EXTENDING SATELLITE OCEAN COLOR MEASUREMENTS TO ESTIMATE NET COMMUNITY PRODUCTION

1. EXTENDING SATELLITE OCEAN COLOR MEASUREMENTS TO ESTIMATE NET COMMUNITY PRODUCTION Toby K. Westberry Peter J. le B. Williams Michael J. Behrenfeld

2. Distribution of in situ NCP observations • Paired measurements of 24 hr light/dark bottle O2 incubation • Too sparse/uneven for global analyses!

3. Route from P to R to NCP • NCP = P – R • NCP is an arithmetic difference, not a physiological process. Thus, direct models might be questionable • R ~ f(P) – so given a parameterisation of the functional relationship between P and R, a route to model NCP exists

4. Route from P to R to NCP – one approach Global map of P PvR analysis PvR relationship + R = aPb Global Distribution of R Global fields of Particle Export ≈ Global Distribution of NCP = P - R

5. Issues • Satellite NPP versus O2 incubation P • Variability in PQ/RQ • Robustness of PvR fits • Sensitivity to particular NPP model • Contribution to export from DOC • etc ….

6. Previous PvR analyses Duarte & Agusti (1998) Robinson & Williams (2005) UNITS: mmol O2/m3 day

7. Apply PvR Relationships to Global Satellite Data NCP (mol C m-2 a-1) Particle Export (Dunne et al. 2005) • White areas – negative NCP • ~80% of the ocean is net heterotrophic (NCP<0) • Annual NCP ~ -700-800 x 1012 mol C a-1 ~7-10 Pg C a-1

8. Latitudinally dependent PvR 1) Bin field data into 4 broad latitudinal bands 2) Derive individual PvR relationships within these regions 4 3 2 1 2 3 4

9. Latitudinally dependent PvR

10. Latitudinally dependent PvR NCP (mol C m-2 a-1) Particle Export (Dunne et al. 2005)

11. Field measurements at HOT NCP (mol C m-2 a-1)

12. Revised PvR • Remove data collected between 10°-40° latitude

13. Revised PvR NCP No data No data Particle Export (Dunne et al. 2005)

14. Annual zonal sums for NCP and PE

15. Annual cycle @ HOT

16. Annual cycle @ BATS

17. Annual cycle @ Station P

18. Field measurements at HOT - Quay et al. (2010)

19. Take home message(s) • We present a path from satellite NPP to global NCP via PvR • Scaling-up of existing PvR relationships suggest whole ocean to be severly net heterotrophic (>800 Tmol C a-1) • Measurements in the oligotrophic gyres present major problems of carbon balance • By deriving PvR relationships which ignore measurements from oligotrophic waters, we arrive at global NCP ~ Export (~700 Tmol C a-1)

20. Satellite- versus O2 incubation-based production • Incubation based measurements • NCP = GPP - ARl - ARd – HR (the light bottle measurement) • Resp = ARd + HR (dark bottle measurement) • PO2 = NCP + Resp = (GPP - ARl - ARd - HR) + (ARd + HR) • PO2 = GPP – Arl • Satellite-based measurements • Psat = GPP - ARl – Ard • Thus, the O2-based production will always be larger than satellite-based production by a factor of ARd (in other words, • PO2=Psat + ARd or PO2=Psat(1+ARd/Psat)).

21. PQ and RQ

22. Results using different satellite NPP models VGPM VGPM-Eppley CbPM

23. Contribution of DOC to export production x1012 mol C a-1