1. 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 processes
Global Biogeochemical Cycles 17
Murray et al (1994)
Physical and biological controls on carbon cycling in the equatorial Pacific.
Science 266,
Landry et al (1997)
Iron and grazing constraints on primary production in the central equatorial Pacific:
An EqPac Synthesis.
Limnology and Oceanography 42,
Coale et al (1996)
A massive phytoplankton bloom induced by an ecosystem-scale iron
fertilization experiment in the equatorial Pacific Ocean. Nature 383,

2. 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

3. 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).

4. 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 > 2 mMol
Chl < 1 mg/m3 & no blooms!
Primary production lower than expected
At start of EqPac we did not expect much variability because of HNLC conditions.
In fact, when an El Nino was forcast we requested an extra field season from the US JGOFS SC but
were turned down because most didn’t expect to see much variability in this region.

5. Differences Between HNLC Regions
Note especially differences in:
Seasonality and light
Temperature
Source of iron (atmospheric versus Upwelling)

6. Oceanic New Production & f-ratio
Primary Production (PP) depends on two N-sources:
1) Regenerated by food web
e.g. NH4 & Other DON
2) "New" inputs to euphotic zone
e.g. Deep Water (NO3), Atmos (N2) and Terrestrial
New Production (NP) = f PP
f = "f-ratio“ = New/( New + Regenerated)
Typically:
NP ≈ r NO3 [ m mol m-2 d-1 ]

7. Approach: Provocative HNLC Issues: Question:
Similarity of Subarctic, Equatorial & Southern Ocean
striking given different environments
Largest CO2 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

8. Data Sources Observations span several years & seasons
Subarctic Pacific:
12 Cruises (Canadian JGOFS)
Varela & Harrison, 1999
Diana Varela
Frank Whitney
Philip Boyd
Equatorial Pacific:
9 Cruises (US & France JGOFS
& Others)
Aufdenkampe et al., 2001
--- [NO3] = 2 mMol
Large Diversity in Conditions
El Nino
Mild La Nina
Transitional
With a Cross-Cutting Matrix of Kelvin Waves and Tropical Instability Waves

9. Zonal Flux Cruise April 1996
Pacific Map
Zonal Flux Cruise
April 1996
Tahiti
New
Caledonia
Hawaii
SeaWifs
Multiyear Mean

10. Measuring Oceanic New Production

11. from Landry et al (1997)

16. Natural iron fertilization

17. A summary of open ocean iron enrichment experiments that have been conducted to date.
Prepared by Francisco Chavez.
IronEx I: equatorial Pacific, fold increase in chl. Patch subducted 4 days into the experiment. Martin et al., 1994
IronEx II: equatorial Pacific, 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 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 Dispersion into an eddy. AGU
SEEDS: western subarctic Pacific Ocean, summer fold increase in chl, 13 µM drawdown in NO3. AGU
SOFeX: Pacific sector of Southern Ocean, summer N. and S. of Polar Front. Long observational window. SOFEX web site

20. Drift tracks of lagrangian drifter buoys in IronEx II

21. IronExII
a) temperature, b) SF6, c) iron, d) chlorophyll, e) nitrate, f) PCO2
(from Coale et al (1996) Nature 383, 495)

22. Cellular iron uptake mechanisms:
Prokaryotes
Eukaryotes
siderophore systems
Fe3+/Fe2+ membrane
transport
*classical, ligand exchange,
and amphiphilic siderophores
*cell-surface reduction,
ligand production,
phagotrophy