Jerome Fiechter Ocean Sciences Department University of California, Santa Cruz ROMS Workshop, Grenoble, 6-8 October 2008 Seasonal and Interannual Ecosystem Variability in the Coastal Gulf of Alaska

Andy Moore – University of California, Santa Cruz Chris Edwards – University of California, Santa Cruz Ken Bruland – University of California, Santa Cruz Manu Di Lorenzo – Georgia Institute of Technology Zack Powell – University of California, Berkeley Al Hermann – NOAA / PMEL Enrique Curchitser – Rutgers University Hernan Arango – Rutgers University Kate Hedstrom – ARSRC, Fairbanks Collaborators

Outline Physical/biological properties of Coastal Gulf of Alaska (CGOA) Physical/biological properties of Coastal Gulf of Alaska (CGOA) Ocean circulation, ecosystem, and iron limitation models Seasonal and interannual ecosystem variability (EOFs) Summary

CGOA Physical and Biological Properties Physical Variability Downwelling-favorable wind regime (Stabeno et al., 2004) AS intrinsic mesoscale variability (Combes and Di Lorenzo, 2007) Anticyclonic (Yakutat) eddy passages (Okkonen et al., 2003) Biological Variability CGOA: high-productivity shelf, fisheries Subarctic Gyre: HNLC region (Lam et al., 2006) Iron limitation on primary production (Strom et al., 2006) Interannual Variability El Niño; 1999 La Niña 1999 NEP “Cold” Regime Shift (Peterson and Schwing, 2003) 2002 NEP Subsurface Cold Event (Curchitser et al., 2005)

Ocean Circulation Model: CGOA-ROMS ROMS: ~ 10 km horizontal resolution, 42 sigma levels One-way offline nesting with North East Pacific ROMS Monthly mean atmospheric and open boundary forcing 5-year simulation (1998 through 2002)

Lower Trophic Level Ecosystem Model NEMURO: 11 components; 83 parameters (Kishi et al., 2007) NEMURO: 11 components; 83 parameters (Kishi et al., 2007) Strom et al., 2007 PS: Nano P PL: Diatoms ZS: Ciliates ZL: Copepods ZP: Krill Fe Iron-limited phytop. growth (Fiechter et al., 2008)

Surface Chlorophyll and Nutrients: Seaward Line, 2001 NEMURO-Fe (x)GLOBEC in situ (squares)

Surface Chlorophyll: NEMURO-Fe vs. SeaWiFS SeaWiFS NEMURO

Surface Chlorophyll EOFs: NEMURO-Fe vs. SeaWiFS

Surface Chlorophyll EOFs: Diatoms vs. Nanophytop.

Sea Surface Height and Eddy Kinetic Energy EOFs

Alongshore Wind Stress and Wind Stress Curl EOFs

Spring Bloom Variability and Winter Ekman Pumping

Wind Stress Curl, Ekman Pumping, Nutrient Upwelling

Aleutian Low Classification (Bering Sea Winter Climate) Sea level pressure (hPa) Rodionov et al., 2005 (La Niña) (El Niño) (Split Center Pattern)

Summary Ecosystem model reproduces chlorophyll seasonal cycle and interannual variability, but underestimates fall bloom Ecosystem model reproduces chlorophyll seasonal cycle and interannual variability, but underestimates fall bloom Ecosystem model reproduces phytoplankton community structure (diatoms on shelf and nanophytoplankton offshore) Ecosystem model reproduces phytoplankton community structure (diatoms on shelf and nanophytoplankton offshore) Seasonal cycle and interannual variability account for 80% of explained variance in model and 40% in observations Seasonal cycle and interannual variability account for 80% of explained variance in model and 40% in observations Spring bloom interannual variability correlated with winter Ekman pumping (i.e., wind stress curl) in northern CGOA Spring bloom interannual variability correlated with winter Ekman pumping (i.e., wind stress curl) in northern CGOA Connection to Aleutian Low variability in North Pacific?