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This 8 page Class Notes was uploaded by Erica on Thursday September 24, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 70 views.
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Date Created: 09/24/15
Waves and Tides Cont Climate Change Atmospheric C02 concentration 0 Since the industrial era it s increased 35 0 Increasing by about 23 ppm each year So in about 10 years it will be 420430 ppm The increased C02 in the atmosphere created a persistent energy imbalance in the earth system that accumulates heat energy over time like rolling up the window on your car a little further Goal to limit global warming to 2 degrees Celsius above preindustrial levels During the last ice age there was 4 km of ice on top of Ithaca and average global temperatures were 4 degrees Celsius colder Humans are now the trigger that moves C02 into the atmosphere At million year time scales volcanic activity can massively change C 02 levels and earth s climate We are now more certain of human caused global warming than we are that smoking causes cancer Greenhouse Gas E ect 1 Sunlight passes through the glass window short wavelength radiation 2 This energy is absorbed into car heat energy is radiated as long wave length radiation infrared 3 The window that let short wavelength radiation through then absorbs the long wavelength radiation and prevents heat from leaving the car 4 The car heats because more energy enters the car than leaves it 5 The inside of the car heats until the glass gets so hot that it radiates heat energy out at the same rate as sunlight enters Same amount of sunlight energy is coming into earth but less infrared energy is leaving 9 now we have more energy coming in than out so the earth warms Atmospheric C02 has a lifetime of 10000 years We have 500 Gt of C02 remaining that can be put into the atmosphere We currently emit about 50 Gt a year 9 do we keep emitting at 50 Gt per year for 20 years 9 do we slow down emissions starting now and make the 500 Gt last longer At some point we will absolutely need to transform our living to a zero carbon emission society but what path do we take Accumulation of Heat Energy in the Earth System 1 Most daily heat imbalance that is produced by increased greenhouse gasses now accumulates in the earth system 2 Majority of the accumulated heat is taken up by the ocean Global warming isn t evenly distributed and the polar regions are very sensitive Atmosphere now has a C02 concentration of 400ppm humans didn t exist the last time this happened 9 the last time this occurred global temperatures were 510 degrees Fahrenheit higher than today sea level was about 75120 feet higher and there wasn t a permanent sea ice cap in the arctic OJ C O CO Concentration C02 Win 0 3 fx 0 C Global Temperature Q l Holocene 2 Eemlan Last lce Ag T Anomaly 0C 5 39 Sea Level m Sea Level O O 400 350 300 250 200 l 50 l 50 0 Time thousands of years before present Natural Climate Forcing Factors small compared to current human forcing o The timing of the ups and downs in C02 concentrations in the atmosphere coincide with the frequency of orbital forcing o Triggering mechanism on a time scale of 10000 years small variations in 3 orbital parameters produce small variations in the pattern of solar energy reaching the earth 0 Affect causes C02 to redistribute most likely moving C02 from deep ocean into atmosphere 0 Increased C02 in atmosphere green house effect warming 0 Orbital Variations the principle trigger mechanism of temperature change at large time scales with atmospheric C02 acting as the actual forcing mechanism Ocean Circulation I Ocean Surface Currents 1 Large subtropical gyres rotating clockwise in N hemisphere and counter clockwise in S hemisphere 2 Subpolar gyres rotating counter clockwise in the N clockwise in the S 3 Antarctic Circumpolar Current moving eastward around the Antarctic continent Deep Circulation in Oceans 1 Cold surface water sinks at high latitudes amp moves to lower latitudes at depth 2 Deepwater returned to the surface layer through broad diffusive upward vertical mixing Coriolis Force 1 It arises from real physics related to the conservation of angular moment 2 In the northern hemisphere the Coriolis Force is always directed to the right of the water parcel motion 3 In the southern hemisphere the Coriolis Force is always directed to the left of the water parcel motion The Basic Rule to determine the direction of the Coriolis Force is to 1 point your nose in the direction of the ocean current or wind is moving and then 2 stick your hand directly out from your side to get the direction of the Coriolis force right hand for the northern hemisphere or left hand for the southern hemisphere Atmospheric Circulation 0 Material is warmed when it absorbs radiant energy Much of the visible radiant energy from the sun short wavelength radiation passes right through the atmosphere without being absorbed and consequently without much direct heating of the atmosphere from the sun The earth s surface absorbs a lot of the sunlight energy and so it becomes warm The warm earth surface radiates infrared radiation long wavelength radiation from its surface and this energy is absorbed by the atmosphere and consequently warms the atmosphere So the atmosphere is heated from below by absorbing long wavelength radiation emitted from the warm earth surface Atmospheric Convection O The warm ocean surface heats the atmosphere from below Warm surface air is able to hold a lot of water vapor and so it becomes moist Warm moist surface air has low density so it rises like a hot air balloon and as it moves aloft it expands and cools Cooling of air aloft causes water vapor to condense and precipitate Condensation releases latent heat that drives the upward convection even higher Solar Heating 0f the Earth 5 Surface 0 Solar heating of the earth surface is most intense at the equator where the solar radiation is most direct 0 So atmospheric convection and precipitation is strongest along the equator Vertical Distribution ofSeawa ter Density Vertical distribution of density directly in uences the vertical movement of water in the ocean Salt concentration and water temperature jointly determine seawater density I Surface ocean temperature is determined by the exchange of heat between ocean surface and the atmosphere Adding heat to the ocean is sunlight being absorbed 9 surface is warmed by gaining more heat than losing I Sunlight doesn t penetrate to the bottom of the ocean it is relatively shallow I 9 most heat energy is absorbed O30m of water Permanent thermocline uniformly cold to abrupt change in temperature Seasonal thermocline temporary thermocline above subtropical gyres PycnocIine strong change in density with depth change Adding more heat amp mixing summer it s hard for mixing when it isn t too warm the winds easily get water mixed in to about 70 m Spring 9 summer hotter and hotter less mixing Warm water 9 blown up beach ball cold water 9 Shriveled up beach ball Winds mix cold beach ball easily 1 Ekman Transport A slab of surface ocean water moved by wind forcing I This slab moves at 90 degrees to the direction of the wind forcing Exactly to the right northern hemisphere Exactly to the left southern hemisphere Due to Wind force Friction force Coriolis Force Ekamn Spiral spiraling of thin ocean currents within Ekman layer It is the rate of total water transported in the layer About 50100m thick 2 Geostrophic Currents Currents move along lines of constant pressure I Coriolis force always pushes the uid to the right of its present direction of travel I The point at which currents move with steady speed with Coriolis and pressure gradient forces in prefect opposition is referred to as geostrophic balance and the resulting current is referred to as a geostrophic current I fully developed geostrophic currents move along lines of constant pressure Formation of Subtropical Gyres Q If a mound of water builds up at the surface of the ocean a central high pressure develops under the mound and circular geostrophic currents develop Development of the Subtropical Gyre in Response to Forcing by the Westerly and Trade Wind Belts Westerly and Trade Winds drive the Ekman Layer to the center of the gyre to create a mound of surface water The uid initially moves away from the center of high pressure The push of Coriolis turns the uid until it travels along concentric lines of constant pressure 9 geostrophic balance Currents on western side of all subtropical gyres are called western boundary currents 0 they are very swift and narrow jets that bring warm water from the tropics to high latitudes Currents on eastern side of all subtropical gyres are called eastern boundary currents 0 they are broad and slow and bring cold water from the high latitudes toward the tropics Equatorial Upwelling 0 North East Trade Winds drive Ekman Transport of the surface layer to the north 0 South East Trade Winds drive Ekman Transport of the surface layer to the south 0 Surface water also piles up on the western side of the ocean basin forcing a downward tilt to the thermocline 0 Eastern Equatorial Pacific Cold Tongue due to equatorial upwelling AND the close proximity of the thermocline to surface Ekman Depth 0 Western Equatorial Pacific Warm Pool upwelling still occurs but the thermocline is much deeper than the surface Ekman Depth so upwelling just draws more warm water to the surface with no effective cooling Deep Ocean Abyssal Circulation Atlantic Ocean Temperature at Depth 0 Warm thin surface layer 0 Cold thick deep layer 0 Thermocline separates the warm and cold layers Atlantic Ocean Salinity at Depth 0 High salinity in surface layer in subtropics o Deepocean salinity more uniform and generally matches the surface salinity at higher latitude especially northern high latitudes TemperatureSalinity Signatures of the 3 makor water masses 1 NADW North Atlantic Deep Water 2 AABW Antarctic Bottom Water 3 AAIW Antarctic Intermediate Water Circulation of Deep Water in Global Ocean 0 Cold dense water sinks in the North Atlantic and around Antarctica to form deep water 0 North Pacific salinity is too low to sink even though temperatures are just as cold as the North Atlantic 0 Deep water in the North Atlantic moves south and mergers with Antarctic water in the Southern Ocean as they both swing around Antarctica and up into the Indian and Pacific Ocean basin Conveyor Belt Circulation Schematic of Heat Transport by the Global CBC 0 Heat is gained by the surface ocean at low latitudes and transported via the winddriven surface circulation western boundary currentsto higher latitudes 0 Heat is given up by the ocean to the atmosphere at higher latitudes to warm these regions 0 After giving up heat at high latitudes surface water sinks and enters the thermohaline deep Circulation and eventually is returned to the surface to pick up more heat and start the journey all over again Most Heat Transport to High Latitudes is Done by Strong Western Boundary Currents