2.1.6 Part 2: Ocean-Atmosphere Fluxes & Pumps

How much anthropogenic CO₂ is absorbed by the oceans annually?

Approximately 25% of annual emissions (~2.5 GtC/year) via physical diffusion.

Why do polar waters absorb CO₂ more effectively than tropical waters?

CO₂ solubility is significantly higher in colder water temperatures.

How much carbon do phytoplankton fix globally per year?

Approximately 50 GtC per year (equivalent to total terrestrial plant photosynthesis).

What percentage of dissolved inorganic ocean carbon exists as bicarbonate ions?

Approximately 90%, serving as a semi-permanent carbon store.

How much has surface ocean pH fallen since 1750 due to ocean acidification?

Fallen by 0.1 pH units, representing a 30% increase in acidity.

Contrast upwelling and downwelling regions in the carbon cycle.

Upwelling: Deep, carbon-rich waters rise and release CO₂ to the air (net source). Downwelling: Cold surface water sinks, transporting carbon to deep stores (net sink).