1. Carbon-Based Net Primary Production and Phytoplankton Growth Rates from Ocean Color Measurements Toby K. Westberry 1, Mike J. Behrenfeld 1 Emmanuel Boss 2, David A. Siegel 3 1 Department of Botany, Oregon State University 2 School of Marine Sciences, University of Maine 3 Institute for Computational Earth System Science, UCSB

2. Modelling NPP NPP ~ [biomass] x physiologic rate NPP ~ [Chl] x P b opt NPP ~ [C] x  Scattering (c p or b bp ) Ratio of Chl to scattering (Chl:C) General Chl-based C-based

3. C-based approach Scattering coefficients covary with particle abundance (Stramski & Kiefer, 1991; Bishop, 1999; Babin et al., 2003) Scattering coefficients covary with phytoplankton carbon (Behrenfeld & Boss, 2003; Behrenfeld et al., 2005) Chlorophyll variations independent of C are an index of changing cellular pigmentation Laboratory Satellite I g (Ein m -2 h - 1 )

4. CBPM In a nutshell Invert ocean color data to estimate [Chl a] & b bp (443) (Garver & Siegel, 1997; Maritorena et al., 2001) Relate b bp (443) to carbon biomass (mg C m -3 ) (Behrenfeld et al., 2005) Use Chl:C to infer physiology (photoacclimation & nutrient stress) Propagate properties through water column Estimate phytoplankton growth rate (  ) and NPP given: PAR, Chl, K490, b bp (443), Z eu, MLD Carbon-Based Production Model (CBPM)

5. Depth-resolved CBPM Nutrient-limited &/or light-limited + photoacc. Uniform (e.g., [Chl/C] sat ) Light-limited + photoacc. * Iterative such that values at z=z i+1 depend on values at z=z i * z=z NO3 z=MLD z=0 PAR(z)

6. Light-limitation Index I g (Ein m -2 h -1 ) ~(1-e -3PAR(z) )  I k ~0.6 CBPM details (2) 1. Let surface values of Chl:C indicate level of nutrient-stress -nutrient stress falls off as e -  z (  z=distance from nitracline) 2. Let cells photoacclimate through the water column - Iteratively calculate spectral attenuation 3. Account for light limitation I g (Ein m -2 h -1 ) Chl : C  (divisions d -1 )

7. CBPM details (3) - SeaWiFS: nLw( ), PAR, K d (490) - GSM01: Chl a, b bp (443) - FNMOC: MLD - WOA 2001: Z NO3 - Chl, C, & Chl:C -  - NPP INPUT (surface) OUTPUT (  (z)) Run with 1 ° x1 ° monthly mean climatologies (1999-2004)

8. Depth (m) Example profiles Eastern Pacific (20 ° N, -110 ° E, Jan) Eq. upwelling (0 ° N, -130 ° E, Aug)

9. NPP patterns (Jun-Aug) This work ∫NPP (mg C m -2 d -1 ) VGPM (Chl-based model) ∫NPP (mg C m -2 d -1 ) large spatial & temporal differences in carbon-based NPP from Chl-based results (e.g., > ±50%) Chl-based model interprets high Chl areas as high NPP differences due to photo- acclimation and nutrient-stress related changes in Chl : C

10. Seasonal NPP patterns (N. Atl.) Western N. Atl Eastern N. Atl CBPM VGPM

11. Annual NPP ∫NPP (Pg C)VGPMThis model Annual4552 Gyres8 (18%)13 (26%) High latitudes15 (34%)12 (23%) Subtropics?18 (39%)25 (48%) Southern Ocean (  <-50 ° S) 2 (4%)3 (5%) Although total NPP doesn’t change much (~15%), where and when it occurs does

12. Example NPP profiles (HOT) - Uniform mixed layer (step function) v. in situ incubations - Discrepancies due to satellite estimates, NOT concept