Download Bathymetry

Bathymetry and Sea Floor Topography
CBGS Marine Science
Sara Beam
Bathymetry is the study of the depth
of the oceans and the topography of
the sea floor
• Sea Floor
topography is a
function of the
plate tectonic
processes
shaping the
earth’s surface.
• At spreading
centers we find
oceanic ridges
• At subduction
zones we find the
greatest ocean
depths- trenches.
Ocean depths have corresponding
ecological zonation
Cross sectional view of the
Atlantic passive margin
• Coastal plain--Continental shelf-Continental shelf---shelf break---slope--rise---Ocean floor
This is an image of a
the spreading center
called the
Mid-Atlantic ridge
This is a picture of the
pillow basalts that
come out of the
spreading center.
So how fast is
the sea floor
spreading ?
• A theoretical model of the formation of magnetic striping.
New oceanic crust forming continuously at the crest of the
mid-ocean ridge cools and becomes increasingly older as
it moves away from the ridge crest with seafloor spreading
: a. the spreading ridge about 5 million years ago; b. about
2 to 3 million years ago; and c. present-day. Kios and
Tilling, 1996, Dynamic Earth, USGS
The African Rift Valley is a new
spreading center being born!
(extends from Lebanon in the north to Mozambique in the south)
California’s Central Valley and the San
Andres fault are NOT spreading centers; the
SA is a transform fault, where NA plate is
sliding along the Pacific plate
The Peru Chile
trench is easily
seen here
This is an area of
intense subduction
where the Nazca
plate is being
detroyed and is
pushing up the
Andes mountains
in the process.
Note the very narrow
continental shelf at
the active coastal
margin, wide shelf
at passive margin
• The Aleutians
and the
Islands of
Japan are two
island arcs
formed by the
subduction of
oceanic crustthis is why
there is so
much seismic
activity in
Alaska and
Japan !!
• (and tsunamis
in the Pacific!)
Seamounts are submerged volcanoes
more than 1000m above sea floor
• Seamounts
can stand
alone or
more often
in island
arcs or
chains- like
the
HawaiianEmperor
Chain
Coral atolls are the visible
remnants of volcanic islands
The Hawaiian Islands are formed by a “hot
spot”
• Hot spots are
formed when
magma wells up
from deep in the
mantle and
breaks through
the ocean crust,
resulting in
island chains.
This magma is
different from
island arc
because it
comes from
deep in the
Earth’s interior.
• In the old days, ships had
to go out and make manual
soundings with lines and
lead weights OR in this
map, they ran transect lines
of the coast with early
sonar and plotted them on
navigational charts like this
• Bathymetric images
can clearly outline
the features on the
continental shelf and
show us the deep
holes, shoals, the
channels.
• mouth of Bay of
Fundy
• Northeast Channel
• Stellwagen/Georges
Banks
Submarine canyons form
during the active history of a
plate margin
• Monterey Canyon is a
major conduit of
terrigenous sediment
from land out to sea
• Hatteras Canyon may be
a drowned river valley
from lower sea level
**Note the narrow vs. wide
continental shelves
Active coast- narrow shelf
Passive coast- wide shelf
Sonar
Methods
• Multibeam
• sidescan
• This image
of the sea
floor was
created
using
multibeam
bathymetric
sonar
• bumps and dips in the
ocean surface are
caused by minute
variations in the earth's
gravitational field. For
example the extra
gravitational attraction
due to a massive
mountain on the ocean
floor attracts water
toward it causing a local
bump in the ocean
surface; a typical
undersea volcano is
2000 m tall and has a
radius of about 20 km.
This bump cannot be
seen with the naked eye
because the slope of the
ocean surface is very
low. These tiny bumps
and dips in the geoid
height can be measured
using a very accurate
radar mounted on a
satellite
Gravity= G m1*m2
d2
So we can use sonar to map sea floor
bathymetry, but how can we find out
what’s going on down there ?
• Sonar technology sees hard rocks.
• Submersibles and cameras can only look at
pinpoint locations in the deep sea…
• How can we study life on the bottom of the
ocean in the deepest places effectively ?
• How do we find hydrothermal vents ?
Cross sectional view of sea floor spreading.
Hydrothermal vents occur at spreading centers
and the breaks in the crust are faults where
adjustments to the crust occur.
http://www.onr.navy.mil/Focus/ocean/habitats/vents1.htm
• http://www.youtube.com/watch?v=rFHtVRKoa
UM&feature=related
The Discovery of HTV’s is one of
the greatest modern discoveries
which may help to explain the
origins of life on Earth.
Extremophiles
• http://video.nationalgeographic.com/video/player/environm
ent/habitats-environment/oceans/hydrothermal-vents.html
Two Modes of Primary Production
on Earth
Chemotrophs are organisms that obtain
energy by the oxidation of electron donating
molecules in their environments.
One of the greatest mysteries
yet to be solved…
• How do these vent organisms colonize
new hydrothermal vents ?
• Vents are ephemeral, they turn on and
off, they may only persist for a short
time (evolutionarily)
• How do organisms spread there
colonists over thousands of miles in the
deep ocean ??????