The Global Water Cycle

Transcription

1 The Global Water Cycle

2 Water Unusual properties Central role in biogeochemistry Agent in global weathering cycles

3 Water Outline Most abundant molecule on earths surface (1) Water: Properties and importance in biogeochemistry (2) The hydrologic cycle in brief (3) Earth s surface: Water reservoirs (4) Earth s energy balance and water (5) Global water cycle: Fluxes (6) A closer look at rivers

4 Part I: H 2 O An introduction to Water

5 Recall Atomic structure: Its all About Attractions and Repulsions Nucleus: Protons (+ Charge) ( & neutrons: mass, no charge) Orbiting: Electrons (-) Charge: But some commitment Phobia not too close.. Not too far Electrons exist in specific orbits ( or orbital shells )

6 The Periodic Table Remember this thing? Filling up electrons in outer orbital shells.. Electro-Positive ( Lose a few electrons =full outer shell) Electro-negative ( Gain a few electrons =full outer shell)

7 IF The GOAL: To Attain a Full shell: HOW CAN EACH DO` THIS?

8 H 2 O 2 atoms Hydrogen : Total Electron WIMP ( why? Only 1e in outer shell lose 1 more, has a + charge.. But outer shell happiness!)

9 H 2 O 1 Atom Oxygen : Voracous Electron Pilfering! ( why? 6 e in outer shell Gain 2 = Nirvana!)

10 One more thing: Notice way bonds are drawn: H s are not in strait line (not linear) Tetrahedral geometry due to fact orbitals have specific spatial shapes

11 Consequence: Strong Polarity + -

12 Leads to: 1) Intense Dissolving power. Ie: Salts dissolve VERY well in water.

13 Why? A salt is broadly defined anything made of two ions one positive, one negative Stuck together mainly by electrostatic attraction (ionic interactions)

14 Water molecules can surround both negative and positive charged Ions very effectively!

15 Dissolution

16 Consequence II : Hydrogen bonding Hydrogen Bonds: Strong polarity coupled with weak ionic bonds allows water molecules to attract each other forming hydrogen bonds.

17 Think of liquid water of as a seething mass of H 2 O molecules in which hydrogen-bonded clusters are continually forming, breaking apart, and re-forming. Stefan Lower

18 Hydrogen bonding means that every molecule is sort of attached to everything around it.. Think of a sort of spider web of weak but sticky attractions..

19 WHAT ARE the ENVIRONMENTAL Consequences

20 Surfaces for water bugs Surface tension - imagine that web of molecules all stuck to each other

21 Another Consequence of STICKYNESS Takes extra ENERGY to evaporate or condense water (must break apart all those sticky H bonds) WATER CAN STORE HUGE AMOUNTS OF HEAT (ENERGY)

22 Recall Temperature : = Molecular MOTION.

23 Aside: Boiling point vs. Mass Increasing Boiling Point Increasing size (molecular wt) Heavier molecules take MORE ENERGY to get airborne. So higher BP!

24 Boiling point vs. Mass take 2 Increasing Boiling Point Increasing size (molecular wt) WHATS GOING ON?? Some LIGHTER molecules take MORE ENERGY to get airborne???

25 H bonding consequence: You have to add LOTS of heat energy to water and it will not evaporate because of all the stickiness WATER CAN STORE and TRANSPORT HUGE AMOUNTS OF HEAT (ENERGY)

26 Also : 2) Oceans strongly modulate climate- due to vast heat storage

27 Other key properties: freezing point vs. density

28 Increasing salinity changes this: at 24.7 max density is freezing point

29 Sum, WATER S PROPERTIES Distinctive physical and chemical properties Include: Found in all three states at ambient conditions Required for life for all (known) biochemistry Extreme dissolving power: Main mass link between continents and ocean geological / oceanic cycles High specific heat capacity (second only to ammonia), high heat of vaporization Hydrologic cycle key for Global heat balance Climate: Water vapor an important greenhouse gas Albedo of frozen water is highest of any earth surface Controls on stratification/ heat balance of ocean and freshwaters: Temperature of maximum density (above or at freezing point) Fresh water, Tmax density is 3.98 C Cold deep convection blocked by density change Frozen river/lake, coldest near ice, sediment bed is warmer Sea water, Tmax density, 1.9 C, at/near freezing point Cold currents vs. deep convection

30 II: Basic Hydrologic Cycle H 2 O

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32 Basic hydrologic cycle Define Reservoirs and sizes Does not count water in minerals in earths interior Determine fluxes Determine Salinity and composition For geochemical cycles, determine the content of other molecules (salinity)

33 1) Evaporation Basic components 2) Precipitation (rain or snow) 3) Interception (by plants) turns into organic matter 4) Infiltration/groundwater store 5) Runoff into streams 6) Discharge into ocean (streams and groundwater direct)

34 Oki and Kanae (2006)

35 Reservoirs* Reservoir Amount Think about (10 3 km 3 ) Ocean 1,338,000 How could this change through time? Glaciers and snow 24,064 What are its vulnerabilities? Groundwater 23,400 What is the residence time? Permafrost 300 Effects of global warming Lakes 175 Wetlands 17 Soil moisture 17 Water vapor Greenhouse gas Over ocean Over land 10 3 Rivers 2 Importance in fluxes Biological water 1 TOTAL fresh 47, % of total TOTAL all 1,385,989 *Sometimes reservoirs are expressed in equivalent depths; e.g., comparison of Atm water vapor (13) vs. ocean reservoirs (1,338,000) Ocean mean depth of 3850 m, vs. 3.7 cm equivalent depth for atm reservoir.

36 Residence times Vary vastly by reservoir How would you calculate them?

37 Earth s Radiation and Energy Balance Drives hydrological cycle Balance of incoming solar radiation and outgoing radiation at top of atmosphere Importance of water in greenhouse effect Berner and Berner (1996) Figure 1.4

38 III. Energy Balance: Clouds, Ice, and greenhouse Reflected short wave radiation EARTH S ALBEDO 31% Importance of clouds (1/2 of this) Solar radiation absorbed and re radiated as longwave (>4 um), 69% 20 units absorbed by ozone, water vapor, carbon dioxide 41 units heat surface, re radiated with maximum in IR at 10 um, lots reabsorbed in atmosphere

39 Contributions to Albedo

40 The greenhouse effect 1. Incoming Energy Budget : The Black Body Effect warm earth radiates energy 2. Radiation Adsorption by certain molecules Heat

41 Greenhouse Gases Current Anthro Absorp Radiativhouse Green- Green- pogenic Global -tion Amount band Forcing Effect house Warming Greenhouse Gas (ppm) (µm) (W/m2) (W/m2) Effect Potential Water Vapor (H 2 O) ~ , ~100 >13 Carbon Dioxide (CO 2 ) , ~50 3% 1 Res. Time (years) 7 Methane (CH 4 ) , % Nitrous Oxide (N 2 O) % Ozone (O 3 ) , % CFC-11 (CFCl 3 ) , % CFC-12 (CF 2 Cl 2 ) , %

42 Fluxes * 10 3 km 3 equals g Sometimes also done in units of equivalent depth (Annual evaporation from ocean removes equivalent of 100 cm)

43 Evaporation, precipitation & rivers Net effect: 45.5 x 10 3 km 3 /yr of net water vapor transport to land from ocean results in net river flux of 45.5 x 10 3 km 3 /yr (This is a bit bigger than the 1Svoften used as typical estimate). (Aside Hydrothermal circulation through all oceanic crust may be about same as all river flux but most cooler off axis)

44 Why Do Rivers Matter So much? Major conduit for water and weathering products to reach ocean Small reservoir, but large flux, short residence time Mass Link between continents and oceans (key for biogeochemistry) Human use and diversion

45 Oki and Kanae (2006)

46 Major conduit for water and weathering products to reach ocean Suspended solids (Al, Fe, Si, Ca, K, Mg, Na, P) Dissolved majors (bicarbonate, Ca2+, SO42, H4SiO4, Cl, Na+, Mg2+, K+) Dissolved nutrient elements (N, P) Suspended and dissolved organic matter (= reduced carbon linkage)

47 Big Rivers Matter A Lot! First 13 rivers are 38% of total discharge Amazon ALONE is 17% of total discharge! Table 5.1, Berner and Berner

48 Future Trends? What will be effects of Warming to date, and anticipated future warming? Is Intensification of hydrological cycle happening? (paper for Friday)