INTRO TO MARINE SCIENCE - Chapter 5 Reading Notes

The Chemistry of Seawater

Ions

a charged atom or group of atoms

Cation

an ion with a positive charge

Anion

an atom with a negative charge

Ionic Bonds

electrons are transferred from a metal atom to a nonmetal atom

Why are ionic bonds easily broken?

because of the polar nature of the water molecule

Parts per thousand

g/kg

Parts per million

mg/kg

Parts per billion

µg/kg

A typical 1 kg sample of seawater is made up of ______ g of water and ____ g of salt.

965, 35

Salinity

the total quantity of dissolved salt in seawater

Major Constituents of Seawater

• chloride

• sodium

• sulfate

• magnesium

• calcium

• potassium

• bicarbonate

What is the first major constituent of water?

chloride

What is the second major constituent of water?

sodium

What is the third major constituent of water?

sulfate

What is the foruth major constituent of water?

magnesium

What is the fifth major constituent of water?

calcium

What is the sixth major constituent of water?

potassium

What is the seventh major constituent of water?

bicarbonate

Conservative constituents 

do not change with changes in total salt contents and are not generally moved or added by living organisms

Non conservative constituents

do not change in concentration because of biological and chemical processes that occur in some areas of the ocean

What supplies and removes chemicals to the ocean water?

hot water vents on the seafloor

What is associated with hotspots and ridge formation and may play an important role in stabilizing the ocean’s salt composition?

hydrothermal activity

How are salt ions removed from seawater?

• sea spray from the waves is blown ashore

• shallow sea becomes evaporated, and the salts have been left behind as sedimentary deposits called evaporites

Adsorption

the adherence of ions and molecules into a particle’s surface

What does adsorption do?

removes other ions and molecules from seawater

Ion exchange

when strongly adsorbable ions replace weakly adsorbable ions

Where are magma chambers formed?

where molten rock fuses from the mantle into the crust

Principle of constant proportion 

regardless of variations in salinity, the ratios between the amounts of major ions in open ocean water are constant

Saturation concentration

the maximum amount of any gas that can be held in solution

Colder water holds ______ dissolved gas than warmer water

more

Which holds more dissolved gas: less salty or more salty?

less salty

Which holds more gas: water under more pressure or water under less pressure?

water under more pressure

Euphotic zone

where there is sufficient sunlight to carry out photosynthesis

Compensation Depth

the depth at which the rate of photosynthesis balances the rate of respiration

What is produced above the compensation depth?

oxygen

What is produced below the compensation depth?

carbon dioxide

Oxygen can only be added __________.

at the surface

Anoxic

oxygen using

Anaerobic

non oxygen using

Supersaturated

oxygen values at the surface rise above the equilibrium value to 150% or more

Biological pump

the transfer of carbon from CO2 to organic molecules by photosynthesis results in the addition of CO2 to the inert mediate and deep ocean water where the organic material sinks and decays

What are responsible for about 40% of Earth’s total production of organic material by photosynthesis?

phytoplankton

In pure water, the pH is ____.

7

Seawater is slightly ________.

alkaline

What is seawater’s pH?

between 7.5 and 8.5

Buffer

a substance that prevents sudden, or large, changes in the acidity or alkalinity of a solution

The lower the concentration of CO2 in the water, the _______ its pH and the more ________ it becomes.

higher, alkaline

Anthropogenic Carbon Dioxide

carbon dioxide produced by human activities

Keeling Curve

the most widely recognized measurement of human impact on the environment in existence

During which seasons does the concentration of CO2 decrease?

late spring and summer — as plants increase active photosynthesis 

During which seasons does the concentration of CO2 increase?

fall and winter — plants lose their leaves and CO2 is released into the atmosphere by the decay process

Ocean Acidification

the increasing concentration of CO2 in the water causing a decrease in the pH of the water

What is the most important sources of CO2 in seawater?

• direct transfer of the gas from the atmosphere

• respiration of marine organisms

• oxidation of organic matter during decay

Nutrients in Seawater

• nitrogen

• phosphorous

• silicon

Redfield ratio

the relative molar abundance of carbon, nitrogen and phosphorous in marine phytoplankton is C:N:P = 106:16:1

____% of the world’s table salt is extracted from seawater

30

____% of the world’s supply of magnesium comes from the sea

60

____% of the world’s supply of bromine comes from the seas

70

Desalination

the process of obtaining fresh water from salt water

Electrodialysis

uses an electrical field to transport ions out of solution and through semipermeable membranes

Osmosis

the movement of water across a semipermeable membrane; the water moves from the side with the higher concentration of water molecules (low salinity) to the side with the lower concentration of water molecules (high salinity)

Reverse Osmosis

produces fresh water from seawater by applying pressure to seawater and forcing the water molecules through a semipermeable membrane