BI380: Chapter 7 - Ocean Chemistry

Key Concept 1

Water is a powerful solvent. The concentration of dissolved inorganic solids in water is its salinity.

Key Concept 2

Though salinity may vary with location, the ratio of dissolved solids and seawater is constant

Key Concept 3

Gases dissolve in seawater. Cold water can hold more gas in solution than warm water (why colder water is more nutrient rich)

Key Concept 4

The ocean is a vast reservoir of carbon. The dynamics of carbon exchange between ocean at atmosphere affect Earth's climate

Key Concept 5

The ocean's acid-base (pH) balance varies with depth and dissolved components. Carbonate chemistry serves to serves to moderate (buffer) wide swings in oceanic pH.

hydrologic cycle

The cycle through which water in the hydrosphere moves; includes such processes as evaporation, precipitation, and surface and groundwater runoff

Vast majority of the Earth's water is where?

On the Earth's surface (97.5% in the ocean)

solution

made of two components: the solvent and solute

solvent

usually a liquid and more abundant than constituent

solute

usually a dissolved solid or gas (less abundant)

Mixture

A combination of two or more substances that are not chemically combined (like sand and water)

ion

at atom or small group of atoms that has an unbalanced electrical charge

Salinity

The total amount of dissolved salts in a water sample. (ocean's salinity varies from 3.3% to 3.7%)

Heat capacity of water decreases with increasing salinity

(less heat is necessary to raise the temp of seawater by 1 degree than is required to raise the temp of freshwater by the same amount)

Salinity increases

freezing point of water decreases (salt acts as an antifreeze)

Which evaporates faster, seawater or fresh water?

Fresh water. Sea water lingers longer because the dissolved salts tend to attract water molecules

colligative properties

properties of a solution that depend only on the number of particles dissolved in it, not the properties of the particles themselves. The main ones are boiling point elevation and freezing point depression.

osmotic pressure

the pressure exerted on a biological membrane when the salinity of the environment is different from that within cells, rises with increasing salinity

trace elements

elements present in amounts less than 0.001 (1 ppm)

excess volatiles

components of ocean water whose proportions are not accounted for by the weathering of surface rocks

Deeply trapped volatile substances escape to the exterior by

the movement of tectonic plates, outgassing through volcanoes and rift vents

What are some examples of excess volatiles?

carbon dioxide, chlorine , sulfur, hydrogen, fluorine, nitrogen and water vapor

Forchhammer's Principle

The constant proportion of solids or salts in seawater, aka principle of constant proportions

Salinity is calculated by seawater's

conductivity (measure of the water's ability for electrical currents to pass through)

What are some elements present in the ocean?

Bicarbonate, calcium, sulfate, sodium, magnesium, chloride, Hydrogen, carbon dioxide and hydrochloric acid

salinometer

An electronic device that determines salinity by measuring the electrical conductivity of a seawater sample.

residence time

average length of time an atom of an element spends in the ocean

conservative constituents

seawater constituents that occur in constant proportion or change very slowly through time, long residence times

nonconservative constituents

substances dissolved in seawater that are ties to biological or seasonal cycles or to very short geological cycles (short residence times)

ex. dissolved oxygen, co2, silica and calcium compounds

What is the most abundant gas dissolved in sea water?

Nitrogen (48% of dissolved gas in seawater in nitrogen)

What do living organisms use nitrogen for?

use it to build proteins and other important chemicals

How much oxygen is dissolved in the ocean?

36%

The ocean is a vast carbon reservoir

CO2 combines chemically with water to form a weak acid; water can hold a thousands times more co2 than either nitrogen or oxygen

Gas concentration vary with depth

As oxygen decreases in water, CO2 increases and vice versa

Acid

substance that releases a hydrogen ion in solution

base

substance that combines with a hydrogen ion in a solution

alkaline solution

solution containing a base

pH scale

measures the concentration of hydrogen ions in a solution

Buffer

compound that prevents sharp, sudden changes in pH;
rivers and lakes have a much smaller buffering capacity

What is the average pH of seawater

8, with bicarbonate ion being most prevalent

The ocean serves as a natural sink for excess CO2

about 25% of the CO2 emitted by human activity in 2000-2006 was taken up by the ocean

Increasing acidity decreases the concentration of calcium carbonate in the water

this makes it hard for construction of some hard parts (shells, skeletons, rigid coverings)

What would be affected by the loss of coral reefs?

loss of species diversity; people; infrastrcuture; lagoon and marine ecosystems; mangrove forests; fisheries; aquaculture operations; tourism and many more