Class 28: Oceanography

Class updates:  Reading: Section , , 16.5 Today’s topics:  Ocean water  Ocean currents  El Nino/La Nina Class 28: Oceanography

 Continents: green/tan avg. height 840m  Oceans: blue avg. depth 3800m, cover 66% planet The Oceans

 Mostly Chlorine (Cl), Sodium (Na)  Minor amounts: SO 4, Mg, Ca, K  Dissolved salts ~4 % Ocean Water Composition

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 Salty Origin

Ocean is not getting saltier, so where?  Shells/hard parts:  Chemical sediments: clays, oozes Where do ions go?

Ocean salt balanced by:  Balancing Water (red) Rain Stream input Evaporation  Balancing Salt (purple) River/volcanic input Reduction by sediments and hard body parts Salt Balance

Salinity = amount of salt in the water Factors for balance change over Earth Salinity of Ocean Surface

Shallow surface mixed zone (< 450 m) Transition zone (< 1500 m thick) Deep zone Changes with depth

Shallow surface mixed zone –mixed by wind and currents –Uniformly warm –Generally higher salinity (surface evaporation) Top: Mixed Zone

Transition zone (< 1500 m thick) –Temperature decreases rapidly - thermocline –Salinity decreases rapidly - halocline Middle: Transition Zone

Bottom water –Very cold, near freezing < 4˚C –Relatively low salinity Bottom: Deep Zone

Thermocline narrow at poles Thermocline-top ~ 30, equator From North to South

Ocean conveyor belt surface bottom Water is moving

Warm water cools in North Atlantic Cold water sinks: cold = densest The Water Pump

Cold water sinks and flows south along bottom: Atlantic Deep Water

Conveyor Belt = simplified Actual surface flow in currents Surface Currents

Map flow with oceanographic instruments Current flow is more complex: turbulence Adding complication

Persistent winds push water Subtropics: Trades (from E) Mid latitudes: Westerlies Currents and Winds

Why do winds and currents go East or West?

Coriolis Effect Anything moving from equator (look along arrow) bends to the right

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

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

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

Southern Oscillation El Nino and La Nina are the extreme hot and cold parts of the Southern Oscillation cycle