1. MenuPreviousNext 8 - 1 nA source of sea salts appears to be minerals and chemicals eroding and dissolving into fresh water flowing into the ocean. nWaves and surf contribute by eroding coastal rock. nHydrothermal vents change seawater by adding some materials while removing others. nScientists think these processes all counterbalance so the average salinity of seawater remains constant. nThe ocean is said to be in chemical equilibrium. The Inorganic Chemistry of Water Chapter 8 Pages 8-16 to 8-18 Why the Seas Are Salty

2. MenuPreviousNext 8 - 2 Salinity, Temperature, and Water Density nMost of the ocean surface has average salinity, about 35‰. Waves, tides, and currents mix waters to make them more uniform. nPrecipitation and evaporation have opposite effects on salinity.  Rainfall decreases salinity by adding fresh water.  Evaporation increases salinity by removing fresh water.  Freshwater input from rivers lowers salinity.  Abundant river input and low evaporation results in salinities well below average. The Inorganic Chemistry of Water Chapter 8 Pages 8-18 to 8-19

3. MenuPreviousNext 8 - 3 Salinity, Temperature, and Water Density nSalinity and temperature also vary with depth.  Density differences causes water to separate into layers.  High-density water lies beneath low-density water. The Inorganic Chemistry of Water Chapter 8 Pages 8-18 to 8-19

4. MenuPreviousNext 8 - 4 Salinity, Temperature, and Water Density nWater’s density is the result of its temperature and salinity characteristics:  Low temperature and high salinity are features of high- density water.  Relatively warm, low-density surface waters are separated from cool, high-density deep waters by the thermocline, the zone in which temperature changes rapidly with depth.  Salinity differences overlap temperature differences and the transition from low-salinity surface waters to high-salinity deep waters is known as the halocline.  The thermocline and halocline together make the pycnocline, the zone in which density increases with increasing depth. The Inorganic Chemistry of Water Chapter 8 Pages 8-18 to 8-19

5. MenuPreviousNext 8 - 5 Salinity, Temperature, and Water Density The Inorganic Chemistry of Water Global Salinity Chapter 8 Pages 8-18 to 8-19

6. MenuPreviousNext 8 - 6 Acidity and Alkalinity npH measures acidity or alkalinity. nSeawater is affected by solutes. The relative concentration of positively charged hydrogen ions and negatively charged hydroxyl ions determines the water’s acidity or alkalinity.  It can be written like this: The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

7. MenuPreviousNext 8 - 7 Acidity and Alkalinity nAcidic solutions have a lot of hydrogen ions (H+), it is considered an acid with a pH value of 0 to less than 7. nSolutions that have a lot of hydroxyl ions (OH-) are considered alkaline. They are also called basic solutions. The pH is higher than 7, with anything over 9 considered a concentrated alkaline solution. The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

8. MenuPreviousNext 8 - 8 Acidity and Alkalinity The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

9. MenuPreviousNext 8 - 9 Acidity and Alkalinity npH can be measured chemically or electronically. nPure water has a pH of 7 - neutral pH. nSeawater pH ranges from 7.8 to 8.3 - mildly alkaline. nOcean’s pH remains relatively stable due to buffering.  A buffer is a substance that reduces the tendency of a solution to become too acidic or alkaline. The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

10. MenuPreviousNext 8 - 10 Acidity and Alkalinity nSeawater is fairly stable, but pH changes with depth because the amount of carbon dioxide tends to vary with depth. nShallow depths have less carbon dioxide with a pH around 8.5. nShallow depths have the greatest density of photosynthetic organisms which use the carbon dioxide, making the water slightly less acidic. The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

11. MenuPreviousNext 8 - 11 Acidity and Alkalinity nMiddle depths have more carbon dioxide and the water is slightly more acidic with a lower pH.  More carbon dioxide present from the respiration of marine animals and other organisms, which makes water somewhat more acidic with a lower pH. The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

12. MenuPreviousNext 8 - 12 Acidity and Alkalinity nDeep water is more acidic with no photosynthesis to remove the carbon dioxide.  At this depth there is less organic activity, which results in a decrease in respiration and carbon dioxide. Mid-level seawater tends to be more alkaline. nAt 3,000 meters (9,843 feet) and deeper, the water becomes more acidic again.  This is because the decay of sinking organic material produces carbon dioxide, and there are no photosynthetic organisms to remove it. The Inorganic Chemistry of Water Chapter 8 Pages 8-20 to 8-22

13. MenuPreviousNext 8 - 13 Acidity and Alkalinity The Inorganic Chemistry of Water The variation of pH and total dissolved inorganic carbon with depth. Chapter 8 Pages 8-20 to 8-22

14. MenuPreviousNext 8 - 14 The Organic Chemistry of Water Chapter 8 Pages 8-23 to 8-30

15. MenuPreviousNext 8 - 15 The Organic Chemistry of Water Chapter 8 Pages 8-23 to 8-24 Biogeochemical Cycles nOrganic chemistry deals mainly with chemical compounds consisting primarily of carbon and hydrogen. nInorganic compounds such as dissolved sea salts account for the majority of dissolved solids in seawater. nDissolved organic elements also interact with organisms on a significant scale.  These elements are crucial to life and differ from the sea salts in several ways.

16. MenuPreviousNext 8 - 16 Biogeochemical Cycles nProportions of organic elements in seawater differ from the proportions of sea salts because:  The principle of constant proportions does not apply to these elements.  These nonconservative constituents have concentrations and proportions that vary independently of salinity due to biological and geological activity. The Organic Chemistry of Water Chapter 8 Pages 8-23 to 8-24

17. MenuPreviousNext 8 - 17 Biogeochemical Cycles nAll life depends on material from the nonliving part of the Earth.  The continuous flow of elements and compounds between organisms (biological form) and the Earth (geological form) is the biogeochemical cycle. The Organic Chemistry of Water Chapter 8 Pages 8-23 to 8-24

18. MenuPreviousNext 8 - 18 Biogeochemical Cycles nOrganisms require specific elements and compounds to stay alive.  Aside from gases used in respiration or photosynthesis, those substances required for life are called nutrients. nThe primary nutrient elements related to seawater chemistry are carbon, nitrogen, phosphorus, silicon, iron, and a few other trace metals. nNot all elements and compounds cycle at the same rate. nThe biogeochemical cycle of the various nutrients affects the nature of organisms and where they live in the sea. The Organic Chemistry of Water Chapter 8 Pages 8-23 to 8-24

19. MenuPreviousNext 8 - 19 Carbon nCarbon is the fundamental element of life. nCarbon compounds form the basis for chemical energy and for building tissues. nThe seas have plenty of carbon in several forms. It comes from:  Carbon dioxide in the air.  Natural mineral sources - such as carbonate rocks.  Organisms - excretion and decomposition. The Organic Chemistry of Water Chapter 8 Pages 8-24 to 8-26