Transcript Chapter 15

Chapter 15
Section - 1
Factors that Influence Ocean
Currents
• Ocean currents are masses of ocean water that flow
from one place to another
• surface currents develop from friction between the
ocean and the wind that blows across its surface
o some currents are short- lived and affect
only small areas

these are a response to local/seasonal
influences
o other currents are relatively permanent
that extend over long areas of the oceans
• the major horizontal movements of surface water is
closely related to the general circulation pattern of
•
Ocean Circulation Patterns
Gyre = the large circular surface current pattern found in each ocean
o eg, North Pacific Gyre
 the center of each gyre coincides with the subtopics at about 30
degrees North or South latitude, so they are often called
subtropical gyres
 there is a correspondence between the direction of surfacecurrent flow and the major wind belts of the world
 subtropical gyres rotate clockwise in the Northern Hemisphere,
and counterclockwise in the Southern Hemisphere
this is because wind generates surface currents, as well
as...
o the Coriolis Effect
 the deflective force of Earth's rotation on all freemoving objects, including the atmosphere and
oceans
there are four main currents within each gyre
if an object is dropped into a gyre it would take about six years to go
completely around
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•
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More Ocean Circulation Patterns
• the circular motion of gyres leaves a large
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central area that has no well-defined
currents
o in the North Atlantic, this zone of calmer
waters is known as the Sargasso Sea,
named for large amounts of Sargassum, a
type of floating seaweed
Indian Ocean is influenced by summer and
winter monsoons
o when the winds change direction, the
surface currents also change direction
Ocean Currents of the World
Ocean currents
•
Ocean currents
Warm currents- move from low to high latitudes (move heat from warmer to
cooler areas)
 North American current keeps Great Britain and western Europe
warmer than would be expected based on their latitude
Cold currents- move from high to low latitudes( moderate temperatures in
tropics and mid-latitudes)
 Benguela Current (western Africa), Peru Current, California
Current
 Cause fogs and droughts/deserts along the west coast of
continents ( Atacama, Namib)
 Maintain Earth’s heat balance- ¼ heat transported from tropics
to poles is transported by water, the rest is by wind
Peru Current
"GS103 - Lecture Outlines Sp08." GS103 - Lecture Outlines Sp08. Web. 22 May 2013.
<http://nsm1.nsm.iup.edu/hovan/classes/GEOS103_OL_sp08.html>.
Upwelling
• Upwelling is the rising of cold water from
layers below the surface.
o Induced by wind
o Brings nutrient rich water to the surface
 Supports marine organisms
• Most common on west coasts
o Most distinguished: California, Western South
America, and West Africa
• Cause of upwelling
o Coastal winds and Coriolis effect cause
surface water to move away from the shore
Upwelling
• Cause of upwelling
o Cold water from below replaces warmer
surface water

Results in lower surface temperatures
• For example, Atlantic temperatures in August are
21°C or higher and Pacific temperatures are 15°C
Deep-ocean Circulation
• Deep ocean Circulation is governed by
gravity and driven by density differences
- Density differences are caused by
temperature and salinity differences.
Because of this Deep-ocean circulation is
often also called thermohaline
circulation.
-Density differences cause denser
water to sink and slowly spread out
beneath the surface
Deep-Ocean Circulation
• Deep-ocean currents
-Deep-ocean currents are created when
the water involved with thermohaline
circulation begins in high latitudes at the
surface and then sinks.
-The water at high latitudes was there
because the salinity, the amount of salt in
the water, of the cold water increased due
to sea-ice formation.
Thermohaline Circulation
Thermohaline Circulation. 2011. Photograph. N.p
Various Components of the Coastal Zone
Shorelines Are Dynamic-
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topography
geologic makeup
climate
Shore-
area that extends between the lowest tide level and the highest
elevation on land that is affected by storm waves
Shore is divided into two parts Foreshore-area exposed when the tide is out and submerged
when the tides in
 Backshore-landward of the high tide shoreline. Usually dry,
being affected by waves only during storms
Two other zones Nearshore Zone-lies between the low tide shoreline and the line
where waves break at low tide
 Offshore Zone-seaward of the nearshore
Shoreline-
line that marks the contact between land and sea
Various Components of the Coastal Zone
Coast-extends inland from the shore as far as ocean related features can be
found
Coastline-marks the coast's seaward edge, whereas the inland boundary is
not always obvious or easy to determine