Primary Production

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Lecture 14 Primary Production Nutrient
Stoichiometry
Topics Stoichiometry Biolimiting Elements
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Annual Mean Surface Nitrate
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High-Nitrate-Low-Chlorophyll (HNLC) Regions
Subarctic Pacific HNLC
mg Chl/m2
North Atlantic Non-HNLC
NO3, Levitus et al, 1994
Day of Year
Frost, 1993 Parsons Lalli, 1988

• Characterized by
• NO3 gt 2 mMol
• Chl lt 1 mg/m3 no blooms!
• Primary production lower than expected

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Motivation Why are HNLC Regions
Important? There are Three Major Ocean Areas
that are Iron Limited but Have a Major Impact
on Global New Production Equatorial Pacific,
Subarctic North Pacific, Southern Ocean All
Three Studied During JGOFS
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HNLC Characteristics 1. High Nitrate
year-round. 2. Low Chlorophyll year-round (no
blooms!). 3. Growth rates still significant
(doubling times of 1-2 days). 4. Small
phytoplankton dominate, even though big ones
around. 5. If Fe is added, increase in primary
production, and get a bloom of big
phytoplankton (e.g., diatoms).
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Differences Between HNLC Regions
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N-S Cross Sections Atlantic Ocean
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N-S Cross Sections in the Pacific Ocean
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Zonal (E-W) Cross Sections in S. Pacific Ocean
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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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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 I and II.
• 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)
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Primary Production Chemical Tracers
Topics Production (primary, new, export, net,
gross) Respiration
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Units Many different units are used for primary
production. mmolC m-2 d-1, mgC m-2 d-1 , gC m-2
y-1, and Gt C y-1 (1 Gt 1 Pg 109 tons 1013
kg 1015g) Chemical Oceanographers always
recommend that moles be the preferred unit,
mmol C m-2 d-1 Use of moles makes comparison
of stoichiometric ratios between nutrients and
carbon easier.
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How is primary production measured? 14C From
satellites O2 mass balance Light models d18O
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Global Annual Net Primary Production from remote
sensing models NPP APAR (400-700nm) x ? (7
APAR absorbed by plankton 31 by land
plants) (from Field et al., 1998, Science, 281,
237) total 104.9 Pg y-1
tC terrestrial 56.4 (53.8 of total) ? 426 gC
m-2 y-1 ? 99.8 of biomass ? 19y ocean
48.5 (46.2 of total) ? 140 gC m-2 y-1 ?
0.2 of biomass ? 2-6 d
gC m-2 y-1
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Example Global Carbon Cycle What is Net
Primary Production?
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Food Web Cartoon
Follow the N! Follow the C! Follow the O2!
Fe plays a role!
DON
Euphotic Zone (100m)
At steady state New NO3 O2 flux to atm
PON (and DON) export
PON
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Food Web Structure Different N Sources New
Production - NO3 - as N source (from
diffusion/upwelling from below and
from the
atmosphere via nitrogen fixation and
nitrification) Regenerated Production - NH4 and
urea as N source New/Net/Export Flux The
f-ratio f NO3 uptake / NO3 NH4 uptake
(defined by Dugdale and Goering, 1969) If we
write P gross production and R respiration
then we can also approximate f as f P - R
also called the ratio of net to gross
production P
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Measuring Primary ProductivityClassic Approach
14C

• Method
• Add known amount of 14C to a bottle containing
  plankton.
• Let photosynthesis happen.
• 3) Filter POC-14C
• 4) Measure how much 14C has been fixed by
  phytoplankton.

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Global Net primary Production by 14C (from Berger
et al., 1988, 1989)
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Global Average Ocean Chlorophyll
Chlorophyll from space (upper 20m)
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Global Ocean Primary Production -from space using
chlorophyll
What are the factors that determine these
patteerns?
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17? Method to Calculate GPP

• Developed in late nineties by Boaz Luz and Eugeni
  Barkan at the Hebrew University of Jerusalem (Luz
  and Barkan, 2000)
• Based on a small but measurable isotopic anomaly
  in atmospheric O2 caused by mass independent
  fractionation in the stratosphere (Thiemens et
  al., 1991)
• 17O/16O in atmospheric O2 is anomalously low
• Atmospheric and photosynthetic O2 (derived from
  water) have distinct isotopic signatures that are
  immune to subsequent mass dependent fractionation
  (respiration)

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17? formulas, terms, notation

• 17? (?17O 0.518 ?18O) 1000 (Luz and
  Barkan, 2000)
• Units per meg (1 per mil 1000 per meg)
• Range of 0.25 of a per mil (250 per meg)
• Atmospheric O2 (Standard)
• 0 per meg
• Seawater in equilibrium with atmosphere (i.e. no
  photosynthetic O2)
• 16 per meg
• Photosynthetic O2
• 249 per meg

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From Hendricks, 2004
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Analytical Methods

• Water is carefully drawn from Niskin into a
  pre-evacuated egg half full
• In the lab, eggs are equilibrated and drained
• O2 and Ar are separated cryogenically
• Each run consists of 75 paired measurements
  against an internal O2/Ar standard
• Internal precision 7 per meg
• Comparisons of duplicates 10 per meg
• Extraction/analysis contributes 20 uncertainty
  to GPP (overall 40-50)

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GPP from 17?
(17?diss 17?eq) (17?photo 17?diss)

• GPP Kas O2eq
• Kas the air-sea O2 exchange rate in units of m
  d-1
• Calculated from parameterization of Nightingale
  et al., 2000
• Wind speed measurements from buoys
• Averaged over residence time of O2 in the ML (for
  CalCOFI 5-10 days)
• K ranged from 1-6 for this study
• O2eq the saturation concentration of O2 in mmol
  m-3
• 17?diss measured from sample
• 17?eq 16 per meg
• 17?photo 249 per meg
• Our estimates are preliminary because this does
  not include mixing/advection!

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14C PP the good

• Measures C uptake directly
• Long time series, easy to do
• Integrates both mixed layer AND photic zone below
  mixed layer

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14C PP the bad

• Snapshot estimate (6 to 24 hours)
• Incubations are time consuming
• Difficult to obtain spatial coverage
• Must sample from research vessel
• In vitro effects are a big unknown (Marra, 2002)
• Shipboard incubators vs in situ
• Extrapolation to large space and time scales
• Uncertainty in what it actually measures (Marra,
  2002)
• Something between GPP and NCP
• Recycling of labeled C
• Excretion of labeled DOC

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17O GPP the good

• Much easier to obtain spatial coverage
• Can sample from non-research vessels
• Integrates over the residence time of O2 in the
  mixed layer (a few days to two weeks in the
  coastal ocean)
• Closer to the integration time used by
  satellite-based methods
• It measures GPP unambiguously

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17O GPP the bad

• Uncertainty due to gas exchange parameterization
  is high ( 30)
• Uncertainty in relating O2 to fixed C
• Variation in Photosynthetic Quotient (PQ)
• 1.1 for regenerated, 1.4 for NO3 supported (Laws
  et al., 1991)
• O2 from photorespiration and Mehler reaction
• 10 to 20 (Bender et al., 1999, Laws et al.,
  2000)
• Only integrates through mixed layer

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N/G ratio (export efficiency)

• N/G (C/Csat 1)
• C/Csat biological saturation based on measured
  O2/Ar compared to O2/Ar at saturation
  concentration
• N NCP
• G GPP
• N/G does NOT involve gas exchange (Kas)
• Somewhat comparable to f-ratio

(17?diss 17?eq) (17?photo 17?diss)
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Mixed Layer Comparisons
Nov 2005 Apr 2006 Jul 2006 All
Stns ML (Prod) 18 (9) 38 (15) 38 (15) 94 (39)
GPP (PZ) 255 (327) 138 (179) 186 (372) 180140
NCP 21 mmolO2m-2d-1 21 mmolO2m-2d-1 24 mmolO2m-2d-1 2221
NCPGPP 0.08 0.18 0.18 0.160.12
Fraction of 14C PP within ML (Avg dep) 0.78 (38m) 0.77 (43m) 0.50 (24m)
Kas avg 2.7 m d-1 (2-4) 2.1 m d-1 (1-3) 3.2 m d-1 (1-6)
Bio O2 Sat 104 104 104 1044.4
GPP 14C PP Avg 4.0 3.6 3.9 3.81.8
Averags and standard deviation for mixed layer
estimates GPP and NCP in mmol of O2 m-2 d-1
Photic zone in parentheses Average mixed layer
depth in parantheses Ratio of 18O GPP14C PP
2.2 (Laws et al., 2000)
HOT GPP 70 to 185 N/G -0.13 to 0.13 Bio
Sat 99-101 K 3.8 to 8.1 Juranek and Quay,
2005
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Spatially Integrated Mixed Layer PP

• Mean 17O GPP 1170 720 mg C m-2 d-1 (100 to
  5680)
• Mean 14C PP 500 340 mg C m-2 d-1 (110 to
  1810)

Conversion of GPP to mg C mmol O2 12
(0.85/1.25)
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14C PP vs 17O GPP
Conversion of GPP to mg C mmol O2 12
(0.85/1.25)
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Lines represent 21 and 31 molar ratios (mol GPP
O2 mol C 14C PP)
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Production by ocean and land areas (from Pilson)
139 gC m-2 y-1
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Historial estimates of total ocean primary
production Value (Gt C
y-1) Koblents-Mishke et al (1968) 23 Ryther
(1969) 20 Eppley and Peterson
(1979) 19.1 23.7 The best
value for ocean Romankevich (1984) 25
appears to be about Martin et al
(1987) 51 50 Gt C
y-1 Berger et al (1987) 26.9 Field et al
(1998) 48.5 Note 1 Gt 1Pg 109 tons
1012 kg 1015 gms
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Total Global New Production from NO3 upwelling
(from Chavez and Toggweiler)
estimated upward velocity, NO3 concentration
advected up and then
new production
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O2 Flux Method
Gas exchange
Write a mass balance
P ? O2
R
Mixing
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O2 Flux Method
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Internal Rotating Sphere (IRS) Sediment
Trap Hedges and Peterson (UW)
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Particle Interceptor Traps (PITs) Knauer and
Martin (Moss Landing)
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Primary Production by Ocean Provinces from POC
Export (from Martin
et al., 1987)
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Controls on Atmospheric CO2
Remarkable consistency for glacial/interglacial
concentrations of CO2 Main Control on atm CO2 is
B flux!
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Broecker two-box model (Broecker, 1971)
see Fig. 2 of Broecker (1971)
v is in cm y-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 his model Vr
10 cm y-1 Vmix 200 cm
y-1 so Vmix / Vr 20
fraction of input 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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Example Perturbation Analysis Double River
Input
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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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What is primary production? DINutrients ?
POM Primary Producers Autotrophs Mo
stly photosynthesizers (they use light energy)
called phytoplankton phyto light
plankton small drifting organisms Some
chemotrophs (dont need light) live in unusual
environments like hydrothermal vents, anoxic
environments
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Variability - CalCOFI Sampling Grid
Is this sufficient to describe variability?
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Coastal T and Chl California Current (by CZCS
satellite) Chlorophyll left SST right
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NASA SeaWiFS data for ocean chlorophyll and
primary production For Animation of Global Data
go to http//earthobservatory.nasa.gov/Observat
ory Note 1. High Latitudes high and
variable Spring Bloom in N. Atlantic (NABE) 2.
Coastal Regions high and patchy 3. Central
Gyres - low 4. Equatorial Regions (EqPac)
higher and El Nino 5. Arabian Sea response to
monsoon forcing 6. Southern Ocean seasonal 7.
Seasonality