Ocean Chemistry and Composition Brian Schuster

Chemical Properties of Sea Water polar: unequal sharing of electrons hydrogen bonding: intermolecular dipole-dipole interaction between H 2 O molecules cohesion: sticking of H 2 O molecules to each other resulting from hydrogen bonding; causes surface tension adhesion: sticking of H 2 O molecules to other polar materials capillarity: movement of water up a small tube latent heat: energy stored in water that doesn’t change it’s temperature

Acidity/Alkalinity ocean: pH 7.5 to 8.5 due to carbonate (CO 3 -2 ) from dissociation of calcium carbonate freshwater: pH 6.5 to 7.5 due to carbonic acid (H 2 CO 3 ) bicarbonate buffering, resistance to pH change –H 2 O + CO 2  H 2 CO 3 (carbonic acid=weak acid) –H 2 CO 3  H + + HCO 3 - (bicarbonate=buffer) –CaCO 3  Ca +2 + CO 3 -2 (carbonate=base)

Temperature depth dependent thermocline: rapid change in temperature around a certain depth; more defined near equator; less prominent at poles isotherm: line of constant temperature

Global isotherms display currents

Salinity isohaline: line of constant salinity residence time: average time a molecule spends in a certain reservoir salinometers: determine salinity through conductivity halocline: rapid change in salinity constancy of composition: major ion constituents exist in constant proportions water is the “universal solvent” ocean salinity: 35ppt, brackish: 17ppt, brine: >50ppt saltiest sea: Dead Sea

Salinity (continued) Long-term sources: –hydrothermal vents & volcanoes –weathering of rocks cation: positively charged ion anion: negatively charged ion salinity effected by: –precipitation, evaporation –freezing, thawing –river input Top six constituents –chlorine (Cl - ) 55% –sodium (Na + ) 31% –sulfate (SO 4 -2 ) 8% –magnesium (Mg +2 ) 4% –calcium (Ca +2 ) 1% –potassium (K + ) 1%

Desalination 1.reverse osmosis 2.freezing & thawing 3.ion exchange 4.distillation (evaporation & condensation)

Density pycnocline: rapid change in density freshwater most dense at 4 °C, saltwater most dense just before freezing saltwater freezes at -2 °C (freezing point depression) density affected by: –temperature –salinity –depth, pressure: minimally isopycnal: surface of constant density

Pressure and Gases rises by 1 atm (14.7 psi, kPa) for every 10 m (33 ft) depth absolute pressure at 20 m is 3 atm gauge pressure at 20 m is 2 atm isobar: line of constant pressure

Dissolved Gases Henry’s Law: more gas can be dissolved under high pressure more gas is dissolved in deep, cold water oxygen minimum zone: depth depends on productivity and aerobic respiration atmospheric gases resemble ocean’s due to mixing

Calcium Carbonate (CaCO 3 ) used in shells, compound of limestone and calcite, base of coral reef sources and sinks –chemical precipitation, dissolution –weathering of limestone and calcite –organisms solubility increased by: –greater depths –higher acidity (lower pH) carbonate compensation depth (CCD): dissolution rate of CaCO 3 equals supply rate

Nutrients eutrophication: excessive addition of nutrients oligotrophication: excessive removal of nutrients iron is the limiting nutrient for most algae South Atlantic phytoplankton bloom

Heat Transfer conduction: molecules speed each other up by physically bumping convection: carried by movement of fluid radiation: electromagnetic radiation is absorbed and raises temperature heat is conducted faster in water than in air, so divers can get cold faster

Sound in water, speed of sound = ~1500 m/s (3500 mph), 5x speed in air speed changes with density sound travels farther in water than light, so it is good for cetacean communication SOFAR (sound fixing and ranging) channel: sound travels slower around 1000 m, and can go farther; sound gets stuck in this channel

Light penetration –long wavelengths (red) absorbed first –mid-range wavelengths (green, blue) go farthest attenuation: decrease in light intensity due to absorption and scattering by suspended particles turbidity increases attenuation index of refraction (n) = 1.33

Other conservative property: mostly affected by mixing and diffusion (ex: salinity) non-conservative property: affected mostly by processes other than mixing and diffusion (ex: dissolved oxygen relating to productivity) temperature-salinity diagram: unique to different bodies of water; shows lines of constant density in sigma units