Primary Fields of Oceanography
Announcements
-Not quite done with exams. (Will need to work on
them this weekend.)
-ESCI 322: Bellingham Bay sampling – we’re on, but it
will be cold and wet. Meet at Taylor St dock.
Geology
Sediment
erosion
deposition
Chemistry
Water depth
Basin geometry
Circulation pattern
mixed-layer depth
upwelling
-Second problem set due Nov. 3rd
Physics
Biology
Light attenuation
Bottom topography
Pressure gradients, Coriolis,
and wind-driven circulation
Physical Oceanography
Patterns of Ocean circulation
I. Pressure gradients and geostrophic flow
II. Wind-driven circulation
III. Surface currents
IV. Weird currents
a. Antarctic circumpolar current
b. Equatorial convergence and divergence zones
c. Greenland-Iceland-Norwegian Seas
V. Upwelling and El Nino
VI. Recent advances in physical oceanography
I. Geostrophic flow:
(Pressure-gradient, coriolis balance)
II. Wind-driven circulation
Ekman spiral
Ekman depth
(opposite of surface
current direction)
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Balance of forces on a water parcel moving at constant velocity
in the Northern Hemisphere
Pressure gradient terms
Pressure gradient
Geostrophic flow
Velocity
• Barotropic fields
• Baroclinic fields
Isobars and isopyncnals parallel
Isobars and isopyncnals inclined
Coriolis
Friction
Wind-driven
flow
Coriolis
Wind stress
Velocity
Sea surface
Isobar
Isopycnal
Level surface
Locations: 1
2
Calculating the baroclinic component
of geostrophic flow from salinity and
temperature distributions
Distance offshore (km)
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Water depth (m)
Water depth (m)
Velocity
Force
Direction of flow (out of screen)
Blue (negative velocity) is into the page
Red indicates low velocity
Distance offshore (km)
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Large-scale patterns of atmospheric circulation
Polar Cell
Ferrel Cell
Hadley Cell
Why doesn’t the Antarctic circumpolar current turn left?
In northern hemisphere
In southern hemisphere
Pressure Gradient
Sea-surface slope
Downwelling
Upwelling
Convergence
Divergence
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Terrigenous
Abyssal clay
Siliceous radiolarian ooze
Siliceous diatom ooze
Calcareous ooze
Image from: http://wps.prenhall.com
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North Atlantic Deepwater formation and East Greenland Current
Pressure, wind and flow in EGC (from Hopkins 1991)
Patterns of water flow and dynamic
height in Greenland, Iceland, and
Norwegian Seas:
New current discovered in Greenland sea
Largest Nordic dense-water plume to feed the ocean conveyor
Top: Surface circulation
Bottom left, computed sea-surface
height (dynamic height)
East Greenland Current
Bottom right, temperature at 200 m
Below, figure from textbook
North Icelandic jet
Våge et al. Nature Geoscience 2011
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Ocean circulation
• Rules of thumb:
– Geostrophic flow
• Water moves right of pressure gradient in NH
• Water moves left of pressure gradient in SH
– Wind-driven flow
• Surface water moves ~ 45° right of wind in NH (left in SH)
• Average flow 90° right of wind in NH (left of wind in SH)
Numerical simulations of ocean
circulation
Computed sea level + satellite altimetry
• Example: NASA’s perpetual ocean
• http://svs.gsfc.nasa.gov/vis/a010000/a01080
0/a010841/3827_Perpetual_Ocean-540MASTER_high.mp4
Westward intensification and skewed “mounds” within gyres
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Thermohaline circulation (Formation and transport of water masses
in the deep ocean)
Atlantic:
N. Atlantic Central water
(9oC, 35.3 %o)
N. Atlantic Deep Water
(2.5oC, 35.03 %o)
Gr/Ic/Nor Sea Deep Water
(-0.5oC, 34.9%o)
Some of the water sources for NADW.
Caballing:
NADW sinks in winter, assisted by wind-driven evaporative cooling.
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south
Pacific Ocean
Top 1000 m
Top 1000 m
Atlantic Ocean
T
S
T
S
Neutral density
γn
O2
γn
O2
north
south
north
south
north
south
north
Neutral density (γn) across
the Atlantic from W to E
(Florida to West Africa)
Flow to north
Dashed line: hypothetical
level surface
Flow to south
Baroclinic pressure
gradient direction
Plot from WOCE dataset
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Coastal Upwelling
• Patterns are due to combination of wind,
coriolis and pressure
• Net results:
– Delivery of cold, nutrient-rich water to the
shoreline
– Enhancement of coastal productivity
ENSO – El Nino/La Nina
Southern Oscillation
Upwelling off WA state
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El Niño Southern Oscillation
ENSO – El Nino/La Nina Southern Oscillation
• El Niño:
–
–
–
–
–
–
Reduction in trade winds
Sea-level rises in E. Pacific, drops in W. Pacific
Pycnocline deepens in E. Pac, shallows in W. Pac
Surface water warms in E. Pac.
Flooding in E. Pac, coral bleaching in W. Pac
Droughts in Asia (W. Pac) because rain falls over
Pacific Ocean before making land fall
– Relatively mild, dry winter in WA state
ENSO – El Nino/La Nina
Southern Oscillation
•
•
•
•
Data from latest NOAA report
Current research topics:
Satellite oceanography – Ocean surface topography
Current conditions: El Nino
Little snow at Mt. Baker this winter
Don’t buy a season pass.
What about The Blob?
– Warm high pressure and water in N Pacific
facilitates development of El Nino.
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Satellite oceanography – Surface wind field
From microwave measurements of sea-surface roughness
Surface wind-velocity field from satellite images of surface waves
Satellite oceanography – Sea-surface temperature
Important topics in physical oceanography:
Weather forecasting – winds, currents and sea surface temperature
Global climate change – heat and mixing in the ocean
Coupled physical-biological models of the ocean
Coastal processes – coastal erosion, sediment transport
Climate change effects on circulation, mixing and sea ice
Model of ocean circulation (NOAA, NASA):
http://svs.gsfc.nasa.gov/vis/a010000/a010800/a010841/3827_Perpetual_Ocean-540-MASTER_high.mp4
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Fukushima-derived 134Cs
134Cs
in water
134Cs
in organisms
Computer simulation of the spread
of radioactive 137Cs from Fukushima
From Buesseler et al. PNAS 2012
Behrens et al. Env. Sci. Res. Lett. 2012
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