Ocean Acidification

Question 1

Atmospheric CO2: now and in the past

Answer 1

• Charles Keeling (San Diego’s Scripps Institution of Oceanography) receives the Medal of Science in 2001.
• Increase of ~ 2.7 ppm/year in the last 15 years.
• 415 ppm is thought to have been attained 4.5 million years ago in the Pliocene.

Question 2

Causes and mechanism

Answer 2

• Fossil fuel combustion and deforestation are the two main contributors.
• Total emissions since the industrial revolution exceed 1,500 billion tons.
• 50% of total emitted CO2 remains in the atmosphere, 25-30% is absorbed by the oceans, and 20-25% by land.

Question 3

Issue of OA to Calcifying Organisms

Answer 3

• Chemical reactions: CO2(aq) + H2O H2CO3; H2CO3 HCO3- + H+; HCO3- CO32- + H+; CaCO3(s) Ca2+ + CO32-.
• Ocean Acidification: CO2 (aq) + H2O + CO32- 2HCO3-.
• Impact on marine organisms: pteropods, foraminifera, coccolithophores, corals, mussels, sea urchins, brittlestars, algae, and more.

Question 4

Issue of OA to Fishes

Answer 4

Physiological implications: hypercapnia symptoms, metabolic performance, activity, reproduction, early life survival and growth, neurosensory and cognitive impairment, respiratory acid-base disturbances.

Question 5

Overall

Answer 5

pH decrease from 8.2 to 8.1 since pre-industrial times (26% increase in H+).
Predicted reduction of pH by 0.15-0.45 units by 2100.
pH of 7.8 not experienced in seawater for the last 50 million years.
pH decrease from 8.2 to 7.7 triples the concentration of [H+].

Question 6

Historical Facts

Answer 6

Charles Keeling’s research on atmospheric CO2 levels.
CO2 emissions since the industrial revolution.
Human release of CO2 in 2019.

Question 7

Is Ocean Acidification Happening?

Answer 7

pH decreasing at a rate of about 0.0012-0.002/year.
Trends observed at Station ALOHA and the Hawai‘i Ocean Time-series (HOT) Program

Question 8

Proof of OA affecting Calcifying Organisms

Answer 8

Impact on corals, coccolithophores, pteropods, Dungeness crabs, gastropods, and more.
Experimental manipulation studies showing varied responses to increasing levels of seawater CO2.

Question 9

What does ocean acidification do ?

Answer 9

decreases pH and carbonate ion concentration, affecting calcifying organisms’ ability to build their shells and skeletons.

Question 10

What are the chemical equations?

Answer 10

CaCO3(s) Ca2+ + CO32-
Solubility product (Ksp) determines saturation levels:
If W > 1, supersaturation.
If W < 1, undersaturation

Question 11

Types of Carbonate Minerals

Answer 11

• Calcite and Aragonite
• Aragonite is about 1.5 times more soluble than calcite

Question 12

Aragonite saturation depth

Answer 12

• Varies widely across oceans
  Pressure affects solubility; harder to calcify at depth
• In some shallow areas, sediments accumulate carbonate minerals, while dissolution occurs in deeper areas.

Question 13

Impact of Antropogenic CO2

Answer 13

Shallowing of saturation depth with OA observed
Differences between oceans due to biological respiration

Question 14

OA in coastal waters

Answer 14

pH changes expectations from CO2 uptake alone
Various drivers: CO2, light, upwelling, chlorophyll, temperature, alkalinity, salinity, PDO

Question 15

Direct and Indirect Causes of OA in Coastal Waters

Answer 15

Direct: CO2 increase, acid rain, upwelling
Indirect: Nutrient inputs, freshwater delivery, trace metal bioavailability

Question 16

Unexpected Results and Learning Outcomes:

Answer 16

Some organisms show resilience or adaptation to OA.
Studying OA impacts on organisms and ecosystems is complex and ongoing.

Question 17

What was the focus of the study on shallow-water corals?

Answer 17

The study investigated the impact of ocean acidification on the skeletal growth of eight-day-old corals.

Question 18

How was the experiment conducted?

Answer 18

Corals were placed in aquarium seawater at different saturation levels to simulate varying levels of acidity.

Question 19

What was observed regarding coral growth?

Answer 19

The study found that higher acidity negatively impacted the skeletal growth of the corals.

Question 20

How does ocean acidification (OA) affect fish?

Answer 20

OA can lead to hypercapnia symptoms in fish due to higher CO2 concentrations, impacting metabolic performance, activity, reproduction, early life survival and growth, neurosensory function, and respiratory acid–base balance.

Question 21

How does ocean acidification affect calcifying organisms?

Answer 21

Ocean acidification reduces pH and carbonate ion concentration, making it harder for calcifying organisms to build their shells. The solubility product (Ksp) determines whether the seawater is supersaturated (W > 1) or undersaturated (W < 1) with respect to calcium carbonate (CaCO3).

Question 22

How does ocean acidification affect calcifying organisms in relation to carbonate minerals?

Answer 22

Ocean acidification reduces the saturation state of carbonate minerals like aragonite and calcite, crucial for calcifying organisms. Aragonite requires a higher concentration of carbonate ions ([CO32-]) for saturation to occur compared to calcite.

Question 23

What defines the aragonite saturation depth?

Answer 23

The aragonite saturation depth is where the solubility product (Ksp) equals 1. Above this depth, conditions favor precipitation, while below it, dissolution is favored.

Question 24

How does ocean acidification affect the saturation depth of calcite and aragonite?

Answer 24

Ocean acidification causes a shallowing of the saturation depth for calcite and aragonite in the ocean. As pressure increases with depth, the solubility of calcite and aragonite also increases, leading to changes in the saturation depth.