CarbonBased Net Primary Production and Phytoplankton Growth Rates

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

Modelling NPP General Chl-based C-based NPP ~ [biomass] x physiologic rate NPP ~ [Chl] x Pbopt NPP ~ [C] x m Scattering (cp or bbp) Ratio of Chl to scattering (Chl: C)

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 Satellite 0. 080 0. 013 0. 065 0. 011 0. 050 0. 009 0. 035 0. 020 0. 007 0. 005 0 1 2 3 0 Ig (Ein m-2 h-1) 1 2 3 Chl: C (mg mg-1) Laboratory

CBPM In a nutshell • Invert ocean color data to estimate [Chl a] & bbp(443) (Garver & Siegel, 1997; Maritorena et al. , 2001) • Relate bbp(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 (m) and NPP given: PAR, Chl, K 490, bbp(443), Zeu, MLD Carbon-Based Production Model (CBPM)

Depth-resolved CBPM PAR(z) z=0 Uniform (e. g. , [Chl/C]sat) z=MLD Nutrient-limited &/or light-limited + photoacc. z=z. NO 3 Light-limited + photoacc. * Iterative such that values at z=zi+1 depend on values at z=zi *

CBPM details (2) 2. Let cells photoacclimate through the water column - Iteratively calculate spectral attenuation 3. Account for light limitation Chl : C Ig (Ein m-2 h-1) Light-limitation Index -nutrient stress falls off as e-Dz (Dz=distance from nitracline) m (divisions d-1) 1. Let surface values of Chl: C indicate level of nutrient-stress ~(1 -e-3 PAR(z)) Ik ~0. 6 Ig (Ein m-2 h-1)

CBPM details (3) INPUT (surface) - Sea. Wi. FS: n. Lw(l), PAR, Kd(490) - GSM 01: Chl a, bbp(443) - FNMOC: MLD - WOA 2001: ZNO 3 OUTPUT ( (z)) - Chl, C, & Chl: C - m - NPP Run with 1° x 1° monthly mean climatologies (1999 -2004)

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

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

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

Annual NPP ∫NPP (Pg C) VGPM This model Annual 45 52 Gyres 8 (18%) 13 (26%) High latitudes 15 (34%) 12 (23%) Subtropics? 18 (39%) 25 (48%) 2 (4%) 3 (5%) Southern Ocean (q<-50°S) • Although total NPP doesn’t change much (~15%), where and when it occurs does

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