SME
Oceanography · Problem type
Carbon fixed from the nitrate used
Use this for “Nitrate drops by 8 μmol/kg in a bloom. How much carbon and phosphate went into the plankton?”
Chart
A log scale: each grid line up is 10 times the one below.
This is an example. Type your own values to start a new problem.
ΔC (μmol/kg)
:
ΔN (μmol/kg)
:
ΔP (μmol/kg)
=
106
:
16
:
1
Formulas
ΔC
=
106
×
ΔN
16
53
=
106
×
8
16
ΔP
=
ΔN
16
0.5
=
8
16
Assumptions
•
Plankton take up carbon, nitrogen and phosphorus in the Redfield ratio, 106 carbon and 16 nitrogen atoms to each phosphorus atom.
•
All the nitrate that disappears went into the plankton; none was mixed away or used another way.
•
Amounts are micromoles in each kilogram of seawater, μmol/kg.
Step-by-step
WE KNOW
ΔN = 8 μmol/kg
FIND
carbon fixed (ΔC), phosphate used (ΔP)
Step 1 · Find carbon fixed (ΔC)
Use ΔC = 106 × ΔN ÷ 16
For every 16 nitrogen atoms taken up, 106 carbon atoms are fixed.
ΔC
=
106
×
8
16
ΔC
=
848
16
ΔC = 53 μmol/kg
Step 2 · Find phosphate used (ΔP)
Use ΔP = ΔN ÷ 16
One phosphorus atom goes with every 16 nitrogen atoms.
ΔP
=
8
16
ΔP = 0.5 μmol/kg
Check
Put the numbers back in. Both sides should match.
53
=
106
×
8
16
✓
0.5
=
8
16
✓
Topic check
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