“The highest form of human intelligence is the ability to observe without judging” Oceanography Krishnamurti Lecture 15 “The intuitive mind is a sacred gift and the a. Seawater Chemistry: rational mind is a faithful servant. We have Sources of Sea salts – Constancy rule created a society that honors the servant c. Residence time: Steady-state and has forgotten the gift” d. Dissolved gases Albert Einstein e. The carbonate system and Carbon cycle “The mind is everything, what you think you become” Buddha Vertical Temperature & Salinity Density Structure of the Oceans: Depth Temperature vs Depth Salinity vs Depth Salinity (‰) Temperature (°C) 34 34.5 35 35.5 36 0 5 10 15 20 0 0 1000 1000 Thermocline Halocline 2000 2000 (m) (m) Depth 3000 Halocline 3000 Depth 4000 4000 5000 5000 The Ocean can be divided into three structures: Surface layer; Pycnocline; Deep-layer. Pycnocline: Amounts to ~18% of the Oceans volume) Salinity • By weight, 96.5% of the Ocean are water, whereas the remainder 3.5% are composed of dissolved substances (salts). So, What is salinity? • Oceans: 1,370.103 km3. • Total weight of salts: 1,370.106 km3 ! 1.1015 cm3/km3 ! 1.03 g/cm3 ! 0.035 4.94! 1022 g of salts ~50 000 Trillion Tons!!!!! ! Could cover the entire planet with an even layer > 50 m in thickness! Salinity: Composition Major Elements Only 7 elements belong to this class > 100 ppm Common Concentration Percent Constituent form (ppm) by weight Chloride Cl- 18,980 50.08% Sodium Na+ 10,556 30.63% - Sulfate SO4 2,649 7.69% Magnesium Mg2+ 1,272 3.69% Calcium Ca2+ 400 1.16% + Only 12 elements make up 99.9% of the dissolved Potassium K 380 1.10% Carbon HCO - 140 0.41% constituents of seawater! 3 Total 34.377 99.76% Minor Elements Trace Elements Only 5 elements belong to this Important trace elements: class 1 ppm > x > 100 ppm Concentration < 1 ppm Common Concentration Percent Common Concentration Percent Constituent Constituent form (ppm) by weight form (ppb) by weight Nitrogen N 280 <0.001 Bromide - Br 65 0.19% Lithium Li 125 Strontium Sr2- 8 0.02% Iodine I 60 Boron B3+ 4.4 0.01% Phosphorus P 30 Zinc Zn 10 Silicon Si(OH)4 4.9 0.01% Iron Fe 6 Fluorine F- 1.4 0.004% Aluminum Al 2 Manganese Mn 2 Total 83.7 0.234% Etc… … Salinity distribution Uniformity? Uniformity? Sea water chemistry Uniformity of Ocean Water Principle of constant proportions 75% of the total Ocean volume • In 1865, the chemist George Forchammer noted that, have a although the total amount of dissolved solids (salinity) • Temperature: 0-5°C might vary among samples, the ratio of major salts in • Salinity: 34-35‰ samples of seawater from many locations was Oceans’ depths are filled with constant! cold water (colder than the ~17.5°C average T of the Na/Cl = 0.56; S/Cl = 0.14; Mg/Cl = 0.07 Oceans’ surface waters). ! Most of this water must have Regardless of changes in salinity (total amount of salts)! originated in polar latitudes, where it was chilled by losing The way salinity changes throughout the Oceans heat to the frigid air. depends almost entirely on: ! Uniformity of T and salinity - evaporation/precipitation balance, and of subsurface seawater from Ocean to Ocean suggests that - extent of mixing between surface and deep waters. Ocean basins are open systems! Departure: Departure: Ø Extensive areas of warm, shallow waters (i.e. Ø Utilization of carbon, calcium and magnesium by Bahamas), characterized by very active chemical biological activities (hard skeletons) and/or biological precipitation of calcium carbonate leading to changes in Ca2+ and HCO - to Ø Enclosed seas: estuaries and other regions can 3 total salinity. receive substantial inflow of river water which may contain less salts in different proportions Ø Areas of sea-floor where interstitial (pore) waters in sediments react with sediments ! Ø Basins, Fjords, etc., where bottom circulation is leading to large changes in ionic ratios. severely restricted (i.e. Black Sea). Complete - Ø Regions of sea-floor spreading and active utilization of O2 followed by SO4 . Ø Regions of sea-floor spreading and active submarine volcanism where heated seawater circulates through cracks of the oceanic crust. Ionic ratio in hydrothermal solutions are very different from those of normal seawater Example: Water on Earth Sources of Sea Salts? ! Water is a great solvent: a great many substances can dissolve within its matrix. ! Rain and river dissolve continental crustal rocks due to the formation of acids (H2CO3; H2SO4, HCl) and the solvent properties of water. ! H2O + CO2 " H2CO3 (acid) ! SO2 + OH + H2O # # H2SO4 (acid) !These dissolved species then reach the Oceans !So, does that mean that Oceans: through surface flow in rivers (rivers provide most of the dissolved elements to the Oceans!). • Have a diluted but similar composition as crustal rocks? • Are concentrated versions of river water? Sources of Sea Salts? Sources of Sea Salts? !So, does that mean that Oceans: !So, does that mean that Oceans are: • Have a diluted but similar composition as crustal rocks? • Concentrated versions of rivers? The three most abundant Rain Element % by weight elements in the crust (Si, Al, Fe) Si 28.2 do not appear at all in the Al 8.2 major-minor dissolved elements Fe 5.6 of the Oceans. Why? Ca 4.2 River Na 2.4 ! K 2.4 Solubility and reactivity of Mg 2.0 different elements. Ti 0.6 ! Si, Fe, Al (very common) not Mn 0.1 very soluble. Remain as particles P 0.1 ! Na, Ca, K, are relatively Seawater soluble and remain in solution Average percentages by weight of the ten most abundant elements (other than oxygen) in the Earth’s crust Sources of Sea Salts? Sources of Sea Salts? ! So, what is it? Origin of Chloride: It’s a matter of how fast the “clock ticks”… Negligible proportions of chloride in river water comes from weathering. • As water moves through the hydrological cycle on Chlorine comes from volcanism ! Continents, it picks up salts (dissolved constituents) (excess volatile) Weathering. So does sulfur! • Salts can then be maintained in solution for a long time But, if input is so small how can (rates!). the total mass be so high? Simplified Examples: H2O + CO2 " H2CO3 (acid) 2+ - • CaCO3 (calcite - sed) + H2CO3 (acid) " Ca + 2 HCO3 (bicarbonate) • 2NaAlSi3O8 (albite - metam/ign) + 5H2CO3 " Al2Si2O5(OH)4 + (kaolinite) + 2Na + H2CO3 + 4 SiO2 (partly sol) Ocean Salinity Sources of Sea Salts? Residence time! • Paradox: Oceans contain, in high concentrations, Total mass of dissolved compounds in the Ocean elements that are rare in Earth Crust; and, in low Rate of supply (or removal) concentrations, elements that are abundant in the Earth’s crust. Chloride: 261 1014 t/2.54 108 t/yr – Selective weathering – Residence time 1.03 108 yrs 103 Million Years! (Corrected ! ) Iron: 1.4 109 t/0.22 108 t/yr 64 yrs! Changes in residence time = Changes in reactivity Residence time – reactivity – mixing rate Steady State ! It seems so for several 100’s of My! And how do these elements leave? Ø Biological uptake/Chemical precipitation Ø Precipitation/Adsorption Ø Reverse weathering Ø Hydrothermal fluids Major elements Minor elements Biolimiting elements Steady State ! It seems so for several 100’s of My! Dissolved gases in water And how do these elements leave? Take a break, Grab a soda… • Biological uptake/chemical precipitation: Let’s assume we have a clear bottle of soda… Ca2+ + CO 2- " CaCO 3 3 You pop the lid ! gas escapes! (pressure) • Precipitation/Adsorption ! Fe + particles ! Iron-rich Clay particles You shake it more gas escapes! (mixing) Sediment diagenesis (Fe, Mn, S, metals) You warm it up ! even more gas escapes! • Reverse Weathering (temperature) Does it stop? ! 5Al Si O (OH) + 2K+ + 2HCO - + 4SiO " 2 2 5 4 3 2 ! 2KAl5Si7O20(OH)4 (Illite)+ 7H2O + 2 CO2 When final gas content of soda is at equilibrium + - with temperature and pressure ! Aluminosilicate + Na + HCO3 + SiO2 " Na0.33Al2.33Si3.67O10(OH)2 (Montmorillonite)+ H2O + CO2 • Hydrothermal fluids (1979) Sink for Mg. But source of Ca, K, Si, Fe… (?) Dissolved gases in water Take a break, Grab a soda… Density structure of the Ocean The total amount of gas that can be dissolved eventually reaches an equilibrium concentration which is proportional to: - Atmospheric concentration of gas in atmosphere - Temperature, - Pressure, - Salinity of water. The amount of gas usually $ as: P $ T % S % Dissolved gases in the Ocean Oxygen in the Ocean CO2(gas) + H2O + Energy " H12C6O6 (sugar) + O2 (gas) Photosynthesis possible only in photic zone (0-200 m) CO2(gas) + H2O + Energy " H12C6O6 (sugar) + O2 (gas) Oxygen minimum (utilization) at pycnocline – O2 Minimum Photosynthesis only in possible in photic zone (0-200 m) Oxygen limitation (utilization) at pycnocline – O2 Minimum Dissolved gases in the Ocean Temperature is the most important controlling factor! Dissolved gases in the Ocean The most abundant gases in the atmosphere: - N (78%) Argon and the other noble gases (He, Ne, Kr, and Ra) and 2 Nitrogen are essentially unreactive in the Oceans: - O2 (21%) - Argon (0.9%) Conservative gases - CO (0.03%) 2 In contrast, CO2 and O2 concentrations are altered by many The most abundant gases in the Oceans: biological and chemical processes in the sea. Non-conservative gases - CO2 (94.3%). Much more soluble! - N (3.4%) 2 Photosynthesis/Respiration: - O2 (2%) - Argon (0.3%) CO2(gas) + H2O + Energy # H12C6O6 (sugar) + O2 (gas) Difference due to the reactivity of CO2 is seawater leading to the various carbonate and bicarbonate equilibria H12C6O6 (sugar) + O2 (gas) # CO2(gas) + H2O + Energy + - + 2- CO2(gas) + H2O " H2CO3 " H + HCO3 " H + CO3 Dissolved gases/nutrients in the Ocean Dissolved gases in the Ocean CO2(gas) + H2O + Energy " H12C6O6 (sugar) + O2 (gas) Photosynthesis only possible in photic zone (0-200 m) CO2(gas) + H2O + Nutrients (N,P) + Energy " OM + O2 (gas) Oxygen limitation (utilization) at pycnocline – O2 Minimum.