Hydrological Cycle Dissolved Gases/Ocean & Atmosphere

1. Hydrological CycleDissolved Gases/Ocean & Atmosphere

2. Water budgets • Water and heat intimately related • Evaporation removes H2O and heat • Latent heat of evaporation – heat released to atmosphere as vapor rises, cools, condenses and falls back to earth (rain or snow) • Amount of water on earth’s surface has remained relatively constant for billions of years so we can make a budget (see Fig.) • Reservoirs and fluxes • Reservoirs; a place where water resides; contains an average amount over time; unit of mass or volume • Fluxes; water is always moving among reservoirs; volume per unit time

3. Where is the water • Ocean is the primary reservoir for water on Earth • Small quantities on continents and in atmosphere can be considered to be in transit back t the ocean

4. Hydrologic Cycle • Water cycles between oceans, atm, and land – driven by solar energy • Bulk of water is in the oceans • Evaporation removes water from the oceans • FW phase is highly dependent on atm as a conduit • Water residence time in the oceans ~4000 yr • Large exchanges between land/oceans and atm – evaporation and precipitation

5. Fig. 4-24a

6. Hydrological Cycle

7. Reservoirs • Ocean • Glaciers and ice • Groundwater & soil • Rivers & lakes • Atmosphere

8. Fluxes • Evaporation (from oceans and lakes) • Precipitation (over land and sea) • Wind transport (from sea to land) • Condensation (clouds and fog) • Sublimation (from snow on land) • Runoff (rivers, etc) • Underground flow

9. Small nettransport(balanced by runoff) Fig. 4-24b

10. Balance • Overall balance • Locally, may be net evaporation over ocean or net precipitation over land (but that would run of into the ocean to balance things globally) • Properties of climate zones are determined mostly by earth’s surface temperature and evaporation/precipitation ratios

11. Equatorial regions • Hot, moist rain forests; ppt >> evap • Subtropical deserts • Hot, dry; evap >> ppt • Temperate zones • Cool, moist; ppt >> evap • Polar areas • Cold, dry; evap & freezing >> ppt

12. Residence time • Time water (or anything else) spends in any one reservoir on average. • Units of time [volume/(volume/time)] or volume/flux • Larger reservoirs often have longer residence times • Residence time in the ocean is long • Implications for dumping garbage in the ocean! • But, residence times vary depending on fluxes • Implications for water quality and planning

13. Ice is second largest reservoir for water • High altitudes on major mountain chains • High latitudes, e.g., Greenland and Antarctica are capped by glaciers. Antarctica is surrounded by ice. Arctic always ice-covered. • 10% of earth’s surface covered by ice (freshwater). • Life cycle of a glacier – accumulation of snow, compaction, “flow” down slope under their own weight, melting and evaporation • Ice that makes it to sea can break off and form icebergs in a process called calving.

14. Ice-covered continents • Ice cap extends over edge of land • Breaks off to form icebergs • Largest iceberg ever found was in the Ross Sea (near Antarctica) and measured 100 by 350 km (twice the size of Connecticut).

15. Properties of water • High heat capacity • High dissolving power • Exists in all 3 phases at Earth surface conditions • Ice floats in water

16. Water • Unique properties – important for understanding interaction between ocean & atmosphere • Climate • Dissolved constituents can affect water’s properties

17. What is Water • H2O • Covalent & hydrogen bonding • Water as a solvent • Density • Heat Capacity and specific heat • Salinity (next time)

18. A covalent bond exists when two electrons are shared by two non-metallic atoms. Dipolar. **Electron density higher around oxygen, giving that end a partial negative charge.

19. Oxygen has 6 electrons, and wants 2 more electrons for stability. • Hydrogen has 1 electron and wants 1 more electron for stability.

21. Electrons and “charge” not distributed evenly so molecule becomes polar. 104.5°

22. Hydrogen bond is a weak bond formed when a charged part of a molecule having polar covalent bonds forms an electrostatic (charge, as in positive attracted to negative) interaction with a substance of opposite charge. The weak bonds are easily and rapidly formed and broken under normal biological conditions. They are extremely important in biological systems and Their presence explains many of the properties of water.

23. H-bonding imparts adhesion and cohesion of water. Creates surface tension and wetting ability

24. Water cohesion (imparted by the H-bonding between water molecules) causes surface tension & capillary action. Adhesion allows water molecules to “stick” to other things or get wet.

25. Water is a powerful solvent

26. Ionic molecules dissolve well in water. Ethanol dissolves well in water because it is polar. On the other hand, oil is repelled by water because it is non-polar, and thus does not dissolve well in water.

27. Water & heat • Temperature – how rapidly molecules are vibrating • Response to addition and removal of heat • Heat capacity • Amount of heat required to change the temperature of a substance (raise or lower) • Calorie is the amount of heat required to raise temperature of 1 gram water by 1 oC • Heat capacity of water is among the highest of all known substances • This high heat capacity is a result of water’s structure (H-bonding)

28. Many metals have low heat capacities (change temperature with small changes in heat content)

29. Significance of heat capacity • Water is a good buffer for heat • Land temperatures change more easily and rapidly than water • Compare daily changes on land and in the sea • Compare land near the coast with inland

32. Heat transfer

33. Latent heat • Latent heat does not cause temperature change • Much higher for vaporization than for fusion • Must break H bonds for vaporization • Evaporation has a cooling effect because heat is removed from water • Evaporation is a huge source of heat flow between the atmosphere and the ocean

35. 4 J ≈ 1 calories (kg)

36. Sensible heat versus latent heat

38. Water and density • Density is mass per unit volume • Density curve is NOT linear • Normally, as you heat something, molecules move faster and then density decreases and vice versa • Density and state (liquid, gas, solid) • Solid ice is less dense than liquid water • Changes bond angle between oxygen and hydrogen atoms in water (from 104.5 to 109o) allowing lattice structure

39. Maximum density of water is about 4oC

40. Normal substances

41. 3-D Water

42. Implications of density • Ice floats • Density differences drive thermohaline circulation • Salt increases density of water (fresh water should float on salty water) • Water column stable when density stratified (less dense water rises and denser water sinks)

43. Salt and properties of water • Salt water is 96.5% water and 3.5% dissolved solids and gases • Salt changes water’s density • Salt changes water’s freezing behavior • Maximum density of seawater is about –2oC • Why does ice that forms from seawater still float? (salts don’t freeze!) • We’ll talk more about salinity next time.

45. Properties of water • High heat capacity and dissolving power • Storage and transport of heat • Transport of mass • Water can exist in all three phases on Earth • Water involved in biogeochemical processes • Hydrogen bonding – max density at 4 deg C • Ice is less dense than water • Water transports heat (energy and matter) among Earth’s system components.

46. Heat transport • Along with circulation, water cycle redistributes heat • Weather and climate are the response of the atm to unequal latitudnal distribution of energy

47. Remember Fig. 5-15 Poleward heat transport in the Northern Hemisphere.

48. Annual changes in air temperature depending on air movement Ocean breezes buffer heat by causing evaporation that takes up heat

49. Water Vapor – High heat loss in tropics due to evaporation

50. Annual changes in sea ice in Antarctica Over 18,000 km3 of polar ice thaws and refreezes each year -- high seasonal latent heat movement