1. Chapter : Seawater Fig. 6-19

2. Density of seawater 1.022 to 1.030 g/cm 3 Ocean layered according to density Density of seawater controlled by temperature, salinity, and pressure Most important influence is temperature Density increases with decreasing temperature

3. Salinity greatest influence on density in polar oceans Pycnocline, rapid change of density with depth Thermocline, rapid change of temperature with depth Polar ocean is isothermal

4. Seawater Salinity=total amount of solid material dissolved in water (g/1000g) Typical salinity is 35 o/oo or ppt Brackish (hyposaline) < 33 ppt Hypersaline > 38 ppt

7. Measuring salinity Evaporation Chemical analysis Principle of Constant Proportions Chlorinity (19.2 ‰ ) Electrical conductivity (salinometer)

8. How salinity changes Salinity changes by adding or removing water Salinity decreases by Precipitation (rain/snow) River runoff Melting snow

9. Salinity increases by Evaporation Formation of sea ice Hydrologic cycle describes recycling of water

10. Horizontal variations of salinity Polar regions: salinity is lower, lots of rain/snow and runoff Mid-latitudes: salinity is high, high rate of evaporation Equator: salinity is lower, lots of rain Thus, salinity at surface varies primarily with latitude

11. Vertical variations of salinity Surface ocean salinity is variable Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) Halocline, rapid change of salinity with depth

12. Fig. 6-20

13. Dissolved substances Added to oceans River input, dissolving crustal rock (primarily) Excess volatiles (not through weathering) Circulation through mid-ocean ridges Removed from oceans Salt spray Recycling through mid-ocean ridges Biogenic sediments (hard parts and fecal pellets) Evaporites

14. Residence time Average length of time a substance remains dissolved in seawater Long residence time = unreactive Higher concentration in seawater Short residence time = reactive Smaller concentration in seawater Steady state Ocean salinity nearly constant through time

16. Mixing Time Amount of time it takes to mix constituents evenly in seawater Estimated to be around 1600 years Constituents that have long residence times are evenly mixed

17. Dissolved gases Solubility depends on temperature, pressure, and ability of gas to escape Gases diffuse from atmosphere to ocean Wave agitation increases amount of gas Cooler seawater holds more gas Deeper seawater holds more gas

18. Conservative vs. nonconservative constituents Conservative constituents change slowly through time Major ions in seawater Nonconservative constituents change quickly due to biological and chemical processes Gases in seawater

19. Oxygen and carbon dioxide in seawater Nonconservative O 2 high in surface ocean due to photosynthesis O 2 low below photic zone because of decomposition O 2 high in deep ocean because source is polar (very cold) ocean

20. CO 2 low in surface ocean due to photosynthesis CO 2 higher below photic zone because of decomposition Deeper seawater high CO 2 due to source region and decomposition

21. Conservative & Nonconservative Constituents Conservative Chloride Sodium Magnesium Potassium sulfate Nonconservative Oxygen Carbon dioxide Nitrates Phosphates Biologically important

22. List the following gases in order of abundance (greatest – Least): Carbon dioxide Oxygen Nitrogen

23. Dissolved Gases Nitrogen = 48% Oxygen = 36% Carbon dioxide = 15% Page 172

24. Acidity and alkalinity Acid releases H+ when dissolved in water Alkaline (or base) releases OH- pH scale measures acidity/alkalinity Low pH value, acid High pH value, alkaline (basic) pH 7 = neutral

25. Carbonate buffering Keeps ocean pH about same (8.1) pH too high, carbonic acid releases H+ pH too low, bicarbonate combines with H+ Precipitation/dissolution of calcium carbonate CaCO 3 buffers ocean pH Oceans can absorb CO 2 from atmosphere without much change in pH

26. Fig. 6-17

27. Hydrologic cycle Fig. 6-19