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Lecture 19 HNLC and Fe fertilization experiments
Not in course pack
But see:Aufdenkampe and Murray (2002)Controls on new production: The role of iron and physical processesGlobal Biogeochemical Cycles 17
Murray et al (1994)Physical and biological controls on carbon cycling in the equatorial Pacific.Science 266, 58-65.
Landry et al (1997)Iron and grazing constraints on primary production in the central equatorial Pacific: An EqPac Synthesis.Limnology and Oceanography 42, 405-418
Coale et al (1996)A massive phytoplankton bloom induced by an ecosystem-scale ironfertilization experiment in the equatorial Pacific Ocean. Nature 383, 495-501
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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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High-Nitrate-Low-Chlorophyll (HNLC) Regions
Characterized by: NO
3 > 2 Mol
Chl < 1 mg/m3 & no blooms! Primary production lower than expected
NO3, Levitus et al, 1994
mg
Chl
/m2
Day of Year
Subarctic Pacific HNLC
North Atlantic Non-HNLC
Frost, 1993; Parsons & Lalli, 1988
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SubarcticPacific
EquatorialPacific
SouthernOcean
Seasonality High Low High
Temperature (oC) 10 25 2
Light Moderate High Low
Mixing Low High Moderate
Upwelling Iron Low High Moderate
Atmospheric Iron High Moderate Low
Ammonium (mM) 0.5 0.1 1
Silicate Moderate High High/Low
Differences Between HNLC Regions
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Oceanic New Production & f-ratio Primary Production (PP) depends on two N-sources:
1) Regenerated by food web e.g. NH
4 & Other DON
2) "New" inputs to euphotic zonee.g. Deep Water (NO
3), Atmos (N
2) and Terrestrial
New Production (NP) = f PP f = "f-ratio“ = New/( New + Regenerated)
Typically:
NP ≈ NO3 [ m mol m-2 d-1 ] 3
3 4
NOf
NO NH
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Provocative HNLC Issues: Similarity of Subarctic, Equatorial & Southern Ocean striking given different environments Largest CO
2 fluxes
Potential for enhanced biological pump
Question:What controls NP variability within & between regions?
Approach: Regression analyses on synthesis of HNLC data to quantify extent variability explained by other factors
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Data Sources Observations span several years & seasons
Subarctic Pacific:12 Cruises (Canadian JGOFS)Varela & Harrison, 1999Diana VarelaFrank WhitneyPhilip Boyd
Equatorial Pacific: 9 Cruises (US & France JGOFS
& Others)Aufdenkampe et al., 2001
--- [NO3] = 2 Mol
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Pacific Map
SeaWifs Multiyear Mean
TahitiNewCaledonia
Hawaii
Zonal Flux CruiseApril 1996
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Measuring Oceanic New Production
UW
Collect 15NO3 Addition
in-situon-deck
incubate
~ 6 hr
15NO3 PO15N
Mass spectrometer
filter
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from Landry et al (1997)
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Natural iron fertilization
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A summary of open ocean iron enrichment experiments that have been conducted to date. Prepared by Francisco Chavez.
IronEx I: equatorial Pacific, 1993. 3-fold increase in chl. Patch subducted 4 days into the experiment. Martin et al., 1994
IronEx II: equatorial Pacific, 1996. 10-fold increase in chl, 90 µ atm drawdown in CO2, 5µM drawdown in NO3. Coale et al., 1996
SOIREE: Pacific sector of Southern Ocean, summer 1999. South of Polar Front. 6-fold increase in chl, 25 µ atm drawdown in CO2, 2 µM drawdown in NO3. Boyd et al., 2000
EisenEx-1: Atlantic sector of Southern Ocean, spring 2000. Dispersion into an eddy. AGU
SEEDS: western subarctic Pacific Ocean, summer 2001. 40-fold increase in chl, 13 µM drawdown in NO3. AGU
SOFeX: Pacific sector of Southern Ocean, summer 2002. N. and S. of Polar Front. Long observational window. SOFEX web site
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Drift tracks of lagrangian drifter buoys in IronEx II
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IronExII
a) temperature, b) SF6, c) iron, d) chlorophyll, e) nitrate, f) PCO2
(from Coale et al (1996) Nature 383, 495)
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Cellular iron uptake mechanisms:
Prokaryotes Eukaryotes
siderophore systems Fe3+/Fe2+ membrane transport*classical, ligand exchange,
and amphiphilic siderophores *cell-surface reduction, ligand production, phagotrophy
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