on
•Developed coastal regions
•Low-lying island nations
•Intensity of coastal flooding during
storm surges
•Coastal ecosystems (e.g. mangroves,
estuaries)
More intense
storms…
Hurricanes get their energy
and staying power from warm
water in the tropical oceans.
As waters get warmer, we
expect that hurricanes will
become more intense.
Significant change not yet
observed.
Oceanography and Climate - millenial timescales
Vertical circulation of the ocean
MOVIE:
The Day After Tomorrow
Oceanography and Climate
Climate changes are defined to occur
on different space and time scales.
What makes it interesting is that
processes happening on different
temporal and spatial scales are not
separable and interact with each other
 COMPLEXITY and NONLINEARITY
WHY?
The ocean has a very long memory.
We will learn about this, and about the mechnism
of interaction between ocean-atmosphere-landecosystems.