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