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Class 28: Oceanography
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Class 28: Oceanography
Class updates:
 Reading: Section 15.1-15.3,
16.1-16.2, 16.5
Today’s topics:
 Ocean water
 Ocean currents
 El Nino/La Nina
The Oceans
 Continents: green/tan
avg. height 840m
 Oceans: blue
avg. depth 3800m,
cover 66% planet
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Ocean Water Composition
 Mostly Chlorine (Cl), Sodium (Na)
 Minor amounts: SO4, Mg, Ca, K
 Dissolved salts ~4 %
Salty Origin
Dissolved ions come from:
 Chemical weathering:
Rivers dump 2.5 billion
tons/yr of dissolved salts
 Volcanic activity:
-outgassing: sulphur, bromine
-hydrothermal circulation:
hot water dissolving rocks
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Where do ions go?
Ocean is not getting saltier, so where?
 Shells/hard parts:
 Chemical sediments:
clays, oozes
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Salt Balance
Ocean salt balanced by:
 Balancing Water (red)
• Rain
• Stream input
• Evaporation
 Balancing Salt (purple)
• River/volcanic input
• Reduction by sediments
and hard body parts
Salinity of Ocean Surface
Salinity = amount of salt
in the water
• Factors for balance
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change over Earth
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Changes with depth
• Shallow surface mixed zone (< 450 m)
• Transition zone (< 1500 m thick)
• Deep zone
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Top: Mixed Zone
• Shallow surface mixed zone
–mixed by wind and currents
–Uniformly warm
–Generally higher salinity (surface evaporation)
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Middle: Transition Zone
•Transition zone (< 1500 m thick)
–Temperature decreases rapidly - thermocline
–Salinity decreases rapidly - halocline
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Bottom: Deep Zone
• Bottom water
–Very cold, near freezing < 4˚C
–Relatively low salinity
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From North to South
• Thermocline narrow at poles
• Thermocline-top deep @ ~ 30, thicker @ equator
Water is moving
Ocean conveyor belt
• Warm @
surface
• Cold @
bottom
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The Water Pump
• Warm water cools in North Atlantic
• Cold water sinks:
cold = densest
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Atlantic Deep Water
• Cold water sinks and flows south along bottom:
Surface Currents
• Conveyor Belt = simplified
• Actual surface flow in currents
Adding complication
• Map flow with oceanographic instruments
• Current flow is more complex: turbulence
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Currents and Winds
• Persistent winds
push water
• Subtropics:
Trades (from E)
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• Mid latitudes:
Westerlies
Currents and Winds
• Why do winds and currents go East or West?
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Coriolis Effect
• Anything moving from equator (look along arrow)
bends to the right
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El Nino-Step 1
• NORMAL CONDITION:
• Trades (E to W) push water to W Pacific
• W Pacific water = warm, E Pacific = upwelling cold
• Air over warm water rises
• Air over cold sinks
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El Nino-Step 2
• EL NINO CONDITION:
• Trades (E to W) push less
• Thermocline flattens: less upwelling cold water
• Rain moves E:
– Australia/Indonesia
dry
– Peru/Central Am wet
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El Nino-Step 3
• LA NINA CONDITION:
• Trades (E to W) push extra hard
• E Pacific = more upwelling cold
• Air over warm water rises
• Air over cold sinks
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Southern Oscillation
• El Nino and La Nina are the extreme hot and cold
parts of the Southern Oscillation cycle
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