1. Seawater and Ocean Chemistry

2. Seawater Chemistry Water Water Seawater Seawater Salts in seawater Salts in seawater

3. Composition Composition Properties Properties Water

4. Water is … a chemical compound (H 2 O) comprising two atoms of hydrogen and one atom of oxygen, in liquid state...

5. Ques tion: The fusion of how many deuterium atoms would create a carbon atom? nitrogen atom? oxygen atom?

6. Two hydrogen atoms share their electrons with one oxygen atom to form the electrically polarized water molecule + - + + + - - - - - - - + - + - + - + + + - - - - - - - + - + -

7. + - + + + - - - - - - - + - + - 105° + - + + + - - - - - - - + - + - 109° When water freezes to ice, the angle of hydrogen bonding expands from 105° to 109°. As the space taken by 27 water molecules is now used by 24 molecules, the density of ice is less than the density of water, i.e., water freezes over.

8. Hydrogen bonding of these electrically polarized molecules gives water the properties of cohesion, adhesion and dissolving power.

9. Common salt (NaCl) thus dissolves in water most readily. It is the ocean’s most abundant constituent, therefore.

10. Atomic Number Atomic Weight (or Mass) Number of Electrons Number of Protons Number of Neutrons Sodium (Na) 11 23 11 12 Chlorine (Cl) 17 35 17 18

12. Fresh water comprises Oxygen: 857.8g (=85.8%) Hydrogen: 107.2g (=10.7%)

13. 0.0 0.5 1.0 1.5 2.0 909498102106110 1.53.04.56.07.5 Depth (km) Concentration of dissolved gases (parts per million, by weight) CO 2 O2O2O2O2 O2O2O2O2 Dissolved gases (O 2 and CO 2 contents here) tell us much about biological activity in the ocean: Deep waters show increasing gas content with depth. Deep waters show increasing gas content with depth. An oxygen minimum layer is often seen at intermediate depths. An oxygen minimum layer is often seen at intermediate depths. Surface waters often have excess O 2 and lack CO 2. Surface waters often have excess O 2 and lack CO 2.Why?

14. Nitrogen (N 2 ) Oxygen (O 2 ) Carbon dioxide (CO 2 ) 78.08% 20.95% 0.035% 48% 36% 15% atmosphereseawater % of gas, by volume in Dissolved Gas Most of carbon from the Earth’s atmosphere eventually ended up in the ocean

15. Major constituents of Seawater at 3.5% Salinity Constituent Water: Oxygen (O) Hydrogen (H) The most abundant ions Chloride (Cl - ) Sodium (Na + ) Sulfate (SO 4 2 - ) Magnesium (Mg 2+ ) Calcium (Ca 2+ ) Potassium (K + ) Bicarbonate (HCO 3 - ) 85.8% 10.7% 1.9% 1.1% 0.3% 0.1% 0.04% 0.01% only 2% of Cl in seawater could have come from land sources only 20% of sulfur in seawater could have come from land sources

16. Constant Proportions and Conservative Constituents 1.Some constituent salts in seawater occur in constant proportions, e.g., Thus, for average seawater with Cl = 19.2‰, salinity = 1.80655 × 19.2‰ = 34.7‰ 2.The constituents of seawater that occur in constant proportion (i.e., change very slowly) are known as conservative constituents or elements. Dissolved Salts in Seawater (‰) Chlorine in Seawater (‰) =1.80655

17. Salt brought in by run-off from land can explain only ~2% of Cl and ~20% of S in the seawater

18. Why is seawater salty? Hydrothermal activity on the seafloor can provide the Hydrothermal activity on the seafloor can provide the – sources for excess Cl and S and – sinks to balance the continued enrichment in sulfates and magnesium by streams. We should also note that, compo- sitionally, seawater has remained remarkably uniform through the earth’s history We should also note that, compo- sitionally, seawater has remained remarkably uniform through the earth’s history

19. 1,000 1 10 100 10,000 Quadrillion (10 15 ) Metric Tons Estimated existing quantity Annual volcanic output x Age of the Earth Water Sulfur Nitrogen Carbon Chlorine This comparison of the total quantities of selected substances in the oceans and atmosphere with what could have come from volcanism favors the volcanic origin of these substances. Adapted from Robert Decker & Barbara Decker: VOLCANOES (W.H. Freeman, New York, 1996)

20. During the initial 2 Ga of its history, Earth may well have received 2 x 10 8 to 1 x 10 17 metric tons of cometary matter by way of bombardment episodes. Comets may well have contributed significantly, therefore, to the hydrospheric mass of 1.4-1.7 x 10 18 metric tons. Indeed, all this water could have been produced by either ~10% of the cometary mass or entirely by the asteroidal source if initial bombardment was of carbonaceous chondrites. The case for extraterrestrial origin of the oceans Deuterium Total Hydrogen ratio Comet Halley Earth’s Oceans 0.06-0.48 ppt 0.16 ppt Comets are >40% water. The deuterium/hydrogen ratio of comets and oceans overlap. Adapted from C.F. Chyba & C. Sagan in COMETS AND THE ORIGIN AND EVOLUTION OF LIFE (Ed: P.J. Thomas, C.F. Chyba & C.P. McKay; Springer-Verlag, New York, 1997).

21. A trio of frames from Polar's Visible Imaging System (VIS), taken 6 seconds apart last December 31st, captures an object rapidly descending toward northern Europe. Because the camera's filter isolates emission from hydroxyl (OH) radicals, the incoming object must have contained abundant water (the map of Earth is intended for reference).

22. Suppose annual influx from outer space is 50- 100 billion gallons of water vapor into the atmosphere, and that Compare this to the total amount of water in the oceans = 1370x10 6 Km 3 (volume)  10 9 m 3 /Km 3  264.2 gallons/m 3 =362  10 18 gallons of water this rate has been constant through geological history (~4.5 billion years). This amounts to 225- 450 x 10 18 gallons of water.

23. Therefore, there is no problem in accepting the extraterrestrial possibility, except that this requires a much smaller ocean anda much smaller ocean and an appreciably weaker hydrological cyclean appreciably weaker hydrological cycle in the past, than at the present. But there is no geological evidence to support this possibility.