Linking ocean physics / biology / chemistry Flashcards
What can be used to trace water masses in the deep ocean?
Phosphate concentration (As decomposition enriches the deep ocean with nutrients.)
Put these ocean masses in order from surface to depth - NADW, Antarctic Intermediate water, Mediterranean outflow, Antarctic Bottom Water.
Mediterranean outflow > Antarctic Intermediate Water > North Atlantic Deep Water > Antarctic Bottom Water.
What increases with age of water and why?
The nutrient concentration - as it becomes more enriched by decomposition.
What can nutrient concentration tell you about the North Pacific compared to the South?
It is older and filled with deep waters.
Globally, both surface and deep concentrations of nitrate and phosphate are very similar. What do they reflect?
Surface concentrations reflect upwelling (so higher concentration in equatorial / coastal regions and high latitude winter mixing zones).
Deep water concentrations reflect the movement of deep water masses (Therefore high in the North Pacific, South Atlantic and Indian oceans - and lower in the South Pacific, North Atlantic and Southern ocean).
Given our knowledge of the oxygen cycle compared to other nutrients, what is its distribution in the ocean?
Opposite to phosphate - and decreases with age of water masses.
At what concentration is an oxygen minimum zone declared? Where are these prevalent?
[O2] < 50µmol O2 per litre. Found in the equatorial east pacific and indian oceans.
Why do concentrations of nitrogen and phosphorus vary together in a 16-proportion in the ocean? (N:P = 16:1)
Because decomposition, and photosynthesis at the surface, both occur in Redfield proportions, and dominate both the nitrogen and phosphorus cycles in the ocean.
Why do some observations of nitrogen and phosphate concentration plotted against each other, not follow the slope/redfield ratio of 16?
These coincide with low oxygen areas as when decomposition occurs in anaerobic conditions, denitrification occurs, as bacteria start to use NO3- instead. Therefore the observations show low levels of nitrogen.
What process is active in oxygen minimum zones?
Denitrification
What is the condition for a phosphorus limitation?
[NO3-] > 16x[PO43-]
What limitation is experienced by most of the ocean, if only marginally? What is the condition for this?
Nitrogen limitation, where [NO3-] < 16x[PO43-]
Why is the N:P ratio of phytoplankton almost identical to the one of seawater?
Conicidence? - they are not exactly equal, seawater is 1:15 not 1:16
Adaptation of phytoplankton - changed their elemental ratio to match the environment.
Regulation by phytoplankton - Redfield argued that they control seawater concentration.
Why does the redfield ratio not characterise nitrogen fixers / what does?
They are independent of common nitrogen forms, their growth is slower as N2 triple bond is energy demanding, they live in nitrogen-limited and nutrient poor environments.
How do nitrogen fixers control the chemical composition of the ocean?
- A net biological uptake of PO43- occurs in the absence of NO3-
- Nitrogen fixers work to draw N2 gas into the ocean and increase [NO3-] until = 16x[PO43-] at which point nitrogen fixers die off.
What do cells take in via their membrane in the ocean, and how does the SA:V affect this?
- Take in DIC, DIN, PO3-. The higher the SA relative to Volume, the better the uptake.
SA:V can be calculated as equal to what? This means that smaller organisms do better in what type of environment?
3/r. As this shows SA:V is inversely proportional to cell size, smaller organisms do better in oligotrophic, low nutrient environments.
How does the SA:V explain the distribution of prochlorococcus and synedochus in the oceans?
As they are the smallest phytoplankton, therefore having the largest SA:V ratio, they are found in the nutrient limited waters (of between 30 degrees N/S).
What is proximate limiting and ultimate limiting?
Proximate limiting = short term, local
Ultimate limiting = long term
Why is there high anthropogenic CO2 concentration along the NW Atlantic and E American coasts?
Due to the newly formed NADW current
Where is surface C02 highest and why?
The subtropical Atlantic, as Revelle factor is lowest here - warmer, less alkaline.
State the three key reasons why the North Atlantic has high vertical penetration?
- Ventilation of the main thermocline
- Deepwater formation
- Flow patterns of lower thermohaline circulation (involves flow of waters from the southern hemisphere, modification and convection of these waters, and outflow in a thick deep layer)
Why is air/sea gas exchange inhibited in S. Atlantic?
Short residence time of surface waters, as well as dilution of deep and bottom waters by subsurface mixing.
What is CO2 air/sea flux a function of?
pCO2 difference and transfer velocity (the diffusivity of gas in water and effect of physical processes -turbulence - within the boundary layer).
What is the transfer velocity rate determined by?
The difference in DIC across the top and bottom of the water boundary layer. Rate of diffusion increases with temperature.
Which ocean is the most saline?
The North Atlantic.
