14 C-assimialtion rate (µg C L -1 d -1 ) 0 1 2 3 4 5 6 7 Depth (m) 0 50 100 150 200 Trapezoidal integration Depth (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
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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.
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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