Water – The Universal Solvent Water is often called the universal solvent because …? Why do so many substances readily dissolve in water?

Solubility Solubility is the ability of a substance to dissolve in a liquid. This is determined by the molecular arrangement of the liquid and the substance. Solvent = does the dissolving Solute = is the substance dissolved

Water is polar. Substances with (+) and (-) surface charges are attracted to the (+) and (-) ends of the water molecule. Hydrogen bonding of these electrically polarized molecules gives water the properties of cohesion, adhesion and dissolving power.

Composition of Seawater Seawater consists of about 3.5% (by weight) of dissolved minerals; typically expressed in parts-per-thousand (‰) Salinity (NaCl) Average salinity is 35‰

Relative proportions of water and dissolved components in seawater

Ions in Seawater HMS Challenger: 1884 Dittmar found that the relative concentration of ions is the same all over the world (took over 77 samples from various depths and locations). Sources: Chlorine, sulfates from volcanic activity Na, Mg, K, Ca ions come from the weathering of feldspar-rich rocks (granites and other igneous rocks).

Sulfur – hydrothermal vents

Salinity Sources of sea salts Chemical weathering of rocks Outgassing – gases from volcanic eruptions Surface salinity in the open ocean ranges from 33‰ to 38‰ Processes that decrease salinity (add water) Precipitation Runoff from land Icebergs melting Sea ice melting Processes that increase salinity (remove water) Evaporation Formation of sea ice

Ocean temperature variation with depth Low-latitudes High temperature at the surface Rapid decrease in temperature with depth Called the thermocline High-latitudes Cooler surface temperatures No rapid change in temperature with depth

Variations in ocean water temperature with depth

Variations in the ocean’s surface temperature and salinity with latitude

Ocean Density Density is mass per unit volume – how heavy something is for its size (g/cm3) Determines the water’s vertical position in the ocean Factors affecting seawater density: Temperature - the greatest influence Salinity

Variations in ocean water density with depth

Ocean Layering Three-layered structure Shallow zone(300 – 450 m) Surface mixed zone Sun-warmed zone Zone of mixing ~2% of ocean water Transition zone Between surface layer and deep zone Thermocline and pycnocline ~18% of ocean water Deep zone Sunlight never reaches this zone Temperatures are just a few degrees above freezing Constant high-density water ~80% of ocean water

Layering in the ocean

Thermohaline Oceanic Circulation