Lecture 19 HNLC and Fe fertilization experiments Not in course pack But see: Aufdenkampe and Murray...
-
Upload
charla-henderson -
Category
Documents
-
view
217 -
download
0
Transcript of Lecture 19 HNLC and Fe fertilization experiments Not in course pack But see: Aufdenkampe and Murray...
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