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Basic
Structures and Dynamics |
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Ekman transport |
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Geostrophic currents |
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Surface
Ocean Circulation |
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Subtropicl gyre |
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Boundary current |
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Deep
Ocean Circulation |
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Thermohaline conveyor belt |
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Upper
Ocean (~100 m) |
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Shallow, warm upper layer where light is abundant and where most
marine life can be found. |
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Deep
Ocean |
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Cold,
dark, deep ocean where plenty supplies of nutrients and carbon exist. |
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Temperature |
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warm
on the upper ocean, cold in the deeper ocean. |
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Salinity |
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variations
determined by evaporation, precipitation, sea-ice formation and melt, and
river runoff. |
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Density |
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small
in the upper ocean, large in the deeper ocean. |
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Currents are in geostropic balance |
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Each gyre includes 4 current components: |
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two
boundary currents: western and eastern |
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two
transverse currents: easteward and westward |
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Western boundary current (jet stream of ocean) |
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the fast, deep, and narrow current moves warm water polarward (transport ~50 Sv or greater) |
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Eastern boundary current |
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the
slow, shallow, and broad current moves cold water equatorward (transport ~
10-15 Sv) |
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Trade wind-driven current |
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the moderately shallow and broad westward current (transport ~ 30
Sv) |
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Westerly-driven current |
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the wider and slower (than the trade wind-driven current) eastward
current |
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Western Boundary Current |
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Gulf
Stream (in the North Atlantic) |
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Kuroshio Current (in the North Pacific) |
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Brazil Current (in the South Atlantic) |
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Eastern Australian Current (in the South Pacific) |
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Agulhas Current (in the Indian Ocean) |
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Eastern Boundary Current |
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Canary
Current (in the North Atlantic) |
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California Current (in the North Pacific) |
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Benguela Current (in the South Atlantic) |
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Peru Current (in the South Pacific) |
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Western Australian Current (in the Indian Ocean) |
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Mixed Layer |
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Currents
controlled by frictional force + Coriolis force |
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à
wind-driven circulation |
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à Ekman
transport (horizontal direction) |
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à
convergence/divergence |
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à
downwelling/upwelling at the bottom of mixed layer |
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Thermocline |
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downwelling/upwelling
in the mixed layer |
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à pressure
gradient force + Coriolis force |
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à
geostrophic current |
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à Sverdrup
transport (horizontal) |
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The Equatorial
Counter Current, which flows towards the east, is a partial return of water
carried westward by the North and South Equatorial currents. |
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Evaporation: Extremely cold, dry winter air enhances
evaporation from the relatively warm ocean è increase salinity in
the ocean. |
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Formation
of Sea Ice: When sea ice forms, salts are left in the ocean è increase
salinity |
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Surface Water |
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to
a depth of about 200 meters |
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Central Water |
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to
the bottom of the main thermocline |
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Intermediate Water |
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to
about 1500 meters |
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Deep Water |
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below intermediate water but not in |
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contact with the bottom |
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Bottom Water |
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in
contact with sea floor |
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Once a water parcel is removed from the surface
layer its temperature and salinity do not change until it rises back up to
the surface again, usually many years later. |
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Water masses with well-defined temperature and
salinity characteristics are created by surface processes in specific
locations, which then sink and mix slowly with other water masses as they
move along. |
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Water masses are always identified by capitals.
For example, "Bottom Water" can stand for Antarctic, Arctic, or
other Bottom Water but always refers to a water mass, while water found at
the bottom of an oceanic region may be
referred to as "bottom water" without implying that it is
a known and well defined water mass. |
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Theoretically, there should be 6 types of air masses (2
moisture types x 3 temperature types). |
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But
mA-type (maritime Arctic) does not exist. |
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cA: continental Arctic |
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cP:
continental Polar |
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cT:
continental Tropical |
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mP:
maritime Polar |
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mT:
maritime Tropical |
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Thermo è
temperature |
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Haline è salinity |
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If we
date a water parcel from the time that it leaves the surface and sink into
the deep ocean |
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è Then the youngest water is in the deep north
Atlantic, and the oldest water is in the deep northern Pacific, where its
age is estimated to be 1000 year. |
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the
waters in the deep northern Pacific. |
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The
man-released CFC and the chemical tritium and C14, which were
released through atmospheric atomic bomb test in the 1950s and 1960s,
entered the deep ocean in the northern Atlantic and are still moving
southward slowly. |
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Those
pollutions just cross the equator in the Atlantic è They
have not reached the deep northern Pacific yet!! |
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If the
warming is slow |
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The
salinity is high enough to still
produce a thermohaline circulation |
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The circulation will transfer the heat to deep
ocean |
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The warming in the atmosphere will be deferred. |
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If the
warming is fast |
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Surface ocean becomes so warm (low water density) |
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No more thermohalione circulation |
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The rate of global warming in the atmosphere
will increase. |
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One
major climate effect of sea ice is to seal off the underlying ocean from
interaction with the atmosphere. |
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Without
an sea ice cover, high-latitude oceans transfers large amount of heat to
the atmosphere, especially in winter. |
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With an
sea ice cover, the heat flux into the atmosphere is stopped. In addition,
the ice surface absorbs little incoming solar radiation. Winter air
temperature can cool 30°C or more near a sea-ice cover. |
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The Antarctic Ice Sheet holds the equivalent in
seawater of 66 meters of global sea level. |
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The Greenland Ice Sheet holds the equivalent of
6 meters of global seawater. |
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Ice cores retrieve climate records extending
back thousands of years in small mountain glaciers to as much as hundreds
of thousands of years in continental sized ice sheets. |
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The antarctic ice sheet has layers that extend
back over 400,000 years. |
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The Greenland ice sheet has layers that extended
back 100,000 years. |
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This hypothesis argues that millennial
oscillations were produced by the internal interactions among various
components of the climate system. |
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One most likely internal interaction is the one
associated with the deep-water formation in the North Atlantic. |
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Millennial oscillations can be produced from
changes in northward flow of warm, salty surface water along the conveyor
belt. |
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Stronger conveyor flow releases heat that melts
ice and lowers the salinity of the North Atlantic, eventually slowing or
stopping the formation of deep water. |
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Weaker flow then causes salinity to rise,
completing the cycle. |
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