Unformatted text preview: Atmosphere & Circulation
Atmosphere & Circulation
What goes around comes around Questions Questions • Can water freeze at extreme ocean depths? No. • The salt content depresses the freezing point. BUT it does freeze at the surface in the Arctic & Antarctic!
If density changes sound speed how can sonar be accurate at extreme depths. It can’t be 100% accurate, and the SONAR has to approximate based on speed of sound at estimated water temperature/ salinity & pressure Thermocline….what depth it ends Thermocline….what depth it ends at?
• Hard to say exactly where it ends and deep water begins. This is an arbitrary estimation. Basically just remember that the thermocline is a zone if RELATIVELY rapid temperature change with depth Can fish with air bladders get Can fish with air bladders get bends?
• Yes, catch one with a fishing pole and if you raise it to the surface too fast, its stomach is popping out of its mouth
• Cosmogenous sediments? I didn’t mention them because they are rare at bottom of ocean. These are small amounts of cosmic dust and dust from meteorites and asteroids. Are dense colder waters more Are dense colder waters more buoyant than lighter warmer waters? No, just the opposite! • How deep can humans go without having •
• pressure crush the body
free dive (Francisco Ferreras)............................417ft 127m
Do deep water organisms see colors other than blue light? Generally no, but some have eyes to see bioluminescence (sort of light blue) and there is even some red bioluminescence Calories and water temperature?
Calories and water temperature?
• A calorie (little c) is a unit of energy and to raise water temperature you need energy. 1 calorie needed to raise 1 ml water 1 degree C.
• A Calorie used to express energy in food is a Kilocalorie (1000 calories). What is point of Secchi Disc?
What is point of Secchi Disc?
• It is a simple way to tell how clear water is. • Plankton and sediment reduce clarity.
Example: in 1968, the Secchi depth in Tahoe was 102.4 ft. In 2005 it was 72.3. Last year 67.7. This is because of nutrients entering the lake plus sediments from “development”. By containing nutrients it is hoped the clarity will get better. Water Density
• The colder that seawater is, the denser it is.
• The saltier it is, the denser it is.
• Salt content and temperature are the two main determinants of water density
• What temperature does seawater freeze at? Depends on salinity. Seawater of 35 PSU freezes at 1.8 C (28.9 F) Why Dead Sea so salty?
Why Dead Sea so salty?
• Remember that Dead Sea not connected to ocean. It is 89 X saltier than ocean. In ancient times the Red Sea dumped into the Dead Sea and salts deposited after water evaporated.
• Red Sea is connected to ocean and is salty because of high evaporation and low freshwater input. Halocline/Thermocline….how do Halocline/Thermocline….how do they relate?
• Usually can be totally unrelated. Thermocline is • • just below mixed layer, but halocline can be almost anywhere.
Why no thermocline near poles? Because surface waters warm up very little because little sunlight. Also storms mix the water preventing stratification
Another ice age? Yes, someday. Not in our lifetimes! We’re on a warming trend What does nm stand for (used What does nm stand for (used when talking about visible light wavelength)?
• This means nanometers. A nm is one •
billionth of a meter
100 Centimeters in a meter
10 mm in a centimeter
1000 um (micrometers) in a milimeter
1000 nm in a um CO2 in seawater? Where does it CO2 in seawater? Where does it go?
• We will learn about the “Biological Pump”
• CO2 dissolves from the air into seawater, then phytoplankton take up the CO2 in photosynthesis. Eventually the phytoplankton are eaten by zooplankton etc. and this carbon slowly falls to the deep as fecal pellets or exoskeletons etc where it stays for thousands of years. SOFAR vs SONAR
SOFAR vs SONAR
• SOFAR is the sound channel at about 1000 m • where sound speed is slow and which traps sound in the channel so it can be heard over long distances
SONAR is a system for measuring depth or detecting fish or submarines. It uses sound “pings” and measures distances by timing how long it takes for the echo to come back. More
• Need to bring books to class? No
Are all lectures on iLearn? Yes
Law of Constant Proportions? Just means that the ratios of salts to one another in ocean is always the same even if the total salinity goes up or down.
• Go Over Thermocline & seasonal changes
• Go over refraction & marchers in the sand Light Refraction
• Air and water have different refractive indexes, so light bends when going through water, relative to its path in air. Thermocline
• Strong thermocline when there is high warming of surface waters. In winter, when less sunlight, thermocline is weaker or not existent The sun’s energy reaching the The sun’s energy reaching the Earth is either reflected or radiated • Input of energy to earth from sun is balanced by •
• the loss to space. If it were not in balance we would be either heating up (as is slowly happening from global warming) or cooling down. About 30% of incoming short wave radiation is reflected by the atmosphere, clouds & land. The major heat loss from the earth leaves as long wave radiation (it leaves as heat rather than light). • Because the earth is a sphere, higher (polar) latitudes receive less energy from the sun per area of earth surface than lower (equatorial) latitudes.
• Thus we have atmospheric & water temperature differences between these two areas. This sets up a convection cell circulatory pattern • Warm air rises at the equator, and cooler, dense air is drawn in from more polar areas to replace the warm air.
• The replacement air then heats up, becomes less dense and rises.
• This is a giant CONVECTION CELL. • A Convection Cell circulates air or water due to temperature/density differences from one area of the cell to another. Convection Current can be
demonstrated in an aquarium • There is more heat loss to space at the poles than there is at the equator.
• Tropical regions have a surplus of energy.
• This surplus energy is carried by atmospheric circulation to the poles where it is lost by radiation. Next slide shows global surface Next slide shows global surface temperature
• Note that the land can be colder or warmer than the water.
• This is because water is slower to warm or cool than the land. Coriolus force
• Because of the rotation of the earth, atmospheric •
• and oceanic circulation becomes more complex.
Coriolus force deflects moving objects to the right in the northern hemisphere and to the left in the southern.
For example, the cities of Buffalo & Quito are on the same line of longitude but they travel at different speeds as the earth rotates. Since Quito is where the earth’s circumference is wider, it moves at a faster speed. If there was a war between Quito and If there was a war between Quito and Buffalo and cannons were shot at each city, what would happen to the cannonballs? • Because Quito’s cannonball is already going • about 1000 mph in an eastward direction and is heading toward a slower traveling Buffalo, the cannonball is deflected to the right
And because Buffalo’s cannonball is traveling more slowly eastward as it heads toward faster traveling Quito, it also is deflected to the right! Another explanation
• What happens to a rolled ball on a spinning disc? Airplane
compensate SO what effect does this have on SO what effect does this have on water and air movements?
• Basically, water and air that are moving are always going to be deflected to the right in the N hemisphere and to the left in the S. hemisphere.
• More on this later! Convection cells
• The earths atmospheric circulation (convection) • cells are broken up into Hadley Cells between the Equator and temperate areas, and Ferrel Cells, between temperate and Boreal areas.
Rising air results in high rainfall. Descending air is dry. Thus rainforests are where air rises and deserts are where it descends. Note the dry Sahara Desert & Middle Note the dry Sahara Desert & Middle East and the rainforest in the equatorial area. How do these areas relate to the Hadley Cell? Winds
• The NE Trades are found under the Hadley Cell.
• Horse latitudes (doldrums) are areas of weak winds and are where the air descends.
• Prevailing Westerlies are under the Ferrel Cells These winds affect the circulation These winds affect the circulation of the oceans
• BUT, because of the Coriolus force, water doesn’t go in the same direction as the wind. When the Norwegian oceanographer Nansen was When the Norwegian oceanographer Nansen was frozen into the Arctic ice for 3.5 years (in 1890s), he had a lot of time to watch the ice. • The ship, the FRAM is now in a museum in Oslo. Nansen
Nansen Ekman Spiral
• Nansen noticed that when the wind blew over •
• pieces of loose ice, they moved at about 45 o to the right of the wind direction.
When he got home he asked a physicist friend, Ekman, about this, and Ekman explained what was happening (because of Coriolus force).
Because the direction water is deflected turns more to the right as you go deeper in the water, overall, Ekman transport moves water 90o to the wind. Along coast of California wind Along coast of California wind blows mainly from the north toward the south • Transport of surface water is to the right, moving •
• water offshore.
Cold water from the depths rises to the surface to replace the water pushed offshore (UPWELLING).
This cold water from the depths is nutrient rich, and it stimulates photosynthesis by phytoplankton.
The cold water also chills the air and causes fog Both the wind and the California Both the wind and the California current move from N to S along our coast.
• Ekman Transport moves surface water westerly, thus causing upwelling. • Because Coriolus force deflects to the left in the Southern Hemisphere, Ekman Transport is to the left there Note the cold (red) water upwelling Note the cold (red) water upwelling off South Africa Note the cold (blue) water Note the cold (blue) water upwelling off our coast Cold (blue) upwelled water off Cold (blue) upwelled water off northern California Upwelling: NW Africa, SW Africa, Upwelling: NW Africa, SW Africa, Peru, W coast USA
• Yellow/red = high productivity Langmuir Circulation Cells. Wind Langmuir Circulation Cells. Wind blowing on water can set up small convection cells On a windy day it is easy to see these On a windy day it is easy to see these cells. Buoyant material and foam collects in lines where the water sinks. Indian Ocean
• Winter Monsoon: land is cool, water is warm and wind blows from land to ocean.
• Summer Monsoon: Land heats up and draws in moist oceanic air, thus causing heavy rains. SW Monsoon (L), NE Monsoon, SW Monsoon (L), NE Monsoon, (Rt) Note high phytoplankton from upwelling on left Equatorial Upwelling
• Winds blowing along the equator deflect surface water (Coriolus Force again!) to the right in north and left in south
• This leads to upwelling to replace the lost surface water
• This nutrient rich water stimulates photosynthesis by phytoplankton The higher chlorophyll (light stripe) The higher chlorophyll (light stripe) concentration along the equator is due to the upwelling of nutrients there El Niño
• Surface winds in tropical Pacific normally move from •
• East to West.
Every 38 years High pressure builds up in W Pacific and Low pressure in E Pacific.
Winds then reverse direction (called Southern Oscillation)
This causes a reversal of water currents and warm water that had built up in W Pacific flows to the east and usually arrives around Xmas time and this stops the upwelling off Peru (called El Niño).
El Nino – Southern Oscillation abbreviated to ENSO With El Niño (upper) water height on the With El Ni
eastern Pacific increases (white). La Niña is opposite and water height is lower Major global effects from El Niño
Major global effects from El Ni
• Changes in weather patterns globally, more tornados in US
• Warm water along California coast kills cold water species (i.e. Kelp), much higher rainfall.
• Upwelling off Peru ceases, thus depressing anchovy fishery Circulation of water in the ocean is Circulation of water in the ocean is also caused by giant convection cells
• The deep water circulation is about 90% of total water movement in the oceans and circulation is caused by density differences from one place to another
• Surface water circulation is the remaining 10% of oceanic water movement. Global circulation of oceans
Global circulation of oceans
• Major area of sinking of cold dense water which •
• will become the ocean’s deep water is off Iceland & Greenland.
This water travels south and some upwells near Antarctica, then gets colder and more dense. Becomes Antarctic Bottom Water.
Rest of deep water travels to Pacific, slowly comes to surface, then slowly travels through the Indian Ocean, around S tip of Africa, then back to N Atlantic. Takes about 2000 yrs. The next slide shows “The Great The next slide shows “The Great Ocean Conveyer Belt”
• You should know this for an exam. You might be asked to draw this.
• From the previous slide you saw water sink in the North Atlantic and head south.
• The “Conveyer Belt” shows the whole system. The Major Ocean Surface currents The Major Ocean Surface currents consist of circular gyres.
• Surface currents are generated because of winds blowing over the surface of the oceans
• Clockwise in northern hemisphere
• Counter clockwise in Southern
• Why? The largest current in the world is The largest current in the world is the Antarctic Circumpolar Current • Water travels in a westward direction around the continent Study Guide: What you should Study Guide: What you should know. Be able to explain
• Convection Cell, Cause & Effects of Coriolus Force on ocean & atmospheric circulation, Hadley & Ferrel Cells & effects on weather, NE Trade Winds, Doldrums & Prevailing Westerlies Ekman Spiral and water movement, Upwelling, Langmuir Cells, Equatorial Upwelling, Cause and effects of El Nino, La Nina, Global Oceanic Water Circulation (Global Conveyer Belt…be able to draw this!), Global Surface Current patterns. That’s all!
That’s all! ...
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- Fall '08
- Convection, Phytoplankton, coriolus force