Music today:
Little Mermaid, “Under the Sea”
WELCOME OSU MOMS!!
Deep Ocean Circulation
Motion in the Ocean, Part 2, or
Who wants to ride the Great
Conveyor Belt?
Surface Circulation
How does the Deep Ocean
respond to Surface Circulation?
 The
main gyres move heat and salt
 Resulting DENSITY variations lead to
vertical flow (sinking)
 Formation of “water masses”,
characterized by Temperature,
Salinity
Density Variation in Sea Water
North Atlantic Circulation
Density-Driven Water Flow
 Called
“Thermohaline Circulation”,
because temperature and salinity
together determine density of
seawater
“Thermo” = temperature
“haline” = salt
Where does the Ocean’s
Deepest Water Come From?
 The
densest seawater is cold and salty
 This is formed at high latitudes in the
North and South Atlantic:
North Atlantic Deep Water (NADW)
Antarctic Bottom Water (AABW)
Density Rules!
Underwater “Waterfalls”
Water Masses
and ocean
mixing
Thermohaline Circulation
The Great Conveyor Belt
Semi-Enclosed Basins:
Mediterranean Water
Mediterranean Water
Mediterranean Water
Tracking Motion (direction & velocity)
fixed
mobile
Consequences of Global Flow
Consequences of Global Flow
 Ocean
turnover is about 1500 years (time
for a round trip on the conveyor belt)
 Deep water (made in the polar Atlantic)
contains abundant O2 and CO2
 The high O2 content promotes oxidation of
bottom sediments (e.g., CaCO3)
 The CO2 content controls CCD (Carbonate
Compensation Depth)
Carbonate Compensation Depth
(CCD)
Cold,
acidic, salty
Cold,
acidic, salty
Carbon Cycle and Global Warming
 The
temperature of bottom water formation
determines how much CO2 is dissolved in
deep ocean water
 The rate of overturn of the oceans
determines the “burial rate” of C from the
atmosphere
 Organic C accumulates in sediments,
depending on the O2 content of deep ocean
Carbon Cycle and Global Warming
 Organic
C in sediments is reduced to
CH4 (methane gas)
 Methane gas migrates upward and can
be trapped as frozen “gas hydrates”
near the ocean floor
Gas Hydrates
“Salem Sue”
New Salem, ND
Gas Hydrates
Gas
Hydrates:
Ice w/fuel and
fire inside
Light w/match
Gas Hydrates
Hydrate Ridge
Image courtesy of Ocean Observatories Initiative Regional Scale Nodes Program, UW
Hydrate Ridge
Yaquina Bay,
Newport
Image courtesy of Ocean Observatories Initiative Regional Scale Nodes Program, UW
Hydrate Ridge
Image courtesy of Ocean Observatories Initiative Regional Scale Nodes Program, UW
Climate Change Concerns
 What
happens when sea level falls?
 What happens when deep water warms?

What about underwater landslides & earthquakes?
 All
of these liberate gas hydrates (CH4),
which combines with O2 to form CO2,
ultimately reaching the atmosphere
Deep Ocean Circulation
 The
ocean has an enormous capacity to
absorb and release greenhouse gases
 So, the rate, temperature and
composition of seawater circulating
through the deep ocean is vitally
important in assessing long term climate
change