Chemistry of Seawater Flashcards

Flashcards about the chemistry of seawater.

Define salinity as a concentration.

the total amount of solid material dissolved in water, typically expressed in parts per thousand (ppt or ‰).

What are the three ways salt concentration can be expressed?

Weight (g/kg or parts per thousand), Volume (g/L), and Moles (moles/kg or moles/L).

What is the typical ocean salinity?

35 ppt or 3.5% salt

Name the major constituents of seawater and explain how they don’t vary in the open ocean.

chloride, sodium, sulfate, magnesium, calcium, and potassium, exist in constant proportions throughout the open ocean. This is known as the principle of constant proportions.

Explain how the sources and sinks of solutes in seawater balance.

The rate of salt addition to the oceans equals the rate of salt removal, keeping the salt content stable over long periods.

What are the sources of dissolved gases in seawater?

Physical processes, chemical processes, and biological activity.

What factors affect the solubility of gas in solution?

Temperature (↑T = ↓G), Salinity (↑S = ↓G), Pressure (↑P = ↑G)

Explain the vertical distribution of oxygen in seawater.

Oxygen concentrations are highest in surface layers due to photosynthesis and diffusion from the atmosphere. Oxygen minimum zones occur at intermediate depths due to high biological activity and low mixing. Oxygen concentrations can increase again in deeper water.

Define pH.

a measure of the concentration of H+ ions in a solution

How is pH buffered in the oceans?

The carbonate buffer system maintains a relatively constant pH in the oceans (7.5-8.4).

List the major inorganic limiting nutrients and describe their distribution in the oceans.

Nitrogen (as nitrate, nitrite, ammonium), phosphorus (as phosphate), and silica are major limiting nutrients. Their concentrations are low in surface waters due to photosynthesis and high in deep waters due to decomposition and respiration.

What is the Principle of Constant Proportions?

Regardless of variations in salinity, in the open ocean the ratios between the amount of major ions in seawater are constant.

What two factors change salinity?

Evaporation and precipitation.

Define a conservative constituent:

Major dissolved ions not generally removed or modified by organisms. Relatively low rate of chemical reaction.

Define non-conservative constituents:

Generally present at much lower concentrations and concentrations modified by biological and chemical processes (dissolved gases, nutrients, etc.).

Give examples of sources of seawater solutes.

Volcanic activity (chlorides, sulfates) and continental crust weathering (Na+, Mg2+, Ca2+, K+).

Give examples of sinks of seawater solutes.

Biological activity, adsorption (ion exchange), chemical reactions, sediment, crust and evaporites.

What is the Redfield Ratio?

The molar ratio of elements in marine phytoplankton: C:Si:N:P = 106:40:16:1.

What are three main methods of desalination?

Change of water’s state (evaporate or freeze seawater), ion exchange columns and semipermeable membranes.