Week 7 Flashcards
(34 cards)
What drives vertical mixing in the ocean?
Buoyancy, determined by temperature and salinity.
Where does deep water formation occur and why?
In polar regions, where surface water is cold and salty (dense and heavy).
Why is vertical mixing suppressed in most ocean regions?
Surface water is warmer (less dense) than deeper water.
What causes vertical mixing in the surface ocean?
Wind stress creates a mixed layer ~100 m deep.
What are the residence times of water in ocean reservoirs?
Mixed layer: 18 years
Intermediate ocean: 40 years
Deep ocean: 120 years
How long does it take for the entire ocean to equilibrate with atmospheric CO₂?
About 200 years.
How much fossil fuel CO₂ can the oceanic mixed layer absorb directly?
Only ~6%.
What controls fossil fuel CO₂ uptake by oceans?
Rate of deep water formation and surface mixing.
How does phytoplankton contribute to CO₂ uptake?
Through photosynthesis and forming organic carbon.
What happens to the organic carbon produced by phytoplankton
90% is respired/decayed back to CO₂(aq)
10% sinks (biological pump) to deep ocean.
What limits biological productivity in surface oceans?
Nutrient supply from deep ocean (upwelling), especially nitrogen.
How much carbon does the biological pump transfer yearly?
~7 Pg C yr⁻¹
How much CO₂(aq) is transported by deep water formation per year?
~40 Pg C yr⁻¹
How much fossil fuel CO₂ is absorbed by oceans?
About 30%.
CO2 seasonal cycle- summer- northern hemisphere
CO2 drops as plants absorb CO2 during growth
CO2 seasonal cycle- winter- northern hemisphere
microbes decompose organic matter releasing CO2
How is ocean alkalinity maintained?
Weathering of basic rocks followed by river run off
How does a decrease in pH due to ocean acidification
Oceans absorb less CO2
Impact of rising NPP on CO2 sinks
Rises in forest regrowth and waeming may increase the sink of CO2
What is deposition controlled by?
Solubility of species in water-wet
Amount of precipitation-wet
Terrain and type of surface cover-dry
Factors determining dry deposition
- Atmospheric tubulence -governs rate of species delivered to surface
*Chemical properties of depositing species e.g. reactivitt - Nature and reactivity of surface
Vertical dry deposition flux- equation
F=-vdC
= - Deposition velocity * Local concentration at reference height
How is dry deposition decribed?
- Aerodynamic transport down through atmopsheric surface
- Molecular (Brownian) transport for gases across the quasi-laminar sublayer to the surface
3.Uptake at the surface
Dry deposition resistance model- ra
Aerodynamic resistance- ra= tranport occurs by turbulent diffusion (surface layer)
