From satellite-based primary production to export production Toby K. Westberry 1

1. From satellite-based primary production to export production Toby K. Westberry1 Mike J. Behrenfeld1 David A. Siegel2 1Department of Botany & Plant Pathology, Oregon State University 2Institute for Computational Earth System Science, University of California Santa Barbara

2. Export production NPP Motivation What is the fate of net primary production (NPP)? (i.e., export v. recycling) Satellite based Falkowski et al. (1998) Iverson et al. (2000) Goes et al. (2000), (2004) 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)

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

4. m NPP Chl Depth (m) mg Chl m-3 d-1 mg C m-3 d-1 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)

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

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

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

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

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

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

11. NPP Losses Biomass accumulation NPP to Export – mechanistic (2) • Ad hoc approach -- look at dC/dt, dm/dt, dNO3/dt to constrain • one of the processes

12. Export under oligotrophic conditions % ML phyto. C lost NPP to Export – mechanistic (3) Example 1 dC/dt ~ EXPORT

13. Export from seasonal nutrient drawdown % ML phyto. C lost NPP to Export – mechanistic (4) Example 2 dNO3/dt - dC/dt ~ EXPORT

14. NPP to Export – END • CbPM provides critical pieces of information for diagnosing • export from satellite (m, C, NPP) • Haven’t solved the whole problem … yet • Can estimate time varying fields of export (and recycling) toby.westberry@science.oregonstate.edu www.science.oregonstate.edu/ocean.productivity www.science.oregonstate.edu/ecophysiology

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

16. EXTRA

17. Motivation What is the fate of net primary production (NPP)? (i.e., export v. recycling) Satellite based - Applications of empirical results - [Chl], NPP, and SST are not sufficient Falkowski et al. (1998) Iverson et al. (2000) In situ observational studies - 15N incubations - Sediment traps - Geochemical balances - 234Th 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)

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

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

20. CbPM (4) - Patterns VGPM - CbPM (Jun-Aug) • 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) mg C m-2 d-1

21. Export – empirical (2) 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

22. Export – empirical (2) Total Export (Gt C yr-1) Fraction of total export

23. 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 (m) in addition to NPP to construct a mass balance for phytoplankton C in the mixed layer

24. NPP to Export – nutrient constraints • surface NO3 (SSN) ~ 0 • - dC/dt < 0 ---- (export) • SSN ~ 0 & dNO3/dt > 0 • - dC/dt > 0 • - dC/dt ~ 0 & dm/dt > 0 ----(recycling) • - dC/dt ~ 0 & dm/dt ~ 0 ---- (export) • SSN > 0 & dNO3/dt < 0 • - similar to above • SSN > 0 & dNO3/dt ≥ 0 • - light or Fe limitation ….??

25. 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? 2 1 m NPP [C] OR NO3- 3

26. NPP to Export – mechanistic (2) t1 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? [NO3-] m1 [C1] NPP1 t2 [NO3-] m2 > m1 NPP1 [C2] > [C1]