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

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 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.

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

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 ]

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

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

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

Measuring Oceanic New Production

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