Topic 6: Ocean Acidification

Pteropods

Free-swimming sea snails with wing-like flaps

• found in upper 10 m of all oceans

• Some shelled, some not shelled

• Important source of food – ‘potato chips of the sea’ for mackerel, salmon, herring, whales

Pteropod experiment

Shells placed in sea water with pH and carbonate levels projected for the year 2100

Pteropod experiment results

Damaged shells (ridges, cloudy, weak spots) due to ocean acidification

Ocean acidification

Consequence of excess carbon dioxide in the atmosphere resulting in excess CO2 in seawater (and therefore decreased pH)

Time for ocean system to buffer

1,000 to 100,000 years

pH scale

Specifies the acidity or basicity of an aqueous solution

Acidity

Concentration of H+ in solution; with increased concentration of H+, pH decreases

Buffering

Minimize pH changes (doesn’t work in ocean right now because of how fast pH is dropping)

Two ocean buffering reactions

Ocean acidification reaction

3 types of carbon created when CO2 enters ocean (in order)

1. carbonic acid

2. bicarbonate ion

3. carbonate ion

Dissolved inorganic carbon (DIC)

Total amount of carbonic acid, bicarbonate ion, and carbonate ion in the ocean

Step 1: ocean acidification

Atmospheric CO2 combines with seawater to form carbonic acid, then form bicarbonate ions and free H+

Step 2: ocean acidification

Bicarbonate ions dissociate

What are calcite and aragonite

Polymorphs of CaCO3

4 Characteristics of calcite

1. Trigonal crystal system

2. Stable

3. Varying amounts of Mg²+

4. Plankton, sponges, brachiopods,

   echinoderms, bivalves (parts of

   shell

5 Characteristics of aragonite

1. Orthorhombic crystal system

2. Strong at higher P

3. Metastable state

4. Greater solubility

5. Corals, pteropods, most molluscs

Type of ocean we live in today (calcite vs aragonite?)

Aragonite sea

Calcite vs aragonite seas

Shift over geologic time, means that different organisms are reef-builders

3 Causes of shifting calcite vs aragonite seas

1. Climate cycles

2. Submarine volcanism

3. Seafloor spreading rates

Step 3: ocean acidification

Steps 1 and 2, moving right or left

3 Climate effects of ocean acidification

1. Decrease in the pH (increasing acidity) of the Earth's oceans (caused by the uptake of carbon dioxide (CO2) from the atmosphere)

2. Difficult for organisms (calcifiers) to create hard parts (less carbonate available + requires more energy)

3. Decrease in the ocean’s capacity to absorb CO2

Effects of ocean acidification on specific organisms

1. For calcifiers: smaller shell sizes, more ‘fragile’ shells, dissolving shells, low reproductive rates in oysters

2. Weaker byssal threads in mussels (cannot stay attached to things as easily)

4 Effects of ocean acidification on humans + animals

1. Loss of biodiversity

2. Affects food security

3. Money loss (aquaculture, tourism)

4. Loss of coastal protection