From satellite-based primary production to export production Toby K. Westberry 1 Mike J. Behrenfeld 1 David A. Siegel 2 1 Department of Botany & Plant Pathology, Oregon State University 2 Institute for Computational Earth System Science, University of California Santa Barbara

What is the fate of net primary production (NPP)? (i.e., export v. recycling) Motivation In situ observational studies Eppley & Peterson (1979) Suess et al. (1980) Buesseler et al. (1998) Ecosystem models Fasham et al. (1990) Laws et al. (2000) Dunne et al. (2005) Satellite based Falkowski et al. (1998) Iverson et al. (2000) Goes et al. (2000), (2004) NPP Export production

CbPM (1) - Overview 1. Invert ocean color data to estimate Chl a & b bp (443) (Garver & Siegel, 1997; Maritorena et al., 2001) 2. Relate b bp (443) to phytoplankton carbon biomass, C 3. Use Chl:C to infer physiology (photoacclimation & nutrient stress) 4. Estimate phytoplankton growth rate (  ) and NPP Carbon-based Production Model (CbPM) (Behrenfeld et al., 2005; Westberry et al., submitted to GBC)

CbPM (2) – Details We can push model vertically through the water column: Spectral accounting for underwater light field Cells photoacclimate through the water column Nutrient-stress decays as nitracline is neared (using climatological nutrient fields) **Westberry et al., (submitted to GBC) Chl  NPP Depth (m) mg Chl m -3 d -1 mg C m -3 d -1

CbPM (3) – Results & Validation Surface patterns Data from Winn et al. (1995); Durand et al. (2001) **Westberry et al., (submitted to GBC) HOT BATS

CbPM (4) – Results & Validation **Westberry et al., (submitted to GBC) Depth patterns BATS summerwinter summer

CbPM (5) – ∫NPP Patterns  NPP (mg C m -2 d -1 ) Onset and peak of blooms can be delayed (~1-2 months) Spatial (and temporal) patterns of NPP are different compared to Chl-based model (VGPM, Behrenfeld & Falkowski, 1997 ) VGPM – CbPM (Jun – Aug)

NPP to Export – empirical (1) Annual particle export predicted from Laws et al. (2000) Zonal regions as in Yoder et al. (1993) CbPM = 11.2 Gt C yr -1 VGPM = 10.6 Gt C yr -1

NPP to Export – mechanistic (1) Biomass accumulation NPPLosses Apr biomass mg C m -3 Aug biomass mg C m -3 % of “expected biomass” Aug biomass

NPP to Export – Dilution Change (%) in ML phytoplankton C due to ML deepening % phyto C lost

NPP to Export – mechanistic (2) Biomass accumulation NPPLosses Ad hoc approach -- look at dC/dt, d  /dt, dNO 3 /dt to constrain one of the processes

NPP to Export – mechanistic (3) dC/dt ~ EXPORT Example 1 Export under oligotrophic conditions % ML phyto. C lost t1t1 t2t2 [NO3] 1 =[NO3] 2 11 = 22 C1C1 >C2C2

NPP to Export – mechanistic (4) Export from seasonal nutrient drawdown % ML phyto. C lost t1t1 t2t2 [NO3] 1 >[NO3] 2 11 = 22 C1C1 ≥C2C2 Example 2 dNO 3 /dt - dC/dt ~ EXPORT

NPP to Export – END CbPM provides critical pieces of information for diagnosing export from satellite ( , C, NPP) Haven’t solved the whole problem … yet Can estimate time varying fields of export (and recycling)

NPP to export – Export Map? Mean Annual fraction of phyto. C exported

EXTRA

What is the fate of net primary production (NPP)? (i.e., export v. recycling) Motivation In situ observational studies - 15 N incubations - Sediment traps - Geochemical balances Th inventories Eppley & Peterson (1979) Suess et al. (1980) Buesseler et al. (1998) Ecosystem models Fasham et al. (1990) Laws et al. (2000) Dunne et al. (2005) Satellite based - Applications of empirical results - [Chl], NPP, and SST are not sufficient Falkowski et al. (1998) Iverson et al. (2000)

CbPM (2) – Details Spectral accounting for underwater light field Cells photoacclimate through the water column Nutrient-stress decays as nitracline is neared Mixed layer Photoacclimation + Relaxation from nut. stress Photoacclimation Particle loss **Westberry et al., (in review GBC) Realistic profiles with no assumptions about shape

CbPM (3) – Results & Validation Chl  NPP Depth (m) mg Chl m -3 d -1 mg C m -3 d -1 **Westberry et al., (in review GBC) Surface patterns Depth patterns HOT BATS

CbPM (4) - Patterns Both spatial AND temporal patterns of NPP are different wrt Chl-based model (VGPM) ~30% more NPP in open ocean (and ~30% less in northern high latitudes) Onset and peak of blooms can be delayed (~1-2 months) VGPM - CbPM (Jun-Aug) mg C m -2 d -1

Export – empirical (2) VGPMCBPM > 60°N46%22% 30°N - 60°N22%19% 0° - 30°N10%11% 0° - 30°S8%12% 30°S - 60°S6%14% > 60°S8%23% Total (Gt C yr -1 ) Fraction of total export CbPM suggests much more production in open ocean and So. Ocean and less in N. hemisphere high latitudes and upwelling regions

Export – empirical (2) VGPMCBPM Oligotrophic1.9 (18%)3.1 (28%) Mesotrophic3.6 (34%)4.4 (39%) Eutrophic5.1 (48%)3.7 (33%) Total > 60°N46%22% 30°N - 60°N22%19% 0° - 30°N10%11% 0° - 30°S8%12% 30°S - 60°S6%14% > 60°S8%23% Total (Gt C yr -1 ) Fraction of total export Total Export ( Gt C yr -1 )

How to assess export? 1. Apply **new** CbPM patterns to existing empirical export algorithms (i.e., Laws et al., 2000; Dunne et al., 2005) 2. Use biomass (C) and growth rate (  ) in addition to NPP to construct a mass balance for phytoplankton C in the mixed layer

NPP to Export – nutrient constraints surface NO 3 (SSN) ~ 0 - dC/dt <  (export) SSN ~ 0 & dNO 3 /dt > 0 - dC/dt > 0 - dC/dt ~ 0 & d  /dt >  (recycling) - dC/dt ~ 0 & d  /dt ~  (export) SSN > 0 & dNO 3 /dt < 0 - similar to above SSN > 0 & dNO 3 /dt ≥ 0 - light or Fe limitation ….??

NPP to Export – mechanistic (2) Considerations 1. Are there nutrients IN the mixed layer? 2. Were nutrients entrained into the mixed layer? Drawn down? 4. Was there an increase in biomass? Decrease? 5. Was there an increase in growth rate? Decrease? [C] NPP  NO OR

NPP to Export – mechanistic (2) Considerations 1. Are there nutrients IN the mixed layer? 2. Were nutrients entrained into the mixed layer? 4. Was there an increase in biomass? Decrease? 5. Was there an increase in growth rate? Decrease? [C 1 ]NPP1  [NO 3 - ] t1t1 t2t2 [C 2 ] > [C 1 ] NPP1    