A Simple Approach to Modeling Iron Limitation of Primary Production in the Gulf of Alaska A Simple Approach to Modeling Iron Limitation of Primary Production in the Gulf of Alaska J. Fiechter 1, A. Moore 1, C. Edwards 1, J. Fiechter 1, A. Moore 1, C. Edwards 1, K. Bruland 1, E. Di Lorenzo 2, T. Powell 3, K. Bruland 1, E. Di Lorenzo 2, T. Powell 3, C. Lewis 4, E. Curchitser 5, and K. Hedstrom 6 C. Lewis 4, E. Curchitser 5, and K. Hedstrom 6 1 Dept. of Ocean Sciences, University of California, Santa Cruz 1 Dept. of Ocean Sciences, University of California, Santa Cruz 2 School of Earth and Atmos. Sciences, Georgia Institute of Technology 2 School of Earth and Atmos. Sciences, Georgia Institute of Technology 3 Dept. of Integrative Biology, University of California, Berkeley 3 Dept. of Integrative Biology, University of California, Berkeley 4 NATO Undersea Research Center, La Spezia 4 NATO Undersea Research Center, La Spezia 5 Institute of Marine and Coastal Sciences, Rutgers University 5 Institute of Marine and Coastal Sciences, Rutgers University 6 Arctic Region Supercomputing Center, Fairbanks 6 Arctic Region Supercomputing Center, Fairbanks ROMS Workshop, Los Angeles, 2 October 2007 ROMS Workshop, Los Angeles, 2 October 2007

Outline Ocean circulation model: CGOA domain Ocean circulation model: CGOA domain Ocean circulation model: CGOA domain Ecosystem model: NPZD + iron limitation Ecosystem model: NPZD + iron limitation Ecosystem model: NPZD + iron limitation Ecosystem model: NPZD + iron limitation Results Results Results Results 1) monthly “climatology” ( ) 1) monthly “climatology” ( ) 2) Intra-annual variability (2001) 2) Intra-annual variability (2001) 3) Interannual variability ( ) 3) Interannual variability ( ) Summary Summary Summary Summary

Coastal Gulf of Alaska Ocean Circulation Model ROMS: ~ 10 km horizontal resolution, 42 sigma levels ROMS: ~ 10 km horizontal resolution, 42 sigma levels ROMS: ~ 10 km horizontal resolution, 42 sigma levels One-way offline nesting with North East Pacific ROMS One-way offline nesting with North East Pacific ROMS One-way offline nesting with North East Pacific ROMS One-way offline nesting with North East Pacific ROMS Monthly mean atmospheric and open boundary forcing Monthly mean atmospheric and open boundary forcing Monthly mean atmospheric and open boundary forcing Monthly mean atmospheric and open boundary forcing 10-year simulation (1995 through 2004) 10-year simulation (1995 through 2004) 10-year simulation (1995 through 2004) 10-year simulation (1995 through 2004)

NPZD Model with Iron Limitation NPZD Model (Powell et al. formulation in ROMS) NPZD Model (Powell et al. formulation in ROMS) NPZD Model (Powell et al. formulation in ROMS) Nitrate-limited phytop. growth rate: Nitrate-limited phytop. growth rate: Iron Limitation Model Iron Limitation Model Iron Limitation Model Iron Limitation Model Dissolved (available) Iron: Dissolved (available) Iron: Phytop.-associated Iron: Phytop.-associated Iron: Iron uptake:Optimal Fe:C: Iron uptake:Optimal Fe:C: Realized Fe:C: Realized Fe:C: Iron-limited phytop. growth: Iron-limited phytop. growth:

Nitrate and Dissolved Iron Initial Conditions Nitrate Climatology Nitrate Climatology WOA 2001, Monthly WOA 2001, Monthly 1° x 1° Spatial Resolution 1° x 1° Spatial Resolution Dissolved Iron Dissolved Iron Annual “Climatology” Annual “Climatology” VERTEX (Martin et al., 1989) VERTEX (Martin et al., 1989)

10 Year (1995–2004) Simulation, Monthly Averages

RESULTS: PART I MONTHLY “CLIMATOLOGY” ( ) SURFACE MAPS

MODEL OBSERVATIONS (SEAWIFS) Monthly “Climatology” ( ) Simulated and Observed Chlorophyll, Spring Bloom

MODEL OBSERVATIONS (SEAWIFS) Monthly “Climatology” ( ) Simulated and Observed Chlorophyll, Summer

Monthly “Climatology” ( ) Nitrate and Iron Limitation on Phytoplankton Growth

SURFACE CHLOROPHYLL SEA SURFACE HEIGHT Monthly “Climatology” ( ) SSH and Chlorophyll Variability, Spring Bloom

RESULTS: PART II INTRA-ANNUAL VARIABILITY (2001) GAK STATIONS (CROSS-SHELF) IS MS OS Kenai Peninsula

GAK Intra-annual Variability (2001): Chlorophyll Profiles

GAK Intra-annual Variability (2001): Nitrate Profiles

RESULTS: PART III INTERANNUAL VARIABILITY ( ) GAK LINE (CROSS-SHELF) IS MS OS Kenai Peninsula

GAK Line Interannual Variability ( ) Simulated and Observed Sea Surface Height MODELAVISO

GAK Line Interannual Variability ( ) Simulated and Observed Surface Nitrate MODELGLOBEC

GAK Line Interannual Variability ( ) Simulated and Observed Surface Chlorophyll MODELSEAWIFS

Summary Simple approach to iron limitation on phytoplankton growth Simple approach to iron limitation on phytoplankton growth Simple approach to iron limitation on phytoplankton growth Simple approach to iron limitation on phytoplankton growth  Nitrate budget for N, P, Z, D Nitrate budget for N, P, Z, D Nitrate budget for N, P, Z, D  Iron budget for dissolved and P-associated Fe Iron budget for dissolved and P-associated Fe Iron budget for dissolved and P-associated Fe  Phytoplankton growth limited by realized Fe:C ratio Phytoplankton growth limited by realized Fe:C ratio Phytoplankton growth limited by realized Fe:C ratio Reproduces seasonal and cross-shelf variability Reproduces seasonal and cross-shelf variability Reproduces seasonal and cross-shelf variability Reproduces seasonal and cross-shelf variability  Primary production dominated by spring bloom (APR-JUN) Primary production dominated by spring bloom (APR-JUN) Primary production dominated by spring bloom (APR-JUN)  Inner- and mid-shelf dominated by seasonal variability Inner- and mid-shelf dominated by seasonal variability Inner- and mid-shelf dominated by seasonal variability  Outer-shelf dominated by mesoscale variability Outer-shelf dominated by mesoscale variability Outer-shelf dominated by mesoscale variability  Outstanding issues: PAR, Fe cross-shelf gradient, tides Outstanding issues: PAR, Fe cross-shelf gradient, tides Outstanding issues: PAR, Fe cross-shelf gradient, tides Future work Future work Future work Future work  14-component ecosystem model (NEMURO + Fe limitation) 14-component ecosystem model (NEMURO + Fe limitation) 14-component ecosystem model (NEMURO + Fe limitation)  Adjoint sensitivity studies with NPZD + Fe limitation Adjoint sensitivity studies with NPZD + Fe limitation Adjoint sensitivity studies with NPZD + Fe limitation

CGOA ROMS + NEMURO w/ IRON LIMITATION: MAY “CLIMATOLOGY” ( ) PHYTOPLANKTON AND ZOOPLANKTON COMMUNITY STRUCTURE