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Extending Satellite Ocean Color Measurements for Estimating Net Community Production

Explore the route from P to R to NCP through in situ NCP observations and paired light/dark bottle O2 incubation measurements. Discover the global distribution of NCP and Particle Export. Consider issues like satellite NPP, variability in PQ/RQ, and sensitivity to NPP models.

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Extending Satellite Ocean Color Measurements for Estimating Net Community Production

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  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

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