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

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

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).

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

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

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

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

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

Pacific Map

SeaWifs Multiyear Mean

TahitiNewCaledonia

Hawaii

Zonal Flux CruiseApril 1996

Measuring Oceanic New Production

UW

Collect 15NO3 Addition

in-situon-deck

incubate

~ 6 hr

15NO3 PO15N

Mass spectrometer

filter

from Landry et al (1997)

Natural iron fertilization

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

Drift tracks of lagrangian drifter buoys in IronEx II

IronExII

a) temperature, b) SF6, c) iron, d) chlorophyll, e) nitrate, f) PCO2

(from Coale et al (1996) Nature 383, 495)

Cellular iron uptake mechanisms:

Prokaryotes Eukaryotes

siderophore systems Fe3+/Fe2+ membrane transport*classical, ligand exchange,

and amphiphilic siderophores *cell-surface reduction, ligand production, phagotrophy