Nutrient Dynamics

Question 1

Redfield Ratio

Answer 1

1P:16N:106C
N:P drawdown in the environment is 16:1

Question 2

Si requirement in phytoplsnkton

Answer 2

Only those with Si shells need it
No consistent ratio of Si:N needed
Different species use varying levels of Si to N
Dependent on species, nutrient availability and iron availability
2:1 and 0.5:1 are common

Question 3

Phosphorus Cycle

Answer 3

Nutrient consumption occurs in the euphotic zone
Respiration releases nutrients from organic matter – occurs mainly at depth

So light and nutrients are physically separated

DIP in consumed by photosynthesis and produces organic phosphate
Respiration consumes organic phosphate and produces DIP in the euphotic zone

Most organic phosphate sinks and releases DIP in deep ocean through respiration
Mixing or upwelling required to bring nutrients to surface (most nutrients come from below)

Question 4

Processes that bring nutrients to the surface

Answer 4

Upwelling
Mixing
Surface cooling - convention q

Question 4

Mix Layer in June

Answer 4

Shallow mix layer
Warming surface and light winds

Question 4

Mix Layer November

Answer 4

Mixed layer cool and deepening

Question 4

Fall Nutrient/Phyto Dynamics

Answer 4

Decreasing light and increasing nutrients
Mix layer deepens
Nutrients in the layer below the summer mixed layer are added to the fall mix layer

Question 4

Mix Layer February

Answer 4

Mix layer coldest and deepest
Cool surface leads to convection and strong winds

Question 4

Summer Nutrient/Phyto Dynamics

Answer 4

High light and low nutrients
Previous productivity used up nutrients in the euphotic zone
Low productivity
Some mixing at euphotic base supplying small amount of nutrients upwards

Question 5

Early Spring Nutrient/Phyto Dynamics

Answer 5

Increasing light and high nutrients
Mix layer shoals with warming surface
Critical depth becomes deeper than mixed layer
Bloom until nutrients consumed

Question 5

Winter Nutrient/Phyto Dynamics

Answer 5

Low light and high nutrients
Deep mixed layer with high surface nutrients
Concentrations mixed from below
Not enough light so low productivity

Question 6

Hawaii Waters Nutrient Dynamics

Answer 6

Mix layer never deeper than critical depth
Nutrients are always depleted

Question 7

Labrador Sea Nutrient Dynamics

Answer 7

Winter mix layer to 1500m in some places

Question 8

4 Types of Ocean Nutrient Dynamics

Answer 8

1) High nutrient winter and low nutrients summer
Classic bloom (North Atlantic)

2) Low nutrients always
High year-round light and shallow mix layer (Hawaii)

3) Episodic High Nutrients
Coastal upwelling zone

4) High Nutrients Always
Some other factor limits (Northern Pacific or Southern Ocean)

Question 9

Typical Nitrogen and Phosphorus Levels

Answer 9

0-3 micromol P and 0-45 micromol N
Most data close to 16:1
Some data sit below

Question 10

Nitrogen Cycle

Answer 10

Primary production consumes nitrate or ammonium in euphotic zone
Respiration releases ammonium in euphotic zone
Phytoplankton prefer ammonium

Organic phosphate sinks into dark ocean and respired to produce ammonium
Nitrification uses ammonium and O2 to produce nitrate in dark ocean (chemosynthesis)
Light inhibits nitrification, and little ammonium in dark O2 rich waters

Mixing and upwelling brings nitrate to surface
New production fueled by nitrate
Regenerated production fueled by ammonium

Denitrification comsumes nitrate when oxygen not available (NO3 to N2)

Question 11

Where does denitrification occur

Answer 11

Where O2 is not available

Anoxic Saanich Inlet: nitrate is consumed, ammonium builds up

North/South Eastern Tropical Pacific and Arabian Sea

Question 12

Nitrogen Fixation

Answer 12

Adds N to cycle
Use N2 gas to create more bioavailable Nitrogen
Energy intensive – only advantageous when nitrate and ammonium low

Question 13

Membrane Importance

Answer 13

Hydrophilic head and hydrophobic tail
Polar ions – phosphate, nitrate and ammonium can’t move across
Need transport enzymes to move through

Question 14

Energy Associated with Transport Enzymes

Answer 14

Specific transport enzymes for each nutrient
Need to make many

Transport Requires energy

There is therefore an energetic cost to make and use enzymes

Question 15

Small Size Advantage

Answer 15

Surface area to volume ratio
Smaller cell more SA per volume

Question 15

Why does Surface area matter and why does volume matter

Answer 15

Surface area matters for nutrient uptake
Volume matter for growth rate

Question 16

When is small cell size selected

Answer 16

Smaller cell more efficient nutrients supplied for growth
Nutrient limitations selects small cell size

Question 17

Growth vs Nutrients

Answer 17

At low nutrient levels: growth increases with increasing nutrients

At high nutrients: no relationship (other factor must limit)

Question 18

What does kN tell us?

Answer 18

Lower kN indicates more efficient nutrient uptake at low nutrient concentration
Will outcompete at low nutrients

Question 19

What drives species succession over blooms?

Answer 19

Mix layer nutrients concentration decreases over the bloom and light levels increase

These changes drive species succession

Question 20

Dominant species types in bloom successions

Answer 20

Early Spring: low light so low kI species dominate
Later: High nutrients and high light so higher Pmax and Gmax species dominate
Later Still: Low nutrients so low kN species dominate

Question 21

Transport Enzymes and Nutrient Uptake Tradeoff

Answer 21

More transport enzymes per SA mean higher nutrient uptake
But energetic cost tends to suppress Gmax

Species kN can acclimatize based on the environment, and adjust transport enzymes based on conditions

The energetic cost of enzymes only advantageous at low nutrient concentrations

Question 22

How are the requirements for Si different from N and P

Answer 22

Only phytoplankton with Si shells require Si and it has no consistent ratio

Question 23

Why do you think the plankton requirements for nutrients are so similar to the ratio of their availability in ocean water?

Question 24

Phytoplankton are generally very small, particularly compared to terrestrial plants. What advantages are conferred by such small size?

Answer 24

They don’t sink as easily and they can take up nutrients better due to SA:V ratio