IV Circulation of the Liquid Earth The Oceans and the Hydrologic Cycle A Origin of the Oceans 1 Where did the water come from Outgassing from the Earth s interior volcanos the same as the atmosphere There have been oceans as far back as we can find rocks almost 4 billion years And there is still another ocean inside the Earth V Circulation of the Liquid Earth A Origin of the Oceans 1 Where did the water come from 2 Where did all the salt come from Early geologists thought they could calculate the age of the Earth from the salt in the ocean Ocean holds 5 x 1019 kg of salt Rivers deliver 4 x 1012 kg of salt year Age of Earth is 13 x 106 years old But Earth is 4 6 x 109 years old what went wrong V Circulation of the Liquid Earth A Origin of the Oceans 1 Where did the water come from 2 Where did all the salt come from Two key assumptions Rivers are the only source of salt All salt that enters the ocean stays there Both are violated Salt is removed from the ocean New salt is also added to the ocean from mid ocean spreading centers V Circulation of the Liquid Earth A Origin of the Oceans Our early geologists did not yet know about Plate tectonics Mid ocean spreading centers Evaporite basins Sea critters that precipitate sea salts in their shells Sea spray to the land V Circulation of the Liquid Earth A Origin of the Oceans 1 Where did the water come from 2 Where did all the salt come from Calculating the age of the Earth this way adds three terms to our view of the Earth as a system Reservoir Flux and Residence Time V Circulation of the Liquid Earth A Origin of the Oceans Reservoir Reservoir a noun it s a thing A volume or mass of something Ocean water salt etc Atmosphere Oxygen water vapor etc Flux a verb it s the action The rate at which energy or matter is transferred between reservoirs The rate at which energy or matter is transferred between reservoirs Expressed in amount per unit time V Circulation of the Liquid Earth A Origin of the Oceans Reservoir Flux Residence time The average time a substance stays in a reservoir Reservoir Flux In our salty ocean example the calculated age of the Earth 13 million years is the residence time of salt in the ocean V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth Reservoirs Reservoir Ocean Mass 1015 kg Residence Time 1 400 000 Snow and Ice 43 400 Groundwater 15 300 Freshwater 360 Atmosphere 16 Biosphere 2 V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth Reservoirs Fluxes 1015 kg year Evaporation from the ocean 434 Evapo transpiration 71 biota and lakes Precipitation 505 MRTocean Reservoir Ocean Mass of the ocean flux of water from atm to ocean Mass 1015 kg Residence Time 1 400 000 Snow and Ice 43 400 Groundwater 15 300 Freshwater 360 Atmosphere 16 Biosphere 2 MRTocean Reservoir Ocean 1 400 000 3000 years 505 Mass 1015 kg Residence Time 1 400 000 Snow and Ice 43 400 Groundwater 15 300 Freshwater 360 Atmosphere 16 Biosphere 2 3000 years MRTatmosphere Reservoir Ocean 16 12 days 505 Mass 1015 kg Residence Time 1 400 000 Snow and Ice 43 400 Groundwater 15 300 Freshwater 360 Atmosphere 16 Biosphere 2 3000 years 12 days V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents Troposphere unstable ocean stable Unlike the troposphere which is heated from the bottom hence is fundamentally unstable and circulates in response to this instability the oceans are heated from the top hence the warmest least dense water is mostly at the surface Stable V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents 1 Surface currents are driven by winds through the frictional coupling between atmosphere and sea surface Surface currents generally restricted to uppermost 100 m Average depth of the deep ocean 4000 m V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents 1 Surface currents winds 2 Coriolis surface currents deflected to right NH or left SH of the prevailing winds Simplified Surface Currents V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents 1 Surface currents winds 2 Coriolis surface currents deflected to right NH or left SH of the prevailing winds We expect simple gyres But simple gyres are complicated by continents Generalized ocean surface currents V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents 1 Surface currents winds 2 Coriolis Actual net motion of water is further complicated by Ekman Spiral V Circulation of the Liquid Earth A Origin of the Oceans B Distribution of water on Earth C Surface currents 1 Surface currents winds 2 Coriolis Ekman Spiral transfer of Coriolis Effect down through the water column Net effect is that surface water moves at right angles to the wind Ekman Transport V Circulation of the Liquid Earth C Surface currents 1 Surface currents winds 2 Coriolis Ekman Spiral 3 Convergence surface water tends to pile up at the center of gyres where downwelling occurs 4 Divergence Winds on both sides of the equator are easterly so net motion of water is N in NH and S in SH creating divergence and upwelling V Circulation of the Liquid Earth C Surface currents 1 Surface currents winds 2 Coriolis Ekman Spiral 3 Convergence downwelling 4 Divergence upwelling 5 Coastal Upwelling Winds moving parallel to the continental coast can result in strong upwelling Southern Hemisphere Strong NW winds Ekman Transport to the SW Upwelling V Circulation of the Liquid Earth C Surface currents 1 Surface currents winds 2 Coriolis Ekman Spiral 3 Convergence downwelling 4 Divergence upwelling 5 Coastal Upwelling Why might we care about areas of upwelling Upwelling brings nutrients to the surface 50 of all fisheries occur in upwelling areas even though they represent only 2 of the ocean surface Northern Hemisphere Northern Hemisphere V Circulation of the Liquid Earth C Surface currents D Deep ocean currents 1 Vertical circulation is controlled by differences in density Density is controlled by temperature salinity Measured as the proportion of dissolved salt to pure water Measured in parts per thousand V Circulation of the Liquid Earth C Surface currents D Deep ocean currents 1 Vertical circulation is controlled by differences in density Density is controlled by temperature salinity Measured as the proportion of