14C-assimialtion rate (µg C L-1 d-1)

0 1 2 3 4 5 6 7

Dep

th (m

)

0

50

100

150

200

Trapezoidal integrationDepth (m) Production

(µg C L-1 d-1)5 6.5

25 6.4

45 5.0

75 3.0

5-75 m Int. 363 mg C m-2 d-1

Area of trapezoid = Height * avg. base

[(25 m -5 m) * )((6.5 mg C m-3 d-1 + 6.4 mg C m-3 d-1)/2)] = 129 mg C m-2 d-1

[(45 m -25 m) * (6.4 mg C m-3 d-1 + 5.0 mg C m-3 d-1)/2] = 114 mg C m-2 d-1

[(75 m -45 m) * ((5.0 mg C m-3 d-1 + 3.0 mg C m-3 d-1)/2)] = 120 mg C m-2 d-1

Sum 5-75 m = 363 mg C m-2 d-1

Primary productivity in the seaD

epth

(m)

50

100

150

200

250

Compensation depth (Pcell = Rcell)

Critical depth (Pwater = Rwater)

∫ 1/p dP/dt >0Z

0

∫ 1/p dP/dt <0Z

0

Net Photosynthesis

Res

pira

tion

Winter mixing introduces nutrients to the upper ocean;

seasonal increases in irradiance results in

deepening of the critical depth and

shoaling of the mixed layer. The result: net

accumulation of biomass.

Critical depth

The Spring Bloom

Mixed layer

Sverdrup (1953)

Nitrogen assimilation• Nitrogen is an essential nutrient found in

amino acids, protein, and nucleic acids.• Nitrogen is assimilated by both autotrophs

and heterotrophs.• In large areas of the world’s ocean, nitrogen

limits primary production.• Nitrogen in organic matter is reduced;

however, most “fixed” nitrogen in the ocean is oxidized (nitrate) and thus requires reductant for assimilation into biomass.

NH4+ Concentration

V (ti

me-1

)

Time (hours)

Subs

trat

e (m

oles

L-1

)NO3

-

NH4+

total V

NO3-

NH4+

The relationships between concentrations and planktonic uptake of reduced and oxidized N

Patterns of NO3-

and NH4+

disappearance due to

preferential uptake of NH4

+

Simultaneous rates of NO3

-

and NH4+

uptake as a function of

NH4+

concentration

New and regenerated production1) new production supported by external input of N (e.g. NO3

- and N2), 2) recycled or regenerated production, sustained by in situ recycling of N.

-Assumes steady state: Input of new N is balanced by export of N.

The f-ratio

f = VNO3- / VNO3

- + ∑NR

Biological production

NO3-

N2

NH4+

N export

new

newregenerated

export

NH4+

NO3- NO2

-

F-ratio describes relative contribution of new production to total production.

NR includes regenerated N uptake (historically thought to include urea and NH4

+)

In steady state N inputs are balanced by export/grazing loss.

Eppley and Peterson (1979)

Eppley and Peterson (1979) determined the contribution of nitrate and ammonium to total

primary production (as determined by 14C-bicarbonate assimilation). This provided a

quantitative evaluation of the amount of production (in carbon units) able to support

fisheries and sink to the deep sea

Oligotrophic N. Pacific

Oligotrophic Med. Sea

S. Cal. Bight

E. tropical Pacific

Coast Rica Dome

Peru upwelling

New production (NO3

- based)~14-45% of total

production across ocean basins

For photosynthetic

organisms, satellites are a

big help.

Some generalizations•Subtropics and tropics: oliogtrophic = low nutrient, low biomass; 1o pro. ~0.5 g C m-2 d-1.•Equatorial upwelling regions: Elevated nutrients (1-10 µM NO3

-) and biomass; 1o pro. ~1 g C m-2

d-1.•High latitude: High nutrients (10-30 µM NO3

-); elevated biomass; 1o pro. ~1.5 g C m-2 d-1.

??

??

??

Not all nutrients are introduced to the euphotic zone from deep

waters…

• Atmospheric deposition (both dry and wet) can form an important source of nutrients.

• Advection: lateral input of nutrients• N2 fixation

Redfield stoichiometry of production and remineralization

Organic matter production:

106 CO2 + 16 HNO3 + H3PO4 + 122 H2O ⇒ (CH2O)106 (NH3)16 (H3PO4)+138O2

Consumes nutrients Produces oxygenConsumes CO2

This equation describes photosynthetic nitrate assimilation

THE RATIO 106C: 16N : 1Pmole : mole : mole

Aerobic remineralization of organic matter:

(CH2O)106(NH3)16H3PO4 + 138O2 ⇒ 106CO2 + 122H2O +16HNO3 + H3PO4

Produces CO2 Produces nutrientsConsumes O2

NO3- + NO2

- (µmol kg-1)

0 10 20 30 40 50

Dep

th (m

)

0

1000

2000

3000

4000

5000

PO43- (µmol kg-1)

0 1 2 3 4 5

DIC (µmol kg-1)

1900 2000 2100 2200 2300 2400

NO3- + NO2

- PO4

3- DIC

N:P

0 5 10 15D

epth

(m)

0

1000

2000

3000

4000

5000

NO3- + NO2

- : PO43-

Station ALOHA nutrient profiles

Aerobic regeneration of nitrogen

Decomposition of organic matter

(CH2O)106(NH3)16H3PO4 + 138O2 ⇒

106CO2 + 122H2O +16HNO3 + H3PO4

NO3- + NO2

- (µmol L-1)

0 10 20 30 40 50

Dep

th (m

)0

1000

2000

3000

4000

5000

O2 concentration (µmol O2 L-1)

0 50 100 150 200 250 300

N+NO2

NO3- + NO2

- (µmol L-1)0 10 20 30 40 50

Dep

th (m

)0

1000

2000

3000

4000

PacificAtlantic