Lecture 17 - Carbon in the Ocean Flashcards
(23 cards)
What is the largest carbon reservoir on Earth’s surface?
The ocean
How much CO₂ does the ocean absorb from the atmosphere annually?
About 2 petagrams (Pg) of carbon per year.
What law describes gas dissolution in seawater?
Henry’s law:
Caq = Kh * P
What affects the solubility of CO₂ in seawater?
Temperature and salinity — solubility decreases as both increase.
What role does wind play in gas exchange?
It creates turbulence that enhances CO₂ transfer between air and water.
What is the gas transfer velocity (k)?
A kinetic factor controlling the rate of gas exchange across the air-sea interface.
How long does it take CO₂ to equilibrate between the ocean and atmosphere?
Around 1 year — longer than for gases like O₂.
What chemical forms does CO₂ take in seawater?
CO₂ (aq), carbonic acid (H₂CO₃), bicarbonate (HCO₃⁻), and carbonate (CO₃²⁻)
What is ocean acidification?
The decrease in seawater pH caused by increased atmospheric CO₂.
What is the average pH of seawater today?
Approximately 8.1 (slightly alkaline).
What is Dissolved Inorganic Carbon (DIC)?
The sum of [CO₂ (aq)], [HCO₃⁻], and [CO₃²⁻].
What is Total Alkalinity (TA)?
A measure of the ocean’s capacity to neutralize acids (mostly from bicarbonate and carbonate ions).
What happens to DIC and TA during ocean acidification?
DIC increases, TA remains nearly constant → pH drops.
What are the three ocean carbon pumps?
Solubility pump, biological pump, and carbonate pump.
What is the solubility pump?
Cold, dense water sinks at high latitudes carrying dissolved CO₂ to the deep ocean.
What is the biological pump?
Phytoplankton convert CO₂ to organic carbon; sinking particles transfer it to the deep ocean.
How long can carbon be stored in the deep ocean below 1000 m?
A: From 100 to 1,000 years.
What is the carbonate pump?
Calcifying organisms form CaCO₃ shells, which alter DIC and TA and sink to depth.
What happens to CaCO₃ in deep water?
It dissolves due to lower temperature and higher pressure, releasing DIC and TA.
What is the carbonate compensation depth (CCD)?
The depth at which the rate of CaCO₃ dissolution equals its supply; below this, no solid CaCO₃ remains.
How does carbonate dissolution affect alkalinity?
It increases both TA and DIC in a 2:1 ratio.
How do photosynthesis and remineralisation affect the carbonate system?
Photosynthesis removes DIC; remineralisation returns it and consumes O₂.
What do sediment traps measure in the deep ocean?
Particulate organic carbon export and seasonal changes in carbon flux.
