Transcript Chap 2-4: Earth

Chap 2-4: Earth
Shape of the planet
Size of the planet
Orientation to the Sun
Distribution of land & sea
Reference frames
Map Projections
Shape of Ocean Basins
Plate Tectonics (shaper of
ocean basins)
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Chap 2-4: Earth
Earth is an “oblate
spheriod:” equatorial
radius is 21 km
greater than polar
R ~ 6400 km
Rotation axis runs
north-south through
the poles
 points “up” from
north pole and has
magnitude of 1/day
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Chap 2-4: Earth
On the surface,
we use latitude
and longitude
coordinate
reference
system
There are 111
Latitude “Parallels”
km per degree
of latitude but
the spacing
between
degrees of
longitude varies
with latitude
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Longitude
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Chap 2-4: Earth
Longitude
reference is
arbitrary but
convention
defines a
specific
longitude
through
Greenwich
Longitude
Time is also
referenced to Prime “Meridian”
in Greenwich, England
“Greenwich
Mean Time” or
GMT
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Chap 2-4: Earth
Earth rotates on its
axis 15˚ each hour-to
determine longitude
requires knowing the
time of local noon
relative to GMT
(latitude could be
determined by
measuring the
angle between
the horizon and
the north star)
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Chap 2-4: Earth
Today the Global Positions System
(GPS) satellite network makes
location determination easy
worldwide
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Chap 2-4: Earth
Today the Global Positions System
(GPS) satellite network makes
location determination easy
worldwide
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But make sure you have
the correct datum!
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Chap 2-4: Earth
equatorial
cylindrical
(includes
Mercator)
Map Projections
Related topics:
contour lines or isopleths
topography & bathymetry
physiographic (3-D) views
simple polar conic
Upcoming topics:
plan/map views
(vertical) sections
profiles
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polar tangent plane
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Chap 2-4: Earth
Bathymetric Chart: Contour lines connect areas of constant depth
Contours could also be called “isobaths”
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3-D, Shaded-Relief Map
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Chap 2-4: Earth
Water Planet: 71% of Earth’s surface
Northern Hemisphere: 60%
“Continental”
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Southern Hemisphere: 80%
“Maritime”
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Chap 2-4: Earth
Surface area per 5˚ of
latitude
Note:
1) no area at poles
2) ocean area is
dominant, particularly
in s. hemisphere
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Chap 2-4: Earth
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The Hydrological Cycle: where is the water?
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Chap 2-4: Earth
The Hydrological Cycle: where is the water?
Related topics:
Budgets (water budget here; heat budget later)
Residence Time = Volume Reservoir/Rate of Filling
 m 3 
units:  3 1  sec
m sec 
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Chap 2-4: Earth
Pacific
Atlantic
Indian
Arctic
Major Ocean
Basins
-we also refer to the
“Southern Ocean,”
which circles the
globe around
Antarctica
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Chap 2-4: Earth
Major Ocean
Basins
mean depth = 3729m
(~4000m)
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Chap 2-4: Earth
Major Ocean
Basins
mean depth = 3729m
(~4000m)
much of Earth’s surface
is covered by ocean
with depth of about
4000m-6000m
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Hypsographic Curve
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Chap 2-4: Earth
Looking ahead: we want to memorize the components of the
continental margin; First: we’ll look at the geological factors
that have created them
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Chap 2-4: Earth
The Earth
a.k.a. “pac man”
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Chap 2-4: Earth
There is a difference in
composition and density
between continental and
oceanic crust
Thicker, lighter continental
crust “floats” like an iceberg
on the mantle
Isostacy=vertical equilibrium
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Chap 2-4: Earth
Isostacy: Columns of crustal material are unequal in height and
density but generate the same pressure at the same depth
within the mantle
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Chap 2-4: Earth
Part 1: Continental Drift
Alfred Wegner proposed in
1912 that the shape of the
continents appear to fit
together (others before him
had also noted this)
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Chap 2-4: Earth
Part 2: Sea Floor Spreading; Proposed by Harry Hess (1962)
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Chap 2-4: Earth
SPECIAL DATES:
MPA meeting…6 Jul
R/V Pt Sur Cruise…14 Jul
R/V Pt Sur Cruise…25 Jul
Exam-1 (definite)...2 Aug
Exam-2 (Tentative)…1 Sep
Labor Day Holiday...5 Sep
Final Exam...19 Sep
(Sp-226, 1300-1450)
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OC3230 Calendar, Summer 2005
version 13 July 2005
EX 1
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Chap 2-4: Earth
Evidence for sea floor spreading
Distribution of Seismic Activity
Magnetic Reversal Patterns
Age Patterns of Oceanic Crust (related to magnetic reversals)
Sediment Thickness Distribution
Heat Flow Distribution
Direct (GPS) Measurements of Crustal Movement
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Chap 2-4: Earth
Evidence for sea floor spreading
Earthquake epicenters
for 1961-1967
Observed to occur on
“plate boundaries”
depth <100 km
Note: difference
between plate boundary
and coastline
depth >100 km
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Chap 2-4: Earth
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Evidence for sea floor spreading
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Chap 2-4: Earth
Evidence for sea floor spreading
The magnetic time scale:
Pattern of reversals is tied to dates
when molten rock cooled
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Chap 2-4: Earth
Evidence for sea floor spreading
Age of
oceanic
crust
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Chap 2-4: Earth
Evidence for sea floor spreading
Sediment thickness increases away from the mid-ocean ridge
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Evidence for sea floor spreading
Heat decreases away from the mid-ocean ridge
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Chap 2-4: Earth
Global topography from gravity anomalies
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Chap 2-4: Earth
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Chap 2-4: Earth
Million km2
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Chap 2-4: Earth
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Chap 2-4: Earth
Most plate boundaries are at sea
or at a land-sea boundary
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Chap 2-4: Earth
Most plate boundaries are at sea
or at a land-sea boundary
But not all!
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Chap 2-4: Earth
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Chap 2-4: Earth
Convergent Plate Boundaries
Horizontal distance to volcanic activity
(melting of crust) depends on angle of
subducting plate
If the boundary is between continental
and oceanic crust, can have parallel
mountain chains formed inland (e.g.,
Cascade Mountains, Andes Mountains)
or as an Island Arc offshore (e.g.,
Japan)
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Chap 2-4: Earth
Active margins are
found at plate
boundaries
Passive margins,
such as the north
American east
coast, are landsea margins that
occur within a
tectonic plate
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Chap 2-4: Earth
Transform Margins have
fault zones as a results of
sideways motions
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Chap 2-4: Earth
Its our fault!
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Chap 2-4: Earth
Locations of major hot spots
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Chap 2-4: Earth
Locations of major hot spots
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Chap 2-4: Earth
Island/Seamount chains produced by hot spots is one of
the most important indicators of historical plate motions
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Spreading rates: 1-20 cm/yr
Max rates along East Pacific
Rise
Average rate about 5 cm/yr
(similar to fingernail growth)
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Chap 2-4: Earth
MARS
NEPTUNE
Ocean sciences are investing $$ in
cabled observatories
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Chap 2-4: Earth
Global topography from gravity anomalies
(measured by altimeter)
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Chap 2-4: Earth
Acoustic methods
replaced old weighted
lead line techniques with
the 1925 Meteor
Expedition; Today, we
have satellite and
airborne laser (LIDAR)
Side-Scan Sonar
(provides depth and
Single depth trace from echo reflectivity data)
sounder, such as 12kHz unit
Previous: Multi-Beam
on R/V Pt Sur-first used on
Sonar
Meteor Expedition
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Chap 2-4: Earth
CA shelf and slope has been
mapped with variable resolution
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Chap 2-4: Earth
Elkhorn Slough (LIDAR Survey)
Tidal creek,
salt marsh,
and mudflat
habitats
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NOAA/USGS
Coast ©Survey
Data
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Chap 2-4: Earth
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NOAA/USGS
Coast ©Survey
Data
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Hill
Chap 2-4: Earth
Side-scan
sonar data
Multi-beam
sonar data
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CSUMB
images Seafloor
Copyright Mapping
© McGrawLab
Hill
Chap 2-4: Earth
Topography profiles at various latitudes: reflect major mountain
ranges and mid-oceans ridges
What about “typical” ocean margin?
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Chap 2-4: Earth
Shelf Break (~130m) is critical point at the junction between
continental and oceanic crust
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Chap 2-4: Earth
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Continental Shelves of the World (sort of)
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Chap 2-4: Earth
Shelf width varies in
our region from about
50 km in the Gulf of
the Farallones (San
Francisco area) to,
essentially, 0 km off
Big Sur
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Chap 2-4: Earth
Scale of topography in Monterey Submarine Canyon is
comparable to the Grand Canyon
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Chap 2-4: Earth
Deep-Ocean Features
(seamount)
Deepest areas are
the trenches that
are associated with
convergent margins
(11,020 m max in
Mariana Trench)
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Chap 2-4: Earth
Abyssal plain areas
(4000 - 6000 m)
(everywhere that mid
ocean ridges are
not)
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Chap 2-4: Earth
Sediment Cover
Coastal
Origin
Also:
Lithogenous vs
Biogenous sediments
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Ocean
Origin
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(low productivity region)
(high productivity region)
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Chap 2-4: Earth
foraminifera
(calcareous)
radiolarians
(siliceous)
(high productivity region)
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Chap 2-4: Earth
Box Corer
Grab Samplers
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Chap 2-4: Earth
Gravity
Corer
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Piston Corer
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Chap 2-4: Earth
Paleoceanography studies the history of
the oceans and climate looking at the
sediment record
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Chap 2-4: Earth
At finer scales, ocean bottom type is important to marine habitat
characterization and to shallow water acoustics
Seafloor Habitats
Rocky Reefs
Intertidal Zones
Sandy or soft bottoms
Underwater Pinnacles
Submarine Canyons
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