Primary Production

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Lecture 12 Primary Production Nutrient
Stoichiometry
Topics Stoichiometry Biolimiting Elements
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Broecker two-box model (Broecker, 1971)
B VmCd VrCr - VmCs
B
(1-f)B
fB
see Fig. 2 of Broecker (1971)
v is in cm y-1 then flux is mol cm-2y-1
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Broecker (1971) defines some parameters for the
2-box model g B / input (VmixCD VrCr
VmixCs) / VmixCd VrCr f VrCr / B VrCr /
(VmixCd VrCr - VmixCs) f x g In this model
Vr 10 cm y-1 Vmix 200
cm y-1 so Vmix / Vr 20
fraction of input to surface removed as B
because fB VrCr
fraction of element removed to sediment per
visit to the surface
Here are some values g f f x g N 0.95 0.01 0.01
P 0.95 0.01 0.01 C 0.20 0.02 0.004 Si 1.0 0.01 0.0
1 Ba 0.75 0.12 0.09 Ca 0.01 0.12 0.001
Q. Explain these values and why they vary the way
they do.
See Broecker (1971) Table 3
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Why is this important for chemical
oceanography? What controls ocean C, N, P? g
1.0 Mass Balance for whole ocean ?C/ ?t VRCR
f B CS 0 CD CD VU VD VMIX Negative
Feedback Control if VMIX ? VUCD ? B ? f B ?
(assumes f will be constant!) assume VRCR ? then
CD ? (because total ocean balance VUCD ? has
changed sink gt source) B ?
The nutrient concentration of the deep ocean
will adjust so that the fraction of B preserved
in the sediments equals river input!
CS
CD
if VMIX m y-1 and C mol m-3 flux mol m-2 y-1
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Example Perturbation analysis Mass Balance
Control Double Upwelling Rate
sequence of events
Paleo record
Double rate of ocean mixing
VrCr fB at the beginning and at the end! The
deep concentration (Cd) is cut in half
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Example Perturbation Analysis Double River
Input
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Controls on Atmospheric CO2
Remarkable consistency for glacial/interglacial
concentrations of CO2 Main Control on atm CO2 is
the B flux! We need to understand B
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How do we get from the marine food web to a
global assessment of CO2 flux???
With great difficulty!
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Chemical Composition of Biological Particulate
Material Hard Parts - Shells Name Mineral Siz
e (mm) Plants Coccoliths CaCO3
Calcite 5 Diatoms SiO2 Opal 10-15 Silicoflage
llates SiO2 Opal 30 Animals Foraminifera CaCO3
Calcite 100 and Aragonite Radiolaria
SiO2 Opal 100 Pteropods CaCO3
Aragonite 1000 Acantharia SrSO4
Celestite 100
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Soft Parts - protoplasm
from Redfield, Ketchum and Richards (1963) The
Sea Vol. 2 Also for particles caught by sediment
traps.
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The Redfield or "RKR" Equation (A Model) The
mean elemental ratio of marine organic particles
is given as P N C 1 16 106 The
average ocean photosynthesis (forward)
and aerobic
( O2 ) respiration (reverse) is written as 106
CO2 16 HNO3 H3PO4 122 H2O trace
elements (e.g. Fe)
light (h n) ?
( C106H263O110N16P )
138 O2 or
(CH2O)106(NH3)16(H3PO4) Algal
Protoplasm The actual chemical species
assimilated during this reaction
are HCO3- NO3- PO43- NO2- NH4
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• This is an organic oxidation-reduction reaction -
  during photosynthesis C and N are reduced and O
  is oxidized. During respiration the reverse
  occurs. There are no changes in the oxidation
  state of P.
• We assume C has an oxidation state of 0
  which is the value of C in formaldehyde (CH2O),
  that N has an oxidation state of -III and that H
  and P do not change oxidation states.
• 2. Photosynthesis is endothermic. This means is
  requires energy from an outside source. In this
  case the energy source is the sun. Essentially
  plants convert the photo energy from the sun into
  high energy C - C bonds. This conversion happens
  in the plants photosystems.
• Respiration is exothermic. This means it
  could occur spontaneously and release energy. In
  actuality it is always mediated by bacteria which
  use the reactions to obtain their energy for
  life.
• 3. Stoichiometry breakdown of oxygen production
• CO2 H2O ? (CH2O) O2 C
  O2 ? 1 1
• H NO3- H2O ? (NH3) 2O2
  N O2 ? 1 2
• 4. Total oxygen production 106 C 16 N x 2
  138 O2

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5. If ammonia is available it is preferentially
taken up by phytoplankton. If NH3 is used as the
N source then less O2 is produced during
photosynthesis 106 CO2 16 NH3 H3PO4
122 H2O trace elements
light (hn) ?
(CH2O)106(NH3)16(H3PO4) 106
O2 The relationship between O2 and NO3/NH4
is 21 (as shown in point 3) 16 HNO3
16 H2O 16 NH3 32 O2
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Dissolved seawater data from Atlantic GEOSECS
Program (Broecker and
Peng, 1982)
small deficit in NO3
Remarkable congruence between ratios in the ocean
and plankton composition.
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Each class of organic compounds has its own
unique stoichiometry carbohydrates are C rich
but N and P poor (e.g. (CH2O)n) proteins are C
and N rich but P poor (e.g. amino
acids) nucleotides are rich in both N and P (e.g.
4 bases) lipids are C rich Questions Why 161?
Why not 61 or 601? How does an organism end up
with a certain composition? What happens if one
constituent is not available in adequate amounts?
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Stoichiometry based on organic composition
Average Plankton 65 protein 19 lipid 16
carbohydrate
Average formula for plankton biomass C106H177O37N
17PS0.4 Oxidation consumes 154 moles of O2
106 CO2 17 HNO3 H3PO4 122 H2O
trace elements light
(h n) ?
( C106H177O37N17PS0.4 ) 154
O2
Hedges et al (2002) Marine Chemistry
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R RKR P Protein L Lipid C Carbohydrate E
Equatorial Pacific A Arabian Sea 1-3
Southern Ocean 1a Anderson et al
From Hedges et al (2002)