1. 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.

2. 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 10 19 kg of salt. Rivers deliver 4 x 10 12 kg of salt/year. Age of Earth is 13 x 10 6 years old. But, Earth is 4.6 x 10 9 years old…… what went wrong? ?

3. 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.

4. 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.

5. 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

6. 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.

7. 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.

8. V. Circulation of the Liquid Earth A. Origin of the Oceans B. Distribution of water on Earth Reservoirs

9. Reservoir Mass (10 15 kg) Residence Time Ocean 1,400,000 Snow and Ice 43,400 Groundwater 15,300 Freshwater 360 Atmosphere 16 Biosphere 2

11. V. Circulation of the Liquid Earth A. Origin of the Oceans B. Distribution of water on Earth Reservoirs Fluxes (10 15 kg/year) Evaporation from the ocean: 434 Evapo-transpiration: 71 (biota and lakes) Precipitation:505

12. Reservoir Mass (10 15 kg) Residence Time Ocean 1,400,000 Snow and Ice 43,400 Groundwater 15,300 Freshwater 360 Atmosphere 16 Biosphere 2 MRT ocean = Mass of the ocean flux of water from atm to ocean

13. Reservoir Mass (10 15 kg) Residence Time Ocean 1,400,000 3000 years Snow and Ice 43,400 Groundwater 15,300 Freshwater 360 Atmosphere 16 Biosphere 2 MRT ocean = 1,400,000 = 3000 years 505

14. Reservoir Mass (10 15 kg) Residence Time Ocean 1,400,000 3000 years Snow and Ice 43,400 Groundwater 15,300 Freshwater 360 Atmosphere 16 12 days Biosphere 2 MRT atmosphere = 16 = 12 days 505

15. 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.

16. 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

17. 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.

18. Simplified Surface Currents

19. 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.

20. Generalized ocean surface currents

21. 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

23. 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

25. 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.

26. 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.

27. Southern Hemisphere

28. Strong NW winds Ekman Transport to the SW. Upwelling

29. 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.

31. Northern Hemisphere Northern Hemisphere

32. 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 (‰).

33. 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. Typical ocean salinity is 35‰, which means dissolved salts make up 3.5% of the mass of a volume of water.

34. V. Circulation of the Liquid Earth D. Deep ocean currents 1. Vertical circulation is controlled by differences in density. Density is controlled by temperature, salinity What makes up salinity? Mostly Sodium (Na) and Chloride (Cl) 55% 31% With smaller amounts of sulfate, magnesium, calcium, potassium, bicarbonate

36. How is density controlled by temperature and salinity? More denseLess dense ColderWarmer SaltierLess salty (higher salinity)(lower salinity)

37. V. Circulation of the Liquid Earth D. Deep ocean currents 1. Vertical circulation is controlled by differences in density. 2. Thermohaline circulation: Density driven vertical circulation 3. Vertical structure of the ocean

38. V. Circulation of the Liquid Earth D. Deep ocean currents 1. Vertical circulation is controlled by differences in density. 2. Thermohaline circulation: Density driven vertical circulation 3. Vertical structure of the ocean Example: Mediterranean Sea outflow

40. Salinity of the Atlantic Ocean at 1100 meters depth. What does the salinity tell us about the temperature?

41. V. Circulation of the Liquid Earth D. Deep ocean currents 4. Formation of Bottom Water and deep ocean circulation For surface water to sink it needs to be denser than the water underneath it. This requires: Cold Salty Where might these conditions be met?

42. V. Circulation of the Liquid Earth D. Deep ocean currents 4. Formation of Bottom Water and deep ocean circulation Occurs in the northern North Atlantic (very salty and pretty cold) and Around Antarctica (not quite so salty, but very cold)

43. We can use tracers to actually follow deep ocean circulation. In the movie that follows, we take advantage of 30 years of sampling vertical transects through the Atlantic, and analyzing that water. The movie shows the concentration of CFCs, man-made chemicals that were not present before about 1950 to trace how the deep ocean moves.

45. V. Circulation of the Liquid Earth D. Deep ocean currents 4. Formation of Bottom Water and deep ocean circulation. 5. The thermohaline conveyor belt The large-scale motion of the deep ocean based on density differences.

46. V. Circulation of the Liquid Earth D. Deep ocean currents 6. Life in the ocean: how do we measure? Primary productivity: The amount of organic matter produced by photosynthesis. Measured in amount per unit are per unit time (for example: kg/m 2 /year). What is going to control primary production? Sunlight: we know what controls sunlight Nutrients: what controls nutrients?

47. V. Circulation of the Liquid Earth D. Deep ocean currents 6. Life in the ocean: how do we measure? Primary productivity: The amount of organic matter produced by photosynthesis. Primary production occurs in the photic (sunlight) zone, where primary producers are eaten by larger things, that sink when they die, removing nutrients from the surface water.

48. V. Circulation of the Liquid Earth D. Deep ocean currents 6. Life in the ocean: how do we measure? Primary productivity: The amount of organic matter produced by photosynthesis. Sinking dead things decompose in the deep ocean and most of their nutrients are returned to the water column. But below the photic zone where they cannot be easily used.

49. Typical “open ocean” distribution of nutrients vertically in the water column. Much of the surface ocean is nutrient limited.

50. V. Circulation of the Liquid Earth D. Deep ocean currents 6. Life in the ocean: how do we measure? Primary productivity: The amount of organic matter produced by photosynthesis. We expect most primary productivity where deep water returns to the surface = upwelling areas. Fig. 5-13 in the color section of your text shows the global pattern of primary productivity.

51. V. Circulation of the Liquid Earth D. Deep ocean currents 6. Life in the ocean: how do we measure? Primary productivity: The amount of organic matter produced by photosynthesis. Why is primary productivity important? Where we catch all those tasty fish we like to eat…. Exerts strong control on the global carbon cycle

52. V. Circulation of the Liquid Earth D. Deep ocean currents E. Climate impacts of changing ocean circulation…. What might happen if we shut down Thermohaline circulation in the northern North Atlantic? Why might that happen?