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Lecture 19 HNLC and Fe fertilization experiments

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)

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Lecture 19 HNLC and Fe fertilization experiments

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  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, 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 iron fertilization experiment in the equatorial Pacific Ocean. Nature 383, 495-501

  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

  5. Differences Between HNLC Regions

  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. Provocative HNLC Issues: • 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

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

  10. Measuring Oceanic New Production

  11. from Landry et al (1997)

  12. Natural iron fertilization

  13. A summary of open ocean iron enrichment experiments that have been conducted to date. Prepared by Francisco Chavez.

  14. Drift tracks of lagrangian drifter buoys in IronEx II

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

  16. 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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