Oceanography Ocean Chemistry
Formal definition of Salinity
measured in terms of conductivity ratio [R] Salinity is related to the conductivity ratio at 15 C and 1 atm (R15)
Seawater Concentrations
mol/kg NEITHER Molar (mol/L solution) nor Molal (mol/kg solvent)
Evaporation Rate
10 x 10^9 L/s [90% falls back to ocean as rain]
Where do components of Ocean Salinity come from?
Earth's Crust
What processes make the ocean saltier? [2]
Evaporation Sea Ice formation
Residence time of Water Molecule in Ocean
1.37 x 10^21 L / 1 x 10^10 L/s = 1.37 x 10^11 s / 3.15 x 10^7 s/y = 4350 yrs Average water molecule will spend 4350 years in ocean before evaporating [some more/less]
Salinity Calculation
0.0080 - (0.1692)(R15^.5) + (25.3851)(R15) + (14.0941)(R15^1.5) - (7.0261)(R15^2) + (2.708)(R15^2.5)
Potassium (K+) concentrations sea v river
0.01021 mol/kg v 0.059 mmol/L
Calcium (Ca+2) concentrations sea v river
0.01028 mol/kg v 0.374 mmol/L
Sulphate (SO4-2) concentrations sea v river
0.02824 mol/kg v 0.117 mmol/L
Percent Carbon Dioxide Atmosphere v Ocean Surface
0.038% v 15%
Magnesium (Mg+2) concentrations sea v river
0.05282 mol/kg v 0.169 mmol/L
Sodium (Na+) concentrations sea v river
0.469 mol/kg v 0.283 mmol/L
Chloride (Cl-) concentrations sea v river
0.54587 mol/kg v 0.220 mmol/L
Flux from Rivers
1 x 10^9 L/s [20% stems from Amazon]
What regions of the ocean do not have normal ionic ratios? [4]
1. Enclosed seas, estuaries, regions with substantial river influx 2. Basins, Fjords, regions with severely restricted bottom circulation 3. Surface waters where Ca+2 is depleted due to the production CaCO3 shells 4. Regions of seafloor spreading and active submarine volcanism [hydrothermal vents]
Volume of the Ocean
1.37 x 10^21 L
Percent Oxygen Atmosphere v Ocean Surface
20.95% v 36%
Seconds in a Year
3.15 * 10^7 s
Standard KCl solution
32.4356 g/kg
Nitrogen
48% of dissolved gas in seawater [upper layers of oceans saturated] Atmospheric N is useless unless you fix it
Percent Nitrogen Atmosphere v Ocean Surface
78.08% v 48%
Average pH of Seawater
8 [Bicarbonate most present]
Oxygen in Oceans
Abundant near surface as a result of photosynthetic activity Decreases below sunlight layer because of respiration and decay of marine organisms
Carbon Cycle [Oceans]
CO2 combines with water to form H2CO3 Carbonic Acid loses H+ ion to form HCO3 or Carbonic Acid loses 2 H+ ions to form CO3-2 Bicarbonate disassociates to form CO3-2 CO3-2 combines with Ca+2 to form CaCO3 CaCO3 used to build shells/skeletons After Organism dies, CaCO3 falls to seabed where it will redissolve
Major Ions found in the ocean
Chloride (Cl-) Sodium (Na+) Sulfate (SO4-2) Magnesium (Mg+2) Calcium (Ca+2) Potassium (K+)
Anoxia
Depletion of O2 Anaerobic microorganisms use sulphate as alternative source of O2
Salinity Rule of Constant Proportions
Even in ocean waters of different salinities, the ratio of major ions to one another is similar nearly all ions in a sample of water can be determined by measuring only one [Cl-]
Carbon Dioxide in Oceans
Low CO2 levels near surface as a result of photosynthetic activity Increases below sunlight layer as its given off by marine organisms Also Increases with depth because solubility increases with increasing pressure/decreasing temp
Nitrogen Fixation
N2 +6H + 6e- -> 2NH3
PPM of Major Gases in Oceans
N: 10-18 O2: 0-13 CO2: 64-107
Nitrate
NO3- 5-25 mu mol/kg Used in production of Proteins
Biolimiting
Nutrients that are never found in sufficient concentrations that are needed for primary production
Global warming & pH
Ocean is becoming more acidic as it absorbs more CO2 Will make it more difficult for organisms to build hard structures containing Ca+2 (CaCO3)
Biologically Active Nutrients [3]
P, Si, N Actively sought out by autotrophs in the surface waters and are never at sufficient concentrations in euphotic zone
Phophate
PO4-3 0.3 - 1.7 mu mol/kg Used in production of ADP, ATP
What processes make the ocean fresher? [3]
Precipitation Sea Ice Melting Freshwater Runoff from Land
What takes ions from the oceans? [4]
chemical entrapment as water percolates through mid-ocean ride and sea mount systems sea spray uptake by living organisms subduction
Conductivity of seawater
Proportional to salinity Presence of ions allows water to carry a current
Conductivity Ratio
R = conductivity of seawater sample / conductivity of standard KCl solution
Empirical relationship of salinity
S = 1.806 x Chlorinity
Silicic Acid
Si(OH)4 5-60 mu mol/kg Used in production of Opal Shells
Chlorinity
concentration of Cl- in seawater
Relative abundance of Carbon ions
The relative abundance of carbonic acid, bicarbonate and carbonate is a function of pH
Oceans Acid-Base Balance
Varies with dissolved components/depth
Conductivity of Pure Water
Very Poor
Resevoir
a defined area in which various substances flow in/out if in steady state the volume will remain the same at any given time
High pH in Seawater
dominated by Carbonate Ion
Low pH is Seawater
dominated by carbonic acid
How is Na+ removed from the Oceans? [2]
hydrothermal reaction or formation of salt beds
Steady State
input = output A condition where inputs are balanced by outputs
What adds ions to the ocean? [6]
riverine runoff volcanic activity groundwater hydrothermal vents cold springs decay of organic matter
Solubility of O2/N
solubility decreases as temp decreases
Nonconservative constituents
substances dissolved in seawater which are tied to biological or seasonal cycles or very short geological cycles
Residence Time
tau = volume of reservoir / flux in or out
Residence Time
the average amount of time a particular substance spends in a defined area assuming the system is at a steady state
Residence Time of Na+2 in Ocean
total amount of Na in oceans / amount of Na per unit time entering the ocean (1.37 x 1021 L * (0.5 mol Na / L) / (1 x 109 L s-1 * 0.0002 mol Na / L) = 3.14 x 1015 s/ 3.14 x 107 s/yr = 100 million years