1. Environmental Chemistry

2. Water and the Oceans
What are the distribution and flows of water through the Earth system?
What factors control these flows and what conditions do they influence?
What chemical processes occur as a result of water cycling and how do these processes shape the composition of oceans and other bodies of water?
How is ocean composition changing as a result of anthropogenic activities? What are the impacts of these changes on ocean life and ecosystems?

3. Important water properties
Extremely strong intermolecular interactions (hydrogen bonding)
Liquid is more dense than solid  volume minimum at 4 C
High heat capacity  stabilizes temperature swings
High melting and boiling points  water stays liquid over wide T range
Extremely good solvent of ionic and polar compounds

4. Hydrological Cycle
Estimates of the main water reservoirs in plain font (e.g. Soil moisture) are given in 103 km3 and estimates of the flows between the reservoirs in italic (e.g. Surface flow) are given in 103 km3/year. Figure from Trenberth et al. (2007) American Meteorological Society.

5. Water Distribution

6. Water availability
Available renewable fresh water in 1000 m3 per capita per year.

7. Water density Temperature Density kg/m^3 999.868 4 1000.000 10 999.728 4 10 20
Ice at 0
917

8. So What? Ice Floats Seasonal overturn of lakes
Consider a typical lake in the Summer
This is a lake
---- T, r ---->
Epilimnion (25 oC)
Thermocline
Depth
Hypolimnion (15 oC)

9. Lake in the Fall
---- T, r---->
(15 oC)
Mixing
(15 oC)

10. Winter ---- T, r ----> Epilimnion (<4 oC) Thermocline Depth
Hypolimnion (4 oC)

11. Lake in the Spring
---- T, r ---->
(4 oC)
Mixing
(4 oC)

12. What about the ocean
Due to the salts dissolved in seawater, seawater does not have a density minimum.
Cold water is more dense
Saltier water is more dense
Cold, salty water sinks

13. Thermohaline circulation

14. Ocean water composition

15. Notes on units 1 M (molar) = 1 mol L-1
ppm, ppb etc. are on a mass basis (ppmm)
1 ppm = 1 mg/kg = 1 mg/L
Assumes water density of 1 kg/L
Concentrations are sometimes expressed as concentration of an element rather than the compound
E.g., 7 ppm N as NO3-

16. Ocean water composition

17. Solubility Rules

18. Carbonate-silicate cycle
Timescale = 105 – 107 yrs
J. F. Kasting, Science Spectra, 1995

19. Forms of CO2 in water
H2CO3 (aq) ↔ H+ + HCO3-
HCO3- ↔ H+ + CO3-

20. Alkalinity